2019 Vol. 36, No. 5

Display Method:
2019, 36(5)
Proppants for Fracturing Fluids: New Progress Made and Direction of Future Development
GUANG Xinjun, WANG Minsheng, HAN Fuwei, GENG Lidong
2019, 36(5): 529-533,541. doi: 10.3969/j.issn.1001-5620.2019.05.001
Proppant is a key material used in fracturing fluids to prop up artificial fractures for reservoir stimulation. It plays a key role in increasing the success rate of fracturing job and in improving the results of reservoir stimulation. A series of new proppants have recently been developed abroad and the ideas of the new proppant development is worth studying by us. In this paper the status quo of proppant application is analyzed and the newest progresses made in developing new proppants and field experiment of new proppants (including high strength low density proppant, high flow-conductivity proppant, multi-function proppant and intelligent proppant etc.) are summarized. Direction of scientific research and technical development is presented in this paper in connection with the trend of oil and gas exploration and development in China. Researches performed in this direction to develop proppant technologies suitable for fracturing oil and gas reservoirs in China is of great importance to the security of national energy resources.
Synthesis and Evaluation of a New Chemical Borehole Wall Strengthener Made from Chitosan-Catechol
TANG Zhichuan, QIU Zhengsong, ZHONG Hanyi, GUO Baoyu, WANG Xudong, ZHENG Yang
2019, 36(5): 534-541. doi: 10.3969/j.issn.1001-5620.2019.05.002
Borehole wall instability in shale formations is a result of combined action of physical factors and chemical factors. An important measure to stabilize shale formations is to plug the formation with physical particles and to reinforce the chemical bonding of the formations. A new borehole wall strengthener SDGB has been developed with chitosan and a polymer having catechol structure through Schiff base reduction reaction. Study on the performance of SDGB showed that SDGB has aromatic ring, catechol and amino group in its molecules, which can react with metal ions through chelation reaction to form stable covalent bonds. The relative molecular weight of SDGB is about 30,000. The performance of SDGB in strengthening borehole wall through chemical action was studied through lap shear strength test, hot rolling test, uniaxial compressive experiment of rock and SEM experiment. It was found that SDGB had good chemical bonding performance which is able to increase the lap shear strength of rock in water, to increase the compressive strength of rocks after soaking, and to inhibit the hydration and dispersion of shales. SDGB can form cementation in the pore throats of a rock and cement the loose minerals inside the micro fractures of a rock, thereby effectively plugging and strengthening the formation. A water base drilling fluid with stable rheology and filtration property before and after aging at 130℃ for 16 hours, was formulated with SDGB as the key additive.
Study on Dispersion Behavior and Mechanisms of Carbon Nanodot Materials
WANG Lan, TAO Huaizhi, YAO Shiyu
2019, 36(5): 542-547. doi: 10.3969/j.issn.1001-5620.2019.05.003
Shales encountered in drilling operation have very low permeability and very small pore throats which are easy to result in lost circulation and instability of wellbore. Nanometer materials have in recent years been widely used to make nanometer plugging agents which are able to plug the pore throats in shales and to prevent liquid phase from entering into the shales, thereby maintaining the stability of borehole wall. A new nanodot material has been developed with powdered citric acid and ethylene diamine through hydrothermal synthesis. Several ways of dispersion were used to optimize the dispersion of the nanodot material in water. The mechanisms of the dispersion of the nanodot material was studied. Laboratory experimental results showed that the nanodot material disperses very well in alkaline water, simple mechanical agitation and ultrasonic wave can make the nanodot material dispersed completely in water. In bentonite slurry the nanodot material also showed good dispersibility. This study has provided a theoretical and experimental base for the nanodot material to be used as plugging agent in shale gas drilling operation.
