Fundamentals of Sustainable Drilling Engineering

By M. E. Hossain and Abdulaziz Abdullah Al-Majed

The book clearly explains the concepts of the drilling engineering and presents the existing knowledge ranging from the history of drilling technology to well completion. This textbook takes on the difficult issue of sustainability in drilling engineering and tries to present the engineering terminologies in a clear manner so that the new hire, as well as the veteran driller, will be able to understand the drilling concepts with minimum effort.

This textbook is an excellent resource for petroleum engineering students, drilling engineers, supervisors & managers, researchers and environmental engineers for planning every aspect of rig operations in the most sustainable, environmentally responsible manner, using the most up-to-date technological advancements in equipment and processes.

• Language: English
• Publisher: Wiley
• Release date: Feb 4, 2015
• ISBN: 9781119100294

Book preview

Chapter 1

Introduction

1.1 Introduction

This chapter introduces the fundamental aspects of the drilling. It covers the basic definitions related to drilling engineering, importance and the procedure for drilling operations. The applications and history of drilling are also outlined. The systematic approach and the introduction to casing sets are discussed. Finally, the aspects of sustainable drilling operations will be introduced.

1.2 Introduction of Drilling Engineering

Some scholars consider petroleum hydrocarbons to be the lifeblood of modern civilization. The life cycle of petroleum operations includes exploration and development, production, refining, marketing, transportation/distribution to the end user, and final utilization. The drilling technology has been developed through the efforts of many individuals, professionals, companies, and organizations. This technology is a necessary step for petroleum exploration and production. Drilling is one of the oldest technologies in the world. Drilling engineering is a branch of knowledge where the design, analysis, and implement procedure are completed to drill a well as sustainably as possible. In a word, it is the technology used to utilize crude oil and natural gas reserves. The responsibilities of a drilling engineer are to facilitate the efficient penetration of the earth by wellbore and to facilitate cementing operations from the surface to an optimum target depth that prevents any situation that may jeopardize the environment.

1.3 Importance of Drilling Engineering

It is well known that the petroleum industry drives the energy sector, which in turn drives the modern civilization. It is not unlikely that every day human beings are getting benefits out of the petroleum industry. The present modern civilization is based on energy and hydrocarbon resources. The growth of human civilization and necessities of livelihood with time inspired human beings to bore a hole for different reasons (such as drinking water, agriculture, hydrocarbon extraction for lighting, power generation, to assemble different mechanical parts, etc.). There is no surface hydrocarbon resource; rather, all resources are underground on this globe. To keep serving the whole civilization, drilling engineering has a significant role in this issue. Moreover, the world’s energy sector is dependent on the drilling engineering. Without drilling a hole, how are we going to extract the hydrocarbon from underground to the surface of the earth? To the best of our knowledge, right now, there is no alternative technology available to extract hydrocarbon without drilling a hole. If the petroleum industry falls down, the whole civilization will probably collapse. Therefore, for the survival of our existence, we need to know and keep updating our knowledge, especially on the technology, of drilling engineering. Based on this motivation, human necessities of drilling a hole by excavation on earth have motivated the researchers to develop different sophisticated technologies for drilling engineering. In a word, we can say, drilling engineering has a vital role in our daily life, economy, society, and even in national and international politics.

1.4 Application of Drilling Engineering

By the development of human civilization with time, human beings have needed to make a hole in different objects for different purposes. It ranges from just a childhood playing game/toy, to modern drilling of a hole for the purpose of any scientific and technological usage. Humans have been using this technology for underground water withdrawal since ancient times. Drilling technology is a widely used expertise in the applied sciences and engineering, such as manufacturing industries, pharmaceutical industries, aerospace, military defense, research laboratories, and any small-scale laboratory to a heavy industry like petroleum. Modern cities and urban areas use the drilling technology to get the underground water for drinking and household use. The underground water extraction by boring a hole is also used agricultural irrigation purposes. Therefore, there is no specific field of application for this technology. It has been used for a widespread field based on its necessity. As this textbook is only focusing on drilling a hole with the hope of hydrocarbon discovery, here, the drilling engineering application means a shaft-like tool (i.e., drilling rig) with two or more cutting edges (i.e., drill bit) for making holes toward the underground hydrocarbon formation through the earth layers, especially by rotation. Hence, the major application of drilling engineering is to discover and produce redundant hydrocarbon from a potential oil field.

1.5 History of Oil Discovery

Geology and time have created large deposits of crude oil in various parts of the earth. Until the mid-1800s, this vast untapped wealth lay mostly hidden below the surface of the earth. Some oil seeped naturally to the earth’s surface, and formed shallow pools. These oil seeps had long been known and were used for medicinal purposes, to caulk boats and buildings, and to lubricate machinery. Ancient people were using oil mainly as medicine. So, the use of oil is not new in human history. The first oil discovery in human life was in Babylon (Current Iraq) as oil pits in 450 BC. Then, the second discovery was in Macedonia in 325 BC, and this oil was being used by Alexander the Great. The third discovery of oil was in Kirkuk, Iraq. However, according to Wikipedia, the earliest known oil wells were drilled in China in 347. The Chinese were using bamboo as modern drill pipe to extract oil. They were able to drill at a depth of about 800 feet using bits attached with bamboo poles. The use of oil was limited to evaporating brine, producing salt, and for lighting and heating. The petroleum industry in Middle East was established by the eighth century. This was due to the use of tar at the street lights in Baghdad. However, some people believe that in the ninth century, oil fields were developed in Baku, Azerbaijan to produce naphtha. The Persian alchemist, Mohammad ibn Zakariya Razi, produced kerosene from petroleum using the distillation process in the ninth century. Kerosene was used mainly as kerosene lamps. The distillation process of crude oil was also carried out by Arab and Persian chemist to produce flammable products for military purposes. By the twelfth century, distillation process became available in Western Europe through Islamic Spain. History says Baku was the place where shallow pits were dug to facilitate collecting oil. The hand-dug holes, which were up to 115 feet deep, were in use by 1594. In fact, these holes were essentially oil wells and produced about 28,000 barrels of oil so far. The first break through in the oil industry’s drilling history was the year 1849, when Russian engineer F.N. Semyenov used a cable tool to drill an oil well on the Apsheron Peninsula. In the west, Canada was the first place of commercial oil production, when James Williams drilled the first oil well in North America in 1857. Later, in 1859, the first well in the USA was drilled near Titusville, Pennsylvania under the supervision of Colonel Edwin L. Drake, and it was about 69 feet deep. Table 1.1 shows the oil discovery in the different places around the world as an example case.

