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2025, Volume 42,  Issue 5

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FORUM
Progresses in Researching Phase Change Materials for Drilling Fluid Cooling
MA Jie, ZHANG Yao, LI Hui, WANG Li, LAI Jingjuan, ZHANG Xuan, WU Yuanpeng
2025, 42(5): 567-574. doi: 10.12358/j.issn.1001-5620.2025.05.001
Abstract(112) HTML (49) PDF (2451KB)(19)
Abstract:
As wells are drilled deeper and deeper to explore nonconventional oil and gas resources, drilling fluids, downhole tools and detection instrument are experiencing higher formation temperatures, and high efficiency cooling technology is urgently required. The methods of cooling a drilling fluid presently in use include natural cooling and cooling with surface instrument, whose cooling effect is limited. Phase change materials have advantages of high heat storage density and adjustable phase change temperature, hence can be used in a specific well section to achieve temperature response. With phase change materials, precise cooling in a depth near a downhole device such as RSD and LWD can be achieved, and phase change materials are thus becoming the research hotspot in drilling fluid cooling technology. Presently phase change materials though have been widely used in photothermal storage of solar energy, building temperature regulation as well as heat management for electronic devices etc., their use in deep and ultra-deep well drilling and exploration is still in an initial exploration stage. This paper focuses on the classification of phase change materials, the research status of medium and high temperature phase change materials, the properties of phase change materials required for use in drilling fluids, as well as the existing literatures on application studies of drilling fluid cooling. In the future, cost effective phase change materials of high thermal conductivity can be developed through numerical simulation and field test. By strengthening multifunction design of these phase change materials, optimizing their compatibility with drilling fluids, and investigating environmentally friendly, highly efficient, stable and intelligent new phase change materials with multiple functions such as cooling, lubricating and reservoir protection etc., an innovative solution to drilling fluid technology can be developed.
DRILLING FLUID
Formulation Design of Drilling Fluid Loss Control and Plugging Strategies in Deepwater Subsalt Reservoirs
XU Chengyuan, ZHONG Jiangcheng, ZHU Haifeng, XIANG Ming, LIN Zhiqiang, YANG Jie, CHEN Jiaxu
2025, 42(5): 575-586. doi: 10.12358/j.issn.1001-5620.2025.05.002
Abstract(507) HTML (388) PDF (4975KB)(20)
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Subsalt oil and gas resources are abundant worldwide, with significant reserves located in the deepwater offshore regions of Brazil. The Mero field is a typical example of deepwater subsalt oil and gas resources, located in the southeastern Santos Basin offshore Brazil. The reservoir depth exceeds 5000 meters, with an overlying salt gypsum layer ranging from 150 to 3000 meters. The subsalt reservoirs are primarily composed of Lower Cretaceous BVE and ITP carbonate rocks. The Mero3 block in the Mero field experiences the most severe lost circulation, with a total loss of 17,105 m3. Through geological and drilling data analysis, the main causes of lost circulation were identified, including the development of faults and natural fractures, weak formation layers, and the strong heterogeneity of the formation. These factors collectively result in poor pressure-bearing capacity of the sealing layer, leading to repeated lost circulation incidents. This study collected commonly used plugging materials in the Mero field and conducted performance evaluation experiments on particle size distribution, friction coefficient, compressive strength, and compatibility. A database of plugging material performance parameters was established, and high-performance plugging materials suitable for deepwater subsalt reservoir loss prevention and plugging operations were selected. Based on different loss rates, three loss prevention formulas were designed using efficient bridging and dense filling methods, and the application process for these formulas was refined. Furthermore, a strategy for fine-tuning drilling techniques and maintaining a combination of loss prevention and plugging was proposed. This strategy includes strengthening the precise control of the wellbore ECD in loss-prone formations, reducing downhole overpressure, and minimizing the occurrence of induced fractures. The research results achieved significant success in the field plugging operations at the NW8 well of the Mero3 block. In cases with varying loss rates, the plugging strategy effectively slowed down the loss rate. This provides valuable technical support for the oil and gas development of Brazil's Mero field and other similar subsalt reservoirs, promoting the safe and efficient extraction of oil and gas resources.