Laboratory Study on Water Base Filming Drilling Fluid Resistant to 240℃
LI Ying, TAN Xianfeng, HAN Weichao, LI Kaijun, GUO Mingyi
2019, 36(5): 548-554. doi: 10.3969/j.issn.1001-5620.2019.05.004
A water base filming drilling fluid has been developed to deal with problems encountered in deep well drilling, such as borehole wall instability, rheology fluctuation and high filtration rate. The drilling fluid, which is formulated with an inorganic filming agent and an organic filming additive, is resistant to high temperatures to 240℃. The drilling fluid was formulated through orthogonal experiment. The filming performance, inhibitive capacity, rheology and filtration rate etc. of the drilling fluid were studied using optical microscope, hot rolling test, mud ball soaking test, HTHP filtration test, particle size analysis, SEM, as well as the observation of the micro morphology of mud cakes. These studies in turn helped optimize the properties of drilling fluid. The experimental results showed that at 240℃, the drilling fluid had stable rheology, suitable yield point, low filtration rate (API filter loss after aging at 240℃ was 5.6 mL, and HTHP filter loss at 200℃ was 14 mL), thin mud cake, good filming performance and superior inhibitive capacity and plugging ability, indicating that this drilling fluid will find wide application in deep well drilling and high temperature geothermal well drilling.
Evaluation and Improvement of the Performance of Oil Base Drilling Fluids for Shale Gas Drilling
WANG Jianhua, ZHANG Jiaqi, XIE Sheng, YAN Lili
2019, 36(5): 555-559. doi: 10.3969/j.issn.1001-5620.2019.05.005
As one of the key technologies in drilling horizontal shale gas wells, oil base drilling fluids are used to maintain the stability of borehole wall and to clean the hole. In this paper the rheology, plugging capacity, solids content and property stability etc. of the oil base drilling fluids used in PetroChina's Chuanyu development area are evaluated. From the evaluation and analyses of downhole troubles encountered in Chuanyu area it is concluded that plugging capacity of an oil base drilling fluid is the key in maintaining the stability of borehole wall. By increasing the φ6 reading and flow rate of the drilling fluids, hole cleaning can be improved. Deterioration of the performance of a drilling fluid comes mainly from the increase of low-density solids content in the drilling fluid. To resolve problems encountered in maintaining borehole wall instability, hole cleaning and mud property maintenance, a method has been established to evaluate the plugging capacity of nanometer and micrometer particles. A method of calculating the content of harmful low-density solids in a drilling fluid is determined, and a set of technical norms for maintaining the properties of oil base drilling fluids for shale gas development is formed, hopefully will provide a technical support to shale gas development with horizontal drilling.
Calculation of Harmful Low Density Solids Content in Oil Base Drilling Fluids Using Linear Regression Method
ZHANG Jiaqi, WANG Jianhua, WEI Fengqi, YAN Lili
2019, 36(5): 560-563. doi: 10.3969/j.issn.1001-5620.2019.05.006
With the large scale development of shale gas, high density oil base drilling fluids are finding wide application in shale gas drilling. During drilling, small particles are continuously entering into the drilling fluid, greatly affecting the performance of the drilling fluid. Presently there is no method for calculating the drilled cutting content of oil base drilling fluids. The standard GB/T 16783.2 only gives a method of calculating the content of low density solids, which is unable to differentiate the wanted low density solids and the unwanted harmful low density solids. By comparing the solids contents of drilling fluid taken from a well and the mud freshly made in laboratory, a method for calculating the content of harmful low density solids was developed through linear regression. This method was also checked for its accuracy using muds taken from fields. Errors between the solids content obtained from linear regression and the solids content actually measured were less than 3%, indicating that this method can be used to accurately calculate the content of harmful solids. This simple method has provided an important standard on which the properties of oil base drilling fluids can be maintained. Small calculation errors make the method valuable and feasible to field application.
