2023 Vol. 40, No. 1

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FORUM
Hole Cleaning Technology for Horizontal and Deviated Drilling: Progress Made and Prospect
CHANG Xiaofeng, SUN Jinsheng, WANG Qingchen
2023, 40(1): 1-19. doi: 10.12358/j.issn.1001-5620.2023.01.001
Abstract(2083) HTML (569) PDF (3943KB)(333)
Abstract:
Although progresses made in horizontal drilling have been very beneficial to the development of conventional and unconventional oil and gas, two factors related to the cleaning of drilled cuttings from the horizontal section of a well seriously hinder the drilling operation. One of the factors is borehole wall instability, and the other is the difficulties in wellbore cleaning. Inability to remove drilled cuttings from a wellbore in a timely manner often results in increases in friction and torque on the downhole drill string, and the frequency of pipe sticking, and the worse is the simultaneous occurrence of lost circulation. First in this paper, the causes of cuttings bed formation and technical parameters for field operation are analyzed and summarized from two aspects, which are hole cleaning mechanisms and the main factors affecting hole cleaning (mud rheology, pipe rotation, hole inclination, sizes of the drilled cuttings, mud weight and flowrate etc.). Second, the methods and mechanisms of cuttings removal were systematically elaborated from the drilling fluid technologies and hole cleaning tools available both in China and abroad to help deal with the difficulties in hole cleaning in deviated and horizontal drilling. Finally, the development direction for horizontal and deviated hole cleaning technology is prospected to provide a reference for the hole cleaning technology development in the future.
DRILLING FLUID
Specific Surface Area Measurement and Adsorption Characteristics of Drilling Fluid Weighting Materials
QIU Zhengsong, WANG Di, ZHANG Shuhao, WANG Qi, ZHONG Hanyi, ZHAO Xin, FAN Lijun
2023, 40(1): 20-27. doi: 10.12358/j.issn.1001-5620.2023.01.002
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In deep and ultra-deep drilling, weighting materials are added to the drilling fluids to produce a pressure that is enough to balance the formation pressure. Weighting materials added to a drilling fluid can adsorb water and additives, thus affecting and even exacerbating the properties of the drilling fluid. To investigate the form and adsorptive characteristics of weighting materials in a drilling fluid, a method of measuring the specific surface area of a weighting material in a liquid has been established based on low-field nuclear-magnetic resonance (LF-NMR). The specific surface area of a weighting material in water based drilling fluids with densities between 1.1 g/cm3 and 2.4 g/cm3 and the specific surface area of the same weighting material in dry powder state, and the change of the specific surface area of the weighting material in liquid and as dry powder were analyzed using the LF-NMR method and particle size estimation method. The adsorption capacity of a weighting material in fluids of different densities were investigated through organic carbon adsorption experiment and rheology measurement. It was found that the weighting material in fluids of different densities has different adsorption capacities for different mud additives. In three 500 mL drilling fluids, each of which has a density of 1.2 g/cm3, 1.8 g/cm3 and 2.4 g/cm3, respectively, the adsorption capacities of the weighting material for sulfonated lignite were 10.83 g, 13.06 g and 17.69 g, respectively. This testing result can be correlated with the specific surface area results obtained with LF-NMR.
A Pickering Emulsion Oil Based Drilling Fluid
LI Chao, DI Wenwen, GENG Tie, REN Liangliang, GAO Yaxin, HAO Tianhao, SUN Dejun
2023, 40(1): 28-34. doi: 10.12358/j.issn.1001-5620.2023.01.003
Abstract(885) HTML (335) PDF (5511KB)(127)
Abstract:
In a Pickering emulsion, the solid particle emulsifier is absorbed at the interface between oil and water, forming a stable interfacial film to prevent the coalescence of water droplets. This property can be used to improve the stability of oil based drilling fluids. However, in studies on the oil based drilling fluids based on Pickering emulsion, the interaction between a water droplet in the oil phase and an inorganic hydrophilic particle has been omitted; the effects of inorganic particles added to an oil based drilling fluid, such as calcium hydroxide, weighting agents and the drilled cuttings, on the existence of the water droplets in the emulsion are not considered. In laboratory study, calcium hydroxide, barite and kaolinite particles of different hydrating capacities were added into a W/O Pickering emulsion. Macro sedimentation experiment and microscope observation with microscopic images have proved that the water droplets are combined with the solid particles, existing in a form of bound water. This explains the aggregation of the solid particles. The bound water was characterized with laser confocal microscope and low temperature differential scanning calorimetry. The solid particles with bound water can be dispersed by treating the system with a dispersant, in this way the stability of the drilling fluid can be improved. An oil based drilling fluid based on W/O Pickering emulsion is not a water-in-oil (W/O) drilling fluid, it is, however, a system in which the bound water droplets are moderately dispersed into an oil phase. In addition, low temperature constant rheology can be achieved by adjusting the rheology of a low density oil based drilling fluid.