A Self-Adaptable High Pressure Bearing Plugging Agent for Synthetic-Based Drilling Fluid in Shallow Extended-Reach Well Drilling in Bohai
LIU Baosheng, TANG Baisong, HUO Hongbo, ZHANG Jun, HOU Xinxin, HE Yinbo, WANG Yijie
2025, 42(5): 587-593. doi: 10.12358/j.issn.1001-5620.2025.05.003
Abstract(116) HTML (45) PDF (3028KB)(14)
Abstract:
The direction in which the properties of the self-adaptable high pressure bearing plugging agent are specifically optimized is understood by analyzing the lost circulation scenarios occurring in shallow extended-reach well drilling in Bohai area, that is, the formations penetrated by the wells have high heterogeneity as well as pores and fractures that are randomly distributed, and lost circulation materials have to effectively plug the pores and fractures with unknown sizes to stop mud losses. The formations penetrated have microfractures that are extremely developed and low pressure bearing capacities, and lost circulation materials must have high compressive strengths. To overcome these difficulties, an oil-absorbing self-adaptable high-pressure bearing plugging agent OBR-1 was synthesized with methyl methacrylate as the backbone and other monounsaturated fatty acid esters with different of carbon chain lengths. Experimental results show that OBR-1 has high volume expansion capacity at rubbery state, high elastic modulus after absorbing oils, good broad-spectrum plugging effect and high pressure bearing capacity. Sand disks of 10-120 μm plugged by a synthetic-based emulsion containing 2%OBR-1 have pressure bearing capacity of 10 MPa. A synthetic-based drilling fluid formulated with OBR-1 as the core material can plug 20-80 mesh sand-beds with pressure bearing capacities of 20 MPa, proving that OBR-1 has excellent pressure bearing capacity and plugging performance, and can provide guarantee for the safe and efficient drilling of offshore extended-reach wells.
Drilling Fluid Technology for Test Well with Ultra-Long Horizontal Section in Shale Oil Block Gulong
GONG Chunwu, XU Nuo, SHENG Yang, LIU Xu, QI Changli, LI Bo
2025, 42(5): 594-599. doi: 10.12358/j.issn.1001-5620.2025.05.004
Abstract(89) HTML (30) PDF (2022KB)(7)
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With the development of the “Daqing Gulong Continental Shale Oil National Demonstration Zone”, wells with ultra-long horizontal sections are drilled to evaluate the correlation between the length of the horizontal section and the oil and gas production rate of a well. The length of the horizontal section is planned to be extended from the present 2000-2500 m to 3000-3500 m. Based on the formation characteristics of the Gulong shale oil block, drilling problems such as borehole wall stability, drag and friction reduction and borehole cleaning etc. that are probably encountered in drilling the ultra-long horizontal section wells were analyzed; the oil-based drilling fluid BH-OBM was optimized for those properties such as density, oil/water ratio and plugging performance, etc. During drilling, a “low viscosity high gel strength” rheology strategy and high drilling parameters were used to ensure hole cleaning and low friction and drag. The drilling operation of the test well GY2-Q9-H47 was successful: the average percent hole enlargement of the Φ215.9 mm was only 3.61% (based on wireline logging data), no borehole wall instability was encountered during drilling, and two new records in the shale gas oil block were set: the deepest well (5526 m) and the longest horizontal section (3123 m).
Mechanism of Multi-field Coupled Wellbore Instability in the Mudstone Section of the Southern Margin of the Junggar Basin
GAO Shifeng, QU Yuanzhi, DU Weichao, REN Han, ZHUANG Yan, HUANG Hongjun
2025, 42(5): 600-608. doi: 10.12358/j.issn.1001-5620.2025.05.005
Abstract(96) HTML (42) PDF (4023KB)(14)
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To understand the mechanisms of borehole wall instability of the easy-to-collapse formations in the southern margin of the Junggar Basin, mudstone cores were taken from the formation and studied through physio-chemical experiment, mechanical experiment and construction of a dynamic formation failure model. The results of the studies show that the mudstones in the southern margin of the basin contain 42% swelling clay minerals, the rate of swelling of the mudstone cores in contact with water is 30% or higher, and the percent recovery of the cores in hot rolling test is lower than 20%, indicating that the mudstone is quite easy to hydrate in water. The strength of the in-situ mudstones is lower than 40 MPa. After hydration, the strength and elastic modulus of the in-situ mudstones decrease exponentially, and the decreasing speed is fast at first, and then becomes slowly. As temperatures increase, the formation strength shows a trend of decrease, the speed of which is becoming faster. The cause of this phenomenon is “expand with heat and contract with cold”. The air in the pores of the formation expands, causing a change in the internal stresses of the rock, thereby reducing its strength. A multifield coupling dynamic borehole wall stabilization model was constructed to more accurately calculate the collapse pressure equivalent densities under different well angles, azimuths and action times. The results of the calculation help reveal the multifield coupling borehole wall instability mechanism of the mudstone formations in the southern margin of the Junggar Basin, and provide a theoretical guidance for maintaining wellbore stability during drilling and for drilling design.
