钻井液与完井液

Abstract:
The national shale gas demonstration block was in Zhaotong city, where the distribution of limestone was uneven. These complex downhole accidents, such as collapse failure and cavernous leakage, sticking of bit, overflow, gas invasion, and leakage, were frequent when high-density oil-based drilling fluid was adopted. The correlation between geological stratification and underground working conditions was found to be poor according to the statistics of complex downhole conditions of 26 wells. This paper first analyzes the non-correlation between geological stratification and downhole complex accidents. And it summarizes the factors such as anisotropy of reservoir geomechanical parameters, a difference of longitudinal horizontal stress, borehole trajectory and formation dip, lithology difference and weak surface structure. Taking safe drilling as the main objective, the risk stratification of wellbore collapse is proposed from the engineering perspective. Compared with traditional geological stratification, it considers the lithological difference and integrates the rock's weak surface structure, in-situ stress state, drilling parameters and other comprehensive indicators. Finally, the collapse risk assessment is carried out for the complex small layers of a typical well, the safe mud density window is optimized, and the well deviation angle and azimuth angle are optimized. It is suggested to drill according to the lower limit of the safe mud density window. In the high collapse risk formation, improving the plugging property of drilling fluid and reducing the wall permeability can largely avoid complex accidents. Exploring risk stratification of wellbore collapse can effectively guide drilling engineering operations, optimize engineering design schemes, and provide a scientific basis for safe drilling in long horizontal stages of deep shale reservoirs to prevent complex downhole accidents.

Application of Polymer Based on Amino Ionic Liquid as Anti-high Temperature Inhibitor and the Mechanism

REN Yanjun, CHEN Huan, YANG Hong

2023, 40(3): 289-295, 302. doi: 10.12358/j.issn.1001-5620.2023.03.002

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Abstract:
A copolymer (PAN) base on amino ionic liquid and acrylamide were synthesized and used as the inhibitors for inhibiting clay hydration under high temperature condition. The molecular structure of PAN was characterized using infrared spectroscopy. The inhibition properties of PAN were evaluated by immersion and dispersion tests, linear expansion and hot roll recovery experiments. The results showed that PAN performed better than KCl, polyether amine D230 and ionic liquid monomers in inhibiting swelling and dispersion, which could also resist high temperatures of 250 ℃. The inhibition mechanism was revealed by XRD, Zeta potential, wettability analysis. PAN exerted excellent inhibition effects by winding and coating the clay particles, increasing the cementation between clay particles, compressing the double electric layers and changing the wettability. The results could provide theoretical and technical supports for the development of novel inhibitors with superior inhibition property and high temperature resistance.

A Model for Hard Brittle Mudstone Collapse Pressure Computation Based on Rock Dilation Strength Criteria

XING Xuesong, YU Baohua, WANG Hengyang, WU Zhiqiang, PANG Zhaoyu

2023, 40(3): 296-302. doi: 10.12358/j.issn.1001-5620.2023.03.003

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Abstract:
Under low confining pressures, a hard brittle mudstone is easy to dilate before the stress acted on the mudstone reaches its peak value. When the stress is greater than the dilation strength of the shale, the weakening of the mudstone by the hydration of the drilling fluid becomes fast and outstanding, resulting in borehole collapse. To avoid borehole collapse, a reasonable mud weight should be used. Through laboratory experiment and theoretical analysis, studies were conducted on the factors such as the fabric characteristics, hydrophysical properties, deforming patterns and strength criteria of hard brittle mudstones, as well as the change of strengths of mudstones after unloading prestress in a drilling fluid. A computation model and parameter computing method based on rock dilation strength criteria were developed for the collapse pressure of a borehole penetrating hard brittle mudstones, and a case study was conducted. The study results show that the mud weight is greater than the collapse pressure calculated on the basis of peak strength criteria and is lower than the collapse pressure calculated on the basis of dilation strength criteria, the formation around the borehole is in a state of dilation, and stress-induced micro fractures are generated around the wellbore, which stimulates drilling fluid hydration, and this is the root cause for borehole collapse. Based on this knowledge, mud weight determined on the basis of dilation strength criteria is more reasonable.

