Theory and Technology of Multiscale Dispersed Particle Gel for In-Depth Profile Control

By Caili Dai, Guang Zhao, Qing You and 3 more

Theory and Technology of Multiscale Dispersed Particle Gel for in-depth Profile Control systematically introduces concepts surrounding preparation principles and methods of DPG particles. The whole preparation process can be divided into two major stages: bulk gel crosslinking reaction period and DPG particle preparation period. The effects of bulk gel strength, shearing time, shearing rate and bulk gel-water ratio on PDPG particles are also systematically analyzed. Zirconium bulk gel, phenolic resin bulk gel, and organic-inorganic cross-linked bulk gel with short gelation time on the ground are introduced, along with gelation properties, gelation influencing factors, thermal stability and applicable conditions.

This book systematically describes the theory and technology of multiscale dispersed particle gel which shows promise as an acceptable alternative to conventional water technologies needed for enhanced oil recovery in high water cut mature oilfields.

• Systematically describes the theory and technology of multiscale dispersed particle gel
• Shows the details of each technology and how easy it is to achieve industrial production of DPG (dispersed particle gel particles)
• Presents technical achievements from 20 successful, established industrial production lines and 17 oilfields at home and abroad
• Includes the development of three new technologies based on DPG particles

• Language: English
• Publisher: Elsevier Science
• Release date: Sep 9, 2021
• ISBN: 9780323998505

Caili Dai

Caili Dai, China University of Petroleum (East China), Professor; qualifications and experience: enhanced oil recovery; profile control and water shut off; gel treatment; steam channel profile control; fracturing fluid research.

Book preview

Preface

Water flooding is the main development method of China’s oilfields. However, long-term water flooding aggravates reservoir heterogeneity, resulting in a high water-cut rate and low oil recovery. Polymer gel is an industry-recognized profile control agent that can decrease the formation heterogeneity and enhance oil recovery. The first-generation polymer gel that originated in 1988 is a chromium cross-linked polymer gel, whereas the second-generation polymer gel that originated in 2001 is a phenolic resin cross-linked polymer gel. These two kinds of gels have been successfully applied for water control in conventional oil fields. However, the oilfields have been gradually shifting from shallow to deep, low permeability or other complex reservoirs, while the traditional polymer gels have inherent drawbacks such as shear degradation due to injection device and seepage shearing in the formation, and dilution caused by contact with the reservoir minerals and fluids. The treatment risk has been increased due to uncontrolled gelation time and uncertainness of cross-linking due to shear degradation, changes in gellant compositions, and dilution effect. Besides, the traditional polymer gels have lower thermal stability, resulting in over cross-linking or syneresis in high temperature (>120°C) and high salinity (>200,000 mg/L) reservoirs. Therefore the polymer gels with the advantage of high temperature and high salinity resistance, controllable gelation, on-site online production, deep injection and migration, and high-strength water control ability are necessary. They bring a new direction for the development of water control technology.

Since 2004, Prof. Dai’s scientific research team has focused on dispersed particle gel (DPG) research and has developed a novel DPG profile control technology. This technology is a complete innovation that overcomes the traditional polymer gel drawbacks. Specifically, DPG particles have been successfully prepared with bulk gel by a high shearing method on the ground. A series of original achievements have been made in preparation theories and methods, bulk gel, process equipment, and a DPG+ system. After 17 years of scientific research, 32 invention patents were authorized, including 14 patents in the United States and Europe, and two computer software copyrights were authorized. Twenty industrial production lines with an annual output of 3000 tons and above have been set up, and the technical achievements have been industrialized in 17 oilfields at home and abroad, including Changqing, Tahe, Shengli, and Bohai, of China, and Kazakhstan. Water cutoff and oil have been enhanced significantly after applying these DPG treatments. Laboratory tests and field applications indicate that the in-depth profile control technology of multi-DPG particles is a new generation technology that provides a reference to water production control in high water-cut oilfields.

This book will help extend the influence of multiscale DPG in-depth profile control technology in the application of enhanced oil recovery, lead the advancement of enhanced oil recovery technology, and provide references for related petroleum technologies.

The authors would like to thank Yining Wu, Lin Li, Yongpeng Sun, Bin Yuan, Long He, Haien Yang, Renwei Qu, and Yingsheng Sun for their great help during the compiling of this book.

It is sincerely hoped that readers can put forward valuable opinions on the problems existing in this textbook, so that they can be revised for the next edition.

