2021 Vol. 38, No. 4

FORUM
Application Prospect of Magnetic Fluids in Drilling Fluids and Completion Fluids
GUANG Xinjun
2021, 38(4): 397-403. doi: 10.12358/j.issn.1001-5620.2021.04.001
Abstract:
Magnetic fluid, a kind of intelligent material, has both the mobility of liquids and the magnetism of solid magnetic materials, and is widely used in auto industry, mechanical engineering, construction field and aerospace industry etc. It also shows good application prospect in oil and gas industry. This paper introduces the advantages of magnetic fluids used in oil and gas industry. Based on the investigation of the application of magnetic fluids in drilling and completion fluids, the application prospects of magnetic fluids in smart drilling fluids, cement slurries, fracture monitoring in fracturing jobs, self-diverting agents in fracturing and temporary plugging, as well as oil and gas production enhancement of a single well. Key technologies in field application are presented in this paper, including rheology of the magnetic fluids, techniques for preparing and modifying magnetic fluids, optimization of the performance of magnetic fluids and equipment for controlling magnetic rheology downhole. The research results will provide reference and ideas for the application of magnetic fluids in oil and gas engineering field to improve the benefits of petroleum exploration and to reduce operating costs.
DRILLING FLUID
Study on High Temperature Stability of Invert Emulsion
LIU Gang, JIANG Chao, LI Chao, LIU Xuejing, DU Na, HOU Wanguo
2021, 38(4): 404-411. doi: 10.12358/j.issn.1001-5620.2021.04.002
Abstract:
The effects of the oil/water interface activity and temperature on two emulsifiers RHJ-I and RHJ-II were studied. An invert emulsion (W/O) was formulated with a synthetic oil (made in China) as the base oil, 25% CaCl2 solution as the water phase and a certain amount of Ca(OH)2. The composition of the emulsion and the effects of aging temperature and the temperature at which the emulsion stand still were investigated, and the stability mechanisms of the emulsion were studied. The results of the investigation and study show that RHJ-I and RHJ-II are able to reduce the interfacial tension between the synthetic oil and water, forming a viscoelastic interfacial film at the interface between the oil and water. The invert emulsion has good dispersion stability, and a synergistic action which improvs the stability can be found between RHJ-I and RHJ-II. After being aged at 180 °C and 232 °C, the stability of the emulsion was found enhanced, probably because of the production of an “organic Ca(OH)2” by the reaction between the emulsifiers and Ca(OH)2 which helps improve the high temperature stability of the emulsion. The stability of the emulsion is significantly enhanced when the oil/water ratio is between 1∶9 and 5∶5.
An Environmentally Friendly High Temperature Water Based Drilling Fluid for Hot-Dry-Rock Well Drilling
LIU Chang, XU Jie, RAN Hengqian
2021, 38(4): 412-422. doi: 10.12358/j.issn.1001-5620.2021.04.003
Abstract:
As the traditional energy reserves are declining, the development of new energy, such as hot-dry-rock, is becoming more and more popular. Hot-dry-rock wells have high bottom hole temperatures and are very deep, and sometimes are drilled directionally. Furthermore, some hot-dry-rock wells are located in an area surrounded by nature reserves. These factors impose strict requirements on the high temperature stability and environmental friendliness of the drilling fluid used to the hot-dry-rock well. If an efficient high-temperature drilling fluid can be formulated, it will do more with less in developing hot-dry-rock energy. In laboratory experiment, regular performance test and hot-rolling aging test were performed on more than 30 additives. The component and concentration of a drilling fluid for hot-dry-rock well drilling were designed and screened through variable control and orthogonal test methods. As a result, a high temperature drilling fluid for hot-dry-rock well drilling was developed. Laboratory experiment shows that this drilling fluid has good stability at temperatures as high as 240 °C. Polymers used in this drilling fluid form a stable network structure which is not easy to be destroyed by high temperature. The mud cakes formed by the drilling fluid is thin and tough, and is able to protect the borehole wall from being eroded. Some white non-polluting materials free of sulfonated and oil-based ingredients were also used in formulating the drilling fluid, they are environmentally friendly and pose very little pollution to the environment.
