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2025 Vol. 42, No. 3

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DRILLING FLUID
Simulation of Action between Epoxy Resin and Solidifier/Formation Minerals Based on Molecular Dynamics
DONG Haoan, LI Zhiyong, ZHANG Jinbo, JIN Xingyu, CEN Haotian, XU Ruixing
2025, 42(3): 283-289. doi: 10.12358/j.issn.1001-5620.2025.03.001
Abstract(57) HTML (18) PDF (2719KB)(19)
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Studying on the hardening process of epoxy resin and the interaction between epoxy and formation minerals has important theoretical significance for their application in petroleum industry. Studies on epoxy in the past mainly focused on the properties of epoxy resin itself, with its interaction with formations being ignored. To extensively investigate the hardening process of epoxy and the interaction between epoxy and formation minerals, molecular simulation method was used to study the molecules of E51 epoxy resin and several hardening agents. The electrostatic potential and interaction energy between the molecules of epoxy and the molecules of the hardening agents, as well as the interaction energy between the products of the hardening process and the formation minerals, were calculated. It was found that the epoxy groups in the epoxy resin molecules have a significant negative potential, which is −0.060 Hartree/e, while the active hydrogen atoms in the molecules of the hardening agents have significant positive potential, ranging from 0.053 Hartree/e to 0.126 Hartree/e. Moreover, mutual attraction exists between the molecules of the epoxy resin and the molecules of the hardening agents, the energy of the attraction ranges from −0.446 kcal/mol to −29.306 kcal/mol. After crosslinking, the interaction energy between the molecules was reduced to −80.987 kcal/mol to −110.844 kcal/mol. Finally, significant mutual attraction also exists between the crosslinking product of the epoxy resin and formation minerals; the interaction energy between a single epoxy molecule and the calcite mineral in the formation ranges from −49.795 kcal/mol to −173.187 kcal/mol, while the interaction energy between a single epoxy molecule and the dolomite mineral in the formation ranges from −44.604 kcal/mol to −147.307 kcal/mol. These research achievements have provided a theoretical base for the application of epoxy resin in oil and natural gas industry, and the research method adopted can be used in optimizing the design of epoxy resin additives.
Preparation and Properties of a Drilling Fluid Non-Fluorescent Flexible Plugging
CHU Qi, MU Guochen, GE Chunmei, ZHANG Tianxiao, YANG Ming, LIU Cong
2025, 42(3): 290-295. doi: 10.12358/j.issn.1001-5620.2025.03.002
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As flexible plugging agents used in drilling fluids, gel plugging agents have great effects on the rheology of the drilling fluids, and asphalt plugging agents have fluorescent effect that interferes with mud logging data acquisition. To solve these problems, a water-based polyurethane emulsion plugging agent SMPU-1 has been prepared with the following monomers: isophorone diisocyanate (IPDI), polytetramethylene ether glycol (PO3G), 2-hydroxyethyl disulfide (HEDS) and dimethylol butyric acid (DMBA) as the chain extenders, dibutyltin dilaurate (DBTDL) as the catalyst, furfuryl alcohol (FA) as the end-capping agent, and triethylamine (TEA) as the emulsifier. Using IR spectrometer, laser particle size analyzer and scanning electron microscope, the molecular structure of SMPU-1 was characterized, and the particle size distribution and the micromorphology of SMPU-1 analyzed. It was found that under the action of high temperature, the SMPU-1 particles are still in nano-micron monodisperse state, and become soft and deformed. Under the action of pressure, the SMPU-1 particles can be squeezed into and hence densely plug the micro-fractures on the surfaces of rocks. The results of the plugging performance test show that the optimum temperature for the SMPU-1 particles to function is 140°C or lower, and the optimum treatment of SMPU-1 is 4%. SMPU-1 has little effect on the rheology of drilling fluids. At the maximum applicable work temperature and the optimum dosage, the API filter loss of a drilling fluid is 6.2 mL, and the high temperature high pressure (HTHP) filter loss is 16 mL, indicating that the drilling fluid still has good filtration and wall-building properties.