High Performance Drilling Fluid for Horizontal Drilling in the Well Jiaoye18-10HF in Fuling Shale Gas Field
ZHAO Sujuan, YOU Yunwu, LIU Haobing, ZHOU Chaoqun, CHEN Changyuan, LUO Zhigang
2019, 36(5): 564-569. doi: 10.3969/j.issn.1001-5620.2019.05.007
The well Jiaoye18-10HF is a development well drilled in Fuling Shale Gas Field (Sinopec), with completion depth of 4 560 m and horizontal length of 1 378 m. The shales encountered in the third section of the wells in this area have high content of brittle minerals. Micro-fractures of micrometer and nanometer in size and bedding planes are so rich in the formations that oil base drilling fluids had to be used to minimize downhole troubles. Based on the study on the nature of the fractured shales encountered in the Wufeng Formation in Longmaxi block, a high performance water base drilling fluid, JHGWY-1, has recently been formulated with several major additives; PEA (amine-terminated polyether) as the core additive to inhibit the surface hydration of shales, vegetable oil oleamide as an extreme pressure lubricant to effectively reduce friction and nanometer plugging agent to strengthen borehole walls. In laboratory experiment, JHGWY-1 showed percent recovery of shale cuttings of more than 98%, coefficient of friction of 0.16 and pressure bearing capacity of the mud cake formed of more than 10 MPa. These properties satisfied the needs of drilling operation in Longmaxi area, such as drilling the micro-fracture-enriched Wufeng Formation, plugging and strengthening of formation with weak cementation, and good lubricity of the drilling fluid in horizontal drilling. This drilling fluid was first used in place of oil base drilling fluids in drilling the third interval of the well Jiaoye18-10HF which penetrated through the Wufeng Formation with designed vertical thickness of 10 m (actually 8-10 m during drilling). Tripping of drill string was smooth and the well was successfully completed. The mud had good rheology, low filtration rate and strong inhibition to shale during drilling, and the needs of drilling the third interval of the well was satisfied.
High Temperature High Density Drilling Fluid Technology for Drilling in Ying-Qiong Basin
LIAO Fengwu, LI Kunyu, HU Youlin, HE Fen, LI Yanjun, YUE Qiansheng
2019, 36(5): 570-574. doi: 10.3969/j.issn.1001-5620.2019.05.008
Formations in the Ying-Qiong Basin have high temperature gradient, high pressure coefficient and narrow safe drilling window. High temperature and high mud density are two key factors for drilling in this HTHP environment. A drilling fluid formulation suitable for drilling the HTHP formations has been developed recently based on the analyses and optimization of the performance of the water base drilling fluids in use. This drilling fluid, after hot rolling at 200℃ for 16 h, has viscosity of 39 mPa·s, yield point of 7 Pa, HTHP (200℃, 3 MPa) settlement factor of 0.512, HTHP filter loss of 8.6 mL, HTHP filter loss through sand bed of 14.4 mL. After contamination with 4 MPa of CO2, the properties of the mud are as follows:viscosity of 43 mPa·s, yield point of 9 MPa, API filter loss of 4.5 mL, HTHP filter loss of 13.6 mL. Laboratory study shows that the properties of this mud, such as rheology, settlement stability, HTHP filtration property, plugging capacity and resistance to acid gas (CO2) contamination are all better than those of the drilling fluids presently in use.
Study on the Methods of Evaluating Static Sedimentation Stability of Drill-in Fluids
LI Jiaxue, JIANG Shaobin, YAN Zhihang, HUI Haijun, CHEN Lin, CUI Changhao
2019, 36(5): 575-580. doi: 10.3969/j.issn.1001-5620.2019.05.009
Serious sedimentation may take place in a drill-in fluid standing for a long period of time at elevated temperatures, resulting in resistance to running tubular goods into the hole or difficulties in starting pump. To resolve this problem, it is necessary to investigate the precipitation stability of a drill-in fluid standing motionless at elevated temperatures. Plenty of studying work has been done by researchers on this issue all over the world, and there is still no standard method for evaluating the sedimentation stability of a drill-in fluid standing motionless at elevated temperatures for a long time. In this study, nine methods used all over the world have been investigated, and four of them, which are falling-rod method, sedimentation coefficient method, penetration degree measurement and static stability stratification index method, were selected for evaluating the sedimentation stability of water base drill-in fluids. Experimental results showed that coefficient of correlation between the SSSI value (measured with the static stability stratification method) and the density of the fluid at the bottom was at least 0.97, indicating that this method is able to be used to predict accurately the sedimentation stability of a completion fluid. The penetration degree measurement method can only be used to predict the sedimentation tendency of a completion fluid, unable to quantitatively evaluate the actual sedimentation degree of the completion fluid. The sedimentation coefficient method is only suitable for evaluating the sedimentation stability of drill-in fluids with low liquid separation rates. The falling-rod method can only be used to roughly predict the sedimentation stability of a drill-in fluid.