Synthesis and Application of Polyether Fatty Acid Rheology Modifier for Oil-based Drilling Fluids

LUO Chunzhi, ZHANG Chujun, WANG Yidi, WANG Yuezhi, LI Haibiao, TAN Tianyu, ZHANG Bo

2023, 40(3): 303-312. doi: 10.12358/j.issn.1001-5620.2023.03.004

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Abstract:
Oil-based drilling fluids have low gel strengths and pipe sticking by the settled drilled cuttings is easy to be encountered. A polyether fatty acid gelling agent LQZ has been developed to deal with this problem. The molecular structure, thermal stability, gelling property and emulsion stability of the synthesized LQZ were analyzed using IR spectroscopy, thermogravimetric curve, gel strength measurement and emulsion stability test. The effects of the base oil for formulating the mud, oil/water ratio, density and temperature on the gelling performance of the LQZ were investigated. It was found that in the LQZ molecules there are polar groups such as hydroxyl, amide and ether bond which can form network structures. The network structures render the LQZ a fast weak gelling characteristics. At 300 ℃, the LQZ has no obvious thermal decomposition. The LQZ is beneficial to the emulsion stability of the oil-based muds at a concentration of less than 0.85%. The LQZ can be used in various nonaqueous drilling fluids formulated with white oil, diesel oil or synthetic fluids, with white oil-based drilling fluids being the best environment for the LQZ. LQZ in an oil-based mud with oil/water ratio of 8∶2 and density of 2.1 g/cm³ has the optimum gelling capacity at 190 ℃, the yield point, the low shear rate, φ₆ andφ₃ reading and the gel strengths are all doubled. Compared with the similar products produced abroad, LQZ has the advantages of increasing gel strengths of a mud, without simultaneously increasing the plastic viscosity of the mud. In field operation, 1% LQZ in a white oil-based drilling fluid and in a diesel oil-based drilling fluid increased the gel strengths of the muds by more than twice, and the plastic viscosity was only slightly increased. The LQZ can be used to improve the suspending capacity of an oil-based drilling fluid.

The Synthesis and Application of an Environmentally Friendly High Temperature Graft Oligosaccharide Filter Loss Reducer

ZHENG Bin

2023, 40(3): 313-318. doi: 10.12358/j.issn.1001-5620.2023.03.005

Abstract(798) HTML (268) PDF (2640KB)(113)

Abstract:
A graft oligosaccharide filter loss reducer CG-FL was developed through inverse emulsion with starch derivative oligosaccharide as the raw material, acrylamide, 2-acrylamide-2-methapropyl sulfonic acid and N-vinyl pyrrolidone as the graft monomers and AIBN as the initiator. The molecular structure of the filter loss reducer CG-FL was characterized by FTIR, SEM and TGA etc. The biotoxicity EC₅₀, biodegradation capacity and heavy metal contents of CG-FL were examined. The performance of CG-FL in drilling fluids was evaluated by performance comparison of single additive, performance comparison of different drilling fluids formulated in laboratory with CG-FL and other additives, as well as field application. Laboratory evaluation of CG-FL showed that CG-FL functions normally at temperatures up to 180 ℃, it is resistant to contamination by 15% salt. CG-FL has good dispersibility and compatibility with other additives. In comparison experiment, CG-FL showed better properties than the counter additives. Field application showed that CG-FL reduced the filtration rate of the drilling fluids, and the drilling fluids, after treatment, showed stable properties, no foaming or carbonization of the additive has occurred.

Development and Field Application of a Drilling Fluid Intelligent Testing and Evaluating System

YANG Chao

2023, 40(3): 319-324. doi: 10.12358/j.issn.1001-5620.2023.03.006

Abstract(867) HTML (252) PDF (5450KB)(131)