Thermoplastic thermosensitive adhesive resin lost circulation material (LCM) and its adhension plugging mechanism
LEI Shaofei, XIAO Chao, SONG Bitao, YANG Shunhui, HE Qingshui, YU Lingling
2025, 42(5): 609-616. doi: 10.12358/j.issn.1001-5620.2025.05.006
Abstract(119) HTML (64) PDF (3745KB)(15)
Abstract:
Aiming at the problems such as low success rate of plugging and insufficient pressure bearing capacity of plugging layer caused by non-bonding force interaction between particles of conventional bridging materials, this paper developed a thermoplastic thermosensitive bonding resin plugging agent using acrylonitrile-styryl-butadiene copolymer as matrix resin and modified by blending maleic anhydride and petroleum resin. The properties of thermoplastic thermo-adhesive resin were characterized by infrared, thermogravimetric, DMA and high temperature and high pressure plugging instruments. The bonding mechanism of thermoplastic resin was analyzed. The results show that the plugging agent has good bonding and plugging performance at high temperature, and the pressure bearing capacity is as high as 8.2 MPa at 180℃. The thermosensitive adhesive resin is granular at room temperature and semi-molten solid after reaching the activation temperature. After entering the crack, it can self-adhesive plug through molecular chain diffusion and entanglement, so as to realize the thermosensitive, adaptive and efficient plugging function. Under high temperature conditions, thermoplastic resin thermosensitive adhesive resin can effectively improve the success rate of one-time plugging and pressure plugging ability, which provides a new theoretical and technical way to solve the problem of lost circulation during drilling.
Development and Performance Evaluation of a Starch-Based Composite Filter Loss Reducer for Use at 220℃
ZHAO Jie, ZHANG Yuchen, LIU Zhanqi, CHEN Xiguo, WANG Baojun, LI Xinliang
2025, 42(5): 617-622. doi: 10.12358/j.issn.1001-5620.2025.05.007
Abstract(115) HTML (58) PDF (3084KB)(10)
Abstract:
Drilling fluid additives with both high temperature stability and environment protection ability are the key to “safe, efficient, economic and green” well drilling. A high temperature environmentally friendly starch-based composite filter loss reducer was developed with a water-soluble starch, a fine walnut shell powder and an environmentally friendly acrylic acid resin. The synthesis is completed through inverse emulsion polymerization with the help of a crosslinking agent. This composite filter loss reducer has a maximum thermal decomposition temperature of 286℃, and has fibrous structure of irregular shapes and different sizes. After hot rolling at 220℃, a 4% bentonite base slurry treated with 2% composite filter loss reducer has its API filter loss reduced from 39 mL to 12 mL, and its HTHP filter loss from 172 mL to 52 mL, a rate of filtration reduction of nearly 70%. At elevated temperatures, the composite filter loss reducer shows a low viscosity filter loss control effect. Zeta potential analysis, particle size distribution measurement and SEM observation show that the molecules of the composite filter loss reducer can be adsorbed on the clay particles, thereby enhancing the colloidal stability and optimizing the particle sizing of the bentonite slurry. Meanwhile, the composite filter loss reducer can plug the pores formed in the mud cakes, making the mud cakes thin and tough, and based on these mechanisms, the high temperature filtration rate of the drilling fluid is finally significantly reduced. The results of this study provide a guidance to the research and development of ultra-high temperature environmentally friendly water-based drilling fluids.
