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2025 Vol. 42, No. 4

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Research and Application Status, Existing Problems and Development Suggestions of Drilling Fluid in China
WANG Zhonghua
2025, 42(4): 425-441. doi: 10.12358/j.issn.1001-5620.2025.04.001
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In response to the need for safe, fast, and efficient drilling, a series of research and applications in drilling fluids have been carried out in China in recent years, and new progress has been made.To facilitate a comprehensive understanding of the current status of drilling fluid technology, promote the continuous standardization of drilling fluid systems, and improve the functionality, performance, and usage level of drilling fluids, this article summarizes the recent research and application of water-based drilling fluids, oil-based drilling fluids and synthetic based drilling fluids, Among them,water-based drilling fluid mainly includes high-performance drilling fluid, ultra-high temperature ultra-high density drilling fluid, foam drilling fluid, environmental protection and reservoir protection drilling fluid,oil based drilling fluids mainly include pure oil-based drilling fluids, water in oil emulsion drilling fluids, and soilless oil-based drilling fluids, synthetic based drilling fluids mainly include Hydrocarbon based synthetic drilling fluids, ester based drilling fluids, and biomass based synthetic drilling fluids, these drilling fluid systems meet the needs of drilling deep and ultra deep wells as well as shale oil and gas horizontal wells.An analysis was conducted on the problems and their causes in the research and application of drilling fluids, And based on the existing problems, propose suggestions for the development of drilling fluid.This review has a certain reference value for the research, application, and standardization of drilling fluids in china.
Advances in Deepwater Drilling and Completion Fluid Technology at Domestic and Abroad
GENG Tie, YANG Jie
2025, 42(4): 442-452. doi: 10.12358/j.issn.1001-5620.2025.04.002
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Global deepwater and ultra-deepwater oil and gas resources account for 44% of total reserves, making their development a crucial pillar of energy supply. In recent years, 70% of major new oil and gas discoveries worldwide have originated from deepwater areas. The South China Sea holds abundant deepwater oil and gas resources, and their development is essential for enhancing China's energy self-sufficiency and ensuring national energy security. However, challenges such as high temperature and high pressure, complex geology, hydrate formation, and wellbore stability impose higher demands on deepwater drilling fluid technology. International oil service companies such as Schlumberger, Halliburton, and BP have made breakthroughs in deepwater water-based, synthetic-based, and high-density drilling fluids, which have been widely applied in deepwater blocks such as the Gulf of Mexico and Brazil's pre-salt oil fields. Domestically, China Oilfield Services Limited (COSL) has promoted independent innovation based on multiple oilfields in the South China Sea, developing key technologies such as deepwater hydrate prevention, high-performance water-based drilling fluids, and flat rheology synthetic-based drilling fluids, significantly improving the safety and efficiency of deepwater drilling. This paper reviews recent advancements in deepwater and ultra-deepwater drilling and completion fluid technologies, with a focus on the latest developments in water-based, synthetic-based, and high-density drilling fluid systems, as well as their applications in deepwater oil and gas development, providing a reference for future deepwater drilling and completion fluid technology development.
Progresses in Drilling Fluid Calcium Resistant Agent Researches in China and Abroad in Recent Ten Years
JIA Wenfeng, ZHANG Baichuan, LIU Hao, YANG Xiaohua
2025, 42(4): 453-461. doi: 10.12358/j.issn.1001-5620.2025.04.003
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Drilling fluid additives function less effectively or even lose their functions at high calcium content. To deal with this problem, many researchers, both in China and from abroad, tried to improve the calcium resistance of drilling fluids and have made some progresses. These researches were mainly focused on filter loss reducers, viscosifiers, shale inhibitors, lubricants as well as thinners. Products resistant to contamination by 25% calcium at 150℃ and resistant to contamination by 11% calcium at 180℃ have been developed. Part of these products have been successfully used in field operations, most of the additives are still in laboratory research though, and are still having difficulties in simultaneously possessing good calcium resistance and high temperature stability. Drilling fluid additives capable of resisting contamination by greater than 200,000 ppm calcium (≥ 20% calcium chloride) are rarely seen. In studying calcium resistant drilling fluid additives, focus should be placed on the prompt conversion of the laboratory research achievements, and cost-effective additives with both good calcium resistance and high temperature stability should be developed from low-cost and easily available biomass resources. In designing the molecular structures of polymer drilling fluid additives, special molecular structures instead of only the traditional ones, such as branched polymers, star polymers and dendrimers should be used. Attentions should be paid to the development of new monomers and the introduction of new materials. AI technology in material science can also be used to help further increase the high temperature stability and calcium resistance, enhance the development efficiency, and improve the compatibility of the drilling fluid additives.