Development and Application of an Environmentally Friendly Compound Filter Loss Reducer
SHU Yong, JIANG Luming, YANG Jun, JIANG Guancheng, WANG Guoshuai, HE Yinbo
2023, 40(1): 35-40. doi: 10.12358/j.issn.1001-5620.2023.01.004
Abstract(996) HTML (369) PDF (2441KB)(148)
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To control the pollution of drilling fluids to the environment from the source and minimize the difficulty and cost of waste drilling fluid treatment, a compound filter loss reducer PLS has been developed through crosslinking modification of plant polyphenol (a biomass material), sodium lignosulfonate and corn starch. PLS is non-toxic and is easy to degrade, it has an EC50 of 7.78 × 104 mg/L, and BOD5/CODCr of 5.05%. Evaluation of PLS shows that a base mud treated with 2% PLS has API filtration rate of only 9.6 mL after hot rolling at 180 ℃ for 16 hours. PLS is better than carboxymethyl starch, CMC-LV and SAP (an amphoteric starch graft copolymer) in resisting salt and calcium contamination. An environmentally friendly water based drilling fluid was formulated with PLS as the only filter loss reducer and other environmentally friendly additives such as bonding lubricant, organo- and hydro-phobic nanometer plugging agent and bionic borehole wall strengthening agent. This drilling fluid was used to drill the horizontal mudstone section of an exploratory well in Dagang oilfield. The rheology, filtration property of the drilling fluid during drilling were very stable, the mud cake had low friction coefficient and was thin and tough. The drilling operation was successful with no downhole troubles encountered throughout the horizontal section.
Development and Application of Environmental Friendly High Temperature Resistant Biomass Synthetic Resin Filtrate Reducer in Yuanba Area
ZHOU Qicheng
2023, 40(1): 41-46. doi: 10.12358/j.issn.1001-5620.2023.01.005
Abstract(771) HTML (322) PDF (5467KB)(117)
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In view of the fact that the marine carbonate formation in Yuanba area is often polluted by acid radical and hydrogen sulfide, which causes the viscosity and water loss of drilling fluid to rise, the temperature resistance to decline, and the flow pattern to be difficult to control, bringing great challenges to on-site maintenance. In this paper, a bio chemical method is proposed to modify lignin to develop an environment-friendly filtration reducer LDR of biomass synthetic resin with a cluster multi branch structure. The performance evaluation results show that the product has a temperature resistance of 200 ℃, a salt resistance of 25%, and a calcium resistance of 3,000 mg/L, showing a strong temperature and salt resistance performance. With this as the core of the high temperature resistant material, a high temperature resistant composite brine drilling fluid system is constructed by introducing potassium, calcium, and sodium plasma. Two wells were applied in Yuanba area. The field application shows that the maximum density of drilling fluid in Yuanba X-701 well is 2.34 g/cm3, the electric measurement shows that the temperature is 157 ℃, and the acid radical content is 21,157 mg/L. The system still has good rheological property and strong anti pollution ability. The two electric measurements successfully reached the bottom at one time, and the drilling fluid viscosity returned for 48 s after 7 consecutive days of standstill. It only took 28.88 days to complete the sidetracking task. The successful application of this system indicates that biomass resources have made a new breakthrough in high-temperature and high-density drilling fluid, effectively meeting the requirements of high-temperature slim hole for drilling fluid, and has good guidance and reference significance for deep wells and ultra deep wells in Yuanba area.