Abstract:
Real-time testing, cloud store of data, intelligent diagnose and automatic optimization suggestion and the prerequisite for the oil and gas industry to achieve intelligent and digital transformation. To achieve the goal of transformation, a drilling fluid intelligent testing system has been developed on the bases of industrial standards, field operational requirements, and in connection with the internet of things (IoT) and big data platforms. This system can be used to fulltime test drilling fluid parameters automatically and continuously in 24 hours a day in 365 days at temperatures between room temperature and 200 ℃ and at pressures between atmospheric pressure and 8 MPa. Parameters tested include drilling fluid temperature, density, rheology, API and HTHP filter losses and changes in concentrations of various ions in the mud filtrates. Using the intelligent analysis module, the real-time parameters tested can be compared with the corresponding designed parameters, thereby helping present optimized drilling fluid treatment to guarantee the safety of downhole operations. Long-term laboratory test and thousand batches of experimental comparison data obtained from field application of the system on many wells indicated that the rheology measurement module and the filtration measurement module have an accuracy of 97.3%, the ion concentration measurement module has an accuracy of 96.2%. The successful application of the drilling fluid intelligent testing and evaluating system has provided an accurate and stable data guarantee for safe, efficient and intelligent oil and gas exploration.

The Use of a High Performance Water Based Drilling Fluid in Drilling the 5000 m Horizontal Section of a Shale Oil Well in Changqing

HU Zubiao, WANG Qingchen, ZHANG Qin, XU Wen, LI Debo, HAN Chengfu

2023, 40(3): 325-331. doi: 10.12358/j.issn.1001-5620.2023.03.007

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Abstract:
In 2019, Changqing oilfield has drilled a well with horizontal section of 4,000 m in length, the first long horizontal section well in Asia. In 2021, a well with horizontal section of 5,000 m was drilled in Changqing with water based drilling fluids. The key issues in drilling the ultra-long horizontal section wells are the lubricity of the drilling fluids and hole cleaning. To deal with these two issues, a high performance gel strength additive TQ-8 and a high efficiency drilling lubricant HTZ were developed with natural materials as the basic materials, and group grafting and fermenting were used in the synthesis process. Using these two additives, a drilling fluid suitable for 5,000 m horizontal section well drilling was formulated. The composition of the drilling fluid is as follows:(4%-6%)HTZ + (0.5%-2%)TQ-8 + (0.5%-2%)mudstone inhibitor YYZ-1 + (1%-2% )PAC-LV + (1%-2%)BLA-LV + (3%-4%)filming plugging agent FDJ-1 + (20%-80%) soluble weighting agent + caustic soda. It was found in field application that the hole cleaning, lubricity and contamination resistance of this drilling fluid were all better than the drilling fluid used in drilling the well with 4,000 m horizontal section. This drilling fluid technology has been used on the shale oil well Hua-H90-3 in Changqing. Friction experienced in the tripping of the drill string before casing running was 400 kN, and the remaining hook load after casing running was 17 tons, meaning that this drilling fluid has the potential of drilling wells with longer horizontal sections.

Study on High Temperature Gas-Cut Resistant Weak Gel Drilling Fluid in Shunbei Oil and Gas Field

ZHAO Haiyang, FAN Sheng, LIAN Shixin, LI Shuanggui, CHEN Xiuping, KE Dian

2023, 40(3): 332-339. doi: 10.12358/j.issn.1001-5620.2023.03.008

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Abstract:
The carbonate Yijianfang formation and the Yingshan formation of the Ordovician system in the Shunbei oil and gas field is developed with microfractures and active gas zones. Serious and frequent CH₄ and CO₂ gas cut ascended fast in the annular spaces, leading to coexistence of mud losses and well blow-out. To prevent gas cut, previous experiences obtained in the Shunbei oil and gas field were borrowed and analyzed, and a high temperature weak gel drilling fluid was developed to deal with the gas cut problem. Several additives were used to formulate this drilling fluid, such as a high temperature stabilizer MG-HT, a high temperature rheology modifier JHVIS, a high temperature filter loss reducer JHFLO and a high temperature plugging agent JHSEAL, as well as other additives selected for this drilling fluid. This drilling fluid has high temperature resistance to 180 °C, good plugging capacity to gas cut and is able to improve the pressure bearing capacity of the formations. This drilling fluid can be weighted to 1.8 g/cm³ and has good rheology, filtration property and contamination resistance. The 6-RPM and 3-RPM readings of the drilling fluid measured on a 6-speed direct-reading rheometer are both greater than 5, and the low-shear-rate viscosity of the drilling fluid is greater than 15,000 mPa·s. Formations strengthened with this drilling fluid have forward and backward pressure bearing capacities of greater than 5 MPa and 1 MPa, respectively. This weak gel drilling fluid, with good gas cut preventing capacity, has provided a technical support to the safe, fast exploration and development of the fractured carbonate reservoirs in the Shunbei oil and gas field.