Table 1.1 First discovery of oil in different places in the world for commercial production.

The first commercial oil well was situated in the southwestern Ontario town of Oil Springs. Williams acquired some property that was known to have oil gum beds. He dug through the gum beds in search of the source of the oily deposits, and discovered crude oil. This first oil well was simply a hole in the ground, with oil rising up close to the surface. With the use of hand pumps, the oil was extracted at a rate of 37 barrels of oil per day. Williams built and operated a local distillery from which he refined and sold kerosene. Ontario’s first oil boom—reflected in town names such as Petrolia—paralleled a larger oil boom in northern Pennsylvania, where energy dynasties were beginning to emerge. Oil was not being used widely in commercial basis before middle of the nineteenth century. Oil had been used as medicine, flaming torches, and for lighting purposes before that. Now a day’s oil is the backbone of nation’s economy and the heart of modern civilization.

1.6 An Overview of Drilling Engineering

A multitude of issues are needed to be resolved even before the consultants or engineers ever see the prospect of the project. Most importantly, these phases of works are being completed before any drilling operation. Here, the principal party is called the operator. This operator is normally the Oil Company, who is a well-known major company or an independent. The operator employs the drilling consultant to protect and negotiate the operator’s interest. Meanwhile, the operator also engages geologists to locate the area where s/he feels to have a good prospect for hydrocarbon reserve. The geologists may recommend drilling a wildcat well (a small exploratory oil well drilled in land not known to be an oil field to get the geological information) into an untested field, or s/he may recommend a development well (a well drilled in a proved production field or area to extract natural gas or crude oil) to get the desired information about the formation. The operator’s next objective is to hire a landman to acquire drilling rights. The oil companies normally have a paid staff of geologists and landmen. The main responsibility of landman is to determine who is going to own the minerals rights in the area to be drilled. He also tries to acquire lease rights from the landowner through a document which is called an oil and gas lease. So, the landman is the representative of the operator who takes care of all of the negotiation parts with landowner so that the terms and conditions would be acceptable for the operator. After getting the lease and approval of license, the operator then hires the drilling contractor (a contractor who owns the drilling rig and employs the crew to drill the well). At this stage, operator hires the specialist consultants (normally service companies) to conduct other rig side jobs, such as casing, cementing, logging, perforating, fracturing, acidizing, lost tool recovery, drilling fluid preparations, etc. The geologists and reservoir engineers are again engaged to analyze the drilling results and to determine which zones, if any, are worth producing. If there are one or more potential zones, the well would be completed for production. On the other hand, if there are no formation zones, the well would be plugged and abandoned in accordance with the regulations that protect the water zones drilled through. The operator cannot just pick up the rig and leave the hole open. Finally, the operator is responsible for producing and selling the hydrocarbons from its proven zones.

1.6.1 Licensing, Exploration and Development

Petroleum and mineral resources are usually owned of by the government of the host country. Normally, the ministry of petroleum/oil and gas (different names in different countries) is empowered on behalf of the government to invite companies to apply for exploration and production licenses within the country. Exploration licenses may be awarded at any time based on company’s reputation and terms and conditions. Exploration licenses do not allow a company to drill any deeper than certain depth and are used primarily to enable a company to acquire seismic data from a given area. Production licenses allow licensees to drill for, develop and produce hydrocarbons from whatever depth is necessary. Costs of field development are so huge that major oil companies normally form partnerships to share the expenses. Typically, oil companies operate in joint ventures to reduce their individual risk as well. One of the companies within the joint venture is designated and empowered to act as an operator that actually supervises the work.

As long as the governments of most nations issue licenses to explore, develop, and produce its oil and gas resources, the company needs to obtain a production license even before drilling an exploration well. Prior to applying for a production license, however, they will conduct an investigation exercise, in which they will analyze any seismic data they have acquired, analyze the regional geology of the area, and finally take into account any available information on producing fields or well tests performed in the vicinity of the prospect they are considering. Based on the above, and a general look at the exploration and development costs, the pricing, and tax regimes, the company will decide whether it would be worth developing the field (if a discovery were made) or not. If the project is considered worth exploring further, the company will try to acquire a production license and continue with the exploration phase of the field. This will allow the company to drill wells in the area of interest. It will in fact commit the company to drill one or more wells in the area. The exploration phase of the field development may begin with the company shooting extra seismic lines in a closer grid pattern than it had done previously. This will provide more detailed information about the prospect and will assist in the definition of an optimum drilling target. Despite improvements in seismic techniques the only way of confirming the presence of hydrocarbons is to drill an exploration well (the well that helps to determine the presence of hydrocarbons).

