2021 Vol. 38, No. 2

2021, 38(2)
Research Progress of Controllable Polymer Gel Lost Circulation Materials
LI Wenbo, LI Gongrang
2021, 38(2): 133-141. doi: 10.3969/j.issn.1001-5620.2021.02.001
Polymer gel lost circulation materials (LCM) have the advantages of high viscoelasticity and deformability. However, the gelation of polymer gel LCM is uncontrollable, severely restricting their use in controlling mud losses. This paper summarizes the research progress made in the development of controllable polymer gel LCM technology and points out that delayed crosslinking, microencapsulation, thixotropic self-healing, shear-response gelling as well as ion-induced gelling, in which the response polymers are stimulated to form LCM suitable for mud loss control, are increasingly becoming a hot spot in the research of controllable LCM. Meanwhile, Study on the stimulus-response functional polymer gel material has become mature, and the environment in drilling fluids can provide stimulus response condition for polymer gel LCM. It is thus concluded that the development of polymer gel LCM with stimulus-response function will be beneficial to the intelligent and controllable mud loss treatment.
Study and Application of a Double Esterified Modified Starch Filter Loss Reducer
ZHANG Kun, MA Hong, SHU Ruhong, LIU Qiang, WANG Wei, SUN Shuang, XIONG Lasheng
2021, 38(2): 142-145. doi: 10.3969/j.issn.1001-5620.2021.02.002
Conventional modified starch as a filter loss reducer, has the shortcomings of high viscosity effect and poor temperature stability. A double-esterified starch filter loss reducer BZ-JLS was developed to overcome these shortcomings. BZ-JLS was synthesized with acetic anhydride, sodium trimetaphosphate and corn starch. BZ-JLS has good dispersion capacity and filtration control property. Laboratory study showed that a base mud treated with 1.5% BZ-JLS after aging at 150 ℃ for 16 hours had API fluid loss of only 9.4 mL. BZ-JLS also shows good resistance to salt and calcium contamination. The biological toxicity, biodegradation property and metal content all meet the environmental requirements. Field application on a well drilled in Dagang Oilfield showed that BZ-JLS had good compatibility with fresh water and salt water. The mud was only slightly viscosified, while the filtration rate was significantly reduced.
Development of A Polymer Filter Loss Reducer for Ultra-High Temperature Water Base Drilling Fluids
GAO Wei, LI Yinting, YU Fuchun, LI Shuanggui, MAO Hui
2021, 38(2): 146-151,157. doi: 10.3969/j.issn.1001-5620.2021.02.003
A new polymer filter loss reducer CLG-240 was developed for use in water base drilling fluids in ultra-high temperature operations. CLG-240 was synthesized with acrylamide, 2-acrylamide-2-methyl propane sulfonic acid and dimethylaminoethyl methacrylate as the monomers, and 2,2'-azobis[2-methylpropionamidine] dihydrochloride as the initiator through free radical polymerization. Using IR spectroscopy, gel chromatography analysis and thermogravimetric analysis, the molecular structure of CLG-240 was characterized and the relative molecular weight and thermal stability of the synthesized product determined. Comprehensive evaluation of the performance of CLG-240 in water base drilling fluids showed that CLG-240 has a number-average molecular weight of 6.461×105, weight-average molecular weight of 7.345×105. Total thermal loss of weight between room temperature and 315 ℃ is 26.5%, demonstrating that CLG-240 has good high temperature resistance and tolerance. Furthermore, CLG-240 showed good filtration control performance both in freshwater base drilling fluids and saltwater base drilling fluids, as well as good shale inhibitive capacity. Laboratory study showed that CLG-240 is resistant to ultra-high temperatures in drilling fluids; in low density drilling fluids, CLG-240 functions normally at temperature up to 248 ℃, while in high density drilling fluids, this temperature is 220 ℃.