Lost Circulation Material and Technology Research of Self-healing Hydrogel
YANG Lili, WU Yunpeng, JIANG Guancheng, XIE Chunlin, ZHANG Yongwei
2023, 40(1): 47-53. doi: 10.12358/j.issn.1001-5620.2023.01.006
Abstract(789) HTML (324) PDF (2749KB)(165)
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Excessive development of pore fractures in the formation during drilling operations can lead to lost circulation and can easily result in safety incidents. In this research, a self-healing hydrogel based on cation-π, electrostatic, hydrogen bonding was prepared by a free radical polymerisation method for formation plugging, forming a dense sealing layer to contain lost circulation and prevent recurrence. Excellent self-healing properties in harsh conditions, with a self-healing efficiency of 70%, and can effectively seal the pores of 180 D sand discs with a sealing rate of nearly 90%. It also shows good sealing ability for other consolidated sand discs (permeability 2 D, 5 D, 20 D) and unconsolidated sand beds (20-40 mesh, 40-60 mesh, 60-80 mesh). Compared to conventional materials, the hydrogel can be self-healing by reducing the operating pressure drop to achieve an efficient seal. The self-repairing hydrogel can effectively improve the denseness of the sealing layers through secondary reduction of the permeability of the sealing layer, which improves the high temperature stability of the hydrogel and still has good sealing ability after high temperature aging. The hydrogel particles are well dispersed in the salt water and maintain stable rheological properties after hot rolling, which is beneficial for drilling fluid circulation. This study shows the potential of self-healing materials as plugging materials in the oil drilling industry.
Study on Construction Parameters of Pressure Bearing Plugging Considering High Stress Difference
QIU Xiaojiang, ZHANG Hongliang, WEI Yimeng, WU Ke, LIU Cheng, YANG Xinhui, YU Huichao
2023, 40(1): 54-59. doi: 10.12358/j.issn.1001-5620.2023.01.007
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As a common technology for the prevention and control of lost circulation in low pressure bearing formations, the theoretical system and plugging materials have made great progress, but the important construction parameters have not been paid enough attention. Therefore, according to the underground in-situ stress environment, this paper selects high-strength plugging materials, and establishes the pressure plugging experimental scheme with different construction parameters and plugging materials while drilling.The self-developed large-scale true triaxial pressure plugging experimental equipment is used to conduct the test on the dense sandstone sample (size: 300 mm×297 mm×297 mm), and the hydraulic-fracture propagation law was observed. Based on the hydraulic-fracture, the pressure plugging experiment was carried out.According to the experimental results, for the formation with weak bearing capacity, the construction parameters will cause the pressure change in the well, thus affecting the plugging effect; repeated plugging operations in the same formation will cause fracture expansion and reduce the plugging effect; the sequence of plugging slurry entering the fracture and the structure of the plugging layer are closely related to the geometric parameters of the fracture. The regular knowledge obtained in this paper can provide some reference for the formulation of pressure plugging scheme.
Study on Compatibility of Drilling Fluid Lubricants and Screw Rubbers
YANG Chuan, MENG Xiangjuan, KOXMAK Sayyara, LI Xu, TIAN Ming, LIU Feng, HUANG qian
2023, 40(1): 60-66. doi: 10.12358/j.issn.1001-5620.2023.01.008
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This paper discusses the experimental studies on the compatibility of drilling fluid lubricants with screw rubbers at high temperature and deep well conditions. At different temperatures and additive concentrations, eight kinds of rubbers were tested for rates of volume increment, rates of mass increment and changes in tensional strength when they were in contact with drilling fluid additives, and the test results were compared and evaluated. The experimental results show that the rubber sample has big changes in drilling fluids treated with the lubricants R-1 and R-3; in the drilling fluid treated with R-1, the rates of volume increment of the rubbers were distributed between 56% and 175%, while in the drilling fluid treated with R-3, the rates of volume increment were distributed between 49% and 148%. When the concentrations of the lubricants were increased, the rates of volume and mass increments of the two rubbers are all increased, and the rubbers swell at higher rates. These results indicate that the raw oil of a lubricant is the key factor affecting the swelling of rubber. Using GC-MS technology, the raw oils were analyzed, and it was found that a lubricant whose raw oil has high content of aromatics has relatively large influence on the swelling of the rubbers. Based on the application properties of the lubricants, some lubricants suitable for use in high temperature deep well drilling were selected. The selected lubricants were used to replace those lubricants with high contents of unsaturated hydrocarbons in the third interval and the reservoir section of the wells drilled in the Taipen block, and rubber disintegration from the screw was significantly reduced. Statistic data showed that times of rubber disintegration was reduced from 11 well times/month in the past to 0.5 well times/month, and this greatly reduced the number of times of tripping and improved the productive efficiency.