Mechanisms Casing Contamination by Drilling Fluids in Ultra-Deep Well Drilling

SONG Hanxuan, ZHENG Lianjie, ZHANG Shiling, GUO Jixiang, ZHANG Xiaojun, GAO Chenhao, LIU Hongyu

2023, 40(3): 340-348. doi: 10.12358/j.issn.1001-5620.2023.03.009

Abstract(799) HTML (276) PDF (6900KB)(88)

Abstract:
By analyzing the residual rate of drilling fluids on the surfaces of casing strings in ultra-deep wells, it was ascertained that temperature is the main factor affecting the residue of drilling fluids on the surfaces of the drilling strings. In high temperature ultra-deep wells, oil-based drilling fluids are apt to lose their emulsion stability and become demulsified, turning from hydrophobic to hydrophilic. Water-based drilling fluids, on the other hand, are dewatered at elevated temperatures, turning from hydrophilic to hydrophobic. Using XRD, element analysis, SARA and FTIR methods, the components of the residues of a water-based drilling fluid and an oil-based drilling fluid commonly used were analyzed. The main components of the residues were known to be cellulose and the mixture of clay and barite particles coated with sulfonated phenolic resin for the water based drilling fluid, and asphalt and barite coated with oleic acid amide for the oil-based drilling fluid. The adsorption effect of the macromolecules in a drilling fluid on the surfaces of casing strings was calculated using molecular dynamics simulation based on the analyses of the residues in the drilling fluids. The calculation showed that the binding energy between porphyrin (the major component of asphalt) and the casing wall is -54.18 kcal/mol, the binding energy between oleic acid and the casing wall is -19.72 kcal/mol, the binding energy between cellulose and the casing wall is -19.09 kcal/mol, and the binding energy between sulfonated phenolic resin and the casing wall is -93.19 kcal/mol, respectively. These results have proved that compared with oil-based muds, the organic components in a water-based are much more adhesive at elevated temperatures. This analysis of the casing contamination by drilling fluids will provide theoretical guidance to the cleansing of casing strings in the future.

Drilling Fluid Technology for Drilling the Slim Hole Horizontal Shale Oil Well Shuaye-3-7HF

JIN Junbin, GAO Shuyang, CHEN Xiaofei

2023, 40(3): 349-355. doi: 10.12358/j.issn.1001-5620.2023.03.010

Abstract(875) HTML (354) PDF (2717KB)(119)

Abstract:
The well Shuaiye-3-7HF is a Φ118 mm slim hole sidetracked horizontal shale oil well drilled in the Qintong block in northern Jiangsu area. Several problems were encountered during drilling, such as instability of shale formations, high pressure losses in the annular spaces, mud losses, higher requirement on friction reduction in drilling the horizontal section, as well as CO₂ contamination etc. A water-based drilling fluid SM-ShaleMud-II for shale drilling was formulated in laboratory. Evaluation of this mud has shown that it has excellent inhibitive capacity, plugging capacity and lubricity, and is suitable for drilling the long horizontal section shale oil wells in the northern Jiangsu area. Field application has shown that the HTHP filter loss of the SM-ShaleMud-II drilling fluid was less than 7 mL, the adhesive coefficient of the mud was less than 0.07, and the overpull encountered during tripping out of hole after drilling to the total depth was less than 16 tons. The stability of the Fu-2 member, a shale reservoir section, was effectively maintained for 110 hours, greatly changed the past understanding of the length of time the Fu-2 member can be exposed to water-based drilling fluids. The length of the Φ118 mm slim hole was drilled to a length of 1,948.66 m, the longest open hole penetrating the shale formations in the area, and the length of the horizontal section is 1,361.66 m, the longest horizontal section in the same area. The experiences obtained in using this water-based drilling fluid have provided a good reference for subsequent slim hole long horizontal well drilling, and have paved the way for large-scale application of the SM-ShaleMud-II drilling fluid in shale oil drilling in the northern Jiangsu area.