The Development and Properties of an Environmentally Friendly Metal Friction Reducer for Coiled Tubing
ZOU Peng, WANG Wenshan, YANG Yanchang, LIU Lin, LIU Chunlong, LIU Song, XIE Tongchuan
2021, 38(2): 152-157. doi: 10.3969/j.issn.1001-5620.2021.02.004
An environmentally friendly oil in water (O/W) metal friction reducer has been developed to address the locking problem encountered in coiled tubing operation in a horizontal well with long horizontal sections. The metal friction reducer was made from several core reactants such as a modified vegetable oil, a surfactant and ethylene glycol. Laboratory experiment was conducted to study the effect of the friction reducer on the coefficient of friction (CoF) of N80, P110 and Cr-13 steels at different concentrations, salinities, pH values and temperatures. The effect of the friction reducer on the environment was also studied through MTT experiment and animal test. It was found that at concentration of 0.5%, the friction reducer performed at its best. At this concentration of the friction reducer, the CoF of N80 steel was reduced from 0.42 (tested with water and N80 steel) to 0.12, or a percent reduction in CoF of 71.4%, the CoF of P110 steel was reduced from 0.475 (tested with water and P110 steel) to 0.16, or a percent reduction in CoF of 66.3%, the CoF of Cr-13 steel was reduced from 0.75 (tested with water and Cr-13 steel) to 0.115, or a percent reduction in CoF of 84.7%. The metal friction reducer can be used at 140 ℃, in a pH range of 1-10, and can tolerate salinity up to 30,000 mg/L. The metal friction reducer has cell proliferation rate between 95% and 150%, and LC50 of about 55,000 mg/L, indicating that the it has no toxicity to cells and animals. The metal friction reducer has excellent friction reduction performance and can satisfy the needs of field coiled tubing operation.
Laboratory Study and Application of a Multifunctional Lubricant for Silicate Drilling Fluids
LIU Zhiqin, GUAN Shen, XU Mingbiao, WU Jiao
2021, 38(2): 158-163. doi: 10.3969/j.issn.1001-5620.2021.02.005
The special formation characteristics of the Beibuwan Basin always leads to borehole wall collapse during drilling operation. Silicate mud, which has the advantage of stabilizing the sloughing formation was introduced to deal with borehole wall instability. The silicate mud has its own problems:poor lubricity and filtration control. A multifunctional lubricant, ALM, was developed to solve these problems. Laboratory study showed that ALM has excellent lubrication capacity and anti-wear performance, it can inhibit the hydration and dispersion of the sloughing rock obtained from the Wei'er member penetrated in the reservoir section. ALM is compatible very well with the silicate mud and when used in the silicate mud, it shows a membrane effect to reduce the filtration rate of the mud. A silicate mud treated with 5% ALM has its filtration rate reduced from 4.0 mL to 2.1 mL, and its HTHP filtration rate from 16.3 mL to 6.8 mL, while the rheology of the mud is not affected. Rate of reduction of coefficient of friction of the silicate mud can be 85.21%. The special properties of ALM effectively improve the lubricating performance and inhibitive capacity of the silicate mud.
Research on Dihexadecyldimethyl Ammonium Chloride As A Poor Solid flocculant for Oil-based Drilling Fluid
JING Minjia, LI Wuquan, JIANG Guancheng
2021, 38(2): 164-169. doi: 10.3969/j.issn.1001-5620.2021.02.006
Drilled cuttings of low quality have great influence on the properties of oil base drilling fluids and are difficult to remove because of their small particle sizes. Flocculants can be used to enlarge the particle sizes of the drilled cuttings through flocculation but are generally used in water base drilling fluid and seldomly are used in oil base drilling fluids. An oil base drilling fluid contaminated with kaolin as the poor-quality solids was studied for the flocculating performance of dihexadecyl dimethyl ammonium chloride (DCDAC) to flocculate kaolin. Observation of the contaminated and DCDAC treated oil base drilling fluid under stationary state, turbidity analysis and observation under microscope of the drilling fluid showed that DCDAC is able to accelerate the settling of kaolin particles; at 5% of DCDAC in the kaolin containing oil base drilling fluid, all the kaolin particles settled to the bottom in 48 hours. After kept stationary for 5 hours, the percent decrease of the turbidity of a kaolin suspension was nearly 80%. Observation under microscope of the drilling fluid showed that when the concentration of DCDAC in the oil base drilling fluid was greater than or equal to 4%, the kaolin particles showed obvious agglomeration behavior. It was also found in the laboratory experiment that the density and solids content of an oil base drilling fluid after centrifugation are inversely proportional to the concentration of DCDAC, while the percent removal of solids is in direct proportion to the concentration of DCDAC. With the increase of the concentration of DCDAC in the oil base drilling fluid, the plastic viscosity and yield point of the drilling fluid were first decreasing and then increasing. All these phenomena shown in laboratory experiment indicate that DCDAC has good flocculating capacity to kaolin in oil base drilling fluids, and can be used in removing low quality solids from oil base drilling fluids.