Remove Detrimental Solids from Recycled Old Drilling Fluids Using Oil-Based Drilling Fluid Flocculants
YUAN Yuehui, GENG Yuan, SUN Minghao, NI Xiaoxiao, YAN Zhiyuan, WANG Bo
2025, 42(5): 623-630. doi: 10.12358/j.issn.1001-5620.2025.05.008
Abstract(75) HTML (77) PDF (3682KB)(8)
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Recycled old oil-based drilling fluids generally contain high concentrations of detrimental solids which result in performance deterioration of the drilling fluids. These detrimental solids can be removed through flocculation. In this study, an oil-based drilling fluid flocculant XN-1 was characterized for its performance in flocculating detrimental drilled solids, the flocculation mechanism of XN-1 was investigated, and the effectiveness of removing drilled solids and optimizing the properties of the oil-based drilling fluids through a combination of flocculation, screening and centrifugation was evaluated. Laboratory study and field experiment show that XN-1 has a good flocculating action in the old oil-based drilling fluid: the sizes of the flocs increase from submicron to 60 μm. After flocculation and screening, about 20% of the detrimental drilled solids are removed from the drilling fluid. After flocculation and centrifugation, 70.50% of the detrimental solids can be removed from the drilling fluid. The old mud, with the detrimental solids being removed, can be used to formulate new muds with significantly optimized properties. The application of the flocculant XN-1 effectively improves the reuse of old oil-based drilling fluids, realizes the effective recycling of old oil-based drilling fluids and greatly reduces of amount of hazardous and waste drilling fluids, and effectively solves the difficulty of removing detrimental solids from oil-based drilling fluids.
The Application of an Oil-Based Drilling Fluid with Strong Plugging Capacity in Pilot Test Shale Oil Wells in Qibei Area
MA Hong, ZHUANG Tao, WEN Fei, WANG Leilei, LI Xiaochen, CHEN Anliang, WANG Yu
2025, 42(5): 631-639. doi: 10.12358/j.issn.1001-5620.2025.05.009
Abstract(79) HTML (46) PDF (3314KB)(8)
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The proved undeveloped shale oil reserves in block Qibei of Dagang oilfield are still very high and their burial depths can be 4,500 m or deeper. This oil and gas enrichment area is located in the Shahejie reservoir which has high content of clays as well as developed interlayer pores and microfractures. Past experiences show that borehole wall instability and difficulties in tripping of drill strings have been encountered. To deal with these problems, three pilot test wells were drilled first in this area with oil-based drilling fluids. In laboratory studies an oil-based drilling fluid was formulated with 2% nanolatex, 2% sized calcium carbonate and 2% oxidized asphalt. Sizing of the particles rendered the drilling fluid high plugging capacity. In field application, the filtration rate of this drilling fluid through 750 mD sand-disks was reduced to 0.8 mL because the particles in the drilling fluid plugged the formation, minimizing the volume of the filtrates into the formations. In this way the wellbore stability was improved. The well QY6-31-2 was drilled in 40.98 d, refreshing PetroChina’s shortest drilling time record of wells with depths raging in 6501-7000 m, and setting 5 records in Dagang oilfield, such as the deepest completed well (6558 m) of horizontal shale oil wells. The use of oil-based drilling fluid has ensured the smooth construction of the pilot test wells.
A Method of Evaluating Drilling Fluid’s Dynamic Adhesiveness
WEN Lu, JI Shuaizhi, WEI Lingyan, ZHANG Junying, ZHANG Jie, GENG Zhiqiang
2025, 42(5): 640-645. doi: 10.12358/j.issn.1001-5620.2025.05.010
Abstract(69) HTML (42) PDF (2965KB)(6)
Abstract:
Most of the traditional drilling fluid lubricity testers only consider the interaction between the interfaces of metals, and omit the effects of the adhesiveness between the drilling tools and drilling fluid, mud cakes and borehole walls on the lubricity of the drilling fluid, causing an inconformity between the evaluation results and the actual field performance of a lubricant. By simulating the interaction between the drilling tool and the borehole wall, the drilling tool and the drilling fluid as well as the drilling tool and the mud cake, a drilling fluid’s dynamic adhesiveness tester was developed. Experimental results show that the drilling fluid’s dynamic adhesiveness tester is easy to operate, and can be used to evaluate torque fluctuations under different pressures and rotational speeds. The results of the evaluation with this tester are accurate and highly repeatable, and can be used to effectively prevent stuck pipe accidents from occurring.