Study on Factors Affecting Filtration Property of Drilling Fluid with Numerical Simulation Software
SUN Yuxue, LI Chengli, BAI Xiangshuang, ZHANG Lichun, ZHAO Jingyuan, GUO Chunping
2019, 36(5): 581-586,593. doi: 10.3969/j.issn.1001-5620.2019.05.010
Numerical simulation software is used to simulate the dynamic fluid loss of drilling fluid during drilling under formation conditions. The effects of filtration time, viscosity of filtrate, differential pressure, permeability of internal mud cake and permeability of external mud cake on the filtration rate of drilling fluid was studied. It was found through the simulation that when the permeability of formation was 100 mD and the permeability of the external mud cake was less than 0.01 mD, more than 90% of the pressure was contained by the external mud cake, and the external mud cake is the main factor affecting the filtration rate of a drilling fluid. When the permeability of the external mud cake was greater than 0.1 mD, 55% of the pressure was contained by the external mud cake, the permeability of the internal mud cake and the formation all contributed to the dynamic filtration rate of the drilling fluid. Under the simulated conditions, the pressure was transmitted to the boundary of the formation quickly, the formation pressure at the same place inside the formation increased gradually and slightly with time, and the filtration rate was basically a constant. From the simulation it can be found that filtration rate is in direct proportion to filtration time, and pressure, and is in reverse proportion to the viscosity of the filtrate of a drilling fluid. The filtration rate, although increases with the permeability of the external mud cake, is not linearly proportional to it.
Development of an Ecological Drilling Fluid and Its Benefits to Saline-Alkaline Soil Reclamation
PU Lei, XU Mingbiao, WANG Chaofei, CHEN Kan, ZHOU Shanshan
2019, 36(5): 587-593. doi: 10.3969/j.issn.1001-5620.2019.05.011
With more and more exploration performed in northwest China, environmental protection policy is becoming more rigorous. Conventional techniques are not able to treat waste muds to have acceptable contamination and damage levels. Xinjiang is rich in salinealkaline lands which can be used as waste mud disposal places. Three ecological additives, JH1, JH2 and JH3 have been developed from natural materials, and an ecological drilling fluid, JH has been formulated with the three additives. The rheology, resistance to contamination, lubricity, inhibitive capacity and environmental friendliness of the JH mud were systematically evaluated. The evaluation results showed that JH had good rheological property at 120℃, API filter loss of 3.4 mL, percent recovery of shale cuttings of 72.6% on hot rolling test, linear rate of expansion of 11.54%, friction coefficient of 0.1058, and good resistance to contamination. These data indicate that JH is able to satisfy the general requirements of drilling operation. The ecological data of JH are as follows:EC50=89 600 mg/kg, BOD5/CODCr=25.9%. JH is easy to biologically degrade. Heavy metal content of JH is low, satisfying the national discharge standards. The JH mud, after neutralization with organic acids, can be used to improve the quality of soil with great efficiency; a piece of saline-alkaline land was treated with the disposed waste JH mud, the saline content of the soil was reduced by 54.3%, pH of the soil restored to 6.85, organic matter content of the soil increased by 49.7%, and N, P, K contents in the soil were increased by a percentage between 59.25% and 113.82%, respectively.
Development of an Environmentally Friendly Strongly Inhibitive Chloride-free Water Base Drilling Fluid
LUO Jiansheng, JIANG Guancheng, WANG Guoshuai, DONG Tengfei, HE Yinbo, LI Bin
2019, 36(5): 594-599. doi: 10.3969/j.issn.1001-5620.2019.05.012
To minimize environmental pollution and damage to the ecosystem by drilling fluids used in the exploration and development of oil and gas, realize "green" drilling and maximize the performance of a drilling fluid, an encapsulator and a bionic borehole wall strengthening agent previously developed were compounded with other selected additives to formulate an environmentally friendly strongly inhibitive chloride-free water base drilling fluid. Laboratory experimental results show that this drilling fluid has superior temperature stability, resistance to contamination and inhibitive capacity. The drilling fluid had stable properties after continuously hot rolled for 72 h at 120℃. It was resistant to contamination by 10% clays, 0.8% calcium, or 30% salt. Percent shale recovery on hot rolling test was 98.5%. Laboratory evaluation shows that this drilling fluid has performance that is superior to that of PHPA/KCl drilling fluid. This drilling fluid can satisfy the needs of general environment protection and contains no chlorides, minimizing its negative effects on soil structure, plant growth and underground water system. EC50 of this drilling fluid is greater than 106 mg/L and BOD5/CODCr 0.633. The content of heavy metals is far lower than standard requirements, and is thus free of biotoxicity, biodegradable and dischargeable. Experimental data and evaluation results demonstrate that this drilling fluid is a novel mud that both satisfies the needs of drilling operation and protects the environment from being polluted, and has good application prospects.