Chapter 1

Introduction

Abstract

This chapter focuses on the development history of particle plugging agents, including prepreparation gel particles (PPG), polymer microspheres, and dispersed particle gel (DPG). The size of PPG particles ranges from 1 to 5 mm which can swell to 10–100 mm after adsorbing water. However, most swellable PPG particles are broken when they flow through the pore throat, which cannot make a complete use of PPG particles. The polymer microspheres are usually prepared by the emulsion polymerization method. The method requires an accurate reaction temperature and reaction time, which is a complex preparation process. Considering the simple preparation, low cost, and industry production demands, a novel particle system named DPG has been successfully prepared by the colloidal mill method using bulk gel systems. The features and advantages of DPG are systemically introduced in this chapter.

Keywords

PPG; polymer microspheres; DPG; profile control and water shutoff

Enhanced oil recovery (EOR) is both an eternal theme of oilfield development and a crucial guarantee for China’s energy strategic security. In China, the water-flooding oilfield accounts for a large proportion (>80%) at present. However, long-term water flooding during the development of the oilfield has resulted in aggravated heterogeneity of reservoirs, and the successive entrance of oilfields into the high water-cut stage which is cancerous for oil recovery. As a result, low recovery and poor economic performance occur, approximately two third of the oil remains underground, and those phenomena are even far worse in complex unconventional reservoirs, such as fractured reservoirs with low permeability and reservoirs with high temperature and high salinity.

Profile control and water plugging technology is recognized as an important method to improve the effectiveness of water flooding, with plugging agents as the key to ensuring its success. Up to now, bulk gels have been the most widely used plugging agents for profile control and water plugging across the world [1,2]. Bulk gels are a kind of viscoelastic material possessing a three-dimensional network structure formed by intermolecular cross-linking between polymers and cross-linking agents. The polymers are mostly partially hydrolyzed polyacrylamides. The cross-linking agents mainly include chromium ion, zirconium ion, phenolic resin, and polyethylenimine. Bulk gels have the advantages of adjustable gelation time and gelling strength, high plugging capacity, and good profile control effect. In practice, the first step is to inject the mixed solution of polymer and cross-linking agent into the target formation, and then shut the well and wait for gelling. Next, the bulk gel plugs the highly permeable zone to reduce the permeability of water. Finally, the production wells are open and the injection wells start to inject water, so that a balanced flooding is achieved and water-flooding effectiveness and oil recovery are improved. The profile control and water plugging mechanism of bulk gel is shown in Fig. 1.1. Although the gel treatments have been successfully conducted on many oilfields worldwide, the gelling solution is easily affected by the shear degradation due to the injection device and seepage shearing in the formation, and dilution caused by contact with the reservoir’s minerals and fluids. It usually leads to uncontrolled gelation time and uncertainness of the systems and increases the treatment risk. Therefore it is difficult to predict the gelation time, gel strength, and the depth of the gelatinization in the formation during the underground gelatinization process, which affects the effectiveness of profile control and water plugging process.

Figure 1.1 The profile control and water plugging mechanism of bulk gel.

In addition, linked polymer solution (LPS) and colloidal dispersion gel (CDG) though different in names, have a similar adhesive nature. Both systems use low-concentration polymers and cross-linking agents to form a colloidal dispersion system with intramolecular cross-linking in the majority and intermolecular cross-linking in the minority. Thus the newly-formed system possesses low viscosity and both a colloid and a solution nature [3,4] (Fig. 1.2). Since there is no continuous network structure, it is able to enter the deep formations and control water production. With the deepening of research and the implementation of field testing, some scholars believe that LPS and CDG are a kind of partly cross-linking system, and that their performance is not only affected by the shear degradation and dilution effect but also by the contaminated water for preparation. Generally, LPS and CDG have poor resistance to high temperature and high salinity, and thus are not suitable for high temperature and high salinity reservoirs.

Figure 1.2 Difference between intramolecular cross-linking and intermolecular cross-linking.

To solve the unpredictable situation during the kinetics reaction in the gelatinization process underground, the experts put forward the method of using prepreparation gel particles (PPG) to plug large pores or the highly permeable layer for profile control, at the ninth national water plugging conference, held in Hainan province in the 1990s. The PPG particles are mainly composed of monomer, cross-linking agent, auxiliary agent, and strength control agent (clay). Under certain conditions, the bulk gel with certain water absorption and swelling properties can be formed, and then a series of solid particles with different expansion abilities, different strengths, and different particle sizes are made through drying, crushing, granulation, and screening [5–7]. The PPG particles with the three-dimensional network structure contain a large number of hydrophilic groups, which can adsorb a great amount of water and swell. The hydrophilic property makes the PPG significantly change its volume under different conditions. The three-dimensional skeleton structure generated by cross-linking gives it an acceptable strength, which results in plugging in the dominant channels and changing the flow direction of the fluid. Meanwhile, the viscoelastic material after water absorption and particle swelling can be reversibly deformed by external forces. When the external force is reduced, the deformation can be recovered to a certain extent of its original shape. In the profile control operation, the amoeba characteristics can be fully utilized to change the local pressure field of the reservoir, so as to realize the purpose of fluid diversion (Fig. 1.3). However, due to the limitation of the preparation conditions, the size of PPG particles often range from 1 to 5 mm, with swelling to 10–100 mm after adsorbing water. Since being affected by formation pressure, most swellable PPG particles are broken when they flow through the pore throat, which cannot make a complete use of PPG particles. In addition, the particle size cannot adapt to deep formations and their adaptability to low permeability reservoirs is weak, so it is unable to realize online continuous integration of production and injection as well.