Laboratory Study on Optimization of Drilling Fluid Used in Southwest Tarim Basin with Nanoemulsion
SHENG Yong, YE Yan, ZHU Jinzhi, SONG Hanxuan, ZHANG Zhen, ZHOU Guangxu, WANG Tao
2021, 38(2): 170-175. doi: 10.3969/j.issn.1001-5620.2021.02.007
The southwest Tarim Basin has plenty of oil and gas resources, rendering this area excellent exploration and development potential. However, the complex geological condition in this area seriously restricts the exploration and development potential. Mud losses, pipe sticking, reaming, borehole wall collapse, resistance to the tripping of drilling tools and well kick have often been encountered during drilling. Among these, mud losses happened for more than 30 times and pipe sticking more than 10 times. The longest drilling time of a well was as long as 719 d. To deal with these problems, the main factors affecting the stability of the borehole wall was analyzed, and based on the analysis, a core nanoemulsion developed by the China University of Petroleum (Beijing) was selected as borehole wall stabilizer. The core nanoemulsion is a nanoemulsion with nano SiO2 as the core, and the D50 of the cores is about 100 nm. The oil phase of the nanoemulsion can be used to inhibit the swelling of clays, and form "soft + hard" plugging system in pores and fractures. Laboratory experiment showed that a drilling fluid optimized with 5% core nanoemulsion had HTHP filtration rate of only 3.8 mL. Pressure transmission test showed that time for the balance of pressure transmission was reduced by 125 min after optimization, and the pressure was reduced by 0.337 MPa. In hot rolling test, the percent recovery of shale cuttings was 85% when tested with the optimized drilling fluid. All these facts prove that the core nanoemulsion can be used as a water base mud additive for optimizing the mud performance.
A Strongly Inhibitive Anti-Sloughing Water Base Drilling Fluid for Shale Reservoir Drilling
WANG Peiping
2021, 38(2): 176-182. doi: 10.3969/j.issn.1001-5620.2021.02.008
Drilling the long horizontal section of the shale gas well W-X1 in Weiyuan area has encountered downhole problems such as borehole wall instability, mud losses and high friction between the drilling string and the borehole wall. A water base drilling fluid with strong inhibitive capacity and anti-sloughing ability was developed to deal with these problems. The drilling fluid was formulated mainly with a poly amino shale inhibitor HCA-3, a compound plugging agent and a high efficiency lubricant RMLUB-1. Evaluation of the formulated drilling fluid showed that it has good rheology, low filtration rate and good lubricity, and is able to satisfy the basic needs of horizontal drilling of shale gas wells. Compared with other water base drilling fluids, this drilling fluid has better shale inhibitive capacity because it can reduce the Zeta-potential of shales to a much lower level. The PPA filtration rate and API filtration rate are all comparable to those of oil base muds, and this water base drilling fluid is able to prevent pressure transmission across the borehole wall and has high plugging capacity. Furthermore, this drilling fluid has good resistance to contamination; the properties of the drilling fluid do not change a lot when salts, drilled cuttings or bentonite clay is/are added. This drilling fluid has been successfully used in drilling the horizontal section (3rd interval) of the well W-X1 in Weiyuan area. During drilling operation, the properties of the drilling fluid were stable and the operation was done smoothly; no borehole wall instability, drag and resistance during tripping of drill string have ever been encountered, and drilling efficiency was enhanced.