A Viscosity Reducer for Oil Based Drilling Fluids and Its Field Application
MING Xiansen, TAO Huaizhi, CHEN Junbin, LUO Taotao
2021, 38(4): 423-427. doi: 10.12358/j.issn.1001-5620.2021.04.004
Abstract:
Invasion of low quality solids, especially the low density solids is one of the major factors causing the thickening of high density oil based drilling fluids. The low quality solids in an oil based drilling fluid, when in contact with the wetting agents and emulsifiers therein, attain a certain degree of activity, thereby strengthening the networking structure and increasing the viscosity and gel strengths of the drilling fluid. A viscosity reducer CQ-OTA with amino groups and amido groups in its molecules was developed with lauramide, octadecanamide and erucamide in a mass ratio of 1∶2∶1. Evaluation on the viscosity reduction capacity of CQ-OTA showed that it can reduce the plastic viscosity and gel strength by 25.0% and 60.0% respectively of a high density thickened oil based drilling fluid containing 48.5% solids. The recommended treatment of CQ-OTA in oil based drilling fluids is 0.5%-1.5%. CQ-OTA was used on the Wei-202HX platform and it effectively improved the rheology of the oil based drilling fluid. The threshold of the low quality solids in the drilling fluid was increased. The plastic viscosity of the oil based drilling fluid was reduced from 53.0 mPa·s to 40.0 mPa·s, the final (10 min) gel strength reduced from 23 Pa to 14.5 Pa, ensuring the successful drilling of the well with the oil based drilling fluid, and enhancing the efficiency of reusing the high density oil based drilling fluid. The drilling cost was thus greatly reduced.
Drilling Fluid Technology for Plugging and Strengthening Formations with Narrow Mud Weight Windows in Deep Water Drilling
LI Zhong, CHEN Haodong, LIU Hexing, LYU Kaihe, BAI Yingrui
2021, 38(4): 428-434. doi: 10.12358/j.issn.1001-5620.2021.04.005
Abstract:
Formations drilled in deep water drilling are generally poorly compacted and have narrow safe mud weight windows, and mud losses in drilling these formations hence occur frequently. To solve these problems, a flexible particle plugging agent was developed with vinyl monomers, a macromolecular crosslinking agent and a silicate mineral with layered structure. Laboratory experimental results show that this flexible particle plugging agent has good toughness, and functions normally at temperatures as high as 160 ℃. In 10% salt water, the plugging agent has stable characteristics and can effectively plug permeable cores, fractures and sand-bed, significantly increasing their pressure bearing capacity. A high temperature drilling fluid for deep water drilling was treated with this plugging agent, and its properties before and after aging at 160 ℃ were stable. This drilling fluid has proper viscosity and gel strengths, and the ratio of the yield points at 4 ℃ and 25 ℃ is less than 1.35, indicating that the drilling fluid has constant rheology at low temperatures. Cores plugged with this drilling fluid have permeability that is near zero, and the pressure bearing capacity of the cores is 11 MPa. This drilling fluid has strong resistance to the contamination by clays and salt, and is of low damage to the permeability of reservoir formations; permeability recovery of plugged cores is at least 90%. The application of this drilling fluid in the Lingshui block in South China Sea effectively increased the pressure bearing capacity by 6-11 MPa, ensuring the safe drilling operation in the complex hole sections.
Preparation and Plugging Performance of Zwitterionic Polymer Gel Micro Spheres
LIU Fengbao, YAN Lili, NI Xiaoxiao, JIANG Guancheng, CUI Xin, WANG Jianhua
2021, 38(4): 435-441. doi: 10.12358/j.issn.1001-5620.2021.04.006
Abstract:
A kind of zwitterionic polymer gel micro spheres have been prepared through suspension polymerization to address the deficiency of plugging capacity of oil based drilling fluids. The raw materials used in the polymerization include N , N -dimethyl acrylamide (DAM), 2-acrylamido-2-methyl propane sulfonic acid (AMPS) and dimethyl diallyl ammonium chloride (DMDAAC), and the crosslinking agent for the polymerization reaction is N , N -methylene-bis-acrylamide (MBA). Using H-NMR spectrometry, the molecular structure of the polymer gel micro spheres was characterized. Effect of the molar ratio of the monomers and the concentrations of the crosslinking agent and emulsifier on the size distribution and plugging performance of the polymer gel spheres was investigated. The optimum molar ratio of the monomers for the polymerization was determined as: DAM∶AMPS∶DMDAAC = 7∶1∶2, the optimum mass concentration of MBA (based on the total mass of the monomers) was 0.2%, and the optimum concentration of the emulsifier (based on the total mass of the monomers) was 3%. The average particle size of the polymer gel micro spheres is about 22 μm. The plugging capacity of the polymer gel micro spheres was tested in oil based muds, and it was found that the polymer gel micro spheres are suitable very well to use in the oil based muds. At 150 ℃, the polymer gel micro spheres can effectively plug fractures of 5-150 μm, a plugging performance better than the combination of oxidized asphalt and fine calcium carbonate. The test results show that the zwitterionic polymer gel micro spheres are a high-performance millimeter-sized plugging agent with good field application potential.
