钻井液与完井液

Abstract:
The second member of Liushagang Formation in Weishan Sag, Beibuwan Basin, is oil shale with highly developed micro-fractures and high brittle mineral content. PLUS/KCl water-based drilling fluid was used in vertical well drilling in the early stage, resulting in serious wellbore instability and frequent blockage. The problems existing in the water-based and diesel-based drilling fluids used in the area were analyzed in the laboratory. Based on the formula of the on-site diesel-based drilling fluid, a set of high performance and low aromatics gas-to-oil drilling fluid system was constructed by introducing low viscosity and low aromatics gas-to-oil production and grading optimal micro-nano sealing agent materials. The system has a lower activity of 0.62, a high recovery rate of 98%, no leakage in 300 μm micro-crack plugging, a settlement factor less than 0.51, better inhibition and plugging, and stable high temperature performance. The gas-to-oil drilling fluid was applied in 8 highly inclined rock oil exploration wells, and the application well operation was smooth, and the diameter enlargement rate was less than 2%. Compared with the diesel-based drilling fluid system, the maximum funnel viscosity and plastic viscosity were reduced by 54% and 41% respectively, and the daily loss was reduced by 50%, and the comprehensive cost was reduced by about 85 million yuan. This technology provides powerful drilling fluid technical support for accelerating the development of offshore shale oil resources.

A Highly Inhibitive Vegetable Oil-Based Drilling Fluid

XIAO Hua, WANG Guangcai, ZHANG Yunda, LIU Wancheng, REN Yun, WAN Shixing, WANG Xiaolong

2025, 42(6): 713-720. doi: 10.12358/j.issn.1001-5620.2025.06.002

Abstract(137) HTML (57) PDF (2592KB)(15)

Abstract:
This study aims at finding a more environmentally friendly and efficient oil-based drilling fluid to reduce drilling costs, to minimize the negative effects of the drilling fluid on the environment, to enhance the safety and quality of drilling operation, and to provide a new green drilling fluid solution. It was well known that vegetable oil-based drilling fluids formulated with base fluids such as peanut oil, soybean oil and castor oil have low ecotoxicity, good lubricity and high inhibitive capacity in stabilizing clay formations, and can be used to replace diesel oil-based drilling fluid. In laboratory experiments a vegetable oil-based drilling fluid was formulated with modified cottonseed oil as the base fluid and other oil-based drilling fluid additives. Laboratory evaluation results showed that the vegetable oil-based drilling fluid has strong capacity in inhibiting clay hydration and swelling, good high temperature stability, strong salt and bentonite contamination resistance, as well as excellent reservoir protection performance. Two well-times of successful use of this drilling fluid in Tuha oilfield showed that the drilling fluid performed very well: it effectively stabilized the borehole wall against collapse, ensuring the optimal and fast drilling of the wells and the safety of the drilling operation. Oil-on-cuttings was tested for its toxicity and the results conformed to the relevant standards. The vegetable oil-based drilling fluid has properties equivalent to those of a diesel oil-based drilling fluid and can be used to replace traditional oil-based drilling fluids in the future.

Evaluation and Field Application of a Rheology Modifier for Non-aqueous Based Drilling Fluids

REN Liangliang, SONG Yu, GENG Tie, LUO Jiansheng, LI Chao, XIA Xiaochun

2025, 42(6): 721-727. doi: 10.12358/j.issn.1001-5620.2025.06.003

Abstract(142) HTML (56) PDF (3019KB)(13)

Abstract:
A rheology modifier for non-aqueous based drilling fluids was prepared in this work. Based on the drilling fluid systems of China Oilfield Services Co., LTD., the influence of dosage, aging temperature and aging time on rheology and electrical stability performance of drilling fluid were studied. The anti-pollution ability were also studied in this work. The results showed the gel strength was obviously improved with the increasing dosage and weakened with the increasing aging time. It indicated that PF-MOVIS is gradually consumed during drilling process and it need to be added with a small number of times in the actual operation process. The temperature resistance of PF-MOVIS reached 170℃. It showed an obvious better gel strength under the temperature of 170℃ when adding the PF-MOVIS. Moreover, PF-MOVIS could obviously improve the electrical stability properties. It has excellent anti-pollution ability and reservoir protection performance. According to the pilot scale study, the performance of the pilot product was comparable to even better than that of the lab sample. At the same time, the field application results showed that PF-MOVIS obviously increased gel strength for non-aqueous based drilling fluids. The field application effect was very well and and it has great popularization value.