A Study on Borehole Wall Strengthening Technique and Its Application in Block Ledong
XING Xijin, XIE Renjun, QIU Zhengsong, LI Jia, GAO Jian
2023, 40(1): 67-72. doi: 10.12358/j.issn.1001-5620.2023.01.009
Abstract(859) HTML (333) PDF (2554KB)(128)
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The Ledong block, a typical high temperature high pressure offshore block, is located in the depression slope zone of the Yinggehai Basin. Some formations drilled in this block have narrow safe drilling windows and mud losses in deep hole occurred frequently during drilling. To deal with the mud losses, the drilling data was studied and the mechanisms and nature of the mud losses were analyzed. Using the viscous element method, the change of the stresses around the borehole before and after borehole wall strengthening was simulated, and the opening of the prefilled fractures predicted. Using a new experiment apparatus which can simulate the plugging of variable fractures, a study was conducted on the particle size distribution and concentration optimization for borehole wall strengthening. The experimental results show that the D50 criterion is a better particle size matching criterion, and a reasonable concentration of the particles is 5%. A drilling fluid that is suitable for use in the Ledong block and has the ability of borehole wall strengthening is developed through optimization experiment. In a comprehensive evaluation experiment, the additives for borehole wall strengthening showed little effects on the rheology of the drilling fluid. Sand bed test showed that the depth of the filtrate invasion was only 1.5 cm. Dynamic pressure bearing capacity of 1mm fractures tested with the drilling fluid can be as high as 12 MPa.
The Field Application of a Drilling Fluid for a Two-Interval Horizontal Well Penetrating Tight Gas Reservoir
KONG Weisheng, LI Xiaoming, HAN Chengfu, QU Yanping, WANG Qingchen, ZHAO Peng
2023, 40(1): 73-81. doi: 10.12358/j.issn.1001-5620.2023.01.010
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Two-interval horizontal well profile is used to develop the tight gas reservoirs in the Sulige gas field. Downhole problems such as coexistence of borehole wall collapse and mud losses, high friction and poor hole cleaning have long remained difficulties during drilling operations. Based on the analyses of the geological characteristics and the collapse mechanisms of shale formations, a model for friction and torque calculation is developed. The changes of friction and torque between different well profiles are compared. A new drilling fluid with good plugging capacity and lubricity was developed with a nanophase emulsion, plugging agents o hard and soft particles, compound lubricants and high efficiency gel strength additives which were all selected through laboratory experiment. This drilling fluid has been successfully applied in field operations. Laboratory study has shown that this drilling fluid has good inhibitive capacity and good plugging capacity, and it can extend the instability period of hard and brittle shales, thereby maintaining the borehole wall stable. This drilling fluid also has good rheology and lubricity, low sand content and solid content. In field application, the resistance to casing string running into the hole was controlled within 350 kN, the friction to drilling string running into the hole was reduced by 24.21%, the torque was reduced by 34.31%, the average drilling time was 29.04 d, the average ROP was 17.64 m/h, which was 36.5% higher than that in drilling three-interval horizontal wells. Time spent in reaming because of borehole collapse was reduced by 89.50%. This drilling fluid has provided a powerful technical support for promoting the application of two-interval horizontal drilling in developing the tight gas reservoirs in the Sulige gas field.
CEMENTING FLUID
Well Cementing Technology for Complex Reservoirs in the Bayan Hetao Basin
YAN Ruichang, XU Ming, YU Haifa, LUO Yucai, FEI Zhongming, QIU Aimin, JIA Lijun
2023, 40(1): 82-88. doi: 10.12358/j.issn.1001-5620.2023.01.011
Abstract(798) HTML (310) PDF (2082KB)(63)
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The reservoir formations in the Baran Hetao Basin have the characteristics of low maturity, high permeability, low strength and high shale content. The formations drilled have high water sensibility, instability and leaking potential. Deep well cementing is faced with many difficulties, such as long cementing section, low displacement efficiency, low bonding strengths of the two interfaces and high requirements on the mechanical performance of the cement sheath in late fracturing jobs, etc. To solve these problems, a batch-mixing batch-injecting DRJ-2S flushing spacer and a slight-expansion high strength rough cement slurry DRE have been developed with two key cementing materials, which are an interface strengthening agent DRJ-2S and an expanding toughening agent DRE-4S. Laboratory studies show that the DRJ-2S flushing space has a flushing efficiency of more than 96%, which is 30% higher than that of clean water, and a spacer of density 1.60 g/cm3 has 7 d compressive strength of 9.6 MPa. The DRE-2S flushing spacer has the ability of remarkably enhancing the compressive strength of mixed fluids and the bonding strengths of the interfaces of a cement sheath. At 90 ℃ and 21 MPa, a high strength tough slight-expansion cement slurry treated with 4% – 6% DRE-4S has compressive strength of at least 24 MPa, elastic modulus of equal to or less than 7 GPa, and linear ratio of expansion of at least 0.02%, indicating that the cement slurry has good adaptability to mechanical alternation. The DRE cement slurry and the DRJ-2S spacer have been used on more than 40 wells in the Bayan Hetao basin, with average well cementing pass rate of 96.5% or higher, greatly improving the quality of well cementing job in the basin. The application of the DRE and the DRJ-2S has provided a powerful technical support for the safe and efficient development of the complex oil and gas wells, and is worth promoting.