Research on A Water-based Drilling Fluid for Shale Gas Drainage and Strong Blocking
KANG Yuan, SUN Jinsheng, LYU Kaihe, LIU Jingping, ZHANG Wenchao, TENG Yuxiang, XIU Zhuoyang, HUANG Ning
2021, 38(4): 442-448. doi: 10.3969/j.issn.1001-5620.2021.04.007
Abstract:
The shale formation of the Longmaxi Formation in Sichuan is highly water sensitive,with micro-cracks and cracks developed. During the drilling process, the shaft wall collapsed frequently,which severely restricted the efficient development of shale gas.In order to solve the above problems, this paper introduces a hydrophobically modified silica plugging agent that can not only inhibit shale hydration expansion and dispersion, but also block pores,micro-cracks and cracks, and make the shale surface hydrophobic.And with the core of the plugging agent, combined with fluid loss additives, lubricants, etc., a hydrophobic and strong plugging water-based drilling fluid was studied. The drilling fluid not only has good rheology and fluid loss reduction properties, but also has excellent inhibition, plugging,hydrophobic and anti-pollution capabilities. The shale recovery rate of the drilling fluid is 90.2%, the penetration depth into the 40-60 mesh sand bed is only 1.5 cm, and the high temperature and high pressure filtration loss is 7.2 mL when the density is 2.2 g/cm3.
An Environmentally Friendly Oil Base Mud
LIU Yongfeng, ZHANG Weiguo, DI Mingli, CHEN Bin, ZUO Kun, WANG Shunwen, KE Dian
2021, 38(4): 449-455. doi: 10.3969/j.issn.1001-5620.2021.04.008
Abstract:
Mineral oils and several oil base mud additives presently in use are highly biologically toxic and the discharge of oil base muds formulated with them are prohibited or limited. To minimize the toxicity of oil base muds, an environmentally friendly oil base mud was formulated with a weakly biologically toxic base oil, a high efficiency low-toxicity all-in-one emulsifier, a new modified high-gel organophilic clay and other additives developed. The concentrations of these additives were optimized to obtain an oil base mud with satisfactory performance. The oil base mud has LC50 of greater than 15,000 mg/L and is biologically degradable. The oil base mud has good rheology, and its electrical stability is at least 800 V. The HTHP filtration rate is less than 6 mL. This oil base mud is resistant to contamination from 5% gypsum or 5% drilled cuttings or 15% salt water. The oil/water ratio of the mud can be adjusted between 60/40 and 90/10, and the density can be controlled between 1.25 g/cm3 and 2.0 g/cm3. This oil base mud has good high temperature stability, it functions normally at 220 ℃. These properties can satisfy the needs of drilling in wells penetrating complex formations and in area with stringent environment protection requirements.
Analysis of the Mode and Mechanisms of Destabilization of Micro Foams
YANG Qianyun, WANG Baotian, YANG Hua, ZHAO Huaizhen
2021, 38(4): 456-461. doi: 10.12358/j.issn.1001-5620.2021.04.009
Abstract:
Micro-foam fluid destabilizes in three ways: separation of the liquid phase, settlement, or both. In our study the effects of several factors on the way of foam destabilization were studied, including the viscosity and gel strengths of the micro-foam, the molecular weight of the foam stabilizer, speed for mixing the foam, temperature, Na+ and Ca2+ etc. The viscosity and strength of the interfacial films of the micro-foam prior to destabilization were compared with each other and the intrinsic mechanisms of the destabilization of the micro-foams were analyzed. These studies shall be able to provide technical references to the formulation of micro-foam fluids with thermal stability and salt-resistance. Generally speaking, when the viscosity and the ratio of yield point over plastic viscosity of the base fluid are low, or when medium for stabilizing the micro-foam is a kind of lightweight gel, the micro-foam destabilizes in a way of liquid separation; when the density of the base fluid stabilizing the micro-foam is high, or when the molecular weight of the gel is too high resulting an in increase in the amount of bound free water, and hence an increase in the thickness and weight of the liquid films, the micro-foam destabilizes in a way of settlement. When the micro-foam is aged at different temperatures or contaminated with different concentrations of metal ions, it destabilizes in a way of both liquid separation and settlement.