DRILLING FLUID
Development and Application of Micro-Nano Organic Plugging Agent for Ultra-Deep Well Drilling Fluids
LIU Fengbao, YIN Da, LUO Xuwu, SUN Jinsheng, HUANG Xianbin, WU Hongyu
2025, 42(4): 462-471. doi: 10.12358/j.issn.1001-5620.2025.04.004
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An ultra-high temperature micro-nano organic plugging agent TSF is developed through a two-step reaction (pre-hydrolysis followed by free radical polymerization) with organic hydrolysable monomers and polymerization monomers such as AMPS, DMAA and BA. Thermogravimetric (TG) analysis shows that the initial thermal decomposition temperature of TSF is 240℃, indicating that TSF has excellent thermal stability. Before and after aging at 220℃, the particle sizes of TSF remain between 342 nm and 825 nm, indicating that TSF has dispersion stability. TSF has a glass transition temperature of 192℃, and can transform from the glassy state to the viscoelastic rubbery state, meaning that it has both plugging capacity through deformation and borehole wall strengthening capacity through adhesion. At 4% TSF treatment, a base drilling fluid, after aging at 220℃ for 16 hours, can have its HTHP filter loss reduced by 43.1%, and have its HTHP filter losses tested on 5 μm and 10 μm ceramic sand discs reduced by 37.1% and 34.5%, respectively. These data show that TSF has excellent filtration control capacity through plugging. At 220℃, TSF produces no H2S, indicating that TSF has good safety performance at ultra-high temperatures. After aging at 220℃, the drilling fluid produced mud cakes whose permeability was reduced by 50.8%. Borehole wall strengthening effect through adhesion of TSF can increase the compressive strengths of core columns by 12.6-17 times, showing that TSF can enhance its ability to plug the fractures in the formations in ultra-deep wells through self-adaptability and to strengthen the borehole wall. These characteristics of TSF have been successfully applied in drilling the ultra-deep well A.
An Environmentally Friendly Ultra-High Temperature Low Solids Seawater-Based Drilling Fluid
WU Wenbing, ZHONG Jie, LIU Tao, HUANG Lianlu, WANG Xiaohui, KANG Yumin
2025, 42(4): 472-477. doi: 10.12358/j.issn.1001-5620.2025.04.005
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The failure of a drilling fluid at high temperatures is one of the main causes of complex downhole accidents. The depths of wells around the Bohai Bay are close to 6,000 m, and the bottom hole temperatures are expected to exceed 200℃. To prevent wellbore collapse and the failure of the drilling fluids, protect the oil and gas reservoirs and the marine environment, high-temperature resistant drilling fluid additives were optimally selected, the high-temperature resistance mechanisms of the additives were explored, and as a result of these researches, an environmentally friendly ultra-high temperature low-solids seawater-based drilling fluid with a temperature resistance of 200℃ and a density of 1.9 g/cm3 was formulated and applied in the well Gaitan-1. The research results and field application effects show that after hot rolled at 200℃ for 16 hours, the filtration rate of this drilling fluid is only 15 mL. It has many advantages such as low filtration rate, high inhibitive capacity, good lubricity, good suspending and carrying capacity, as well as reservoir protection capability. The well was drilled successfully, the rate of wellbore enlargement was small, and the composition of the drilling fluid was simple and environmentally friendly, satisfying the requirements of marine environmental protection. This drilling fluid has helped solve the technical difficulties encountered in oil and gas drilling in deep high-temperature and high-pressure formations in the Bohai Sea area, providing technical support for the exploration and development of deep oil and gas in this area in the future, and also providing a sample for the application of ultra-high temperature low-solids drilling fluids in other deep formations and environmentally sensitive areas.