A Laboratory Test Method for Predicting Mud Ball Generation in Drilling Fluids
WANG Shuyi, XU Mingbiao, YOU Fuchang, DENG Cong, WANG Hangzhi
2019, 36(5): 600-604. doi: 10.3969/j.issn.1001-5620.2019.05.013
When drilling soft mudstones, mud ball will be generated in the drilling fluid flowing upwards in the annulus. To predict the generation of mud balls in a drilling fluid, an evaluation procedure with test parameters was established using drilling fluid measuring apparatus. In the procedure, drilled cuttings containing water and steel balls are mixed together and tested on a hot rolling tester (to simulate the flow of cuttings downhole). Using this procedure, some drilling fluids were tested. Test results showed that this procedure is feasible in predicting the generation of mud balls in several kinds of drilling fluids. The test results conformed to what were observed in field operations. In laboratory test, it was found that conditions for a water base drilling fluid to generate mud balls during drilling were as follows:hot rolling at 90℃ for 20 min. the conditions for an oil base drilling fluid to generate mud balls were:ht rolling at 120℃ for 30 min. Experimental results obtained from this procedure can be used as a base on which drilling fluid is optimized for high efficiency and safe drilling operation.
Development of and Study on a High Temperature Suspension Stabilizer for Oil Well Cement Slurries
LIU Xianghua
2019, 36(5): 605-609. doi: 10.3969/j.issn.1001-5620.2019.05.014
A high temperature suspension stabilizer has been developed to deal with sedimentation of oil well cement slurries at elevated temperatures. The viscosifying property of the suspension stabilizer at high temperatures was tested and the mechanisms of viscosifying at high temperatures analyzed. The effects of the high temperature suspension stabilizer on several properties of cement slurries, such as sedimentation stability, rheology, thickening curve and compressive strength of the set cement, were evaluated through laboratory experiment. It was found that the high temperature suspension stabilizer increases the viscosity of the cement slurry at elevated temperatures through hydrophobic association between molecules. The density difference of the set cement can be controlled within±0.025 g/cm3 by the addition of the stabilizer, indicating that the stabilizer has excellent sedimentation prevention property. The consistency coefficient of the cement slurry was maintained in a narrow range by the stabilizer, between 4.441 Pa·sn and 5.760 Pa·sn, and this made the consistency of the slurry stable. The strength of the set cement, which was almost not affected by the use of the suspension stabilizer, satisfied the needs of well cementing job.
Development and Study on a High Temperature Salt Resistant Filter Loss Reducer for Well Cementing
XIA Xiujian, YU Yongjin, JIN Jianzhou, XU Ming, LIU Shuoqiong
2019, 36(5): 610-616. doi: 10.3969/j.issn.1001-5620.2019.05.015
A high temperature salt resistant zwitterionic filter loss reducer DRF-4L has been developed to deal with problems encountered in filtration control of drilling fluids, such as poor resistance to high temperature, poor resistance to high salinity, viscosifying the mud at low temperatures as well as severe thinning at high temperatures. DRF-4L has special cationic groups in its molecules and is synthesized through free radical water solution polymerization. The molecular structure and temperature tolerance of DRF-4L were characterized using IR spectroscopy, thermogravimetric analysis and ESEM. The performance of DRF-4L was evaluated. It was found that DRF-4L has wide work temperatures (30-210℃) and excellent filtration control ability. at 210℃ (BHCT), a cement slurry treated with 4% DRF-4L had API filter loss of 42 mL. Saturated salt cement slurries treated with DRF-4L had API filter loss less than 50 mL. Cement slurries treated with DRF-4L do not thicken at low temperatures and only very slightly disperse at elevated temperatures. DRF-4L is very beneficial to improving the initial rheology and to enhancing the high temperature stability of cement slurries. Cement slurries containing DRF-4L has fast developed early strength, the 12 h compressive strength of the set cement at 90℃ is at least 14 MPa, and the late strength of the set cement develops normally. Cement slurries with low density, normal density and high density, or latex cement slurries, if treated with DRF-4L as the major treatment agent, have good overall properties, and are able to satisfy the needs of cementing high temperature deep and ultra-deep wells.