Drilling is very expensive, and if hydrocarbons are not found, there is no return on the investment, although valuable geological information may be obtained. With only limited information available, a large risk is involved (on average, only one in eight North Sea exploration wells are successful). If the company decides to go ahead for hydrocarbon presence, an exploration well proposal is drawn up to drill in the most likely position on the reservoir. The length of the exploration phase will depend on the success. There may be a single well or many wells drilled on a prospect in the exploration phase. If a viable discovery is made on the prospect then the company enters the Appraisal phase of the field. During this phase more seismic lines may be shot and more wells will be drilled to establish the extent of the reservoir. These appraisal wells (a well that is drilled to establish the extent (size) of reservoir) will yield further information, on which future plans will be based. The information provided by the appraisal wells will be combined with all of the previously collected data. Engineers will investigate the most cost-effective manner through which they can develop the field. If the prospect is deemed to be economically attractive, this development design will culminate in the production of a field development plan. This plan will be submitted for approval. If approval of the development is received, then the company will commence drilling development wells (a well that is drilled in a proved production field or area to extract natural gas or crude oil) and construction of production facilities according to the development plan. Once the field is on-stream, the companies’ commitment continues in the form of maintenance of both the wells and all of the production facilities.

After many years of production, it may be found that the field is yielding more or possibly less hydrocarbons than initially anticipated at the development planning stage, and the company may undertake further appraisal and subsequent drilling in the field. Once the field is no longer producing economically, the company will be required to abandon the field in a sustainable (i.e., safe and environmentally acceptable) fashion.

1.6.2 Role of Drilling during Field Development

The role of drilling during, or even before, the field development is enormous. There are some step-by-step works that are normally followed by the operators during the development phase of an oil field. Figure 1.1 shows a complete loop for different phases of the development works related to drilling engineering. In addition, to understand the process well, the following steps are mentioned while drilling an oil/gas well continued:

1. Complete or obtain seismic, log, scouting information, or other data

2. Lease the land or obtain concession

3. Calculate reserves or estimate from best data available

4. If reserve estimates show payout, proceed with well

5. Obtain permits from various government authorities

6. Prepare drilling and completion program

7. Ask for bids on footage, day work, or combination from selected drilling contractors based on drilling program

8. If necessary, modify program to fit selected contractor equipment

9. Construct road, location/platforms and other marine equipment necessary for access to site

10. Gather all personnel concerned for meeting prior to commencing drilling (pre-spud meeting)

11. If necessary, further modify program

12. Drill well for production

Figure 1.1 Role of drilling during field development.

Once a decision is made to drill a well, then the drilling engineer’s role comes into play. In this long process, a drilling engineer plays a vital role during drilling operations, including planning, design, and supervision. The following are some of the important responsibilities that are accomplished by the drilling engineer:

Well planning before drilling

Monitor drilling operations including mud fluid

Managing rig side people (i.e., management job)

After drilling, review drilling results and recommend future improvements

Prepare report

General duties

1.6.3 Types of Drilling Wells

If the subsurface hydrocarbon formations are identified from primary seismic survey, a decision is made to either develop the field to get more information from exploration, or to declare the field as abandoned. If the field is decided as a potential area of hydrocarbon production, actual drilling of one or more wells is necessary to determine whether or not sufficient accumulations of hydrocarbon exist as commercial quantities. Based on these strategic decisions and primary outcomes, drilling wells can be categorized into four types, such as exploration well, appraisal well, development well, and abandonment well.

An exploration drilling well is often called a Wildcat well. It is drilled during the initial phases of exploration. The drilling is completed with the hope of getting the information whether the reservoir rocks contain any oil or gas. The main objectives of this drilling well are to determine the presence of hydrocarbons, to provide a geological data (such as cores, logs) for evaluation, conduct flow test through the well to determine its production potential, and to obtain the fluid samples for laboratory analysis. Once hydrocarbons are discovered, more drilling is done to test if the field is commercially viable or not. So, appraisal wells are those wells that are used to establish the extent (size) of the reservoir. This well helps in gathering information such as whether there is a sufficient amount of oil and gas to justify investing money in infrastructure to recover oil/gas to scales. The development wells are sometime called production wells. This well is drilled in a proved production field/area to extract hydrocarbons (i.e., natural gas/crude oil). This drilling well is done to create a flow path from the reservoir to the surface, and then through the production facility. Finally, if no hydrocarbon discovery is found, the well that was drilled to gather the information needs to be closed to prevent possible environmental disaster. The well that is sealed and closed is called an abandonment well. This well can be an exploration or appraisal well.

1.6.4 Sequences of Drilling Operations

The sequences of drilling operations can be categorized into three major steps. The first step is to initiate and accelerate the drilling of a hole on the earth’s surface for hydrocarbon extraction, the second step is the casing operations, and the third step is the completion of well. However, the second and third steps are basically needed to support drilling operations in a sustainable manner. When drilling operations continue, the second step needs to be accomplished simultaneously with drilling. The third step comes once drilling operations reach their target level.

In general, several casing steps are completed to avoid blowout or any other consequences during drilling operations. However, when a well is drilled in high pressured zones, weak and fractured formations, unconsolidated formations, or sloughing shales, the second step must be completed without any excuse to avoid substantial destruction at the rig-side. Different casing sizes are required for different depths. In general, five different casing sizes are used to complete a well. Figure 1.2 shows the different casings, such as outmost casing (or conductor pipe), surface casing, intermediate casing, production casing, and liner. As shown in Figure 1.2, these pipes are run to different depths, and one or two of them may be omitted, depending on the drilling condition. However, they may also be used as liners, or in combination with liners. Based on the above casing concept, the sequences of the drilling operations are outlined, considering an onshore oil field.

Figure 1.2 Typical casing program showing different casing sizes and their setting depths.