An Anti-Collapse Drilling Fluid with Strong Inhibitive and Plugging Capacity for Use in the Fuxian Block in Ordos Basin
CHEN Xiaohua, QIU Zhengsong, FENG Yongchao, BAO Dan
2021, 38(4): 462-468. doi: 10.12358/j.issn.1001-5620.2021.04.010
Abstract:
Borehole wall instability was encountered in drilling the Liujiagou formation, the Shiqianfeng formation and the Shihezi formation in the Fuxian block, and the mechanisms of the instability were investigated and revealed through studies on three aspects, namely, the mineral composition, microstructure and physio-chemical property of the formations in question. These studies are aimed at solving the borehole wall sloughing problem encountered in the drilling operation in the Fuxian block in Ordos Basin, in which the shale contains high content of clays and is developed with pores and fractures resulting in shale hydration. Based on the “synergy of multiple factors” theory, a technical measure for stabilizing borehole wall, which can be described as “physio-chemically plugging/consolidating borehole wall to retard pressure transmission-strengthening the inhibition of clay hydration-supporting the borehole wall with appropriate mud weight”, was presented. A drilling fluid with strong inhibitive capacity and plugging capacity was formulated based on the optimization of each additive in and the whole composition of the drilling fluid to deal with the sloughing of the borehole wall. The drilling fluid has HTHP filtration rate of 8.4 mL, strong inhibitive and plugging capacity, and percent recovery of shale cuttings of 90% in hot rolling test. Plugging of 400 μm fractures with the drilling fluid renders the formation in which these fractures exist a pressure bearing capacity of 6 MPa. The drilling fluid also has good reservoir protection capacity. Field application shows that this new drilling fluid is able to effectively mitigate the tight hole and sloughing, reduce the rate of hole enlargement, and increase rate of penetration. Using this drilling fluid, no downhole troubles have ever happened, providing drilling fluid technical support to the safe and efficient drilling in the Fuxian block.
Field Application of a Plugging Borehole Wall Anti-Collapse Agent XZ-OSD in the Piedmont Structural Belt on the South Margin of Junggar Basin
FU Chaosheng, AO Tian, YU Jiashui, JIANG Guancheng, XIE Chunlin, KONG Dechang, YANG Lili
2021, 38(4): 469-473. doi: 10.12358/j.issn.1001-5620.2021.04.011
Abstract:
Borehole wall collapse and mud losses have been occurring during drilling operation in the piedmont structural belt on the south margin of Junggar Basin. By experimentally analyzing the rock samples and drilled cuttings taken from the target drilling area, the borehole wall collapse mechanisms were understood. The experimental results show that borehole wall collapse results from the broken formations, oil phase damaging and strong water sensitivity of the formation rocks. Based on this knowledge, an oil based drilling fluid was chosen to drill the water sensitive formations, and XZ-OSD, a borehole wall anti-collapse preventing agent with strong plugging capacity, was selected for use in the oil based drilling fluid. XZ-OSD can plug pores of different sizes in the formations, bond the broken formations together, and form oleophobic adsorption layer on the surfaces of the rock, thereby preventing the borehole wall collapse caused by broken formations and oil phase damaging. Field application showed that, compared with the offset wells, the percent rate of hole enlargement of the 3rd and the 4th intervals of the well GHW001 was reduced by 46%-49%. In another well Hutan-1, an exploratory well, the percent rate of hole enlargement in the 5th interval, in which the mud was treated with XZ-OSD, was reduced by 83.3% compared with the 4th interval of the well. The use of XZ-OSD effectively solved the problem of borehole instability in the southern margin of the Junggar Basin, and provided drilling fluid technical support for high quality drilling in this area.