The Technology of Setting Cement Plug for Offshore Ultra High Temperature and Ultra High Pressure Abandoned Wells
LI Zhujun, HAN Cheng, WEI Anchao, LIU Xianyu, YANG Yuhao
2019, 36(5): 617-621. doi: 10.3969/j.issn.1001-5620.2019.05.016
High density abandonment well plugs are set for ultra high temperature ultra high pressure exploratory wells drilled in Yingqiong Basin. Several problems, such as the conflict between mobility and sedimentation stability of the cement slurry, deterioration of the strength of the set cement, long section of cementing, big temperature difference, slow strength development at the top of cement, narrow safe drilling windows, loss of cement slurry and gas channeling etc., were encountered when setting the abandonment plugs. Several measures were taken to resolve these problems. First, spherical manganese ore powder was used to weight the cement slurry and to improve the rheology and sedimentation stability of the cement slurry. Second, a high temperature filming anti gas channeling agent was used to mitigate the risk of gas channeling. Third, an optimized amount of micro silica was used to increase the high temperature compressive strength of the set cement. Fourth, the quality of the spacer was optimized to enhance its ability to prevent loss of cement slurry. Finally, the cement slurry was squeezed into the hole to eliminate potential downhole problems. These measures have been successfully used in cement wells with maximum static bottom hole temperature of 213℃, and the highest density of cement slurry used was 2.50 g/cm3. Field operation showed that the cement slurry for setting abandonment plug has good mobility and sedimentation stability. The high temperature strength of the set cement developed fast and did not deteriorate. The cement slurry had stable thickening time, good anti-channeling and cement slurry loss preventing performance. All high pressure gas zones were successfully sealed off.
Technology for Cementing Deep Reservoirs in Yingxi Area, Qinghai Oilfield
LI Zongyao, ZHANG Haitao, WEI Qunbao, ZHOU Xue, XUAN Feifei, HU Zhonghua, PENG Song
2019, 36(5): 622-628. doi: 10.3969/j.issn.1001-5620.2019.05.017
Qinghai Oilfield has in recent years found deep petroleum reservoirs in the Block Yingxi Shizigou. This is a major breakthrough in oil and gas exploration in the Qaidam Basin. This block not only has huge potential of oil and gas reserves, the complex drilling and geological conditions also bring about great challenges to well cementing operation and subsequent production. Since the horizontal wells in this block is stimulated with multistage fracturing, to establish effective zonal isolation and to maintain long-term seal integrity of the cement sheath, a special cement slurry and prepad fluid have been selected, based on the analyses of difficulties encountered in well cementing. The cement slurry, the prepad fluid and an improved set of well cementing techniques together formed a set of well cementing technology suitable for the horizontal wells drilled in block Shizigou. Using a self-healing agent, the micro-fractures generated inside set cement were filled and the set cement was thus rendered elasticity, ensuring the long-term seal integrity of the cement sheath. The anti-invasion anti-channeling cement slurry also has some thixotropic property and internal viscous force, which are beneficial to cement slurry loss control and channeling mitigation. Since 2018, this set of well cementing technology has been applied with great success in Shizigou for more than 20 times/wells, with average well depth of 5,000 m and average horizontal length of 1,000 m. Wells cemented with this technology satisfied the needs of subsequent spatial fracturing operation. As a key technology for the development of deep reservoirs in Yingxi, this technology will find wide application in the future.