Oil-Based Drilling Fluid Technology for Ultra-Deep Extended Reach Wells in East China Sea
SHE Yunhu
2025, 42(3): 296-301. doi: 10.12358/j.issn.1001-5620.2025.03.003
Abstract(37) HTML (10) PDF (2242KB)(14)
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Difficulties such as borehole wall instability, poor hole cleaning, drag encountered frequently during tripping due to high friction and torque, and difficult reaming, have been encountered in drilling operation in the Baoyunting block and the Pinghu block in east China Sea, which seriously affect the drilling efficiency. By analyzing the characteristics of the variegated mudstone formation, a technology using sized particles to achieve strong plugging was applied and the emulsification stability of the oil-based drilling fluid was improved to solve the problem of borehole wall instability. By optimizing the 6/3 r/min reading of the drilling fluid on six-speed viscometer, efficient cuttings carrying was achieved and the problem of hole cleaning in extended-reach well drilling in the East China Sea was solved. An independently developed lubricant LUBE OB was used to reduce the friction coefficient of the drilling fluid under high loads and the wear of drill strings and casings. This oil-based drilling fluid technology was successfully applied for the first time in drilling the 8000 m ultra-deep extended-reach well KQT-N. The oil-based drilling fluid has strong plugging capacity, high cuttings carrying efficiency and high lubrication performance, the use of which has reduced the time required for reaming in extended-reach wells in the East China Sea from 16.7% to 2.0%, greatly improving the drilling efficiency and providing technical support and guarantee for the safe and efficient development of the oil and gas fields in the East China Sea.
Preparation of a Drilling Fluid Degradable Cuttings Carrying Agent and Its Test in 10,000-Meter Deep Wells
MING Xiansen
2025, 42(3): 302-307. doi: 10.12358/j.issn.1001-5620.2025.03.004
Abstract(31) HTML (18) PDF (3000KB)(27)
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In highly deviated wells, horizontal wells or large diameter wells, drilled cuttings are likely to accumulate on the lower side or at the bottom of the well due to insufficient cuttings carrying capacity of the drilling fluid. This will lead to complex downhole situations such as an increase in the friction of the drill string movement, difficulties in tripping, downhole lost circulation and even pipe sticking. Hole cleaning is therefore one of the key technologies to achieve operation safety and efficiency in highly deviated wells, horizontal wells or large diameter wells. A fiber cuttings-carrying agent that can significantly improve the cuttings carrying capacity of a drilling fluid was developed by blending and reacting an aliphatic polyester polymer with a high molecular weight copolymer. Results of performance evaluation experiments show that in the experimental slurry with 0.2% of the cuttings-carrying agent, the settling time of the cuttings increases from the original 4.12 sec to 19.85 sec. This cuttings-carrying agent has good dispersibility in both aqueous phase and oil phase. After hot rolling at 120℃ for 16 h, the degradation rates in clean water and white oil are 95.48% and 89.87% respectively, and the degradation does not affect the performance of the drilling fluid. Field tests show that this cuttings-carrying technology can significantly improve the cuttings-carrying capacity of the drilling fluid, effectively carry drilled cuttings or sloughing rock pieces out of large diameter wells or horizontal well sections, improve the wellbore cleanliness, and provide a guarantee for safe and efficient drilling.
Drag Reducing Performance of a Nanomodified Material in Water Based Drilling Fluids
GUO Lei, LI Mugang, DENG Chuluan, HE Yinbo, GENG Tie
2025, 42(3): 308-317. doi: 10.12358/j.issn.1001-5620.2025.03.005
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The flow of water based drilling fluids in slim holes fluctuate significantly and the interface resistance between the drilling fluids and the wellbore/drilling tools is high, resulting in high flow energy loss and high equivalent circulation density (ECD) which in turn cause mud losses and stuck pipe to happen. A drag reducer DRA-1 for water based drilling fluids was synthesized with nano silica as the raw material through graft-modification, and its performance was studied. In laboratory experiment, it was found that a base mud treated with 3% DRA-1 has its flow index increased by 366.7% to 0.5064, the consistency coefficient reduced by 90.6% to 0.4847 Pa·sn, and the extreme pressure coefficient of friction reduced by 81.82%. After hot rolling at 120℃ for 16 hours, the extreme pressure coefficient of friction was further reduced, indicating that DRA-1 is resistant to high temperature. When the DRA-1 treated base mud was flowing under the same conditions on a self-made steel plate and a polytetrafluoroethylene plate respectively, DRA-1 performed much better than the same type of field additives in improving the flow behavior of the mud. Operation data obtained from the well A showed that by adding 1% DRA-1 in the water based drilling fluid, the pressure loss along the circulation system was reduced by 1.937 MPa, a reduction rate of 21.61%, and lower ECD was obtained in the whole drilling operation, indicating that DRA-1 helped increase the drilling efficiency and safety, and this is very important to the increase of economic benefits and the avoidance or drilling accidents.