Study on High Water Content Microemulsion Flushing Fluid Used in Borehole Flushing
ZHANG Fan
2023, 40(1): 89-95. doi: 10.12358/j.issn.1001-5620.2023.01.012
Abstract(819) HTML (294) PDF (3434KB)(60)
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Oil based drilling fluids are now more and more used in the continuous development of oil and gas resources because of their excellent performance. Wells drilled with oil based drilling fluids have their borehole wall oil wetted, and this inevitably affects the cementing quality of the cement slurries. One way of dealing with this problem is to use flushing fluid to clean the oil based drilling fluids adhered on the borehole walls, hence turning the borehole wall to water wet. A high water content (≥ 80%) microemulsion flushing fluid was developed with raw materials such as EAB-40, SDBS, n-butanol, kerosene and water. The microemulsion flushing fluid was evaluated of its bubble rate, flushing capacity and ability to reverse the wettability of the borehole walls. The microemulsion was then made into a spacer, and flushing with the spacer fluid was done to investigate the flushing performance of the spacer and the compatibility of the spacer with cement slurries and oil based drilling fluids. The experimental results show that the microemulsion flushing fluid has a bubble rate of 17.07%, a flushing efficiency of at least 99%, and has excellent wettability reversal ability. The spacer made from the microemulsion flushing fluid has a flushing efficiency of at least 99%, and has good compatibility with cement slurries and oil based drilling fluids. As a result, this study has produced a high efficiency, low bubble rate, high water content microemulsion flushing fluid with good compatibility.
Study on the Performance of a New Low Temperature Early Strength Agent for Well Cement Slurries
MENG Shuang, SONG Jianjian, XU Mingbiao, JIANG Xiangguang, BAI Yang, CHEN Rongyao
2023, 40(1): 96-102. doi: 10.12358/j.issn.1001-5620.2023.01.013
Abstract(876) HTML (310) PDF (2957KB)(73)
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A new low temperature early-strength agent ES-22 has been developed through dispersion-coprecipitation method to solve the slow strength development of cement slurries in shallow and low temperature well cementing. In laboratory experiment, the particle size distribution and micro-structure of ES-22 were analyzed, the effects of ES-22 and other inorganic early-strength agents on the strength development of cement slurries at low temperatures were compared. The effects of ES-22 of different concentrations on the properties of cement slurries were also studied. It was found that ES-22 has particle sizes distributed between 15 μm and 25 μm. Compared with other early-strength agents, ES-22 is the best early-strength agent for the development of the early compressive strength of set cement. At low temperatures, ES-22 has even greater contribution to the development of the mechanical property of the set cement. ES-22 has little, if any, effects on the rheology of the cement slurry, the thickening time of the cement slurry becomes only a little short, and the volume of filter loss is reduced. In laboratory experiment, a set cement containing 4% ES-22 had its compressive strength and flexural strength increased by 204% and 136% respectively over the compressive strength and flexural strength of the blank set cement after aging at 20 ℃ for 24 hours. These results indicate that the early-strength agent ES-22 performs very well in oil well cement slurries.