Development of Nanofluid Slickwater System for Stimulating Mahu Tight Glutenite Reservoirs
HE Xiaodong, ZHU Jiawei, SHI Shanzhi, ZHOU Fujian, MA Junxiu, YAO Erdong
2019, 36(5): 629-633. doi: 10.3969/j.issn.1001-5620.2019.05.018
The drag reducer of fracturing fluid in the tight glutenite reservoir of the Mahu Oilfield is a kind of anionic polymer, which is easily precipitated by the reaction with organic or inorganic positive ions in fracturing additives. The precipitations can easily block the pores of tight glutenite, and cause an abnormal pressure increase in the near-wellbore. It will be not conducive to the further extension of the fracture. In order to realize reservoir protection and promote crack propagation, a nanofluid slick water system with in-situ oil displacement ability was developed. Loop test and surface tension test were used to determine the optimal doses of each components in this system. Based on the field data and materials of Mahu oilfield, continuous shearing resistance, salt tolerance, solvency and wash oil ability of the nanofluid system were evaluated. The results show that, under the shearing rate of 1.2×104s-1, the drag reduction efficiency of the fluid is 78.92%. In addition, the nanofluid system can work well at the different salinity of the formation water of Mahu oilfield. At the same shearing rate, the drag reduction efficiency after 20 min shearing is still above 73%. What's more, the wash oil efficiency of the system is determined to be 93.3% by the Soxhlet extraction system with Mahu oil sand.
Study on the Integration of Gelled Acid and Crosslinked Acid to Form High Temperature Retarded Acid
MU Daifeng, JIA Wenfeng, YAO Yiming, YANG Chen, WANG Chengcheng, JIA Jinya
2019, 36(5): 634-638. doi: 10.3969/j.issn.1001-5620.2019.05.019
Gelled acid and crosslinked acid are common retarded acids used in acidizing high temperature carbonate rock reservoirs. As different acids, gelled acid and crosslinked acid both have poor high temperature tolerance, poor compatibility with each other and complex formulating and working procedures. To resolve these problems, a retarded acid has been formulated through integration of gelled acid and crosslinked acid. The base fluid of the crosslinked acid can be used as a gelled acid which can be turned into crosslinked acid by adding crosslinking agents. The composition of the crosslinked acid is:20%HCl+1%SRAP-2 (thickening agent)+ 2.5%SRAI-1 (high temperature primary corrosion inhibitor)+0.5% extender+1%SRAF-1(ferric ion stabilizer for acid fracturing)+1% SRAD-1 (demulsifier for acid fracturing)+1% SRAC-2A (crosslinking agent) and SRAC-2B (delayed crosslinking agent) (SRAC-2A:SRAC-2B=2:12). After shearing at 160℃ and 170 s-1 for 120 min, the viscosity of the gelled acid was 20 mPa·s. Time for the crosslinking of the crosslinked acid was 93 s, indicating that the crosslinked acid had excellent delayed crosslinking property. After shearing at 160℃ and 170 s-1 for 90 min, the viscosity of the crosslinked acid was 55 mPa·s. This integrated acid can stand at room temperatures for more than 10 d, and the dynamic rate of corrosion at 140℃ was 46.1021 g/(m2·h). Research work shows that this integrated acid is able to satisfy the needs for retarded acid in acid fracturing high temperature reservoirs. Integration of gelled acid and crosslinked acid simplifies field operation, and should have good application prospects.
Control the Crack Morphology of Hydraulic Fracture by Fuzzy-ball Fluid in Coal Seam
NIE Shuaishuai, ZHENG Lihui, MENG Shangzhi, WEI Panfeng, ZHANG He, SUN Hao
2019, 36(5): 639-645. doi: 10.3969/j.issn.1001-5620.2019.05.020
The direction of hydraulic fractures in the coal seam is diverted along the direction of cutting and natural fractures, the crack morphology of hydraulic fracture is irregular and elongated. Using Fuzzy-ball temporary plugging natural cracks to form regular cracks. Laboratory tests show that the settlement rate of φ0.9 mm ceramsite in Fuzzy-ball fluid is 0.003 cm/s, meeting the requirements of carrying sand; The pressure capacity of the crack plugged with Fuzzy-ball is 18 MPa, able to prevent hydraulic fractures extending in the direction of cleat or natural fractures. Fuzzy-bal fluid damage coal rock permeability recovery value is 86%, satisfying gas production requirements. Field preparation apparent Fuzzy-ball fluid 520 m3. Separate Shanxi and Taiyuan coal seams by sand for stratified fracturing. During the pumping process of sand carrying liquid, the pump pressure is stable at 14.64-15.99 MPa, indicating that there is no blockage and diversion in the process of hydraulic fracture extension. The simulation results show that the fracture length and height of Taiyuan Formation are 155.7 m and 41.3 m respectively, and the fracture length and height of Shanxi coal seams are 163.9 m and 47.5 m respectively. Therefore, Fuzzy-ball fluid can be used to produce a long crack in coal seam, solving the problem of unsatisfactory hydraulic fracturing effect in coal seam.