Simulation Experiment Study on Lost Circulation Control by Borehole Wall Strengthening
WU Chunlin, WEN Ming, QIU Zhengsong
2025, 42(3): 318-323. doi: 10.12358/j.issn.1001-5620.2025.03.006
Abstract(33) HTML (15) PDF (2177KB)(23)
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Laboratory simulation study was conducted on the strengthening of borehole walls to try to find a way of dealing with lost circulation under pressure and to reveal the micro-mechanisms of fracture plugging to strengthen the borehole walls. By comprehensively considering the effects of the closure pressure of fractures on their openings during borehole wall strengthening, a set of experiment apparatus was developed and a method for evaluating the plugging of fractures with variable openings established. Used with the apparatus and the evaluation method, two quantitative evaluation indicators, which are maximum plugging differential pressure and equivalent plugging position, were proposed. Compared with the commonly used particle size matching criterion, using the revised normal distribution particle size matching criterion, the pressure bearing capacity of a borehole wall can be increased by 2.36 times at most. Equivalent plugging position is inversely proportional to pressure bearing capacity, and the revised normal distribution continuous particle size matching criterion can form at the entry of fractures a thin and dense plugging layer. Increase the strength of the plugging materials to a level as high as possible, the effect of the well pressure fluctuation can be reduced; increase the elasticity of the borehole wall strengthening plugging agents, the adaptability of the plugging layer to the dynamic fractures can be improved. Moreover, appropriately increasing the suspension stability of the plugging system and reasonably reducing its injection rate both are beneficial to the formation of the pressure bearing plugging layer and to the improvement of borehole wall strengthening.
Performance and Mechanisms of Zwitterionic Polymer Modified Nanoparticles in Calcium Resistance, Plugging and Filtration Control
LI Wenzhe, SHEN Xinyu, WANG Rui, YANG Hang, LIU Xingbao, QIAO Qingsong
2025, 42(3): 324-329. doi: 10.12358/j.issn.1001-5620.2025.03.007
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A high temperature calcium resistant plugging agent ZP-NPs has been developed based on the “anti-polyelectrolyte effect” theory to render water based drilling fluids high temperature stability, high calcium resistance and good plugging capacity. ZP-NPs is obtained by grafting zwitterionic polymer molecules onto the surfaces of nano silica. The microstructure of ZP-NPs was observed using infrared spectrum and electroscope, and the performance of ZP-NPs evaluated through dispersion test, filtration test and plugging test. It was found in these tests that ZP-NPs can stably disperse to nanoparticles/submicron particles for a long time in a high temperature high calcium chloride concentration (160℃, 11%CaCl2) solution. A base slurry, after being contaminated by high concentration calcium ions, has a high temperature high pressure (160℃, 3.5 MPa) filtration rate that does not exceed 20 mL, and the mud cakes obtained from the test are thin and tough. Fractures of 5 μm in width plugged by a bentonite slurry treated with ZP-NPs can stand pressures up to 5.5 MPa. The calcium resistant performance, plugging capacity and filtration control property of ZP-NPs were revealed through particle size analysis and EDS, and it was found that ZP-NPs has strong “anti-polyelectrolyte” effect; at high calcium concentrations, the particle sizes of ZP-NPs are still in nanometer size range, they can effectively shield the bentonite particles against the adsorption of calcium ions, thus maintaining the dispersion stability and excellent filtration control performance of a bentonite slurry at high calcium concentrations. This study provides a new theoretical and technical guidance for the development of new plugging agents with good calcium resistant capacity.