Once the location is finalized, depending on primary seismic survey, a large diameter hole (normally 36″) is drilled using a truck mounted mobile rig. This hole is only drilled to a shallow depth. It varies from 40′ – 500′ in length at onshore, and up to 1000′ at offshore. However, the conventional depth is 100′ and normal range is 50′ – 150′. The hole must be lined with steel pipe or casing (usually called conductor pipe). This is the outmost casing string. The main purpose of this casing is to hold back the unconsolidated surface formations and prevent them from falling into the hole. The conductor pipe is cemented back to the surface, and it is either used to support subsequent casing and wellhead equipment, or the pipe is cut off at the surface after setting the surface casing. Once the conductor is in place, the drilling rig is brought on to the site and set up for the next stage. A 30″ casing shoe is used in this example (Figure 1.2).

A smaller diameter bit must be used to drill the next section below the conductor. If the conductor is 30″ diameter, a 26″ bit may be used. This 26″ hole may be drilled down to 2000′ (normal range: 300′ – 5000′) through unconsolidated formations, which may cave in. The hole must be lined with another string of casing (surface casing) which may be up to 20″ diameter as an example (Figure 1.2). The size of the surface casing normally varies from 7″ – 16″ in diameter and the most common sizes are 10¾″ and 13⅜″. The main functions of the surface casing string are to hold back unconsolidated shallow formations that can slough into the hole and cause problems, isolate freshwater formations, and to serve as a base on which to set the blowout preventers. The casing is lowered into the hole joint by joint, and then cemented in place.

The intermediate or protective casing is set at a depth between the surface and production casings. The main reason for setting intermediate casing is to case off the formations that prevent the well from being drilled to the total depth. It is also used to counter balancing the formation pressure. It varies in length from 5000’ – 15,000’ and 7″ and 11¾″ in outside diameter. In such case, a 17½″ bit is used to drill the hole down to 6000′. In case some of the formations in this section prove troublesome (e.g., sloughing shales), another string of casing (13⅜″ intermediate casing) must be run and cemented in place.

The next bit size is 12¼″ and drilling proceeds as before. By this time, we may be approaching the oil bearing formation zone. Any hydrocarbons can be detected by examining the rock cuttings, and if this proves favorable, we may want to evaluate the formation more fully. The drill string is pulled out, and electric logs run on wire line are lowered into the hole. We may also want to take core samples, using a special bit which will allow recovery of a section of rock. A DST (drill-stem test) may be carried out to gain further data. Once all of the test data indicates the positive results, suspended pipes are run from the bottom of the next largest casing string, which is called a liner. Liners are the pipes that do not usually reach the surface. There are several types of liners, such as drilling liner, production liner, tie-back liner, scab liner, and scab tie-back liner. The major advantages of liners are that the reduced length and smaller diameter of the casing results in a more economical casing design than would otherwise be possible, and that they reduce the necessary suspending capacity of the drilling rig. However, possible leaks across the liner hanger, and the difficulty in obtaining a good primary cement job due to the narrow annulus, must be taken into consideration in a combination string with an intermediate casing and a liner.

Before production casing or liner, if all the indications from the above tests are negative or show only slight indications of oil, the well will be abandoned. However, if positive results come, production casing is set through the prospective productive zones, except in the case of open-hole completions. It is usually designed to hold the maximal shut-in pressure of the producing formations. It is also designed to withstand stimulating pressures during completion and workover operations. Production casing provides protection for the environment in the event of failure of the tubing string during production operations, and allows for the production tubing to be repaired and replaced. Production casing varies from 4½″ and 9⅝″ in diameter, and is cemented far enough above the producing formations to provide additional support for subsurface equipment and to prevent casing buckling. Production casing goes up to the formation zone. So, there is no specific length for this casing. It varies well to well, depending on the depth of formation zones. Finally, production tubing is place for hydrocarbon production (Figure 1.2).

The third or final stage of the drilling sequences is the completion phase. As mentioned earlier, the completion of the well involves running the production casing (9⅝″) at total depth (TD) to seal off the oil producing zone (temporarily). Another string of pipe known as tubing 4½″ diameter) is now run with a packer on the outside. When packer is positioned just above the pay zone (Figure 1.2), its rubber seals are expanded to seal off the annulus between tubing and 9⅝″ casing. A set of valves is initiated on the top of the casing to control the flow of oil once it reaches the surface. To initiate the production, a perforating gun is run down the tubing on wireline, and is positioned adjacent to the pay zone. Holes are shot through the casing and cement into the formation. The hydrocarbons flow into the wellbore and up the tubing to the surface.

1.7 Organization Chart and Manpower Requirements during Drilling Operations

Drilling requires many different skills and involves many different companies. The manpower needed to complete the drilling operations is normally engaged from three separate organizations. The organizations, such as drilling contractor, well operator, and drilling services companies, work together and provide manpower as required and requested. A typical drilling organization chart is shown in Figure 1.3. The oil company seeking to exploit the petroleum reserves is known as the Well Operator. The operator bears overall responsibility for drilling operations. The company representative makes the rig-side spot decisions based on the well plan for drilling operations and other services if necessary. The planning of the well is usually done by the operator’s staff engineers working at headquarters/control office in town. They draw up a drilling program that must be followed as the well is being drilled. Usually the operator will have a representative on the rig (sometimes called the company man). His job is to ensure that drilling operations go ahead as planned, to make decisions affecting progress of the well, and to organize supplies of equipment. Any consumable items (i.e., drilling bit, drill pipe, cement, etc.) must be provided by the operator. He will be in daily contact with his drilling superintendent in the main control office in town. There may also be a drilling engineer and/or a geologist on the rig employed by the operator.

Figure 1.3 Drilling rig organizational chart.