Ultra-High Temperature Suspension Stabilizer HPAS for Oil-Based Drilling and Completion Fluids and Its Working Mechanism

KOU Yahao, NI Xiaoxiao, WANG Jianhua, ZHANG Jiaqi, YIN Da, CHI Jun

2025, 42(6): 728-737. doi: 10.12358/j.issn.1001-5620.2025.06.004

Abstract(671) HTML (778) PDF (4425KB)(22)

Abstract:
Oil-based drilling and completion fluids presently in use have poor suspension stability at high temperatures up to 240℃ or higher. To deal with this problem, a strongly hydrophobic suspension stabilizer HPAS was developed based on the principle of strengthening the stability of a colloidal system through spatial grid structure. HPAS was synthesized using sepiolite fiber and n-octyltriethoxysilane as the raw materials. The final product was obtained by treating the intermediate product with hydrochloric acid and then organic modification. Characterization of HPAS with IR, TGA, particle size analysis and surface wettability proved that the modification is successful. A high-density oil-based drilling fluid was formulated with HPAS. After aging at 260℃, the properties of the drilling fluid were still good, the AV and PV of the drilling fluid were about 33 mPa·s and 27 mPa·s, respectively, the YP of the drilling fluid was at least 4 Pa, the electric stability was higher than 800 V, the HTHP filter loss was kept under 5 mL, and the thickness of the mud cake was less than 2 mm. Evaluation of the sedimentation stability of the drilling fluid showed that after standing at 240℃ for 7 d there was no hard sedimentation found, and a glass rod can freely drop through the drilling fluid to the bottom of the mud container. Moreover, the YP of the drilling fluid remained at more than 4.5 MPa at temperatures between 65℃ and 240℃ and pressures between atmospheric pressure and 190 MPa, indicating that the drilling fluid can maintain good suspension stability and solids carrying performance under these conditions. The development of this drilling fluid provides a technical support for the use of oil-based drilling and completion fluids in drilling deep, ultra-deep wells and even wells of ten thousand meters in depths.

A Nanocellulose Filter Loss Reducer for High Temperature Water Based Drilling Fluids

WANG Can, ZHAO Xionghu, JIA Xiangru, Salman Khan

2025, 42(6): 738-747. doi: 10.12358/j.issn.1001-5620.2025.06.005

Abstract(163) HTML (73) PDF (6108KB)(22)

Abstract:
A nanocellulose filter loss reducer CNF-ADDS was developed through aqueous solution graft polymerization. Laboratory experiments were conducted on it to analyze its effects on the rheology and filtration property of drilling fluids, to evaluate its high temperature performance and salt and calcium resistance capacities, and to reveal its filtration reduction mechanism. Experimental results show that the average length of the CNF-ADDS molecules is about 300 nm. Treatment of the base mud of a water-based drilling fluid with 2%CNF-ADDS increases its apparent viscosity to 32 mPa·s and the plastic viscosity to 22 mPa·s. After aging at 260℃, the HTHP filter loss tested at 150℃ is only 16.3 mL. After contamination by 36%NaCl and 3%CaCl₂ respectively, the CNF-ADDS-treated drilling fluids were then aged at 260℃, the HTHP filter losses of the drilling fluids tested at 150℃ were 17.4 mL and 16.5 mL, respectively, and the mud cakes were tough and thin. By self-assembling into a network structure, the CNF-ADDS molecules can be adsorbed onto the surfaces of the clay particles, thereby reducing the filter loss of the drilling fluid in high temperature and high salinity (NaCl and CaCl₂) environment.