Preparation of Composite Nano-Silica and Polymer Gel and Its Function as Lost Circulation Material
YAO Wenshuang, LIU Po, HAO Huijun, YE Yan, CHENG Rongchao, LIU Fan, SONG Hanxuan
2025, 42(3): 330-337. doi: 10.12358/j.issn.1001-5620.2025.03.008
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Gel lost circulation materials (LCMs) presently in use have several shortcomings such as low strength, poor toughness and uncontrollable gelling time etc. A high gel strength composite nanomaterial and polymer gel LCM has been developed to overcome these shortcomings. The composite nanomaterial and polymer gel LCM is synthesized through physical-chemical crosslinking reaction with raw materials such as polyacrylamide (PAM) as the main gelling agents, nano silica as the strengthening agent, sodium carboxymethylcellulose (Na-CMC) as the viscosifier and phenolic resin as the crosslinking agent. In laboratory experiment, the optimum conditions for preparing the composite gel LCM were determined and the gelling performance, swelling capacity and fracture plugging capability of the composite gel LCM evaluated. The crosslinking mechanisms and fracture plugging mechanisms of the composite gel LCM were also analyzed. It was found through the experiment that the best composite gel LCM can be obtained in the following reaction conditions: 1.5%PAM, 3% nano silica, 0.6%Na-CMC, 1.5%crosslinking agent and temperature for the crosslinking is 150℃. The composite gel LCM obtained in these conditions has gel strength of 1,000 Pa, gel viscosity of 6×105 mPa∙s and gelling time of 2 hours. This composite gel LCM has good swelling performance and can be used to plug fractures of different sizes. An LCM slurry formulated with the composite gel LCM and an inert material, after being used to plug fractures of 1-4 mm in width, formed an LCM barrier across the fractures with pressure bearing capacity of 12 MPa (measured at 150℃ and after aging 48 hours). The composite gel LCM is easy to manufacture and cost effective, and can hopefully be used to solve severe mud loss problem encountered in drilling highly porous and fractured formations.
Research and Application of the Oil-absorbing Viscous Polymer for Oil-Based Drilling Fluid Plugging
LIU Wentang, ZHANG Xianmin, HUANG Ning, JIANG Xueqing, LI Xudong, YANG Hai, GUI Fang
2025, 42(3): 338-342. doi: 10.12358/j.issn.1001-5620.2025.03.009
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Lost circulation materials (LCMs), after being wetted by oil-based drilling fluids, have their sliding ability decreased and retention ability increased, causing them to be easy to flow back from the fractures through which the mud is lost and circulation is lost again. Using these LCMs, the success rates of lost circulation control are low. To improve the retention ability of the LCMs and the stability of the plugging layers, an oil absorbing viscous polymer MBS was developed. MBS is mainly composed of butadiene-styrene block copolymer BS and is formed by the coupling and grafting of inorganic minerals at a temperature between 70℃ and 90℃. The rate at which MBS absorbs oil and becomes viscous is controllable. At room temperature, the oil-absorbing rate of the polymer MBS is relatively low, and the viscosity of the LCM slurry is small, making the slurry preparation and pumping very convenient. At the temperature of a lost circulation zone, the oil-absorbing rate of the polymer MBS increases, and the viscosity of the LCM slurry becomes higher, making it convenient for the LCM slurry to be retained inside the fractures through which the mud is lost. Moreover, the inorganic minerals enhance their supporting effects on the LCM slurry. MBS can absorb oils that are 2.94 times of its volume. At a concentration of 5%, the viscosity of the LCM slurry increases, and the fluidity decreases by nearly 50%. When the concentration of MBS is 10%, it can be effectively retained in a smooth fracture with a width of 2 mm, and the pressures bearing capacities in the forward and reverse directions are 0.69 MPa and 0.53 MPa respectively. An LCMs slurry formulated with MBS and other commonly used LCMs was used in the well section of 2,900-3,130 m of the well Puluye XHF. The LCMs slurry effectively stabilized the pressure at 4.2 MPa, achieving the goal of controlling lost circulation and increasing the pressure bearing capacity of the formations. The lost circulation was controlled successfully in the first try.
Technology of Lost Circulation Prevention and Control in Deep Coalbed Methane Drilling in Eastern Ordos Basin
ZHU Mingming, SUN Huan, QU Yanping, SHI Chongdong, ZHANG Qin, HOU Bo, YANG Guang
2025, 42(3): 343-349. doi: 10.12358/j.issn.1001-5620.2025.03.010
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The exploration and development of deep coalbed methane have opened up a new field of developing resources in new formations in the Ordos Basin, ensuring the steady growth of the oil and gas equivalent of the Changqing oilfield. However, due to the deep burial of the target layers and the long open hole section of the upper part, the difficulty of drilling and development has increased significantly. It is mainly manifested in technical problems such as the prominent contradiction between borehole wall collapse and lost circulation in the second interval, the low success rate of lost circulation control in the first try in the second interval Ф311.2 mm borehole, and the instability and collapse of the coal-seam borehole walls in the horizontal section. To deal with these problems, the casing program was optimized, thereby separating the borehole wall collapse and lost circulation in different intervals. Two sets of drilling fluids were developed to ensure the stability of the wellbore. An efficient technology was adopted to improve the efficiency of lost circulation control without tripping drill strings out of hole. Meanwhile key technical measures were implemented, forming a set of lost circulation prevention and control technology suitable for deep coalbed methane development in the eastern part of the Ordos Basin. This technology has been applied on more than 10 wells, and the drilling time has been reduced by 36.5%. This technology has been used to successfully drill the longest horizontal section of 2,222 m, contributing to the deep coalbed methane development in China.