The oil company usually employs a Drilling Contractor to actually drill the well. The contractor provides the rig and the crew to operate it. The drilling contractor is responsible for maintaining the rig and the associated equipment. The rig operation and rig personnel supervision are the responsibilities of drilling contractor. The drilling contractor will have a tool pusher in overall charge of the rig. He is responsible for all rig floor activities, and coordinates with the company man to ensure progress is satisfactory. Since drilling continues twenty-four hour a day, there are usually two drilling crews. Each crew works under the direction of the driller (or tool pusher). The crew will generally consists of a derrick man (who will also be liable for the pump while drilling continues), three roughnecks (working on the rig floor), plus a mechanic, an electrician, a crane operator, and roustabouts (general laborers).

During the course of the well, certain specialized skills or equipment may be necessary (i.e., logging, surveying, etc.). The jobs are done by the appointed service companies. The service companies are employed by the operator. They provide all the specialized logistic supports and rig-side services. The service company’s personnel work on the rig as and when required. Sometimes they are employed on a long-term basis (e.g., mud engineer), or only for a few days (e.g., casing crews), based on demand at rig-side.

1.8 Aspect of Sustainability in Drilling Operations

Drilling is a necessary step for petroleum exploration and production. The conventional rotary drilling technique falls short, since it is costly and contaminates surrounding rock and water due to the use of toxic components in the drilling fluids. Conventional rotary drilling has been the main technique used for drilling in the oil and gas industry. However, this method has showed its limits regarding the depth of the wells drilled, in addition to the use of toxic components in drilling fluids. The success of a high risk hydrocarbon exploration and production depends on the use of appropriate technologies. Therefore, to overcome the limitations of conventional rotary drilling technique, we need to look for other environmentally friendly drilling technologies which may lead to a sustainable drilling operation.

Generally, a technology is selected based on criteria such as technical feasibility, cost effectiveness, regulatory requirements, and environmental impacts. Recently, Khan and Islam (2006) introduced a new approach in technology evaluation based on the novel sustainability criterion. In their study, they not only considered the environmental, economic, and regulatory criteria, but investigated sustainability of a technology. ‘Sustainability’ or ‘sustainable technology’ has been using in many publications, company brochures, research reports, and government documents which do not necessarily gives a clear direction. Sometimes, these conventional approaches/definitions mislead to achieve true sustainability. Figure 1.4 shows the directions of true sustainability in technology devolvement. It shows the direction of nature-based, inherently sustainable technology, as contrasted with an unsustainable technology. The path of sustainable technology is its long-term durability and environmentally wholesome impact, while unsustainable technology is marked by Δt approaching 0. Presently, the most commonly used theme in technology development is to select technologies that are good for t = ‘right now’, or Δt = 0. In reality, such models are devoid of any real basis (termed aphenomenal by Khan et al., 2005), and should not be applied in technology development if we seek sustainability for economic, social, and environmental purposes.

Figure 1.4 Direction of sustainable and unsustainable technology (Khan and Islam, 2006; Hossain et al., 2009).

In addition to technological details of an appropriate drilling technology, the sustainability of this technology is evaluated based on the model proposed by Khan and Islam. Figure 1.5 shows the detailed steps for its evaluation. The first step of this method is to evaluate a sustainable technology based on time criterion (Figure 1.5). If the technology passes this stage, it would be evaluated based on criteria such as environmental, economic, and social variants. According to Khan and Islam’s method, any technology is considered sustainable if it fulfills the environmental, economic, and social conditions (Cn + Ce + Cs) ≥ constant for any time, t, provided that, dCnt/dt ≥ 0, dCet/dt ≥ 0, dCst/dt ≥ 0.

Figure 1.5 Flowchart of sustainability analysis of a drilling technology (redrawn from Khan and Islam, 2008; Hossain et al., 2009).

To evaluate the environmental sustainability, a proposed drilling technique is compared with the conventional technology. The current drilling technologies are considered to be the most environmentally concerning activities in the whole petroleum operations. The current practices produce numerous gaseous, liquid, and solid wastes and pollutants, none of which have been completely remedied. Therefore, it is believed that conventional drilling has negative impacts on habitat, wildlife, fisheries, and biodiversity.

For analyzing the environmental consequences of drilling, conventional drilling practices need to be analyzed, which will be continued, chapter by chapter, in this book on sustainability. In conventional drilling, different types of rigs are used. However, the drilling operations are similar. The main tasks of a drill rig are completed by the hosting, circulating, and rotary system, backed up by the pressure-control equipment. A drill bit is attached at the end portion of a drill pipe. Motorized equipment rotates the drill pipe to make it cut into rocks. During drilling, many pumps and prime movers circulate drilling fluids from tanks through a standpipe into the drill pipe and drill collar to the bit. The muds flow out of the annulus above the blowout preventer over the shale shaker (a screen to remove formation cutting), and back into the mud tanks. Drilling muds are composed of numerous chemicals, some of which are toxic, and which are harmful to the environment and its flora and fauna. These issues will be discussed in the drilling mud chapter. The conventional practice in the oil industry is to use different drilling techniques, where huge capital is involved, and which create huge environmental negative impacts. The technology is also more complicated to handle. Therefore, sustainable petroleum operation is one of the important keys for our future existence in this planet.

1.9 Summary

This chapter discusses some of the core issues related to drilling engineering. Even before starting drilling operations, many activities need to be completed to fulfill the different parties’ requirements, which are well-covered here. Moreover, this chapter addresses issues such as the definition of drilling engineering, different terminologies related to drilling operations, licensing, development plan, work sequences, and responsibilities of drilling engineers and different companies. This chapter covers almost all aspects of drilling management. Finally, the benchmark of sustainability is also discussed in the chapter.