Borehole Wall Stabilization Technology for Drilling the Long Horizontal Section Coal Rock Gas Well JN1H

WANG Zaiming, CHEN Jinxia, SHEN Yuanyuan, ZHU Kuanliang, LI Zhanwei, HOU Yi, DENG Wei

2023, 40(3): 356-362. doi: 10.12358/j.issn.1001-5620.2023.03.011

Abstract(703) HTML (225) PDF (3054KB)(100)

Abstract:
Wells with long horizontal sections were drilled in the eastern margin of Ordos basin and penetrated the 8^# coalbed of the Benxi formation. Borehole stability problems during drilling and completion of the wells made it difficult to drill these extended reach wells. Studies were conducted on the borehole stability of the coalbed methane production wells. X-ray diffraction, SEM, CT and triaxial stress test were conducted on the rock cores taken from the carbonaceous mudstones, the intercalated gangues, and the upper and lower coalbeds that are possibly penetrated by the wells. Analyses of these core samples show that the minimum amount of clay minerals of the cores taken from formations outside the coalbeds is 35%, and the clays are mainly kaolinite and illite. The content of mixed layer illite-montmorillonite is less than 5%. Cores taken from the coalbeds have clay content between 10% and 18%, and is mainly kaolinite, and the content of the mixed layer illite-montmorillonite is about 25%. The widths of the fractures in the cores are generally 25-1,000 μm, mainly around those widths such as 25 μm, 40 μm, 64 μm, 100 μm, 250 μm and 400 μm. The maximum equivalent collapse pressure of the formations is 1.36 g/cm³ and is located in the middle and the lower coalbeds. A drilling fluid was formulated to drill these formations based on three policies, which were “prevent collapse by plugging, ensure the hole is as clean as possible, and prevent pipe sticking with good lubricity of the drilling fluid”. The drilling fluid formulated had these properties in laboratory evaluation: API filter loss of 1.6 mL, HTHP (70 ℃) filter loss of 4.4 mL, and sand bed (400 mD, 100 D) PPT filter loss of less than 15 mL, indicating that it had excellent plugging capacity. This drilling fluid was used to drill the well JN1H whose horizontal section is 2,019 m in length. Drilling and completion This well was successfully drilled and completed in 28.25 days, and stabilization of the long horizontal section of a coal rock gas well was reached.

Mud Loss Control Technology in Qiongdongnan Basin under High Temperature and High Pressure Bearing Conditions

LIN Siyuan, LU Yunhu, ZHANG Liquan

2023, 40(3): 363-367. doi: 10.12358/j.issn.1001-5620.2023.03.012

Abstract(706) HTML (220) PDF (3653KB)(98)

Abstract:
The well XX23-1-1 is a key exploratory well drilled in the Qiongdongnan basin (a basin located in the southeast of Hainan Province). Mud losses were encountered when drilling to 4,186.22 m. A new HTHP pressure bearing lost circulation control technique was presented to deal with the mud losses based on the rate of mud losses and the high temperature high pressure encountered in the mud loss zone. The lost circulation control slurry was formulated with particles, flakes and fibers. Based on the mud loss control mechanisms of “particles to bridge + wedge in to provide pressure bearing capacity + strengthen the borehole wall with mud cakes”, a tight plugging zone with stable structure was formed under squeeze pressure. The channels through which the mud was lost were plugged with the slurry and the loss zone was strengthened. With this technique, the mud losses were successfully stopped. Laboratory evaluation was performed on the particle size distribution, the ability of high temperature resistance and success rate of the slurry. The experimental results show that this slurry has a wide particle size distribution and is able to effectively control mud losses through induced fractures. The HTHP lost circulation materials used in the slurry has low weight losses after aging at 180 ℃ for 16 hours, showing an excellent high temperature durability. Plugging of a 5-3 mm seamed plate with the slurry can stand a pressure of more than 20 MPa. This HTHP pressure bearing mud loss control technique was used in controlling mud losses encountered in the well XX23-1-1, the final pressure bearing capacity of the plugged zone reached 3 MPa and was stabilized at this level for 30 min, with no pressure drop, and the ECD on the bottom of the hole was 1.90 g/cm³, meeting the expected requirements.