Drill-in Fluid Technology for Offshore Ultra-High Low-Permeability Reservoirs
LIU Zhiqin, CUI Yingzhong, YU Yi, ZHANG Yu, HUANG Dengzhu
2025, 42(4): 478-485. doi: 10.12358/j.issn.1001-5620.2025.04.006
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The second member of the Huangliu Formation in the Dongfang F gas field in the western South China Sea is a reservoir with ultra-high temperature, low porosity and low permeability, the temperature which is as high as 205℃. The solid-free drilling fluid used in the previous drilling operations degraded at elevated temperatures, negatively affected field operations and caused water lock damage to the reservoir. To deal with this problem, a temperature-sensitive polymer viscosifier, a viscosity increasing filter loss reducer, and an ultra-high temperature modified starch were selected to formulate a new high temperature solid-free drill-in fluid. The three additives work synergistically in the new drilling fluid to resist the action of ultra-high temperature. The drill-in fluid is stable at 210℃, the filtration rate is less than 10 mL at 150℃, the permeability recovery of the core contaminated with the drill-in fluid is greater than 90%, and the filter cake is easy to break and remove. Meanwhile the selected supporting ultra-high temperature water lock inhibitor does not foam, and can reduce the gas-liquid surface tension and oil-liquid interfacial tension of the drill-in fluid filtrate to 27.7 mN/m and 5.9 mN/m respectively. The new ultra-high temperature solid-free drill-in fluid has been successfully applied on the X2 adjustment well in the Dongfang F gas field. During the operation, the viscosity and gel strength of the system were stable, the filtration rate was small, the hole diameter was regular, the operation was smooth, and the test and production effect was good. The skin factor of this well was only 0.13. The new ultra-high temperature solid-free drill-in fluid is of great significance for reducing the drilling and development risks of such offshore reservoirs and for ensuring the production capacity.
Study on Gel Plugging Agent and Plugging Mechanism Based on Hydrophobic Association
LI Wenzhe, HUANG Tao, TANG Yijia, WANG Rui, XIA Lianbin, WANG Yao
2025, 42(4): 486-493. doi: 10.12358/j.issn.1001-5620.2025.04.007
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lost circulation has long been a major challenge affecting the safety and efficiency of drilling operations.​ In this study, a gel plugging agent (LAS) was synthesized via free radical polymerization using ​lauryl methacrylate (LMA)​ as the hydrophobic monomer and ​acrylamide (AM), ​2-acrylamido-2-methylpropanesulfonic acid (AMPS), and ​acrylic acid (AA) as hydrophilic monomers. The mechanical properties of the gel were enhanced by the coordination interaction between Al3+ metal ions and carboxyl groups on the polymer molecular chains. The results demonstrated that the LAS gel exhibited ​re-crosslinkable characteristics, along with excellent ​plugging performance​ and ​self-adaptive properties​ under high-temperature and high-pressure conditions. Under conditions of ​120℃ and 6 MPa pressure, the leakage volumes of 2% LAS gel for simulated fracture sand beds with particle sizes of ​20-40 mesh, ​40-60 mesh, and ​60-80 mesh​ were ​69.5 mL, ​58.3 mL, and ​41 mL, respectively. This plugging performance significantly surpassed that of conventional gels and traditional plugging agents. Additionally, the LAS gel demonstrated superior ​swelling and rheological properties​ across varying temperatures and salinity levels. It could form a stable plugging layer under formation temperature activation, effectively reducing leakage volume. The ​dynamic re-crosslinking capability​ of the LAS gel ensured robust plugging effects even in extreme high-temperature and high-pressure environments, highlighting its potential for application in ​workflow leakage control.