References

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EPA, 2000. Development document for final effluent limitations guidelines and standards for synthetic-based drilling fluids and other non-aqueous drilling fluids in the oil and gas extraction point source category. United States Environmental Protection Agency. Office of Water, Washington DC 20460, EPA-821-B-00-013, December 2000.

Holdway, D.A., 2002. The Acute and Chronic Effects of Wastes Associated with Offshore Oil and Gas Production on Temperature and Tropical Marine Ecological Process. Marine Pollution Bulletin, Vol. 44: 185–203.

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Khan, M.I., and Islam, M.R., 2006. Achieving True Sustainability in Technological Development and Natural Resources Management. Nova Science Publishers, New York, USA, pp. 381.

Khan, M.I., and Islam, M.R., 2008. Petroleum Engineering Handbook: Sustainable Operations. Gulf Publishing Company, Texas, USA, pp. 461.

Khan, M.I, Zatzman, G., and Islam, M.R., 2005. New sustainability criterion: development of single sustainability criterion as applied in developing technologies. Jordan International Chemical Engineering Conference V, Paper No.: JICEC05-BMC-3-12, Amman, Jordan, 12–14 September 2005.

Patin, S., 1999. Environmental impact of the offshore oil and gas industry. EcoMonitor Publishing, East Northport, New York. 425 pp.

Veil, J.A., 2002. Drilling Waste Management: past, present and future. SPE paper no. 77388. Annual Technical Conference and Exhibition, San Antonio, Texas, 29 September–2 October. Waste Management Practices in the United States, prepared for the American Petroleum Institute, May 2002.

Chapter 2

Drilling Methods

2.1 Introduction

Drilling is one of the oldest technologies. Man used to dig a hole for different purposes. Until internal combustion engines were developed in the late 19th century, the main method for drilling rock was a muscle power of man or animal. Rods were turned by hand, using clamps attached to the rod. The rope and drop method was invented in Zigong, China where they used a steel rod or piston raised and dropped vertically via a bamboo rope. These Chinese wells were drilled using bamboo derricks and reached depths of up to 4800 ft. The first rotary drilling rig was developed in France in the 1860’s. However, it was seldom used because it was erroneously believed that most hydrocarbons were under hard-rock formations that could be easily drilled with cable-tool rigs. The rotary drilling system that circulates fluid to remove the rock cuttings were successfully used in Corsicana, Texas in 1880’s where drillers searching for water, and fortunately they discovered oil. Since then, drilling rigs underwent a revolution of improvement in terms of drilling a well in good, safe and economic manner. There are four main procedures on how to select the appropriate drilling: i) wells design for the same field, ii) the expected loads during drilling, iii) testing and any other related operations, and iv) compare the expected loads with the existing rigs and select the best rig and its appropriate components.

Now days, there are a lot of types of drilling rigs classified into two major types based on the drilling area environment which will be discussed in this chapter. This chapter focuses on the drilling methods used for hydrocarbon exploitation. This chapter covers the cable tool drilling rig, rotary drilling rig and its components, different rotary rig systems, types of rigs, current advancement of rig systems, and the knowledge gap that needs to be filled in this area. In all drilling methods a downward force has to be applied on the tool that breaks the rock, and therefore it is an important parameter for an effective drilling operation. In rotary drilling the cutting tool is the bit and the downward force is the weight of the drill string assembly applied on the bit. The conventional practice in the oil industry is to use heavy drill string assembly for which large capital expenses are required.

2.2 Types of Drilling Methods

There are two basic methods to drill a hole for hydrocarbon withdrawal from an underground system. These are: i) cable tool drilling, and ii) rotary drilling.

2.2.1 Cable Tool Drilling

Cable tool drilling is defined as a drilling procedure in which a sharply pointed bit attached to a cable and is repeatedly lifted and dropped into the borehole. In cable-tool drilling, a heavy carbide tipped drill bit (i.e. along with drill string) is suspended in the hole by a rope or cable. A powered walking beam is operated by a steam engine through which the cable and attached bit assembly are lowered and raised. This upward and downward motion is repeated again and again. The drill bit chisels through the rock by finely pulverizing the subsurface materials. Each time the bit drops it and hits the bottom of the hole and thus cuts the rock. However, the basic principles employed in all cable tool drilling operations virtually have been unchanged since the Chinese first drilled shallow wells for salt water in the ancient days. The first oil well in the United States was drilled with cable tools in 1859 to a depth of 65 feet located near Titusville, Pennsylvania. Then, it was widely used from about 1870 onward. The cable-tool drilling method was in common use until the 1920’s. Now days, cable tool is a traditional way of drilling water wells in different places on earth. The majority of the large diameter water supply wells are completed using this technique. While this drilling method has been replaced in recent years by modern rotary drilling, it is still the most practicable drilling method for large diameter, deep bedrock wells, and in widespread use for small rural water supply wells.

A schematic diagram of cable tool rig is shown in Figure 2.1. The basic components of the cable tool rigs consist of the engine and boiler, the derrick and crown block, the bull wheel and drilling cable, the sand wheel and sanding line for the bailer, the vertical band wheel with a center crank, drill string and the walking beam supported by the Samson post. Band wheels are basically large pulleys (usually 8–10 ft in diameter) driven by a belt from the engine, which reduces the engine RPMs and increases power. A crank on the band wheel’s axle imparts up-and-down motion (via a pitman) to the walking beam. The other end of the band wheel is connected to the drilling cable by the temper screw. The walking beam alternately raises and loweres the drilling tools. Walking beams is typically 26′ × 12″ × 24″ in size. Bull wheels and sand wheels are spools for the drilling cable and sanding (or bailing) line, respectively. Additionally, fishing tools, various hand tools, wrenches, and forge tools are required for the drilling process. The drill string consists of the upper drill rods, a set of jars, and the drill bit. During the drill process, the drill string is periodically removed from the borehole and a bailer is lowered to collect the drill cuttings. Since the drill string must be lowered and raised to advance the boring, casing is typically used to hold back upper soil materials and stabilize the borehole.