Formulation of High Temperature Gas-Kick Preventer and Its Mechanism of Blocking Gas Cut

ZHANG Zhen, YIN Da, SU Xiaoming, FENG Wei

2025, 42(6): 748-755. doi: 10.12358/j.issn.1001-5620.2025.06.006

Abstract(145) HTML (54) PDF (4131KB)(13)

Abstract:
In high temperature reservoir operations, oil/gas cut causes drilling accidents such as well kick and even well blowout. Conventional polymer gels, though can be used to prevent gas channeling from occurring, have poor high temperature resistance. In this study, a high temperature gas-kick preventer was prepared using a high temperature polymer AP-9, a crosslinking agent (polyethyleneimine and aluminum citrate in a ratio of 1∶1) and thiourea. Laboratory experiments were conducted to find the effect of the concentration of each component on the thermostability of the high temperature gas-kick preventer. As a result of the experiments, an optimal composition was determined as: 0.5%AP-9+0.4% crosslinking agent+0.25% thiourea. Laboratory evaluation results show that at 160℃ a gel formulated with 25 000 mg/L Na⁺ saltwater and the high temperature gas-kick preventer has viscosity of 7120 mPa·s after gelling, indicating that the high temperature gas-kick preventer has good salt resistance. After heating for 72 h, the viscosity of the saltwater gel still reaches 3328 mPa·s, and the pressure bearing strength of the saltwater gel is 0.23 MPa/m. The results of this study provide a technical support for effectively preventing gas kick in a high temperature well, they are helpful for achieving whole-process underbalanced drilling, and are of great importance to improving the safety and efficiency of drilling operation.

The Preparation and Properties of a Gel Plugging Agent Made from Copolymerization of Modified Carbon Nanotube

SONG Xiangyuan, LAN Qiang, YANG Shichao

2025, 42(6): 756-763. doi: 10.12358/j.issn.1001-5620.2025.06.007

Abstract(141) HTML (64) PDF (5089KB)(10)

Abstract:
Gel plugging agents usually have the characteristic of good adaptiveness, but the existing drilling fluid gel plugging agents generally suffer from poor stability at elevated temperatures and poor strength. To deal with these problems, a drilling fluid plugging agent was developed by the hybridization of high temperature carbon nanotubes and a terpolymer; the terpolymer gel is used as the matrix and the carbon nanotubes (CNTs) are used as the rigid nanoparticles to aim to solve the problems such as borehole wall instability resulted from the failure of the plugging agents at elevated temperatures in deep well drilling. A nanofiber plugging agent was synthesized by radical polymerization based on a molecular structure design in which maleic anhydride (MAH), alkenyl succinic anhydride (ASA) and styrene (St) were selected as the copolymerization monomers, benzoyl peroxide (BPO) as the initiator, and N, N-methylenebisacrylamide (MBA) as the crosslinking agent. The synthesized high temperature hybridized carbon nanotubes and terpolymer gel plugging agent was evaluated for its functional structures and plugging performance by transmission electron microscopy and sand-disc plugging experiment. The results of the evaluation show that, a drilling fluid treated with 1.0% of the synthesized product has the optimal plugging capacity. At 150℃, the drilling fluid has good rheological properties, good filtration control effect, and can effectively plug nano-micron sized pores and fractures.

Technologies for Lost Circulation Control in Deep Coalbed Methane Drilling in the East of the Junggar Basin

LIU Yingbiao, RONG Kesheng, YANG Ze, GONG Jiaqin, KAN Nizati, ZHANG Hui, AN Jintao

2025, 42(6): 764-771. doi: 10.12358/j.issn.1001-5620.2025.06.008

Abstract(152) HTML (68) PDF (3465KB)(16)