Water Base Drilling Fluid Technology for Ultra-Long Horizontal Drilling in a Tight Gas Well in Changqing Oilfield
HU Zubiao, ZHANG Jianqing, WANG Qingchen, MENG Fanjin, HOU Bo, ZHANG Qin, QU Yanping
2021, 38(2): 183-188. doi: 10.3969/j.issn.1001-5620.2021.02.009
Changqing Oilfield has in the year 2020 drilled three wells with ultra-long horizontal sections in its tight gas well block, the lengths of the horizontal sections are 3321 m, 4118 m and 4466 m, respectively. These long horizontal sections were all drilled with water base muds, and each of the horizontal lengths has consecutively set a new record of the longest horizontal section of onshore wells in Asia. Long horizontal section drilling was faced with challenges such as friction reduction, hole cleaning and borehole wall stabilization. Specific studies were conducted to deal with these difficulties based on the structures of the formation rocks. As a result, a CQSP-RH drilling fluid and technologies for hole cleaning and wellbore stabilization in ultra-long horizontal well drilling were presented. Field application of the technologies and the CQSP-RH drilling fluid has produced good results, the horizontal section of the well was stable during drilling. When running the drill string into the hole, the friction of the drill string encountered was controlled at 500 kN in the open hole, and 350 kN in the cased hole. The well was successfully completed. With more and more development activity in Changqing oilfield going on, long horizontal well drilling technology has to be adopted to develop the water resource conservation and the forest regions and to increase the production of a single well. The successful drilling of these wells has provided a model and an arsenal of technologies for the subsequent development of the oil and gas field.
Preparation and Application of a Temperature-Controlled Expanding LCM Made from Shape-Memory Polymer
YANG Qianyun, WANG Baotian, YANG Hua, LIU Xueming
2021, 38(2): 189-195. doi: 10.3969/j.issn.1001-5620.2021.02.010
An expandable polymer lost circulation material (LCM), SDP, was developed to deal with mud losses into fractured formations. SDP was made from oligomer resin monomer which reacts at high temperatures with a crosslinker and a toughener under the action of a catalyst. SDP is pressure bearable and its expansion is triggered by temperature. When entering into a loss channel, SDP makes itself adaptive to the space where it is and bridges the space, thereby stop mud losses. The SDP developed has compressive strength under ambient temperature of greater than 71.62 MPa, and compressive strength under high temperature of greater than 17.21 MPa. At temperatures triggering the expansion of SDP, the expansion lag time is 40.07-53.43 min. As temperature increases, the lag time becomes shorter accordingly. LCM made with SDP of different particle sizes can stop mud losses through expansion and bridging. The pressure bearing capacity of a 9% SDP LCM slurry is greater than 9.5 MPa, as laboratory experiment indicated. Application of an LCM slurry made by mixing SDP particles, rigid particles, elastic particles and flexible fibers on the well Xing-1 in Ningxia solved the repeated losses of mud into Yan'an formation, a fractured coal zone. The mud loss was 100% stopped at the first try, and the total volume of mud losses was reduced by 77.67%.
Gel Plugging System for Oil-Based Drilling Fluid and Its Application
JI Weijun, YANG Yong, YAN Yongsheng, TANG Guowang
2021, 38(2): 196-200. doi: 10.3969/j.issn.1001-5620.2021.02.011
Based on the research and analysis of modern shale gas drilling, and comprehensively comparing the shortage of oilbased drilling fluid plugging technology at home and abroad, a gel plugging system for oil-based drilling fluid is studied. The related components of the gel system were studied by IR, X-ray diffraction and scanning electron microscopy. The results showed that the binding agent was successfully synthesized. The high temperature and pressure curing kettle was used for curing. The compressive strength of the gel plugging system could reach 3.2 MPa by using the pressure tester. The laboratory tests showed that the rheological properties of the gel were good, the density was adjustable (0.77-1.3 g/cm3), the gel strength was adjustable (1.7-3.2 MPa), and the gel system and the oil-based drilling fluid system had good compatibility, adding 2 to the gel plugging system. The compressive strength of 0 oil-based drilling fluid can also reach 1.8MPa. Field application shows that the compressive strength of gel plugging system for oil-based drilling fluid can reach 6.8 MPa, which perfectly displays the excellent plugging effect of gel plugging system and has broad application prospects.