Rheological Parameter Calibration of Online Drilling Fluid Property Monitoring System
TU Liujun, WANG Jianlong, GUO Xiaobing, WANG Ren, ZHANG Weijie, LYU Sheng’an, LIU Sheng, YANG Zexing
2025, 42(3): 350-358. doi: 10.12358/j.issn.1001-5620.2025.03.011
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In drilling operations, accurate and fast measurement of drilling fluid rheology is essential for safe and efficient drilling. Pipe flow method can monitor the rheological properties of drilling fluids in a real time manner, wall slip phenomenon can seriously affect the accuracy of the measurement though. To deal with this problem, the relationship between pipe flow and the effects of wall slip is discussed in depth, and a rheology calibration method based on pipe flow method is presented. In this method, the measurement is conducted using pipe flow method, the slip velocity is obtained using Mooney and regularization method on the data acquired, time is windowed to form ordered data, and a modal named WOA-SVR for predicting slip velocity is constructed. The shear rate on the wall and the generalized flow index are then corrected using the slip velocity obtained. Using this method, the rheological properties of a drilling fluid are calibrated and the accuracy of the output rheological properties is increased by 75.01%. The results of this study have been used in Tarim, Xinjiang and Huabei oilfields, the instrument measurement results are highly consistent with the results obtained by analyzing the manual samples, indicating that this method is both effective and practical. This method can provide reliable data support for the comprehensive evaluation of the rheological parameters for the online monitoring system of drilling fluid properties, and is of great significance to the improvement of drilling efficiency and safety.
Method of Predicting Drilling Fluid Rheology Based on Generative Adversarial Networks in Digital Twin Environment
GUO Liang, XU Hang, LIU Kaiyong, YAO Rugang, TANG Saiyu, XIANG Yu
2025, 42(3): 359-367. doi: 10.12358/j.issn.1001-5620.2025.03.012
Abstract(20) HTML (8) PDF (4518KB)(9)
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A method of predicting drilling fluid rheology based on genitive adversarial network in digital twin environment has been developed to deal with problems in laboratory measurement of drilling fluid rheology manually, such as low efficiency, high cost and poor stability etc. First, a twin model for drilling fluid formulation and measurement system is constructed in accordance with digital twin five-dimensional model. Information collectors such as sensors in the physical measurement system can collect the live measured data of drilling fluid properties, and the composition of the drilling fluid and the measured drilling fluid properties are integrated and sent to a virtual space to construct a database for drilling fluid property prediction. Second, using the improved generative adversarial network algorithm, a drilling fluid rheology prediction model is constructed. Historical twin data of the drilling fluid are then extracted from the database and are used as a dataset to train the model, and a best-fitting model is thus obtained. The prediction ability of the model is verified through the prediction experiment of drilling fluid rheology. Use of the model shows that the correlation coefficient R between the predicted values and the true values exceeds 0.96, and the mean absolute percentage error (AAPE) is not higher than 4.1%, indicating that the model has higher prediction accuracy, and is able to accomplish the predciiton of drilling fluid rheology.