A New Method of Predicting the Bridging Lost Circulation Materials and Their Particle Size Distribution
ZHU Jinzhi, REN Lingling, LU Haiying, WU Xiaohua, WANG Gui
2021, 38(4): 474-478. doi: 10.3969/j.issn.1001-5620.2021.04.012
Abstract:
Accurate and rapid prediction of the types of lost circulation materials (LCMs) and their particle size distribution (PSD) plays a key role in the digital and intelligent design of bridging lost circulation material slurry. A new method of characterizing and rapid predicting the bridging lost circulation materials and the PSD thereof is presented based on the PCHIP method in an effort to overcome the deficiencies existed in the methods presently in use. Using the data obtained in the experiments on the PSD of a single bridging LCM, the applicability of the new method and the commonly used particle size distribution function methods in characterizing the PSD of LCMs was compared and analyzed. The new method was used to predict the PSDs of different LCM compositions, and the data collected in the measurement were used to verify the reliability of the new method. It was demonstrated that, compared with the commonly used PSD function methods, the new method can be used to more accurately characterize the PSDs of bridging LCM compositions. The cumulative PSD curve predicted with the new method is highly consistent with the measured data. Without the need of pre-setting a PSD function, the new method is suitable for predicting the PSD of particle matters with multiple peaks. The new method can be used to predict the PSDs of mixtures with different ratios of particle sizes.
Drilling Fluid Technology for the Third Interval of Well Changtan-1 in Jilin Oilfield
LIU Tengjiao, YU Yang, ZENG Xiangyu, SHANG Wangtao, WANG Yu, XU Yongqiang, WANG Qinglin
2021, 38(4): 479-485. doi: 10.12358/j.issn.1001-5620.2021.04.013
Abstract:
The well Changtan-1, 5400 m in total depth, is an exploratory well drilled in the Changling rift, south of the Songliao Basin. The third interval of this well penetrated formations with high temperatures and igneous formations which are sloughing in nature. The mud used to drill these formations had low densities based on the designed value, and CO2 contamination deteriorated the properties of the mud. To solve these problems, a drilling fluid having temperature resistance of 200 ℃, good high temperature rheology, high plugging capacity and a certain CO2 contamination resistance, was formulated through laboratory experiments. A sulfonate copolymer filtrate reducer in the drilling fluid rendered it good high temperature performance and contamination resistance through colloid protection at elevated temperatures by the copolymer. Treatment of the drilling fluid with a nanometer SiO2 improved the rheological property and plugging capacity. In field application, the drilling fluid showed good high temperature stability, and effectively inhibit the sloughing of the igneous rocks. After contaminated with CO2, the drilling fluid still retained satisfactory performance and the contamination was easy to treat out. The well Changtan-1 was successfully completed, no downhole troubles were encountered during drilling, and set the record of drilling the deepest well in the Changling area in the south of Songliao basin.
CEMENTING FLUID
Mechanical Properties and Microstructure of Self-healing Oil Well Cement
LIU Rengguang
2021, 38(4): 486-491. doi: 10.12358/j.issn.1001-5620.2021.04.014
Abstract:
The mechanical properties and microstructure of self-healing cement were studied. The adding amount of self -healing emulsion was 0, 5%, 10%, 15% and 20% respectively. The samples were cured under the condition of 90 degrees in the water for 3 days. The results showed that the elastic modulus of cement decreased with the incorporation of self-healing emulsion. With the increase of the dosage, the elastic modulus of cement decreased significantly. The strength of self-healing cement paste was higher than that of normal oil well cement. The compressive strength was higher with small amount addition, and the increase of flexural strength was greater with increase of addition. The microstructure of hydroxide crystal appeared scattered and loose instead of regular hexagonal. Self-healing colloidal particles were distributed between the network structures of hydration product gel. The porosity was reduced and the average and most probable pore size increased of self-healing cement.