Figure 1.3 Mechanisms of particle passing through pore throat [8].

Polymer microspheres, known as Bright Water overseas and originating from the idea proposed by BP Amoco, refer to a system of thermally activated particles (TAP). Featuring good swelling performance, temperature and salt resistance, size-controllability, and other characteristics, those microspheres can be applied to improve oil recovery. They are usually prepared by inverse (micro)emulsion polymerization, with a water-soluble monomer (acrylamide AM, acrylic acid, and salt tolerance of heat-resistant functional monomer AA) as the raw material. Using an emulsifier, the polymer microspheres are evenly dispersed in the oil (mineral oil, kerosene, diesel, etc.) and transformed into a microemulsion after mechanical stirring. The newly made microemulsion then starts a polymerization reaction under the action of the initiator and after that a water-in-oil emulsion system is formed. The particle sizes of the synthesized microspheres are in the nanometer scale, especially in the reverse microemulsion polymerization method, with the particle sizes ranging from 10 to 100 nm. The method requires a large number of emulsifiers and an accurate reaction temperature and reaction time, which is a complex preparation process. In addition, the polymer microspheres also can be prepared without an emulsifier by the method of inverse suspension polymerization and dispersed polymerization, but the particle sizes are relatively large.

Migration, plugging, elastic deformation, remigration, and replugging characteristics of polymer microspheres are the deep profile control and displacement mechanisms in the formation. Through these characteristics of polymer microspheres, the swept volume of the subsequent injected water is expanded [2,9–13]. In order to fully achieve the deep profile control capacity of polymer microspheres, accurate control of the particle size and particle size distribution of the microspheres is a key issue. When the particle size of the microsphere matches the pore throat of the reservoir rock, the plugging rate and elastic deformation migration pressure gradient of the microsphere reach their optima. If the particle size is too small, it cannot produce effective plugging at the pore throat. Comparatively, oversized microspheres cannot migrate to the full depth of the formation; they may even find difficulty in injection, which can bring about an undesired effect of profile control treatment. Field tests have shown that polymer microspheres are generally suitable for deep profile control in low permeability reservoirs. This method is often not suitable for formations with high permeability layers, large channels, and fractures. In recent years, researchers have designed large-sized core–shell structured microspheres to synthesize submicron and micron polymer microspheres, and endowed the microspheres with self-cross-linking function and formation adsorption capacity to solve the above problems. However, the cost is relatively high, and it is difficult for both the microsphere size and the reservoir to respond in time during the injection, which can result in a large matching uncertainty. Therefore their applications in oilfields are limited to some extent.

Due to the adaptability of polymer gels, PPG particles, and polymer microsphere plugging agents as well as the problems exposed in the field application, it is urgent to develop a new plugging agent to meet the requirements of high permeability layers or large pores with different permeabilities in actual reservoirs. That is the plugging agents should be easily injected, effectively plugged, and readily transported. In 2004 our research group initiated a new concept of dispersed particle gel (DPG) and the DPG particles were successfully prepared with a bulk gel by a mechanical shearing method. This new concept moved the chemical cross-linking reaction process from underground to the ground’s surface. The water control mechanism has been transformed from the pouring sausage type of polymer gel to the plugging throat hole type of DPG particles, realizing the visibility of the gel-forming process and the controllability of the profile control distance. It broke through the technical bottlenecks of uncontrollable underground polymer gel. Additionally, the oil phase as the dispersion medium, accurate polymerization conditions, uncontrollable reaction process, complicated process, and the high cost of traditional chemical emulsion polymerization method were also overcome.

Different from polymer microspheres prepared by a chemical method, multiscale DPG is a kind of water-based self-dispersive particle system (Fig. 1.4) [14–16]. In order to be adaptive to a long-term online injection for deep profile control in formations, the physical preparation method progresses from the coaxial cylinder shear cross-linking method and the pipe flow shear cross-linking method in basic indoor research, through the indoor small-scale high-speed mechanical shearing machine method, finally into the colloid mill shearing method available at industrial scale. Table 1.1 lists the comparison of several typical plugging agents.