CEMENTING FLUID
Construction of a deep high-temperature high-density resilient cement slurry system for the bayan oilfield
DUAN Yongqiang, WANG Xiuying, LUO Yucai, LUO Min, SUN De, HUANG Sheng, LI Zaoyuan
2025, 42(3): 368-378. doi: 10.12358/j.issn.1001-5620.2025.03.013
Abstract(21) HTML (5) PDF (3061KB)(9)
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For the gypsum salt layer encountered in wells deeper than 6,000 meters in the Bayan-Hetao Basin, where the bottom hole circulating temperature is around 180℃, conventional high-temperature and high-density cement slurries present several technical challenges, including poor rheological performance and stability, high fluid loss, difficult control of thickening time, and slow early strength development. There is an urgent need to develop a salt-resistant, high-temperature, and high-density resilient cement slurry system with a density range of 2.30 to 2.50 g/cm3. In view of the cement slurry admixture, the fluid loss agent (LHF) was prepared by the structure design of 'inorganic nanoparticles + polymer weak crosslinking', the retarder (LHR) was prepared by the structure design of 'strong adsorption cationic monomer + anionic monomer', and the suspension stabilizer (LHX) was prepared by the structure design of 'temperature sensitive association + micro crosslinking'. The fluid loss, thickening time and sedimentation stability of cement slurry were controlled respectively. Relying on the theory of close packing, and adopting a modified MAA model by correcting the Andrease equation with Dinger and Funk’s approach, a high-density cement slurry system with densities of 2.30 g/cm3, 2.40 g/cm3, and 2.50 g/cm3 is constructed using iron ore powder as the primary weighting agent and GM-1 as a supplementary weighting agent. The particles interact in a ball-bearing manner to reduce friction. To address the issue of slow early development of the mechanical properties of the cement stone, both strength enhancers and toughness improvers are introduced. These additives work at both the nanoscale and microscale to improve the mechanical properties of the cement stone: some fill the pores, while others act as a skeletal structure, forming a configuration similar to "reinforced concrete," which reduces the brittleness of the cement stone. The final cement slurry systems formed with densities of 2.30, 2.40, and 2.50 g/cm3 exhibit good rheological properties, high stability, fluid loss of less than 50 mL, and adjustable thickening times.
Synthesis and Properties of an Early-Strength Retarder Based on AMPS
XIE Yunmei, ZHANG Ye, MA Yong, CHENG Xiaowei, MEI Kaiyuan, ZHANG Chunmei
2025, 42(3): 379-385. doi: 10.12358/j.issn.1001-5620.2025.03.014
Abstract(23) HTML (5) PDF (2625KB)(7)
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With the increase in the depth of oil and gas exploitation, the temperature gradient in the long cementing section becomes increasingly larger. To ensure the safe pumping of cement slurries, a large amount of oil well cement retarder needs to be added, resulting in problems such as super-retardation and slow strength development of the cement slurries in the low-temperature section at the wellhead, which in turn seriously affecting the quality and safety of cementing operations. To deal with these problems, a high-temperature resistant and early-strength type retarder AMND was synthesized with four monomers, namely AMPS, MA, NVP and DEAA, based on the adsorption theory. The molecular structure and performance of the retarder were tested by methods such as infrared spectroscopy, thermal stability testing, gel permeation chromatography analysis and high temperature and high pressure thickening. The test results show that: 1) the retarder AMND has excellent thickening performance at high temperatures; the thickening time of the cement slurry can reach 316 minutes at 150℃, 2) AMND has excellent setting control performance, as well as low temperature sensitivity and dosage sensitivity. It can adjust the thickening time in different temperature ranges, which is beneficial to the safe pumping of the cement slurry at the well site, 3) it has little impact on the mechanical development of the set cement. At a circulating temperature of 150℃ and a curing temperature of 60℃, the strengths of the set cement at 1 day, 2 days, and 3 days can reach 6.34 MPa, 8.24 MPa, and 14.66 MPa respectively, satisfying the strength requirements for cementing operations. The conclusion is that this retarder can alleviate the super-retardation phenomenon in the low-temperature condition, achieve retardation at high bottom hole temperatures, and does not affect the development of the strength of the cement at the wellhead. It has successfully mitigated the super-retardation or non-setting problems in wells with large temperature differences and long cementing sections, and has a very good application prospect.
Contamination of High Density Drilling Fluid at High temperature and Handling thereof in Northeast Sichuan
WANG Junxiang, HU Junhui, WANG Changqin, LUO Yafei, LIU Yangkang
2025, 42(3): 386-391. doi: 10.12358/j.issn.1001-5620.2025.03.015
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The construction drilling fluid density in the Puguang Maoba block, Tongnanba Ma 3 block, Yuanba block in Northeast Sichuan is high. During the cleaning and plugging period , the high-density drilling fluid is common to experience high temperature thickening and consolidation after being contaminated by cementing cement.Due to unclear pollution mechanisms and lack of effective treatment methods, a high proportion of replacement mud is usually required, resulting in long treatment cycles and high costs. This article briefly analyzes and verifies the pollution mechanism of cementing cement on high-temperature and high-density drilling fluid through simulation experiments. The results show that the main reasons for pollution are: firstly, the high pH value of the drilling fluid after pollution leads to high-temperature thickening; secondly, some additives in the cement slurry invade the mud and solidify at high temperature, adsorbing a large amount of free water and causing thickening of the mud.In response to the pollution mechanism, AOP-1, a polymeric aluminum anti collapse agent, was selected as an efficient high-density water-based drilling fluid cement pollution treatment agent, which was successfully applied in four wells. The on-site application shows that AOP-1 has a good treatment effect on high-temperature and high-density water-based drilling fluid well cementing pollution, which avoid a large amount of displacement of drilling fluid after pollution and improving treatment efficiency.