Abstract:
Lost circulation in reservoir drilling has been encountered in deep coalbed methane drilling in the east of Junggar Basin (Xinjiang) because the reservoir formations have insufficient pressure bearing capacity. Based on the characteristics of the lost circulation encountered, the mineral composition of the reservoir formations was analyzed and the morphology of the formations observed using SEM. The mechanisms of lost circulation were determined to be the extension of fractures and the connection of pores in the formations, and a countermeasure for overcoming the lost circulation problem was presented as the synergistic application of “plugging agent + filtration agent + shale inhibitor”. Based on the “reduce costs and increase efficiency” principle, the concentrations of the key drilling fluid additives were optimized. The key additives were then formulated through orthogonal experiment with the basic slurry to form four lost circulation prevention drilling fluids. The four drilling fluids were then tested for their performance in permeability recovery and based on the results, a drilling fluid with the best reservoir protection was determined. Experimental results show that this drilling fluid has stable rheology, the percent permeability recovery can be as high as 87.42%, the API and HTHP filtration rates are 4.16 mL and 9.52 mL, respectively, the filtration rate on sand-bed test is less than 15 mL, indicating that the drilling fluid has good plugging capacity. In inhibitive capacity experiments, the rate of swelling of drilled cuttings tested with the filtrate of the drilling fluid is only 0.96%, and the percent cuttings recovery in hot rolling test with the drilling fluid is as high as 91.6%, indicating that the drilling fluid has excellent inhibitive capacity. In field application of the optimized drilling fluid, lost circulation was mitigated, drilling time shortened, complex working conditions minimized, and reservoirs were protected more effectively. The use of the optimized drilling fluid has provided an important technical support and application reference to safe and efficient drilling of deep coalbed methane.

Lost Circulation Prediction Based on Long Short-Term Memory Network and Random Forest Algorithm

CAI Aiting, SU Junlin, DAI Kun, ZHAO Han, WANG Jiayi

2025, 42(6): 772-780. doi: 10.12358/j.issn.1001-5620.2025.06.009

Abstract(671) HTML (508) PDF (6271KB)(17)

Abstract:
Lost circulation is one of the key factors restricting drilling safety and efficiency. To realize accurate prediction of lost circulation, a hybrid model for the prediction of lost circulation is presented based on long short-term memory (LSTM) and random forest (RF) algorithm. The LSTM model, the RF model and the LSTM-RF hybrid model are constructed based on algorithm principle. Fourteen lost circulation characteristic parameters are selected using correlation analysis method, and are input into three lost circulation prediction models for training. The performance and lost circulation prediction accuracy of the three models are then analyzed and compared. The experimental results show that the root mean square error (RMSE) of the hybrid model on the test dataset is 0.11, the mean absolute error (MAE) is 0.22, the coefficient of determination (R²) is 0.95, and the overall accuracy reaches 84.2%, each indicator is better than that of the single model. Furthermore, hybrid model has successfully predicted 5 times of lost circulation in field application. The results of this study show that LSTM-RF hybrid model is a model with optimal comprehensive performance in lost circulation prediction, it can predict lost circulation more precisely, and can provide reference for the prevention of lost circulation and for the decision making in drilling operation.

CEMENTING FLUID

Low Thermal Conductivity Cement Slurry for Geothermal Well Cementing

DANG Donghong, HUANG Zhongwei, LI Jingbin, LIU Jingli, REN Qiang, LIU Yan

2025, 42(6): 781-787. doi: 10.12358/j.issn.1001-5620.2025.06.010

Abstract(138) HTML (50) PDF (2676KB)(12)

Abstract:
In geothermal energy development, the heat loss of cement sheath plays a key role in affecting heat extraction efficiency. In this study, using class G cement as the base slurry, and hollow glass microspheres and modified palygorskite fiber as composite low thermal conductivity material, a low thermal conductivity cement slurry was formulated through composition optimization. Laboratory experiments on the rheology, stability, thermal conductivity and compressive strength of the cement slurry were all tested. It was found that compared with conventional cement slurries, the thermal conductivity of this cement slurry is reduced by 74.4%, and the 7-d compressive strength of this cement slurry is 19.7 MPa. The use of the low thermal conductivity agents in this cement slurry makes the pores inside the set cement finer and more evenly distributed. This not only reduces the thermal conductivity of the cement; it also improves the mechanical performance and durability of the cement. This technology can be used to reduce the heat loss and enhance the efficiency of geothermal extraction.