Study on Special Dissolving Agent of Marine Epoxy Resin Plugging Agent in Western Sichuan

LAN Lin

2023, 40(3): 410-414. doi: 10.12358/j.issn.1001-5620.2023.03.019

Abstract(674) HTML (222) PDF (2905KB)(72)

Abstract:
The marine facies of the Chuanxi gas field has characteristics of ultra-deep high temperature, salt gypsum layer, and high sulfur content. The development of the triple well system with ultra-deep and high inclination results in frequent malignant and recurrent losses. Epoxy resin plugging agent has the characteristics of pumpability at room temperature, temperature control of consolidation time, high consolidation compressive strength, and significant sealing effect for large cracks. However, its viscosity is relatively high, and it is prone to adhesion and bonding in the wellbore and pipeline. After consolidation, it is insoluble and non melting, making it extremely difficult to dissolve and unblock. In response to the problems related to epoxy resin plugging agent, dissolution mechanism analysis, dissolution orthogonal analysis, and optimization of the anti-corrosion performance of the dissolution agent are conducted, develop a dissolution agent for epoxy resin plugging agent, which has a dissolution rate of 97.82% for epoxy resin plugging agent under conditions of 120 ℃ and 24 hours. The corrosion rate for N80 steel sheet is only 0.0086 g/(m²·h), which is lower than the evaluation standard for slight corrosion (0.022 g/(m²·h)). This provides a new way to solve technical problems such as rapid dissolution, unblocking, and downhole string safety after malignant leakage plugging operations.

CEMENTING FLUID

Control Measures of Cement High-temperature Deterioration Performance under Dry-hot Rock Conditions

DANG Donghong, LIU Ningze, WANG Dan, MEI Kaiyuan, CHENG Xiaowei, SUN Xingjia

2023, 40(3): 368-375. doi: 10.12358/j.issn.1001-5620.2023.03.013

Abstract(695) HTML (234) PDF (3240KB)(60)

Abstract:
When cementing geothermal wells in dry hot rocks, the bottom temperature is often as high as above 200 ℃. Aiming at the problem of strength decline of cement paste caused by high temperature at the bottom of the well under dry-hot rock conditions, this paper directly starts from the chemical composition of cement, and improves this problem by adjusting the ratio of C₃S and C₂S, and compounding low-heat portland cement with lower calcium-silicon ratio under the synergistic effect of silicon powder. Firstly, the mechanical properties of multiphase C₃S-C₂S mineral system are the best when C₃S∶C₂S=1.0. Combined with XRD, TGA and SEM tests, it is known that the reduction of calcium-silicon ratio has a positive effect on the formation of favorable phase xonotlite. Low-grade cement with lower calcium-silicon ratio is introduced to strengthen G-grade cement. The results show that the compressive strength of "30% G-grade +70% low-grade cement" composite cement system (the ratio of C₃S to C₂S is 1.07) is 27.34 MPa under the action of 40% silicon powder. The high temperature resistance of cement paste can be greatly improved from the cement itself by properly adjusting the mineral composition in cement to make the ratio of C₃S to C₂S about 1.0.

Study on a Foam Lightweight Cement Slurry and the Distribution of Its Micro Pores

REN Qiang, LIU Ningze, LUO Wenli, GAO Fei, LIU Jingli, LIU Yan, YANG Yuhang, CHENG Xiaowei

2023, 40(3): 376-383. doi: 10.12358/j.issn.1001-5620.2023.03.014

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Abstract:
Foam lightweight cement slurry is very important to the safety of downhole operation in low-pressure easy-to-leak formation drilling. A high temperature high efficiency foaming agent FPJ-S has been developed to formulate lightweight cement slurries. FPJ-S is prepared from the hydrophilic tetradecanedioic acid methyl ester, the hydrophobic N,N-dimethyl-1,3-diamino propane and a rigid linking monomer 2,2’-dibromobiphenyl. A high temperature foam stabilizer, WPJ-S, was developed with the FPJ-S, a viscosifying foam stabilizer and a synergistic foam stabilizer. A foam lightweight cement slurry was formulated with WPJ-S and experiments were conducted to study the foaming capacity of the FPJ-S and the WPJ-S, as well as the distribution of pores in the set foam cement. The study results show that compared with conventional foaming agents, the foaming capacity of the FPJ-S is increased by 40%, the 1-hour settling distance is reduced by 58.8%. The foam stabilizing capacity and temperature tolerance of the WPJ-S is superior to the conventional foam stabilizers. The density of the foam lightweight cement slurry formulated can be adjusted between 0.90 g/cm³ and 1.6 g/cm³. The cement slurry has good settlement stabilization, and the 24-hour compressive strengths of the cement slurries of different densities are all greater than 3 MPa. Technical characterization based on mercury intrusion method and industry CT (XCT) shows that the foam lightweight cement slurry has pores that are uniformly distributed inside the set cement, and the set cement has regular morphology, and no large number of connecting holes are found in the set cement.