Performance Deterioration of High Temperature Filtration Control Agents by CO2 in Deep Formations and Mechanism Analysis Thereof
ZHANG Kun, LI Yang, MU Jianlei, LI Yonglong, SHI Yahua, PU Lei, XIE Lingzhi
2025, 42(4): 494-502. doi: 10.12358/j.issn.1001-5620.2025.04.008
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In developing deep acidic gas reservoirs, CO2 invasion and contamination cause the properties of high density drilling fluids, especially their ability to control filtration rate, to remarkably deteriorate at elevated temperatures. A new method has been developed to evaluate the contamination of a drilling fluid by CO2 in laboratory, and several typical high temperature filtration control agents were evaluated at 150℃ for their ability to resist CO2 contamination. Based on the macro and micro analyses of the performance of a “filtration control agent + bentonite slurry” system, the mechanisms with which CO2 causes the performance of a filtration control agent to deteriorate were systematically studied. The results of the study show that after being contaminated by CO2, the water solubility of the sulfonate type filtration control agents SAS and SMP-III was reduced, resulting in low viscosity, poor filtration property and reduced colloidal stability of the system. Acrylonitrile filtration control agent NH4-HPAN and cellulose filtration control agent PAC-LV, on the other hand, cause the system to viscosify after being contaminated by CO2. Compared with other filtration control agents, NH4-HPAN performs much better in resisting CO2 contamination, its properties in controlling filtration rate, stabilizing colloid and maintaining good particle size distribution of the system all remain stable.
A Highly Inhibitive Low Activity Brine-Based Drilling Fluid
WANG Guangcai, LIU Wancheng, REN Yun, WANG Xiaolong, XIONG Kaijun, LUO Hao, WANG Lirong, XIAO Hua
2025, 42(4): 503-508. doi: 10.12358/j.issn.1001-5620.2025.04.009
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As a new type of drilling fluid, bring-based drilling fluid manifests its significance in replacing oil-based and conventional water-based drilling fluids. To deal with the serious borehole wall collapse and reservoir protection problems encountered in drilling the Permian system reservoir in Tuha oilfield, a chloride brine was chosen as the base fluid for drilling fluid development. By selecting high efficiency drilling fluid additives, a highly inhibitive low solids low activity brine-based drilling fluid was formulated. This drilling fluid has simple composition and strong inhibitive capacity. Laboratory researches show that this drilling fluid has good high temperature stability and contamination resistance, and results of corrosion test with steel plate and rubber satisfy the standard requirements. This drilling fluid was successfully used in the Qitan-1 block in Tuha oilfield, the average percent hole enlargement of the target zone sections was 3.44%, and no downhole troubles were encountered during drilling, demonstrating that the highly inhibitive low solids low activity brine-based drilling fluid can satisfy the requirements of drilling in the Permian basin. The application of the chloride brine-based drilling fluid is the first in China, and is worth further optimization and promotion.
Research and Application of White Oil-Based Drilling Fluid Technology for Long Horizontal Wells in Western Sichuan
HAN Zixuan, HAN Xiuzhen, WANG Xianguang, LI Daqi, HUANG Hechun, CHEN Xiaofei
2025, 42(4): 509-515. doi: 10.12358/j.issn.1001-5620.2025.04.010
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In order to address the challenges of annular blockage and borehole instability during the drilling process of long horizontal wells in western Sichuan, this study analyzed the geological characteristics of the formation. Experimental research was conducted to understand the mechanism behind borehole instability. The findings revealed that in sea-related geological formations in Western Sichuan Basin, the risk of borehole instability is higher in the direction of minimum principal stress compared to that of maximum principal stress. The reservoir rock exhibits hard brittleness, fractured formations, developed microfractures, poor interlayer cementation, and a tendency for drilling cuttings deposition leading to annular blockage. Under pressure excitation, fractures further expand causing borehole instability. Based on these findings, flow type stabilizer SMRS-1 was developed. Emulsifying agents and nano-micron sealing agent SMNR-2 were carefully selected to construct a high-temperature long-term stable white oil-based drilling fluid system. After 7 days of rolling aging at 160℃, this system exhibited good high-temperature long-term stability with a dynamic viscosity ratio ≥0.20 and a high-temperature high-pressure filtration loss <4.0 mL at 160℃ along with breakdown voltage >600 V. The successful application of this drilling fluid in well PZ5-3 effectively resolved issues related to annular blockage and borehole instability encountered during long horizontal well drilling operations within western Sichuan.