Figure 2.1 A conventional cable tool rig.

This technology has achieved vast improvements in rig mechanisms and labor-saving devices. Some of the examples are modern rotary drilling rigs, powered with an internal combustion engine, electric motor, or steam engine and most sophisticated rig related equipment/tools. However, there are two major disadvantageous of the cable-tool method; first, the drilling has to be stopped often and the bit pulled up so that cuttings of chipped rock could be removed; second, this system has a hard time in drilling soft rock formations. The other disadvantages are: it is very slow, it does not effectively control subsurface pressures, and blowouts are common in cable tool operations.

2.2.2 Rotary Drilling

Rotary drilling is a complex mechanical technique in which a drill bit is attached to the bottomhole assembly where rotational motion is applied to cut the rock in a forward direction. Rotary drilling is new as compared to cable tool drilling. The first rotary drilling rig was developed in France in the 1860’s. At the time, it was believed that most hydrocarbons were under hard-rock formations that could be easily produced by the cable-tool rigs. The first rotary drilling rigs were introduced in 1890 to cut soft formations where cable-tool drilling was extremely inefficient due to caving. However, the rotary drilling system that circulates fluid to remove the rock cuttings was first successfully used in Corsicana, Texas in the early 1900 to get water. The first major success for rotary drilling was at Spindletop, Texas in 1901 where oil was discovered at a depth of 1020 ft and produced about 100,000 bbl/day. With time, the improvement of design of rotary drilling system made it easy to bore a hole up to a depth of 30,000 ft. The conventional rotary drilling rigs for an onshore (Figure 2.2a) and an offshore (Figure 2.2b) are shown in Figure 2.2.

Figure 2.2 A conventional rotary drilling rig.

In the rotary drilling method, a large, heavy drill bit is attached to the tip of the bottomhole assembly where a downward force is applied. The bit is rotated by a drill string composed of high quality drill pipe and drill collar. New sections of drill pipe assembly are added at the top of the hole as drilling progresses. The taller the rig structure, the longer the drill pipe sections that can be strung together. When it is time to replace the drill bit, the whole drill string must be pulled out of the hole. Each pipe is unscrewed and stacked on the rig floor. The cuttings are lifted from the bore hole by injecting drilling fluids (drilling mud) through drill pipe and bit nozzles. The drilling fluid is collected at the surface and passes through different tanks and separators to treat the mud properly. Once the mud is ready, the cycle repeats again.

2.3 Rotary Drilling Rig and its Components

A drilling rig is a complex assembly of large heavy anchored to a mechanical structure (Figure 2.3). The figure shows the different components of the rig above the ground level. Its basic function is relatively simple. The rig structure is a giant crane for lifting and lowering drill pipe, with a rotary table to rotate the drill pipe. The function of rig is to rotate a string of drill pipe and drill a hole in the ground. It must also pull the drill pipe out of the hole for drill bit changes and run the pipe back into the hole. The drilling rig must be able to perform some other functions such as circulating drilling fluid to clean the well bore and support the weight of the drill string so that the weight on the bit can be controlled (Figure 2.4a and b). The figure shows the different components that are underneath the rotary table along with other components above the rotary table. In general, the equipment that are used to drill and complete a hydrocarbon well are usually quite simple. Whether the drilling rig is offshore or onshore, they all have the same basic structure and use the same equipment.

Figure 2.3 A conventional rotary drilling rig with different components.

Figure 2.4 A conventional rotary drilling rig showing different components under rotary table.

A detail rotary rig devices and its different components are illustrated in Figure 2.5. Almost all the parts of a modern rig are leveled in Figure 2.5. A detail rig components names and their description are shown in this figure separately. The definitions and their descriptions are illustrated in Appendix 2A at the end of this chapter.

Figure 2.5 A modern rotary drilling rig and its components.

2.4 Drilling Process

When all the necessary equipment and the drilling rig are in place, the drilling processes start on for drilling activities. The drilling process entails several different systems which are interconnected and drives the whole drilling operations. The process can be categorized as i) power system, ii) hoisting system, iii) circulation system, and iv) rotary system. Sometime these systems are called drilling process subsystem. Most of rig components are engaged with one or more of these systems that are shown in Figure 2.5. This figure show the conventional rotary drilling process along with associated rig components related to the different systems.

2.4.1 Power System

The major components of the power system are the drawworks, mud pumps and rotary table are shown in the rig system (Figure 2.6). The individual components of the circulating system are shown in Figure 2.7. The diesel engine set is shown in Figure 2.8 which transmits power to the three major systems of the rig. Most of the rig power is consumed by the hoisting and circulating system. The other rig systems (such as rotary rig etc.) have much less power consumptions. The hoisting and circulating systems do not generally work at the same time. Power is supplied by large internal combustion engines (prime over) fueled by diesel. Depending on its size and capacity, the rig may have up to 4 prime movers which deliver more than 3,000 hp. A typical prime mover with generating set is shown in Figure 2.8. The diesel engines drive large electric generators. Electricity is then supplied to electric motors connected to the Drawworks, rotary table and mud pumps. Steam power and mechanical transmission systems were used on the early drilling rigs. Steam power and mechanical transmission systems were being used by the older rigs. Nowadays, modern rigs are powered by internal combustion diesel engines and the modern electric transmission enables the driller to apply power more smoothly and hence it avoids shock and vibration of the rigs.