Simulation Study of Sealing Integrity in Abandoned Wells Within CO₂ Sequestration Block

WANG Dian, LI Jun, LIU Penglin, LIU Xianbo, LIAN Wei, LU Zongyu

2023, 40(3): 384-390. doi: 10.12358/j.issn.1001-5620.2023.03.015

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Abstract:
As the main leakage pathway in CO₂ sequestration, the sealing integrity of the abandoned wellbore is directly related to the sequestration effect. To this end, for the abandoned wellbore leakage problem, a three-dimensional finite element model of cement plug-formation is developed based on the cohesive zone method coupled pore pressure. In this paper, we simulated the CO₂ transport process along the abandoned wellbore and analyzed the influence of cement slurry system and bonding quality on the risk of leakage. The simulation results show that: CO₂ accumulation induces micro-annulus at the plug-formation interface, forming a leakage channel, and the micro-annulus tends to develop axially; the risk of wellbore leakage is lower when choosing higher modulus, higher Poisson's ratio, and micro-expansion cement to seal the wellbore; the micro-annulus is extremely sensitive to the poor bonding zone, and the control of bonding quality should be focused when sealing the wellbore. The results of this study have important implications for guiding wellbore abandonment within the CO₂ sequestration block.

Liner Cementing through Precise Pressure Control in the Ultra-Deep Well Tian-X Located at the Southern Margin of the Junggar Basin

FEI Zhongming, LIU Xin, ZHANG Ye, ZHANG Xiaojian, JIANG Shiwei, SHEN Lei, YANG Zufu

2023, 40(3): 391-396. doi: 10.12358/j.issn.1001-5620.2023.03.016

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Abstract:
The well Tian-X is an exploratory well located at the Anjihai anticline (an anticline in the Huomatu anticline zone) in the south edge thrust belt in the Junggar Basin. The 6^th interval (Ф139.7 mm) penetrates a long open hole section of the well with coexistence of high and low pressure zones and narrow annular clearance, and the sandstone reservoir is developed with abundant pores and has active oil and gas. The safe drilling window in this interval is only 0.02 g/cm³, and mud losses have frequently happened during drilling. Narrow safe drilling window also causes difficulties in dynamically balancing the formation pressures and problems such as well kick and mud losses during casing running are quite prone to happen, resulting in poor cementing quality. To solve these problems, precise pressure management during casing running has been performed. Using the precise pressure management equipment, pressures at the wellhead during casing running and well cementing can be precisely controlled an the pressures at the points of mud losses an points of well kicks along the borehole were controlled in the scope of the safe window, thereby realizing pressure balance inside the wellbore. In cementing the liner string, the wellhead pressure was precisely controlled and the cement slurry returned to the designed depth in one circulation, and the cementing techniques were designed specifically to suit for the wellbore conditions. The well cementing job was performed successfully. IBC well logging interpretation shows that the job quality of the cementing section is 100% qualified, no gas channeling occurred at the bell nipple when mud density was reduced. This technology has provided a precious experience and reference significance for cementing wells with narrow drilling windows at the south edge of the Junggar Basin.