CEMENTING FLUID
Mechanical Properties of Filter Cake on Well Cement Sheath: An Evaluation Method and How They Are Affected
LIU Jian, SONG Weitao, LI Jin, Li Zaoyuan, LIU Yaoyao, ZHOU Yong, MAO Jiuxiong
2025, 42(5): 646-655. doi: 10.12358/j.issn.1001-5620.2025.05.011
Abstract(47) HTML (17) PDF (4027KB)(8)
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Shale gas wells are generally fractured with multi-stage fracturing technology, sustained annular pressure will seriously affect their long-term, stable, safe and efficient development. The mechanical state of the borehole cement sheath and the pressure bearing capacity of the interface between the borehole wall and the cement sheath are the key to the long-term sealing of the borehole. The mechanical state of the interface between the filter cake and the cement sheath, which is the weakest part of the borehole, is directly related to the bearing capacity of the interface. Presently it is quite difficult to directly measure the mechanical properties of the filter cake bonded with the cement sheath. In this study, a method of testing the mechanical properties of filter cakes was developed, and the effects on the mechanical properties of the interfacial filter cakes was analyzed. The study shows that the phase of the filter cakes is mainly composed of barite, organophilic clay and calcium carbonate, the sizes of the particles in the filter cakes mainly range from 60 μm to 80 μm, the porosity of the filter cakes mainly range from 10% to 20%, and the permeability of the filter cakes mainly range from 0.05–0.15 mD. Several factors, such as increase in filtration pressure, increase in organophilic clay content, decrease in filter cake porosity as well as decrease in water content of filter cake, all to some extent help enhance the mechanical properties of the filter cakes bonded with cement sheaths. The results of the study have laid an important theoretical and technical foundation for understanding the load distribution on the interfaces of the cement sheath and for optimizing field well cementing technique scheme.
Synthesis and Application of an Ultra-High Temperature Low Viscosity Filter Loss Reducer
WANG Xiaojing, XU Chunhu, WEI Haoguang, MIAO Xia, XU Dawei
2025, 42(5): 656-664. doi: 10.12358/j.issn.1001-5620.2025.05.012
Abstract(56) HTML (21) PDF (3770KB)(11)
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Traditional polymer filter loss reducers have high apparent viscosity, causing high density cement slurries to have excessive initial consistency and hence affecting negatively operation safety. To deal with this problem, a low viscosity quaternary copolymer filter loss reducer SCFL-W was developed with four monomers: 2-acrylamide-2-methylpropanesulfonic acid, vinyl aromatic carboxylic acid, N, N-dimethylacrylamide and acrylic acid. The optimum reaction condition is: reaction temperature = 75℃, pH = 7, monomers’ concentration = 19%, and reaction time = 150 min. The molecular structure of SCFL-W is determined with FT-IR and TGA used to measure the thermal decomposition temperature to be greater than 380℃, meaning that SCFL-W has good thermal stability. Mechanism study proves that in the molecular structure of SCFL-W there are rigid side chains such as olefinic bonds and aromatic rings, among them entangling branches are difficult to form, thereby reducing the viscosity of the polymer. The excellent filtration rate control performance comes from the synergistic effect between the dense mud cakes formed under the action of the low-viscosity polymer and the static adsorption of the aromatic ring carboxyl groups. Evaluation of the performance of cement slurries treated with the filter loss reducer shows that SCFL-W retains most of its viscosity at elevated temperatures and has good compatibility with many additives. SCFL-W has good salt resistance. At 240℃, it reduces the API filtration rate of a saturated salt cement slurry to 45 mL. SCFL-W can be used in cement slurries with densities ranging in 1.88-2.4 g/cm3. Three well-times of field application of SCFL-W show that the quality of well cementing jobs is excellent. The successful use of this filter loss reducer has provided a new clue to the formulation of ultra-high temperature high density cement slurries.
Geopolymer Cement Slurry System for CCUS/CCS Wells
GAO Fei, REN Meng, GUO Yucheng, TIAN Baozhen, FEI Zhongming, GUO Shenglai, DONG Sanbao
2025, 42(5): 665-671. doi: 10.12358/j.issn.1001-5620.2025.05.013
Abstract(57) HTML (20) PDF (2547KB)(9)
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Conventional silicate cement in CCUS/CCS wells is easy to be corroded by the high concentration of CO2, resulting in cement strength deterioration and failure of sealing in annular spaces. To deal with this problem, a low-carbon geopolymer cement slurry was developed. This cement slurry was formulated with solid wastes such as fly ash and slag as the basic materials, and a controlled-release activator produced by the reaction of sodium oxalate and Ca(OH)2 was used in the cement slurry to replace the commonly used NaOH. This new cement slurry has adjustable thickening performance and strong resistance to corrosion. The rheology and the corrosion resistance of the cement slurry are optimized with carefully selected additives. Experimental results show that this cement slurry, with its density being 1.85 g/cm3, has controllable thickening time at temperatures between 70℃ and 120℃, 24 h compressive strength of 40 MPa and elastic modulus of 6.5 GPa. After corrosion by CO2 for 30 d, the strength of the set cement does not decline, and the permeability of the set cement increases only by 9%. Five CCUS wells were cemented with this cement slurry, and the job quality all met the standards. The results of this study provide new ideas and engineering practice bases for optimizing the well cementing system used in a highly corrosive environment.