Study on and Application of a Low Temperature Low Density Early Strength Cement Slurry
SUN Jianfeng, FU Yueying, QIU Weihong, LIU Jingli, ZHAO Qiuyu, CAO Hongchang
2025, 42(3): 392-397. doi: 10.12358/j.issn.1001-5620.2025.03.016
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Coalbed methane (CBM) well operations in the north usually have to deal with problems such as low ambient temperature, formations with low pressure bearing capacities and extremely low fracture pressures, and low-density cement slurries that do not cure and develop strength for a long term in low temperature environment, et al. By optimizing an early-strength supplementary materials and supporting additives, a low temperature low density early strength cement slurry with density between 1.03 g/cm3 and 1.30 g/cm3 and suitable for cementing CBM wells was developed. Laboratory studies show that this cement slurry has good settling stability, a fluidity of 19-22 cm, a water bleeding ratio of 0%, a thickening time that is adjustable, and an API filter loss of less than 50 mL. After aging for 48 h at 4℃, the compressive strength of the set cement is at least 7.0 MPa. This cement slurry has been used for 12 well times, of all the cemented well sections, 93.03% met the well cementing quality requirement, 86.70% were cemented with excellent quality, and the job quality of cementing the shallower pay zones in winter was obviously improved.
Study on Factors Affecting Properties of Flushing Fluids for Removing Mud Cakes to Improve Well Cementing Quality
WU Yanxian, ZHAO Zengxin, GONG Jiaqin, ZHANG Hao, WU Baokang, ZHANG Hui, LI Jun, LI Zhiqi
2025, 42(3): 398-405. doi: 10.12358/j.issn.1001-5620.2025.03.017
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Filter cakes generated during drilling on the surfaces of the borehole walls seriously affect the bonding quality of the interface between the cement sheath and the borehole walls if the filter cakes are not removed, resulting in poor cementing quality. Most of the current researches on improving cementing quality aims to displace the drilling fluid completely and does not consider the influence of the filter cakes. To improve the cementing quality, three Herschel-Bulkley fluid flow models for spacer fluid, drilling fluid, and filter cake in a three-dimensional eccentric annulus were established, taking into account the regulating effect of the flushing fluid on the drilling fluid. The effects of the changes in the density, consistency coefficient, flow behavior index and yield point of the drilling fluid affected by the flushing fluid on the flushing efficiency of the drilling fluid and filter cakes were systematically studied. The results show that reducing the density and rheological parameters of the flushing fluid can improve the flushing efficiency of the drilling fluid, but it will reduce the flushing efficiency of the filter cake. The density and rheological parameters of the flushing fluid are not the smaller the better. Under the condition of ensuring a high flushing efficiency of the drilling fluid, appropriately increasing the density and rheological parameters of the flushing fluid to maintain relatively high mud viscosity and gel strengths is beneficial to promoting the removal of the filter cakes. Prioritizing the regulation of the flow behavior index of the flushing fluid to make the flow behavior index of the drilling fluid reach an ideal value will significantly improve the cementing quality. The research results will provide theoretical guidance for optimizing the performance parameters of flushing fluids and for improving cementing quality.
FRACTUREING FLUID & ACIDIZING FLUID
Synthesis and Performance of a Salt Resistant Swelling Preventive Aqueous Emulsion Drag Reducer
HUANG Jing
2025, 42(3): 406-412. doi: 10.12358/j.issn.1001-5620.2025.03.018
Abstract(24) HTML (7) PDF (2533KB)(13)
Abstract:
Common inverse emulsion drag reducers have poor salt resistance and hence are unable to be formulated with high salinity formation water and water flowed back in formation fracturing operations. These drag reducers are generally single-functioned, expensive and contain oil phase that causes formation damage. To solve these problems, a new salt-resistant swelling-preventive oil-free aqueous emulsion drag reducer has been developed through aqueous dispersion polymerization. Laboratory evaluation with friction tester and rheometer of the new drag reducer in a slick water system showed that this drag reducer has good stability, and is able to instantly dissolve in water in 15 seconds. The cationicity of the drag reducer is 15.98%. A fracturing fluid formulated with 100,000 mg/L saltwater has viscosity that is not affected by the high salinity of the saltwater. The drag reducer works normally at temperatures up to 180℃. A slick water formulated with this drag reducer was used in field operation, the drag of the slick water was reduced by 82% and swelling inhibition capacity was enhanced by at least 60%. With this drag reducer, high drag reduction rate, online formulation and clay swelling inhibition can be simultaneously achieved, the so-called “one additive with multifunction”. This study has provided a new clue for simplifying fracturing fluid formulation process, lowering operation cost and developing new fracturing fluids with enhanced fracturing efficiencies.