Research and Application of Organic and Inorganic Hybrid Thixotropic Agents

SHI Ye, MU Jianlei, ZHU Feng, LI Xiumei, YANG Hewei, CHANG Qinglu, MA Chunhui, GUO Jintang

2023, 40(3): 397-402. doi: 10.12358/j.issn.1001-5620.2023.03.017

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Abstract:
A thixotropic cement slurry can be obtained by adding thixotropic agent into a common cement slurry, and this thixotropic cement slurry can be used to deal with severe mud losses and difficulties in cementing a well penetrating weak formations. Thixotropic cement slurries presently in use have several shortages such as weak thixotropy, sensitive to temperature changes and poor overall performance etc., limiting their use in dealing with downhole problems. To improve the thixotropy of a cement slurry, a new thixotropic agent was developed by combining an organic polymer TDA-1 and the inorganic bentonite. TDA-1 is a polymer synthesized from isopentenol polyoxyethylene ether (TPEG), N, N -dimethyl acrylamide (DMAA) and acrylic acid (AA). TDA-1 and bentonite were then hybridized to produce the new thixotropic agent CBJ-1. The effects of the new hybridized inorganic thixotropic agent CBJ-1 on the performance of cement slurries were studied. Using IR and XRD, the molecular structure of CBJ-1 was characterized. Using gel strength test, the thixotropy of the cement slurry was measured. The experimental results show that the new thixotropic agent was successfully synthesized. It has wide range of work temperature, thus can be used to mitigate the temperature sensitivity problem of a thixotropic cement slurry. A cement slurry treated with CBJ-1 has big difference between the initial gel strength and the final gel strength, meaning that the cement slurry has good thixotropy. CBJ-1 has no negative effect on the filtration rate and thickening performance of the cement slurry. The experimental results show that CBJ-1 has excellent general performance.

FRACTURING FLUID & ACIDIZING FLUID

Study on Oil Displacement Performance of Rhamnolipid Compound Imbibition Agent in Fracturing Fluid

JIA Fei, CHEN Xianjiang, JI Yongjun, FAN Qinghu, MENg Xianhang, MA Yue, BAI Yelei, CHEN Shengan

2023, 40(3): 403-409. doi: 10.12358/j.issn.1001-5620.2023.03.018

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Abstract:
In view of the problem that low permeability reservoirs are mainly transformed by volumetric fracturing, which cannot continuously improve production and increase the validity period of well development, the low-damage fracturing fluid with aspiration function was studied, and firstly, the combination experiments of rhamnolipid, sulfamic acid anionic surfactant APS-12 and sodium hydroxide were carried out, and the interfacial tension, wettability, oil washing ability, emulsion viscosity reduction and microscopic oil displacement mechanism of rhamnosin compound suctionant were obtained. The experimental results show that the rhamnolipid compound permeate has a strong ability to reduce the interfacial tension of the polymer fracturing fluid, and when the concentration is greater than 0.4%, the ability to reduce the interfacial tension is weakened, and the oil film peeling process takes a certain time, because it takes a long time to transform the hydrophobic substrate surface into hydrophilic. Different concentrations of rhamnosin compound absorbent mixed with heavy oil can form a better emulsion, reduce the viscosity of crude oil, and play a role in emulsification and viscosity, but the washing ability of oil sands at room temperature is limited. However, in the static aspiration experiment at 60 ℃, guanidine gum and polymer fracturing liquid with the same concentration of rhamnosin compound absorbent can exert the effect of permeation, and it is found that it reduces the binding ability of the rock surface to crude oil through microscopic oil flooding experiments, and the surface hydrophilicity gradually becomes stronger, and the capillary force in the pore throat changes from inhibiting the movement of oil droplets to the main driving force of oil droplets, and the functional type of fracturing fluid is expanded.

Governed by：
China National Petroleum Corporation Ltd

Sponsored by：
CNPC Bohai Drilling Engineering Co. LtdPetroChina Huabei Oilfield Company

Editor-in-Chief：Shi-chun Chen（Engineer Technology Research Institute,BHDC）

Deputy Editor-in-chief：

Gui-juan Wang（Engineer Technology Research Institute,BHDC）Qiang Ren（Engineer Technology Research Institute,BHDC）

Address：
Editorial Office of Drilling Fluid and Completion Fluid, Bohai Drilling Engineering Institute, Yanshan South Road, Renqiu City, Hebei Province

Postcode： 062552

Tel：（0317）2725487　2722354

E-mail： zjyywjy@126.com

CN 12-1486/TE

ISSN 1001-5620

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