Anti-Corrosion Cement Slurry Technology for Deep CCUS-EOR Wells in Hetao Basin
YU Haifa, REN Qiang, QIU Aimin, WANG Tao, HE Zilong, TAN Tianyu, YANG Yuhang, SHI Peijian
2025, 42(5): 672-677. doi: 10.12358/j.issn.1001-5620.2025.05.014
Abstract(50) HTML (19) PDF (2889KB)(8)
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CCUS is one of the key technologies for achieving carbon neutrality. CO2 injection into a well causes the well temperature to change and hence produces micro fractures in the set cement. In a damp, high-temperature high-pressure environment CO2 causes a long-term corrosion to the set cement, resulting in CO2 leakage, failure of the integrity of the reservoir and the borehole, as well as production stoppage etc. As the deepest CCUS-EOR engineering in China, the Hetao Basin has long been faced with temperature and pressure changes as well as long-term CO2 corrosion. To deal with these problems, a high-performance anti-corrosion cement slurry was developed by introducing corrosion inhibitive materials and active materials into the mature cement slurries commonly used in the field operations in the basin. This new cement slurry has those characteristics such as high strength, high resistance to CO2 corrosion and micro expansion. Study results show that, compared with other cement slurries, the optimized cement slurry has long-term performance in a damp high temperature that meets the requirements of field operations. At 150℃ and CO2 partial pressure of 40 MPa, the optimized set cement treated with corrosion inhibitors has a 120-d corrosion depth less than 2.00 mm, a compressive strength that declines only by 3.2%, and a permeability that only increases by 14.19%, indicating that the performance of the set cement has been greatly improved. As with the low-density set cement, the 120-d corrosion depth is 2.12 mm, the compressive strength declines by about 4.34%, and the permeability increases by 23.49%. This new cement slurry was used 30 well-times in field operations, with more than 90% of the job quality being excellent, and this has laid the foundation for the CCUS-EOR engineering in the Hetao Basin.
Cementing Technology of PRHH-X Well in Parahuacu Oilfield, Ecuador
LAI Pengfei, LAN Xiaolin, WANG Guoqing, TIAN Guoqiang, ZHONG Kai, ZHANG Zhanchen, ZHANG Dong
2025, 42(5): 678-685. doi: 10.12358/j.issn.1001-5620.2025.05.015
Abstract(44) HTML (20) PDF (2214KB)(6)
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In recent years, in order to maximize the benefits of exploration and development and reduce the issues arising from the long openhole section of the third section in the Parahuacu field in Ecuador, the second well structure of the PRHH-X well has undergone optimization and adjustment. A Φ244.5 mm casing was utilized to seal the BASE TENA oil layer and the abnormally high-pressure Caliza A limestone layer in the second section.In response to the the technical problems faced during the Φ244.5 mm casing cementing in the PRHH-X well, such as low displacement efficiency and low flushing efficiency of large annulus, low casing center degree, the weak wellbore cleaning capacity in the highly deviated section, the active edge and bottom water of the reservoir, and the susceptibility of the cement slurry to invasion by formation fluids, the following measures were adopted. Designing a multi-effect preflush system can effectively flush and dissolve the mud and mud cake in the annulus, enhancing the shear strength of the second interface of cementing. Designing high-performance pioneer fluid with good suspension stability ensures the safety of cementing operations. Analyze the reasons for the invasion of formation fluids into the cement slurry, evaluate the performance of thixotropic agents, and optimize the combination to form anti-invasion cement slurry. Indoor experiments show that compared with the clear water system, the shear strength of the second interface of the cementing in the multi-effect preflush system increased by 526% and 715% at 2 days and 7 days, respectively. The stability of the pioneer fluid is good, and the thickening time is more than 10 hours. The static gel transition time of the anti-intrusion cement slurry is 8 minutes, and the transition time from 40 Bc to 70 Bc is 6 minutes, showing strong thixotropy. 8 h The compressive strength reaches 20.6 MPa, and the SPN value is 2.2756, with good anti-gas channeling performance. Based on the above multi-effect preflush system, pioneer fluid, cement slurry and supporting technical measures (optimizing the type and quantity of centralizers, slurry column structure design, and combined flow state displacement), the cementing technology was applied in the PRHH-X well in 2024 with good results. The cementing quality was qualified, and the high-quality rate of the openhole section was over 85%, providing strong technical support for the technical casing cementing of the φ244.5 mm production layer and abnormal high-pressure gas layer in the Parahuacu oilfield, Ecuador.