Research for low shear rheological properties of low return velocity cementing drilling fluid in Kuqa Piedmont
ZHANG Xiayu, AI Zhengqing, WEN Zhiming, ZHANG Feng, XU Liqun, LIU Rui, ZHANG Xingguo
2021, 38(4): 492-498. doi: 10.3969/j.issn.1001-5620.2021.04.015
Abstract:
In view of the fact that the drilling fluid is in the low shear flow state during the fourth spud in ultra-high pressure gas well in Kuqa mountain front of Tarim Basin, the rheological model and rheological parameters of the drilling fluid were fitted by the rheological test data of the full shear rate. The low shear rate range, corresponding rheological mode and rheological parameters of the drilling fluid and its effect on the cementing annulus were studied The influence of flow friction coefficient. The results show that the shear rate of drilling fluid is obviously less than 1022 s−1 (600 r/min) in the process of cementing with low return velocity, and the corresponding rheological mode and rheological parameters are greatly different from the range of full shear rate, which leads to a certain or even large difference in the friction coefficient of cement injection annulus, which affects the accurate control of the calculation of cementing annulus pressure, For low return velocity cementing, the annular flow pressure loss should be calculated according to the rheological mode and rheological parameters within the low shear rate range, the cementing displacement should be controlled, and the success rate of low return velocity and leak proof cementing should be improved.
The Adaptability and Application of a Water Non-Dispersible Cement Slurry
WANG Jianyao, YANG Kunpeng, MEI Mingjia
2021, 38(4): 499-503. doi: 10.12358/j.issn.1001-5620.2021.04.016
Abstract:
There has long been a water invasion and channeling problem in the water injection blocks and high water cut formations in Changqing oilfield which always happened during and/or after well cementing. To deal with this problem, the field adaptability of the anti-dispersing flocculant BCY-100L was studied taking into account the conditions of field operation. A secondary anti-dispersing agent A was selected through laboratory experiment. Different water non-dispersible cement slurries can be formulated by adding different cement additives to suit different requirements of well cementing. This water non-dispersible cement slurry can maintain its gel structure integrity when water invasion occurs, having outstanding non-dispersing performance and erosion resistance when in contact with water. It is able to resist the invasion of formation water and protect the good bonding at both sides of the cement sheath. This cement slurry has been used twice in wells penetrating water bearing zones, and the pass rate of the quality of the cement sheath with the casing and the borehole wall is 100%, and the high-quality rate of the bonding was 95%. The job quality of the cementing in the water bearing section was increased from 28% to 95%. Field application indicates that this cement slurry has good prospects in cementing wells in water injection area and wells penetrating water bearing formations.
FRACTURING FLUID & ACIDIZING FLUID
Preparation of Salt Tolerant Suspension Dispersion Polymer System and its Application in Brine-based Variable Viscosity Slippery Water System
LIU Fujian, WANG Lixiang, DU Liangjun, LIU Ting, ZHANG Lei, LIU Bin
2021, 38(4): 504-509. doi: 10.12358/j.issn.1001-5620.2021.04.017
Abstract:
In this paper, the zwitterionic polymer molecule P-DHZ containing double tailed hydrophobic monomer was developed by aqueous solution polymerization system. Its viscosity average molecular weight is more than 10 million. It owns excellent salt resistance, drag reduction and gelling properties. It can be used as a drag reducer or thickener for shale gas hydraulic fracturing fluid, and can be directly prepared with highly mineralized backflow fluid. Its salt resistance can reach 60 000 mg/L. In order to meet the process requirements of continuous mixing in shale gas fracturing field, P-DHZ powder was prepared and dispersed in hydrocarbon continuous phase to form a stable suspension system. The best powder size, dispersant, diverting agent and hydrocarbon continuous phase were selected to prepare a suspension system for continuous mixing in field. The proportion of powder accounted for 45% of the suspension system, and it can be solved in high salinity back-flow fluid to prepare fracturing fluid without fresh water resource. The maximum drag reduction rate is more than 75%, and the dissolution time is less than 30 seconds. The viscosity can be changed in real time by adjusting the concentration, and the slick-water system can be quickly transformed into the glue system.