COMPLETION FLUID
A New Self-Generating Foam Workover Fluid for Low Pressure Reservoirs
WU Ying, PENG Li, WANG Hongshen, TIAN Chuming, PENG Jinhong, WANG Shaoqing
2025, 42(3): 413-417. doi: 10.12358/j.issn.1001-5620.2025.03.019
Abstract(17) HTML (5) PDF (2037KB)(7)
Abstract:
An offshore normal temperature low pressure low permeability low water cut reservoir needed to be worked over, the workover fluid can cause contamination and hence damage the reservoir. To deal with this problem, a cleaning low density self-generating foam workover fluid was developed based on an anti-water-block water-based workover fluid. A self-generating foaming agent ZSP and a wettability alteration agent FZJ etc. were used in formulating the new workover fluid. The workover fluid was evaluated for its general properties, and it was found that the workover fluid has good basic performance, its density can be adjusted between 0.5 g/cm3 and 0.9 g/cm3. The workover fluid is well compatible with the formation waters, natural cores after treatment with this workover fluid can have their wetting phase damage near the wellbore being removed, thereby improving the permeability of the oil phase in a disguised way. This cleaning low density foam workover fluid has been successfully used on three wells (well CH33 etc.), no downhole troubles occurred during operation. Two days after the workover operation, the three wells regained their normal production rates, indicating that this new workover fluid has satisfied the requirements of workover operations on offshore reservoirs with low pressure, low permeability and low water cut.
Preparation and Application of a Block Removing Fluid for Eliminating Reservoir Contamination by High Density Oil-Based Drilling Fluids
LUO Zhifeng, LI Ke, YAN Bingsen
2025, 42(3): 418-424. doi: 10.12358/j.issn.1001-5620.2025.03.020
Abstract(19) HTML (7) PDF (2865KB)(15)
Abstract:
High density oil-based drilling fluids have been widely used in the well drilling operation due to their high stability and inhibitive capacity. However, barite filter cakes formed after filtration and migration of the high density oil-based drilling fluids cause great harm to the reservoir, resulting in reduced oil and gas production. The contamination caused by the barite filter cakes is difficult to remove by conventional methods such as acid dissolution and alkali dissolution. In this study, a stable and efficient block removing fluid was formulated with the chelating agent DTPA as the main component, potassium carbonate as the conversion agent, oxalic acid as the catalyst, ammonium persulfate as the oxidant, AEC as the surfactant and ethylene glycol butyl ether as the organic solvent. This block removing fluid, through penetration, chelation, solubilization and washing on the mud cakes, destroys the internal structure of the mud cakes formed by oil-based drilling fluids, reduces the inter-substance adhesive force, and enhances the removal of the contamination by high density oil-based drilling fluids. The composition of the solid-phase chelating liquid for high-density drilling fluids is:20%DTPA+3%oxalic acid+6%K2CO3+0.06%ammonium persulfate+KOH, and the final composition of the oil-phase cleaning liquid is: 12% ethylene glycol butyl ether+0.5%AEC. Evaluation of the performance and oil cleaning ability of this block removing fluid shows that under different temperatures (120℃-180℃), the composite block removing fluid can effectively degrade the filter cakes produced by high-density drilling fluids. Single-stage treatment at 120℃ for 4 hours can reach a filter cake dissolution rate of 66.7%, and multi-stage treatment at 120℃ for 4 hours has a filter cake dissolution rate of 72.22%. Moreover, the filter cake dissolution rate increases with temperature. After the multi-stage treatment at 180℃ for 8 hours, the dissolution rate is 89.24%, and the highest corrosion rate is 1.1537 g/(m2·h). It has excellent block removal performance and temperature resistance. In the same experimental conditions, the dissolution efficiency of the composite block removing method for the mud cakes produced by oil-based drilling fluid is about 20% higher than that of the conventional chelating block removing method. Field tests have proved that this system can effectively solve the contamination and block by high-density drilling fluids, and the production capacity recovery rate can be as high as about 90%.

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