Figure 1.4 Flow chart of the multiscale DPG system: (A) polymers and cross-linkers for reaction; (B) formed bulk gel; (C) shearing and dispersion; (D) further shearing and dispersion; (E) rounding; (F) formed DPG.

Table 1.1

The multiscale DPG particles prepared by this method have the following characteristics:

1. Wide distribution, at the scale from nm to mm.

2. Low viscosity (5–10 mPa·s), easy to inject into deep formations.

3. Shear resistance, good self-growth and coalescence ability, better deep profile control and displacement.

4. Good temperature and salt resistance up to 150°C and 30×10⁴ mg/L, respectively; suitable for wide reservoir conditions.

5. Simple preparation process and easy to adjust, available for online integration of production and injection, and adjusting the preparation parameters intelligently.

6. Easy to operate production equipment, and 2–8 tons/hour of production rate.

7. Environmentally friendly, fulfilling the requirements of national environmental protection.

8. Low cost, 20–40 yuan/ton (concentration used), satisfying the requirements of reducing oilfield costs and increasing efficiency at the low oil price.

According to the characteristics of multiscale DPG particles, the profile control mechanism can be described as follows (Fig. 1.5). When the DPG particles are injected into the formation, the particles preferentially enter high permeability zones. They can be retained and adsorbed on the rock surface when the channels are too large. Although bridging becomes more difficult in such high permeability zones, the particles could combine to form larger aggregates and then increase water flow resistance in these zones. With continuous injecting, the DPG particles could be deformed and enter the deep formation easily. When the DPG particle radius is larger than the pore throat radius, the particles could be trapped and directly plug the entrance of the pore throat. When the DPG particle radius is a little smaller than the pore throat radius, two or three particles will be stranded in the pore throat space and bridge across the pore throats easily. However, when the pore throat radius is much larger than the DPG particle radius, many particles will combine together and form larger aggregates at the pore throat space. By trapping and bridging, the formed large aggregates can bridge across the high permeability channels and effectively reduce the formation permeability. Moreover, once the bridge is consolidated, the newly arriving particles will gather at the pore throat and form an effective plugging capacity, thus decreasing the subsequent water flow rate and yielding the following water into adjacent low permeability zones with high oil saturation, so as to expand the sweep area and enhance the oil recovery [17,18].

Figure 1.5 Schematic diagram of microscopic flooding mechanism of DPG particles.

References

1. Zhao F. Oilfield chemistry(II) China University of Petroleum Press 2010.

2. Sydansk R. A newly developed chromium (III) gel technology. SPE Reservoir Engineering. 1990;5(3):346–352.

3. Mack J, Smith J. In-depth colloidal dispersion gels improve oil recovery efficiency. SPE. 1994;27780.

4. Fielding R, Gibbons D, Legrand F. In-depth drive fluid diversion using an evolution of colloidal dispersion gels and new bulk gels: an operational case history of North Rainbow Ranch Unit. SPE. 1994;27773.

5. Li Y, Liu Y, Bai B. Study on water plugging and profile control technology of bulk expanded particles. Oil Drilling and Production Technology. 1999;21(3):65–68.

6. Bai B, Liu W, Li L, et al. Analysis of internal factors affecting the properties of pre-cross-linked gel particles. Petroleum Exploration and Development. 2002;29(2):103–105.

7. Bai B, Liu Y, Coste J, et al. Cause study on preformed particle gel for in-depth fluid diversion. SPE. 2004;89468.

8. Coste J, Liu Y, Bai B, et al. In-depth fluid diversion by pre-gelled particles Laboratory study and pilot testing. SPE. 2000;59362.

9. Pritchett J, Frampton H, Brinkman J, et al. Field application of a new in-depth waterflood conformance improvement tool. SPE. 2003;84897.

10. Frampton H, Morgan J, Cheung S, et al. Development of a novel waterflood conformance control system. SPE. 2004;89391.

11. Mustoni J, Norman C, Denyer P. Deep conformance control by a novel thermally activated particle system to improve sweep efficiency in mature waterfloods of the San Jorge Basin. SPE. 2010;129732.

12. Lei G. A new depth profile control technique for pore throat scale elastic microsphere China University of Petroleum Press 2011.

13. Yao C. Experimental and simulation study on percolation mechanism of pore throat elastic microsphere. China University of Petroleum 2014.

14. You Q, Tang Y, Dai C, et al. Research on a new profile control agent: dispersed particle gel. SPE. 2011;143514.

15. You Q, Tang Y, Dai C, et al. A study on the morphology of a dispersed particle gel used as a profile control agent for improved oil recovery. Journal of Chemistry.