Low-Density High-Fluidity High-Strength Epoxy Resin Cement Slurry Technology for Wellbore Reconstruction

JIN Xin, CHEN Lei, TAO Qian, ZHOU Shiming, TAN Chunqin

2025, 42(6): 788-796. doi: 10.12358/j.issn.1001-5620.2025.06.011

Abstract(72) HTML (30) PDF (2897KB)(7)

Abstract:
The production rate of a shale gas well generally declines fast, resulting in a low average recovery of the well. Refracturing of an old well with shale gas production pressure depletion can effectively enhance the ultimate recovery of the well, and wellbore reconstruction, that is, re-cementing the well inside the existing casing, is the key to the successful implementation of wellbore refracturing. Researches were conducted on several technical methods, such as the control of the rheology of the cement slurry for wellbore reconstruction, the control of the strength of the set cement and the setting time adjustment and control of the cement slurry, to deal with the technical difficulties that are encountered in shale gas well reconstruction, such as cementing in annular spaces with extremely narrow clearances and extremely high requirements on the fluidity of the cement slurry in the narrow clearance as well as the long-term zonal isolation with the ultra-thin cement sheaths. Based on the close packing theory, the compressive strength, fluidity and high temperature high pressure thickening time of cement slurries at different lengths of aging time were measured through laboratory experiments, and a low-density, high-fluidity high-strength cement slurry system for wellbore reconstruction was designed. The experimental results show that by adding 8%-10% epoxy resin into a cement slurry, the compressive strength of the set cement can be enhanced and the cement slurry still retains good fluidity. The cement slurry has stable properties, and has been used in wellbore reconstruction for 9 well times. In practical engineering application, the cement slurry has a density of 1.63 g/cm³, a fluidity of 27 cm, a flow index of greater than 0.8, a 24 h- and a 48 h-compressive strengths of 16.23 MPa and 20.50 MPa as well as a thickening time that is controllable, satisfying the operational requirements of wellbore reconstruction. The well Jiaoye 5-1HF was the first reconstructed well in which refracturing was conducted, with all technologies being domestically developed. The cementing job quality in the reconstructed well intervals was excellent, and staged refracturing operation was successfully conducted after reconstruction of the wellbore. The shale gas production during well testing has recovered to 88.10% of the production after initial fracturing operation. These researches provide a reference for the reserve growth and production increase in the development of mature shale gas fields in China.

Preparation and Application of an Instant and Quick-Acting Suspending Agent for Well Cementing Prepad Fluids

LIU Hao

2025, 42(6): 797-803. doi: 10.12358/j.issn.1001-5620.2025.06.012

Abstract(65) HTML (28) PDF (2625KB)(10)

Abstract:
Suspending agents presently used in prepad fluids for well cementing are mostly polymer/cellulose compounds. These suspending agents have a major advantage of high thickening ability; they can improve the suspending stability of a prepad fluid, thereby ensuring the safety of well cementing operation. These kinds of suspending agents, on the other hand, generally swell very slowly in water (> 3 h), and are therefore unable to quickly thicken and prepad fluid to improve its suspending stability. Researches have been conducted in an effort to develop a new suspending agent for well cementing prepad fluids. By optimizing the formulae of suspending agents, an instant and quick acting suspending fluid with superior properties has been developed. This suspending agent fluid has low viscosity and low gel strength. Laboratory experimental results show that after being dissolved in water for 3 min, the suspending agent swells completely and the suspending property of the fluid is greatly improved, meaning that the suspending agent has high quick-acting ability. The funnel viscosity of the suspending agent fluid is about 42 sec, meaning that the suspending agent is convenient to use. A prepad fluid formulated with 4%−5% of this suspending agent as the core additive has been used in cementing a well drilled with water-based drilling fluids or oil-based drilling fluids, the suspending agent functioned normally at temperatures of 200℃ or higher. The density difference between the upper part and the lower part of the prepad fluid was less than 0.03 g/cm³, indicating that the prepad fluid had excellent stability. The field operation using the prepad fluid was conducted smoothly and the job quality of the well cementing operation was outstanding, meaning that this prepad fluid formulated with the newly developed suspending agent is able to enhance the displacing efficiency of cement slurries and has higher promotion value.