FRACTUREING FLUID & ACIDIZING FLUID
Plugging Diagnosis and Treatment Measures of Gas Well for Leikoupo Formation in Western Sichuan Basin
LIU Yintao, KANG Zheng, ZHANG Guodong, ZHANG Yao, KE Yubiao, WANG Xudong, HE Linjing
2025, 42(5): 686-695. doi: 10.12358/j.issn.1001-5620.2025.05.016
Abstract(50) HTML (24) PDF (3936KB)(8)
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The Leikoupo Formation gas reservoir in West Sichuan Basin has been significantly plugged for more than 40 wells since the 18 wells were successively started production in 2023, which has seriously affected the gas field production. Based on systematic analysis of plugging composition and origin, combined with machine learning algorithms, this study investigates the influencing factors and distribution patterns of downhole plugging zones. A classification and mitigation strategy has been established using quantitative blockage diagnostics. The results indicate that: ①Plugging types can be categorized into organic, inorganic, and compound plugs. The composition of solid deposits shows certain similarities with those observed in early-stage sour gas fields in other regions of China. ②Early-stage plugging is associated with drilling, stimulation, and completion operations. Most plugs are distributed along production tubing, with slightly higher frequency observed near the wellhead and in the front section of horizontal well production zones. ③Acidizing fluids prepared with 15% HCl achieve a dissolution rate of 65.7% for inorganic deposits and a viscosity reduction exceeding 90% for organic substances. ④The integrated process combining quantitative diagnostics with coiled tubing intervention achieved a 100% success rate in 41 field applications, with an average productivity recovery rate of 128.6% post-treatment. The above technical results can provide a reference for similar sulfur-containing gas well plugging management.
COMPLETION FLUID
Development of High-Temperature-Resistant and High-Density QH-HCF Completion Fluid System and Its Application in Deep and Ultra-Deep Wells
ZOU Jun, HAO Shaojun, HAO Tian, AN Xiaoxu, TANG Zheng
2025, 42(5): 696-704. doi: 10.12358/j.issn.1001-5620.2025.05.017
Abstract(57) HTML (25) PDF (2910KB)(12)
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Addressing the poor suspension stability, rheological deterioration and reservoir damage exhibited by conventional completion fluids in deep and ultra-deep well drilling and completion operations under high-temperature (>200℃) and high-density (>2.0 g/cm3) conditions, this study employs molecular design to develop a high-temperature suspending agent, QH-HSA-III, and uses it as the core to build a novel QH-HCF completion fluid system. QH-HSA-III is synthesized via a terpolymer modification strategy of acrylamide (AM), octadecyl acrylate (ODA) and N-isopropylacrylamide (NIPAM). Through hydrophobic association and thermoresponsive mechanisms, it forms a dynamic three-dimensional network at elevated temperatures, markedly enhancing suspension stability. Laboratory evaluations show that the QH-HCF system maintains an apparent viscosity of 60 mPa·s at 200℃ with a dynamic shear force to plastic viscosity ratio of 0.26. In a 15-day high-temperature settling test, water separation was only 0.3%, cuttings rolling recovery reached 98.5%, particle-size retention was 93.8%, and high-temperature/high-pressure filtration loss remained ≤ 15 mL. In field trials on Well K2-X1 (measured depth 7182 m, bottom-hole temperature 200℃), application of the QH-HCF system reduced circulating pressure loss by 31.8%, achieved a cuttings return rate in excess of 95%, and cut non-productive time by 67%.These results confirm that the QH-HCF completion fluid system delivers outstanding high-temperature stability, dynamic rheological control and reservoir protection, providing robust technical support for the safe and efficient development of deep and ultra-deep wells.

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