Comparison of Cuttings Concentration in Annular Spaces of Horizontal Wells Between Water- and Oil-Based Drilling Fluids
SUN Jialin, ZHANG Jianwei, FAN Sen, CHAI Yifang, CHEN Can
2025, 42(4): 516-522. doi: 10.12358/j.issn.1001-5620.2025.04.011
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Most researchers are presently conducting researches on cuttings transport in water-based drilling fluid. However, with the increasing application of oil-based drilling fluids, it is necessary to explore the differences in cuttings transport between water- and oil-based drilling fluids. A three-dimensional wellbore model was established through CFD (Computational Fluid Dynamics) to investigate the differences in cuttings transport between water- and oil-based drilling fluids, and by comparing with the results of laboratory experiments, the reliability of the established CFD model was verified. Through CFD numerical simulation, it was concluded that under the same drill string eccentricity or drilling fluid inlet velocity, the height of the cuttings bed of the oil-based drilling fluid is lower than that of the water-based drilling fluid; and when the particle sizes of the cuttings are 2-4 mm and the drill pipe rotation speed is less than 80 r/min, the cuttings concentration in the oil-based drilling fluid in the annulus is significantly lower than that of the water-based drilling fluid. Previous studies have shown that the larger the cuttings particles, the more difficult it is to transport them out of the wellbore. However, this study found that the cuttings particles with a size of 2-3 mm are more difficult to transport out of the wellbore than those with a size of 3-4 mm, and it is not that the larger the particle size of the cuttings, the more difficult it is to transport them out of the wellbore. Although previous studies have shown that the greater the eccentricity, the higher the cuttings concentration, this study found that when the eccentricity is lower than 0.3, the cuttings concentration in the annulus of the horizontal well does not change much, but when the eccentricity exceeds 0.3, the cuttings concentration gradually increases. Based on the above research, these results provide a better understanding and guidance for the optimization of drilling parameters of horizontal wells.
Development and Application of the Filming Protecting Agent BHJ-RF for Deep Coal-Bed Methane Reservoirs
JIANG Wei, LIU Huaizhu, WANG Guijun, HU Binbin, LI Ling, CAO Yi, LI Xiaolan
2025, 42(4): 523-530. doi: 10.12358/j.issn.1001-5620.2025.04.012
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The deep formations in the eastern margin of the Ordos basin have plenty reserves of coal-bed methane (CBM), the Shenmu-Jiaxian block in the eastern margin of the basin is an important CBM production area with huge exploration and development potential. Detailed investigation of the mineral characteristics, pore structure feature and cleat development characteristics etc. of the CMB reservoir formations in the Shenmu-Jiaxian block shows that the deep coal rocks are developed with plenty of fractures and are easy to hydrate and expand, the invasion of drilling fluid filtrates during drilling cause the coal rocks to be damaged. To deal with these problems, a filming protecting agent BHJ-RF suitable for deep CBM reservoir protection was developed, and was characterized by means of IR spectrum etc. The performance of BHJ-RF was evaluated using API filtration test etc. Experimental results show that a 4% bentonite base mud and a 2% bentonite base mud have their filtration rates significantly reduced by 25% and 35% respectively after treatment with BHJ-RF, and the accumulated 30-min filtration rate of the BHJ-RF treated base mud is 31.5 mL, 40% lower than that of the non-treated base mud. After the composition of the base mud was determined, a drilling fluid for deep CBM drilling was formulated with the filming protecting agent BHJ-RF as the core additive. Comprehensive performance evaluation of the optimized drilling fluid shows that it has good rheology and an API filter loss of 3.2 mL. The drilling fluid has good permeability recovery capacity; the average percent permeability recovery tested on cores is 87.13%. These properties of the drilling fluid satisfy the requirements of deep CBM drilling and provide a technical support for deep CBM reservoir protection in the Shenmu-Jiaxian block.