Optimization Analysis Of Slurry Column Structure To Improve Cement Displacement Efficiency In Eccentric Annulus
CHEN Lili, GUO Jianhua, LIU Sen, LI Bin, XUE Hu, LI Yatian, YANG Mou
2023, 40(1): 103-110. doi: 10.12358/j.issn.1001-5620.2023.01.014
Abstract(750) HTML (283) PDF (4463KB)(59)
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Casing eccentricity is the key factor that determines the evolution of flow rate and flow pattern in the cementing annulus, which restricts the improvement of displacement efficiency. It is an important way to improve displacement efficiency by optimization of slurry column structure, and the related theoretical mechanism has not been reported. Using computational fluid dynamics of Fluent software, 3 D model horizontal annulus with different eccentric casing were developed, and the changes of displacement efficiency in different eccentric casing were discussed. Combined with the poor displacement efficiency with casing eccentricity of 0.4, the best slurry column structure was recommended through analysis of annulus fluid retention volume fraction in different column structure. The results showed that: ① Due to the combined effect of eccentricity and buoyancy, the displacement efficiency of casing eccentricity of 0.1 is better than that of casing concentricity; When the eccentricity is greater than 0.1, the displacement efficiency decreases gradually with the increase of eccentricity under the coupling effect of casing eccentricity and mass diffusion. ② injecting spacer first and then flushing fluid is beneficial to give full play to displacement effect of spacer under positive density difference, and the flushing effect of low density flushing fluid is utilized to improve displacement efficiency. ③ the velocity of wide side is higher than that of narrow side in the casing eccentricity, which causes the cementing slurry to return from the wide side in advance, while the narrow side retains a large amount of drilling fluid. The simulation results provide an important theoretical basis for the structure design and optimization of slurry column under eccentric annulus.
Optimized Design of Class A Low Permeability Early Strength Oil Well Cement Surry
TIAN Guoqiang
2023, 40(1): 111-117. doi: 10.12358/j.issn.1001-5620.2023.01.015
Abstract(817) HTML (318) PDF (4412KB)(50)
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The class a cement used in the Ecuador project has several disadvantages such as narrow temperature and formation depth ranges in which the cement can be used normally, high initial consistency and poor pumpability etc. To solve these problems, study was conducted to optimize the class a cement slurry composition. a new cement slurry was developed as a result of the study. Laboratory experimental results show that the class a cement has specific area of 4100 - 4500 cm2/g and Na2O content of 0.47%. The upper limit of working temperature of the class a cement slurry is 65 ℃, the 10 h compressive strength of the cement slurry can reach 3.5 MPa, and the set cement has permeability of 0.1936 mD and percent volumetric shrinking of 0.03%. This new cement slurry was used to cement the technical casing of the well Mariann-78. CBL/VDL well logging data show that the quality of the cementing job is excellent; the performance of the class a cement slurry used in the Ecuador project has been significantly improved.
FRACTURING FLUID & ACIDIZING FLUID
Study and Application of an Intelligent Self-Diverting Acidizing Technology for Buried-Hill Reservoir Development
MA Yingxian, TIAN Bohan, MAO Yuan, CHENG Yonghong, MIAO Xin, GUO Jianchun
2023, 40(1): 118-124. doi: 10.12358/j.issn.1001-5620.2023.01.016
Abstract(662) HTML (289) PDF (2521KB)(52)
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The buried-hill reservoirs in the Shengli Oilfield have these characteristics: deep buried depths, high temperatures, large spans and highly developed fractures and vugs. In well acidizing operation, the acids are easy to be lost into the fractured formations, the reservoir formations with low permeability are poorly acidized, and after acidizing operation, different pay zones have permeabilities that are greatly different. To solve these problems, an instant high-temperature stable self-diverting agent was developed by introducing hydroxyalkyl sulfonic acid into long-chain fatty acid amide betaine to improve the solubility and temperature resistance of the latter. A self-diverting acid was then developed by mixing the self-diverting agent and HCl. The acid was carefully formulated and its properties were studied. It was found that this instant high-temperature stable self-diverting acid has the ability of fast viscosity development, and is resistant to the negative effects of high temperature and shearing. It can be used to acidize reservoir formations of 160 ℃. This self-diverting acid has satisfactory viscosity at pH values between 3 and 7, and has good diverting performance. Acid flooding displacement through double cores shows that for parallel cores with permeability difference below 10, these cores can be acidized with good uniformity. This self-diverting acid has been successfully used on 37 wells in the buried-hill reservoir, with average oil production increase of 7.3 t/d per well, and average liquid production increase of 11.5 m3/d per well, showing good performance in oil production enhancement and water production control.