Study on Compatibility of an Anti-Contamination Agent with Cement Slurries and Drilling Fluids

LI Hailong, ZHOU Jinghong, ZHANG Zheng, LEI Lei, ZHANG Shunping, ZHANG Hua, YU Yongjin

2025, 42(6): 804-810. doi: 10.12358/j.issn.1001-5620.2025.06.013

Abstract(80) HTML (35) PDF (2490KB)(7)

Abstract:
In deep well drilling and completion in Chuanyu area, drilling fluids mixed with cement slurries generally became highly viscous because of the poor compatibility between the drilling fluids and the cement slurries. An anti-contamination agent DRP-2S has been developed for use in spacers to deal with this problem. DRP-2S regulates and controls the rheology of a mixture of a drilling fluid and a cement slurry through the coordination action of its carboxyl groups and the steric-electrostatic effects synergistic stabilization mechanism, and it does not react with any chemicals added or blended into the cement slurry and the spacer. Experimental studies show that a spacer treated with DRP-2S has the best control of the properties of the cement slurry-drilling fluid mixture when the pH of the spacer is set at 7. Experiments on the temperature adaptability show that DRP-2S can improve the compatibility between cement slurries and drilling fluids at 60℃, 90℃ and 120℃. In field application, DRP-2S was used in the production casing tie-back operation of the exploration well X in the Chuanyu area, and successfully solved the compatibility problem between the cement slurry and the oil-based drilling fluid, and the qualification rate of well cementing reached 99.5%. This study has provided a solution to the abnormal thickening of cement slurries and drilling fluids, and has important guiding significance to well cementing operation.

FRACTUREING FLUID & ACIDIZING FLUID

Preparation and Application of a Salt- and Shear-Resistant Thickening Agent

YU Shihu, ZHAO Zhiyong, ZHANG Xiaohu

2025, 42(6): 811-820. doi: 10.12358/j.issn.1001-5620.2025.06.014

Abstract(95) HTML (42) PDF (3381KB)(7)

Abstract:
Conventional salt-resistant thickening agents cannot satisfy the requirement of recycling gas-field waters because of their limited salt resistance and poor high-speed shearing resistance. In this study a polymer thickening agent ASCM was developed to deal with this problem. ASCM is synthesized by emulsion polymerization with these monomers: acrylamide (AM), sodium p-styrenesulfonate (SSS), N,N-diethylacrylamide (DEAM), alkyldimethylally ammonium chloride (CnDMAAC). The synthesis conditions were optimized through orthogonal experiments. ASCM has salt tolerance of 85 000 mg/L and Ca²⁺ and Mg²⁺ tolerance of 6 000 mg/L. In standard salt water ASCM has viscosity retention rate of about 80%. After shearing at 2 000 s⁻¹, 90% of the viscosity can be restored. A 1.6%ASCM solution formulated with a gas field water had viscosity of about 50 mPa·s after shearing at 120℃ and 170 s⁻¹ for 90 min. After statically suspending for 2 h, no settlement of sand was found. The gel of the ASCM solution can be broken under control in 30-120 min. The solution after gel breaking had surface tension of 25-27 mN/m, residue content of less than 200 mg/L, and core damage of less than 25%. ASCM fracturing fluid formulated with gas field waters and flowback liquids was used for 9 well times, the accumulated volume of the reused gas field waters and flowback liquids reached 1.43 × 10⁴ m³, the operation parameters and stimulation effects of the fracturing fluid formulated with ASCM were the same with those of the fracturing fluids formulated with fresh water, and the comprehensive cost was saved by more than 20%. ASCM has the characteristics of good shear resistance, high suspending capacity, low formation damage and low friction, satisfying the needs of large-scale reuse of waters with complex water quality, such as gas field waters and flowback fluids.

Experimental Study on Optimization of Acid-Fracturing Technique for Efficient Communication of Multi-Fracture-Cavity Structure Reservoirs

TANG Xiaofan, LUO Pandeng, SONG Zhifeng, HE Zhengquan, LUO Zhifeng

2025, 42(6): 821-828. doi: 10.12358/j.issn.1001-5620.2025.06.015

Abstract(53) HTML (30) PDF (3902KB)(3)