CEMENTING FLUID
Properties of Set Aluminate Cement in 600℃ Ultra-High Temperature Xerothermic Environment
LI Xiaojiang, WANG Yueyang, XIAO Jingnan, WEI Haoguang, YANG Ruiyue, JIA Hui
2025, 42(4): 531-536. doi: 10.12358/j.issn.1001-5620.2025.04.013
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The downhole environment in in-situ mining of oil shale is ultra-high temperature and xerothermic, with temperatures above 500℃, which poses a challenge to the sealing integrity of the oil well cement sheath. To deal with this challenge, the performance evolution patterns of set aluminate cement and set sand-containing aluminate cement in a long-term xerothermic environment at 600℃ were evaluated, and the microscopic structural characteristics and changes in hydration products analyzed. The results of the research show that aluminate has a certain inhibitive effect on the decline of the high-temperature strength of the set cement. After aging in a xerothermic environment at 600℃, the strength of the set cement first increases and then slowly decreases. This is because minerals with higher hardness such as corundum replace minerals with lower hardness such as gibbsite. The set cement is mainly in the form of blocky and granular structures, and the structure is still acceptable, but the sizes of the pore throats become larger and the permeability increases. The strength of the set sand-containing aluminate cement is lower than that of the set cement of pure aluminate. After dry heat curing at 600℃, the contents of quartz and corundum increase significantly. The microscopic structural evolution pattern of the set sand-containing aluminate cement is basically the same as that of the set cement of pure aluminate. The degree with which the quartz sand participates in the reaction is low. Although it can partially optimize the pore throat structure of the set cement, its cementation property becomes poorer, and the number of microfractures inside the set cement increases, leading to an increase in permeability. The research results can provide a reference for the development of aluminate cement slurries suitable for high-temperature working conditions in in-situ mining of oil shale etc.
Preparation and Performance Evaluation of a Solid Anti-channeling Toughening Agent
LI Xiaolin, WANG Qike, XU Yixin, QI Ben, LING Yong, YAN Zhenfeng
2025, 42(4): 537-545. doi: 10.12358/j.issn.1001-5620.2025.04.014
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Styrene butadiene latex used in oil well cement has several shortcomings such as poor storage stability, high concentration required and high labor intensity in cement slurry mixing, etc. To deal with these problems, a solid powdered re-dispersible latex SISBR has been synthesized by introducing sodium p-styrenesulfonate and itaconic acid into the styrene butadiene latex to improve its high temperature stability, salt resistance and hydrophilicity. The effects of the amount of the itaconic acid on the properties of the latex were studied. The latex powders were characterized with IR spectroscopy, Zeta potential measurement, transmission electron microscope and ultraviolet-visible light absorption spectrum, and the high temperature stability and salt resistance of the latex SISBR were evaluated. Laboratory experimental results show that the modified carboxylated styrenesulfonate latex powders can be evenly dispersed in water and have good high temperature stability and excellent dispersibility. The introduction of the sulfonic acid groups and carboxyl groups increases the rigidity of the latex molecules. At an itaconic acid concentration of 3%, SISBR stays stable at 260 °C or higher and has excellent salt resistance. SISBR powders can evenly disperse in a cement slurry and can significantly improve the rheology of the cement slurry. SISBR also has good filming property and filling effect. A set cement containing 2.4% SISBR-3 latex powders can have its mechanical property most remarkably improved, and the cement slurry modified with the SISBR-3 has excellent elasticity, toughness and anti-channeling property.