Reservoir Damage Diagnosis and Acidizing Extended Effect Technology of Massive Sewage Reinjection Wells with Thousands of Cubic Meters
SUN Lin, MENG Xiangli, WU Shenqu, WANG Qiaozhi, QU Qingdong
2023, 40(1): 125-131. doi: 10.12358/j.issn.1001-5620.2023.01.017
Abstract(767) HTML (297) PDF (2138KB)(53)
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The sewage reinjection wells in Bohai C oilfield group with a daily injection volume of thousands of cubic meters which are facing the problems of sharp decline in injection volume and low efficiency of acidification. Using the integration methods of reservoir characteristics and rock physical property analysis, water quality survey and analysis, scaling prediction, software simulation, it is found that the main cause of damage of the well type is particle migration, and the damage radius is 0.3 m~0.5 m. The secondary cause of damage is scaling, solid plugging. The scaling type is calcium carbonate. The scaling amounts of the two kinds of injected water are 287.6 mg/L and 357.1 mg/L respectively. The solid plugging is mainly dolomite minerals, and the damage radius is 0.2 m. At the same time, it is analyzed that the reason for the low efficiency of acidification in the past is the use of online acidification process, which leads to the water injection volume of massive sewage reinjection well far exceeding the acid injection volume, the acid concentration dilution ratio is too large, and the acid can not effectively remove the compound damage. HLCHEM-Y acidification system was developed by using hydrochloric acid, acetic acid, fluorosilicic acid, HEDP main acid, citric acid, quaternary ammonium salt, SDBS and other additives can be used to solve problem of compound injur. The 3 m3/min~4.8 m3/min large displacement tug acid injection process is adopted to solve the problem of poor effect of low displacement acid injection process in massive sewage reinjection well under the limited space of offshore platform. The supporting technology has been applied in 16 wells of C Oilfield Group which has achieved significant results in extending the average injection rate increase from 116,000 m3 to 399,000 m3 after acidification, and the average validity period extend from 44 days to 152 days.
COMPLETION FLUID
Laboratory Study on the Heat-Release Blockage Removing Agent ThermAcid
ZHAO Zhiqiang, LUO Jiansheng
2023, 40(1): 132-136. doi: 10.12358/j.issn.1001-5620.2023.01.018
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Weak gel fluid is used as completion and workover fluids in offshore oil and gas development. The mud cakes and the solids contamination resulted from the use of the weak gel fluids cannot be effectively removed. To deal with this problem, a heat-release blockage removing agent ThermAcid was developed. ThermAcid is water soluble, and can slowly release acid through hydrolysis reaction, thus can be used to effectively remove the contaminants left in the deep part of a reservoir. Hydrolysis kinetics study shows that the hydrolysis rate of ThermAcid increases with pH and temperature. Dissolution of calcium carbonate proves the above rules. Corrosion rate measurement shows that at 120 ℃, the corrosion rate of ThermAcid to steel plate is 2.31 g/(m2·h), less than the corrosion rate of 5% HCl, which is 8.31 g/(m2·h), and this is beneficial to the mitigation of corrosion to downhole drilling tools. Gel breaking experiments on 30 mD and 400 mD sand-beds show that compared with 5%HCl, ThermAcid breaks gel more uniformly and more thoroughly, and the flowback pressure is therefore lower.
Study and Application of Temperature-responsive Blockage Removal Agent in Oilfield
WANG Yaocong, CHANG Du, ZHANG Qingzhu, HOU Yan, QIU Liewei
2023, 40(1): 137-142. doi: 10.12358/j.issn.1001-5620.2023.01.019
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A pore throat blockage sample was tested and analyzed for its composition with high temperature calcination method and X-ray diffraction method. Based on the results of the test and analysis, a temperature-responsive reservoir blockage removing agent MSA is developed with polyethylene glycol, sulfamic acid and lauroyl chloride. The general performance of MSA was evaluated by laboratory experiment. The reservoir blockage used in the experiment is mainly composed of calcite (CaCO3). MSA has a pH of 6.05 at 20 °C and 0.99 at 60 °C, this means that MSA decomposes at 60 °C and produces a large amount of sulfamic acid with which the blockage can be dissolved. More than 82% of the blockage can be dissolved after 30 min of interaction between the blockage and MSA, and at 90 °C, each component of MSA still retains high activity, meaning that MSA has good blockage removing capacity and compatibility with the formation waters. Field application of MSA showed that a production well treated with MSA had oil production increased by 66.9 t in 6 months.

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