Abstract:
Fractured-vuggy carbonate reservoirs are difficult to stimulate because of the complex fracture and vug connection as well as the varied formation structures. Existing technologies cannot be used to efficiently produce the multiple fracture-and-vug reservoirs. To deal with this problem, a visual experimental device for multi-structure node flow reaction was developed and a solid retarded acid used in acid fracturing experiment. Using the experimental device and through the acid fracturing experiment, the flow path of the fracturing fluid was observed and the effects on the concentration of the acid were analyzed, and as a result, an optimization strategy based on dimensionless breakthrough volume as the criterion was proposed. Experimental results show that the solid retarded acid can reduce the acid consumption in the early and middle stages of the fracturing job, enhance the dissolution and permeability-increasing effects in the far-end, as well as extend the lengths of propped fractures. High concentration acid solutions are suitable for acidifying a series-connected fracture and vug structure, since the pressures inside the structure increase fast, the breakthrough time can be shortened, and the volume of acids required can be reduced. In a parallel-connected fracture and vug structure, the acid solution preferentially enters the unfilled fractures, and the use of a high concentration acid solution results in difficulty of flow in the filled areas. Thus, a low concentration acid solution or a “temporary plugging agent + high concentration acid solution” combination is recommended for use in acidifying parallel-connected structures. This study has revealed the flow mechanism of an acid solution in a complex fractured-vuggy structure, and provided a technical support for high-efficiency stimulation of heterogeneous carbonate reservoirs.

COMPLETION FLUID

A Comb Polymer for Dispersing Micro-Manganese Weighting Material

LI Huaike, WANG Zhiyong, ZHANG Yufei, HAO Binbin, WANG Zhengfu, WANG Wenhao, TAN Yebang

2025, 42(6): 829-835. doi: 10.12358/j.issn.1001-5620.2025.06.016

Abstract(76) HTML (29) PDF (3017KB)(9)

Abstract:
To ensure the dispersion of micro-manganese weighting material in a completion fluid, comb polymer dispersants PSH of different compositions were developed using sodium methacrylate and methyl allyl polyoxyethylene ether through free radical polymerization. The molecular structure of the copolymer was determined by infrared spectroscopy and nuclear magnetic resonance. The effects of the dispersants of different compositions on the rheology and settlement stability of a completion fluid were investigated. Based on these researches the mechanism with which the polymer dispersants disperse the micro-manganese weighting material was presented. It was found that the sodium methacrylate-methyl allyl polyoxyethylene ether copolymers can well disperse the micro-manganese weighting agent. The dispersants PSH2, PSH3 and PSH4 all have good thinning effect on micro-manganese slurries. Of these dispersants, the dispersant PSH3, after aging at 210℃, had viscosity reduction rate of 46.7%. When added into a completion fluid, the settlement factor of the completion fluid was reduced from 0.5290, which is the settlement factor of the blank completion fluid group, to 0.5096. If the content of the methyl allyl polyoxyethylene ether monomer in the dispersant is appropriate, the best dispersion effect can be achieved.

Analysis of Components of Gas Well Blocking Substances and Study on a Composite Block Removing System

HE Yu, HE Tianbao, FAN Tianyou, YANG Qiang, XIE Binghong, WU Yang

2025, 42(6): 836-842. doi: 10.12358/j.issn.1001-5620.2025.06.017

Abstract(79) HTML (32) PDF (2404KB)(8)

Abstract:
Gas wells drilled in the Gaoshiti block of the Southern Sichuan Gas District have encountered serious formation blocking problem, resulting in significant decline in the gas production. To restore the gas production, blocking removing needs to be performed with blocking removing fluids in wells where reservoir formations are blocked. By analyzing the blockages taken from the wells with IR and XRD methods, the organic and inorganic components and their contents in the blockages were determined. Based on the blocking removing principles, a composite blocking removing system was formulated with xylene, 15% HCl and isopropnaol, and was then optimized for the material ratio. The effects of action time, solid/liquid ratio as well as temperature on the blocking removing performance of the blocking removing system were investigated. It was found that the blocking removing system formulated with m (xylene)∶m (15% HCl)∶m (isopropnaol) = 17.32∶25.99∶56.69 has the optimum blocking removing performance. At solid/liquid ratio of 1∶15 the efficiency of blocking removing is 90.25%, which is the highest efficiency. This composite blocking removing system can effectively dissolve the blockages found in the Gaoshiti block, and the residues after dissolution have smaller particle sizes, beneficial to discharging from where the formations are blocked. Wells operated with this blocking removing system have their gas production restored.