Figure 2.6 Major components of power system shown in the rig system.

Figure 2.7 Major components of power system.

Figure 2.8 The generator set for power system.

Total power requirements for most of the modern rigs are from 1,000 to 3,000 hp. Generally, the characteristics of power system performance are stated in terms of output horsepower, torque, and fuel consumption for various engine speeds. The heating values of various fuels for internal combustion engines are shown in Table 2.1.

Table 2.1 Heating values of various fuels.

A typical arrangement of an engine with flywheel and pulley system is shown in Figure 2.9. The shaft power developed by an engine can be obtained by the following equation:

(2.1) equation

where;

Equation (2.1) can be written in terms of revolution per minute, weight on pulley and distance travel by the weight with velocity vector. In terms of revolution per minute, Eq. (2.1) can be written as:

(2.2) equation

Figure 2.9 A typical IC engine power output.

In terms of velocity vector and if we consider frictionless pulley system, Eq. (2.1) can be written as:

(2.3) equation

We know that power is the product of force and velocity. So, power of shaft can again be written as:

(2.4) equation

where;

If we use the Eq. (2.3) into Eq. (2.4), the resultant equation turns to Eq. (2.2). The overall engine power efficiency is determined as the power output by power input. Mathematically, it can be written as:

(2.5) equation

where;

Example 2.1: An internal combustion engine is run by diesel fuel in a rig side to generate power for the system. It gives an output torque of 1,600 ft – lbf at an engine speed of 1,150 rpm. The engine consumes fuel at a rate of 30 gal/hr. Calculate the wheel angular velocity, power output, overall efficiency of the IC engine.

Solution:

The angular velocity can be calculated by using the given equation:

equation

The power output can be calculated using Eq. (2.1) as:

equation

(Note: 1 hp = 33,000 ft – lbf / min)

Since the engine is run by diesel fuel, therefore from Table 2.1, the density ρ is 7.2 lbm / gal and the heating value Hf is 19,000 Btu / lbm. Therefore the fuel consumption rate wf can be obtained by unit conversion as:

equation

Therefore, the total heat energy consumed by the IC engine i.e. input power can be calculated by using input power part of Eq. (2.5) as:

equation

(Note: 1 Btu = 779 ft – lbf)

Thus, the overall efficiency of the IC engine is obtained by using the Eq. (2.5) as:

equation

Example 2.2: A diesel engine was running at a speed of 1250 rpm at the drilling operations side. The driller noticed that the engine shaft output is 360 hp. He was trying to pull a drillstring of 600,000 lbf. The engine was running for one hour. Calculate the wheel angular velocity, torque developed by the engine, the drillstring velocity, distance travelled by the drillstring.

Solution:

The angular velocity can be calculated by using the given equation:

equation

The torque output is obtained using Eq. (2.1) as:

equation

(Note: we know that 1 hp = 33,000 ft – lbf / min)

The drillstring velocity can be calculated using the Eq. (2.4) as:

equation

As the engine was running for one hour, so the total distance traveled by the drill string within one hour is obtained by using Eq. (2.4) as:

equation

So,

equation

2.4.2 Hoisting System

Hoisting system is defined as a system which works as a complex pulley system to raise the travelling block and remove the drill pipe and allows adding an extra length of pipe or a new drill bit. The main function of the hoisting system is to lower or lift the drillstring, casing string, and other subsurface equipment into or out of the hole. In addition, making a connection (i.e. the periodic process of adding a new joint of drill pipe as the hole deepens), and making a trip (i.e. the process of removing the drillstring from the hole to change a portion of the downhole assembly and then lowering the drillstring back to the hole bottom) are the two regular tasks that need to be done by hoisting system. The main components of hoisting system are derrick (i.e. steel tower/mast) and substructure, drawworks, and block & tackle. The assembly and components of a hoisting system are shown in Figure 2.10.

Figure 2.10 Different components of hoisting system.

Derrick:

Derrick is the steel structure part of a rig. It provides vertical height required to raise pipe sections (Figure 2.11). It must have sufficient height and strength to perform its functions. Derrick is rated according to its ability to withstand compressive loads & wind loads. The compressive load of a derrick is calculated as the sum of the strengths of the four legs. Each leg is considered as a separate column and its strength is calculated at the weakest section. The wind load is specified in two ways, namely with or without pipe setback based on API derricks.

Figure 2.11 Derrick load system using block and tackle.

The wind load can be calculated as:

(2.6) equation

where;

The total compressive load on derrick can be calculated using the block and tackle arrangement as shown in Figure 2.12. If the system has frictionless pulley, the following relationship is evident:

(2.7) equation

where;

Figure 2.12 Derrick/mast of the hoisting system.

Example 2.3: During a drilling rig structure fatigue test, the operator measured the wind load of 0.5 psi. The rig has ten lines which are strung through the travelling block. A hook load of 250,000 lbf is being hoisted. According to the API standard, calculate the wind velocity, and the total compressive load.

Solution:

The wind velocity can be obtained using Eq. (2.6) as:

equation

(Note: we know that 1 ft² = 144 in²)

Therefore,

equation

The total compressive load on the derrick is obtained using the Eq. (2.4) is:

equation

The load imposed on the derrick i.e. the total compressive load on derrick is greater than the hook load due to the arrangement of lines on the block and tackle (Figure 2.12). Therefore, using the fast line and dead line tension, the derrick load can also be calculated by:

(2.8)

equation

where;

In practical situation, the total derrick load is not distributed equally over all four derrick legs due to the placement of drawworks. Figure 2.12 shows that the tension in the fast line is distributed over only two of the derrick legs (i.e. legs A and C) and the dead line affects only Leg D due to its attachment with this leg only. Table 2.2 shows