FRACTUREING FLUID & ACIDIZING FLUID
Performance Comparison and Selection of a Fracturing Fluid Suitable for High Temperature Offshore Reservoirs
TENG Dayong, DING Qiuwei, JIN Xin, ZHANG Xin, CHEN Qingdong, ZHOU Jiyong
2025, 42(4): 546-553. doi: 10.12358/j.issn.1001-5620.2025.04.015
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Several special problems, such as narrow operation space, high reservoir temperature and formulation of fracturing fluids with seawater etc. exist in offshore fracturing operations and present special requirements for the performance of fracturing fluids. To deal with these problems, a high temperature seawater-based polymer fracturing fluid was developed and evaluated for its high temperature stability, shear resistance performance, viscoelasticity, shearing property at high rate of temperature variation, thixotropy, sand carrying capacity, static filtration property, gel breaking performance as well as the recycle of the flowback fluids etc. A comparative study was conducted with a guar gum fracturing fluid. Research shows that unlike the guar gum fracturing fluid, this high temperature seawater-based polymer fracturing fluid, when undergoing high-temperature shearing at 150℃, initially presents a linear gel state, by which the pumping friction in the well can be reduced. At elevated temperatures, this polymer fracturing fluid has better thickening capacity. When sheared at high temperatures, the structure of the polymer becomes more stable, thereby enhancing the sand carrying capacity of the fracturing fluid. After filtration and gel breaking, the amount of the residues left over is much lower than that of the guar gum fracturing fluid, imposing only slight formation damage. This polymer fracturing fluid can be formulated with simulated flowback fluid, its cost is 12.2% lower than that of the guar gum fluid, and is suitable for offshore fracturing operations.
Preparation and Evaluation of a Solid Sustained-Release Block Removing Stick for Offshore Unmanned Platforms
ZHANG Ning, BAI Jianhua, WANG Shuo, LIU Changqing, WANG Chuanjun, ZHANG Shaoguang, TANG Hao, WANG Baifei
2025, 42(4): 554-559. doi: 10.12358/j.issn.1001-5620.2025.04.016
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Acid job is a common measure taken to remove formation damage caused by blocking. The acids presently used generally have large volumes and storage risks, and are not suitable for operations on unmanned platforms. To solve this problem, a solid sustained-release block removing stick that release additives in a sustained manner has been developed. This solid sustained-release block removing stick is developed using ethylene glycol, polyvinyl alcohol, catalyst and adhesive as coating materials and powdered block removing agents as the wrapped materials. Factors affecting the performance of the solid sustained-release block removing stick, such as the reaction temperature, the type and content of the polyvinyl alcohol, the contents of the catalyst and the adhesive as well as the coating materials and the wrapped materials, were studied, and the optimum synthetic condition of the stick was obtained. Evaluation of the solid sustained-release block removing stick shows that the rate of acid release of the stick in 24 h at 65℃ is 42.3%, and 88.8% of CaCO3 is dissolved by the released acids. The rate of corrosion of the N80 steel plate by this stick is 0.57 g/(m2·h).
Study on and Application of Calcium Fluoride Precipitation Inhibitor for Acid Jobs
HUANG Liping, SUN Lin, ZHOU Jiyong, XIA Guang, YANG Junwei
2025, 42(4): 560-566. doi: 10.12358/j.issn.1001-5620.2025.04.017
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In offshore well stimulation, the secondary precipitation of calcium fluoride (CaF2) generally results in poor acid job quality, and methods for evaluating the quality of inhibitors for secondary precipitation of CaF2 cannot produce stable and reliable results. To deal with this problem, several strong acids were tested for their performance in dissolving the secondary precipitate of CaF2, and the particle size characteristics of the CaF2 generated during acid operation was analyzed. Based on the test results and the analysis, an experimental method of selecting and evaluating CaF2 precipitation inhibitors was established, and a CaF2 precipitation inhibitor BYZ-01 was developed and selected. Field experimental results show that at a concentration of 4%, there is no CaF2 precipitation in mud acid solution, demonstrating that BYZ-01 has remarkable field application effect. The understanding of the characteristics of the CaF2 secondary precipitates generated in acid job and the establishment of the method for evaluating CaF2 precipitation inhibitors for acid job have a significant importance to guiding the study on the inhibition of secondary CaF2 precipitation in acid job and the establishment of new methods for evaluating precipitation inhibitors.

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