Study and Application of a Low Damaging Drag Reducing Hydrophilic Suspension
WANG Pengxiang, ZHANG Xiangfeng, ZHANG Dandan
2021, 38(4): 510-516. doi: 10.3969/j.issn.1001-5620.2021.04.018
Abstract:
A new low damaging hydrophilic suspension dissolvable in alcohol solvents was developed to solve the problems encountered in field application of polymer drag reducers such as long time of hydration and low solubility of the drag reducers, and problems encountered in using hydrophobic suspensions such as poor environmental friendliness. Laboratory and field evaluation of the overall performance of the slick water system was performed. The evaluation results show that the best solvent for the suspension is polyethylene glycol 200. When the concentrations of two thixotropic agents PR and CQ2720 were 1.5% respectively, the suspension has the best stability, and the two thixotropic agents have synergistic effect on stabilizing the suspension. When adding 0.5% dispersant MR312 into the suspension, the drag reducing suspension can stand for 30 d without any sedimentation, and the viscosity of the system remained at 177 mPa·s. The drag reducing suspension can be uniformly dispersed into water, and the slick water prepared with the suspension is clear and transparent. The viscosity of the slick water is adjustable and the rate of drag reduction is great than 70%. In the fracturing job performed on the well Yang-101H1-1, the drag reducer was uniformly dispersed into water, without agglomerating. The fracturing fluid became viscosified quickly and was easy to be flowed back, and it also showed significant environment protection effect.
Study on Characterization of the Performance of Fracturing Fluids in Large Scale Volumetric Fracturing
ZHANG Danian, CHENG Xingsheng, LI Yongping, REN Xiaoke, WEN Xin, HAN Chaolimen
2021, 38(4): 517-524. doi: 10.3969/j.issn.1001-5620.2021.04.019
Abstract:
In the national standard “The evaluation measurement for properties of water based fracturing fluid” (SY/T 5107-2016), the shearing history of a fracturing fluid in large scale volumetric fracturing and the high shear rate of the fracturing fluid when it passes through a perforation cannot be simulated. A study has been performed on the investigation of how to measure the performance of a fracturing fluid in the whole process of volumetric fracturing job. Based on the actual flow rates in field fracturing operation, the shear history of a fracturing fluid flowing through pipes, perforation and formation fractures was simulated. Meanwhile, the dosage of gel breaker was optimized in an effort to find the concentration of the gel breaker when the lowest damaging to the reservoir is required. Thus, the evaluation of a fracturing fluid should be able to quantify two parameters; sand carrying capacity of the fracturing fluid which satisfy the needs of fracturing job and thorough breaking of the gel some time after the fracturing job is completed. Using the transparent parallel board model, the dynamic sand carrying capacity of a fracturing fluid was investigated, and the test results will provide a design basis for the “full fracture propping” in large scale volumetric fracturing. The results of the new evaluation method show that the compound crosslinked guar gum fracturing fluid and the crosslinked polymer fracturing fluid have the highest viscosity losses when passing through perforations at high flow velocity. The emulsion association fracturing fluid is sensitive to gel breaker, if the formation damage caused by gel breaking process is low, the dynamic sand carrying performance will not be able to satisfy the needs of placing proppant particles into the distal end in a fracture. A low concentration guar gum fracturing fluid treated with optimized amount of gel breaker will have good dynamic sand carrying capacity at flow rates prevailing in field operations, and thus satisfy the technical goals of placing proppants into the distal end of a fracture.
COMPLETION FLUID
Ultra-High Temperature Workover Fluid with Flexible Rubber Particles Used in Shunbei Oilfield
KANG Hongbing, NIU Chengcheng, JIA Hu, GAO Dingxiang, DAI Changlou
2021, 38(4): 525-530. doi: 10.3969/j.issn.1001-5620.2021.04.020
Abstract:
The conventional viscosified workover fluid used in the high temperature oil and gas wells in Shunbei Oilfield is easy to lose its viscosity. To solve this problem, a new workover fluid containing flexible rubber particles that is able to resist 180 ℃ was developed based on the fact that the viscosity of a flexible high molecular weight rubber particle changes in a pattern of “disperse, degrade, viscosify, and stabilize viscosity”. The dynamic viscosity of this workover fluid can be adjusted between 20 mPa·s and 140 mPa·s. The density of the workover fluid adjusted between 1.0 g/cm3 and 1.3 g/cm3, which means that the workover fluid can be weighted with or without solid weighting agents. The pattern of the viscosity change of the workover fluid at different temperatures was studied. After aging for 1 day at 180 ℃, the viscosity of the workover fluid was apparently higher than that of a conventional xanthan gum workover fluid, indicating that the new workover fluid had the ability of stabilizing its viscosity. The rate of corrosion of this workover fluid to aluminum alloy is less than 2.22 g/(m2·h). The workover fluid also had very good sand carrying capacity. This study has certain guiding significance for the safe and efficient workover operations of high-temperature oil and gas wells in Shunbei.