Experimental study and application for the conductivity of proppant in multi-scale volume fracturing
LIU Jiankun, XIE Bobo, WU Chunfang, JIANG Tingxue, SUI Shiyuan, SHEN Ziqi
2019, 36(5): 646-653. doi: 10.3969/j.issn.1001-5620.2019.05.021
The effective conductivity of fracture is the main parameter for evaluating the effect of fracturing construction, and it is also one of the most important factors affecting the effect of fracturing. We designed a multi-scale fracture conductivity experimental method, and used a method of single particle size and combined particle size placement to studied the effects of factors such as closure pressure, particle size combination, sanding concentration and stress cycling on the proppant conductivity in main fracture and branching fracture.The experimental results show that:As the closing pressure increases, the difference in the conductivity of the large-size proppant and the small-sized proppant gradually decreases, and the conductivity of the proppant in the main fracture and the branch fracture gradually decreases, and this reduction trend has an obvious turning point.Under the combined particle size placement conditions, there is an optimal proppant combination both in the main fracture and the branch fracture.The higher the sediment concentration of the proppant in the main fracture and the branch fracture, the higher the conductivity will be;As the closing pressure increases, the difference of the conductivity between the high-concentration sanding and the low-concentration sanding becomes smaller.The effect of stress cycling on the proppant conductivity is irreversible.The field application shows that under the premise of meeting the fracturing process requirements, it can effectively improve the fracture conductivity and the post-pressing output by usingthe proppant combination method and the reasonable optimization of the sand adding method.This research provide the basis for the optimization of volume fracturing scheme and on-site construction.
An Elastic Spacer for Preventing Trapped Pressure in Annulus of Deepwater Oil and GAs Wells
GUO Yongbin, WU Zhiming, YANG Yuhao, YU Yi, LIU Zhiqin
2019, 36(5): 654-658. doi: 10.3969/j.issn.1001-5620.2019.05.022
In deepwater oil and gas development, temperature rise in fluid trapped in the annulus between casing string and drill pipe causes an increase in the pressure trapped in the annulus, resulting in collapse or bursting of casing string which brings serious hidden risk to oil and gas production. To resolve this problem, an elastic spacer for preventing trapped pressure in annulus was developed and evaluated with a self-made "HTHP elastic fluid evaluation tester" and a "reciprocating compression tester for elastic materials". The composition of the elastic spacer is:sea water + 0.4% suspending agent + 6% elastic agent + ultra-fine iron ore powder. The density of the spacer is adjustable between 1.10 g/cm3 and 1.90 g/cm3. Laboratory evaluation of the spacer shows that:1) the elastic spacer has high elasticity and high compressive strength, and shows 100% elasticity. 2) the spacer retains its elasticity at different temperatures, effectively relieve accumulation of pressures. 3) the spacer has good compatibility with drilling fluids and cement slurries, and does not affect the use of the spacer and well cementing job. The spacer developed can be used to mitigate and control trapped pressure in annulus in deepwater drilling.
Development and Application of Organic Resin for Controlling Loss of Borehole Fluids in Cased Hole
GUO Gang, LI Qiongwei, YANG Lihua, LU Wenwei
2019, 36(5): 659-662. doi: 10.3969/j.issn.1001-5620.2019.05.023
Cement slurry used as a lost circulation material in controlling loss of borehole fluids through casing string has long been faced with problems such as its poor gas tightness and injectivity. This paper introduces the development of a liquid resin which can be used to replace cement slurry in loss control and the evaluation of the performance of the resin. The liquid resin has been tried in field operations. It was found that after setting at 60℃ for 4.5 h, the resin had compressive strength of 118 MPa, the shear strength of the resin adhered on the casing string was 26.1 MPa, and the bonding strength of the resin with rock reached 10.5 MPa. The resin had good oil resistance and drillability. This resin has been used in the Well Zhen-A for controlling loss of borehole fluids and well produced again with good production rate. In another well Hua-B, after applying the resin, the well was re-fractured with good results. Field practice has provided a technical reference to the use of the liquid resin as a lost circulation material and a reliable technology for dealing with loss across the casing strings.