Crack Width Prediction Model Based On Optimized BP Neural Network
HE Tao, XIE Xiantao, WANG Jun, ZHAO Yang, SU Junlin
2021, 38(2): 201-206. doi: 10.3969/j.issn.1001-5620.2021.02.012
The problem of fractured well loss is a serious threat to the safety and progress of drilling production. At present, the success rate of field plugging is relatively low one of the important reasons is that the fracture width cannot be accurately predicted, and the limitations of fracture width cognition make it difficult to determine the plugging method and material particle size. Therefore this paper puts forward to use the improved BP neural network method to establish the prediction model of lost circulation fracture width in order to solve the problem of fracture width prediction. Firstly, according to the analysis of variance method, the related parameters that affect the crack width are determined which are input into the improved BP neural network model for training, and the accuracy is verified by the sample data prediction. Finally, the slope of the fitting straight line of the test set data is 0.8772, and the intercept is 0.0206. In addition, in order to confirm the stability of the model, the performance of the crack width prediction model is evaluated, and the model's determination coefficient (R2) is 0.89, the average absolute percentage error (PCC) is 0.82, and the root mean square error (RMSE) is 1.35, which proves that the performance of the model is excellent. Finally, the field engineering data is used for example prediction. From the results, it can be seen that the model has high prediction accuracy and can provide better assistant decision-making in plugging engineering operation.
Research on Plugging Technology of Shale Gas Oil-Based Crosslinking Solidification
LIU Wei, MAO Lijun, OUYANG Wei
2021, 38(2): 207-211. doi: 10.3969/j.issn.1001-5620.2021.02.013
Shale gas stream the dragon group, mainly using oil-base drilling fluid microfracture stratum itself development, drilling fluid density is high, easy to generate induced cracks, oil-base drilling fluid leakage occurs, produce the huge economic losses, at home and abroad research on mechanism of oil-base drilling fluid leakage is less, oil-base drilling fluid plugging material varieties for a single, technology is not mature,Oil-based plugging has become a technical problem at home and abroad.The characteristics and mechanism of oil base drilling fluid loss in Longmaxi Formation were studied and analyzed. According to the mechanism of oil base drilling fluid loss, two kinds of cross-linking curing plugging agents CQ-HM1 and CQ-HM2 at different temperatures were developed to form the formula of oil base drilling fluid cross-linking curing plugging slurry. The formula was cured within 70-90 min at 100-150 ℃.The sealing effect is achieved, and the bearing capacity of the 5 mm joint plate is more than 6.0 MPa.Finally, the oil based drilling fluid crosslinking solidification plugging technology was formed.
Development of a Device for Evaluating Lost Circulation Materials at High Temperature High Pressure
YAN Junfeng, WU Jinsheng, JIANG Bing, WANG Yongming, LIU Jianjun
2021, 38(2): 212-217. doi: 10.3969/j.issn.1001-5620.2021.02.014
A device (Model DL-3A) used for evaluating the performance of lost circulation materials at high temperature and high pressure was developed to simulate the deep sea HTHP working environment in which mud losses occur and are being stopped. Relevant literatures at home and abroad were consulted when determining the structure and working principle of the device. This paper explains the operating procedures and the major operating parameters of the device. Test of the device were performed using two bridging LCMs. The test results showed that the testing container and the testing modules of the Model DL-3A device can be heated to 260 ℃ and maintain this temperature, the plugging and flowback pressures can reach and maintain at 10 MPa or higher, indicating that the Model DL-3A device can be used to simulate the HTHP conditions encountered in deep water drilling. The testing results of lost circulation materials with this device can provide a certain reference for performing mud loss control in field operations.
Design and Performance of a Slow-Release Self-Gel-Breaking Completion Fluid for Multilateral Wells
LI Chao, HUANG Yue, LIU Gang, LUO Jiansheng, XU Mingbiao, YOU Fuchang
2021, 38(2): 218-225. doi: 10.3969/j.issn.1001-5620.2021.02.015
Slow-release self-gel-breaking completion fluid for multilateral wells is a new kind of wellbore working fluid. With its special self-gel-breaking capacity in reservoir, this completion fluid helps avoid conventional acid jobs and gel-breaking operation in well completion, and is thus an important technology linking the acid job with subsequent open hole gravel packing. In laboratory study, based on the reservoir characteristics of the multilateral wells in block Enping in Nanhai Oilfield, the design principle of the slow-release self-gel-breaking completion fluids was analyzed, the flow pattern regulator high pyruvate xanthan gum was selected and characterized, and the gel-breaking capacity and reservoir protection performance of the slow-release self-gel-breaking completion fluid was examined. The study showed that the method of designing the low-release self-gel-breaking completion fluid was established based on the structure-function relationship between the core additive xanthan gum and the self-gel-breaking performance of the completion fluid, combined with the gel-breaking and gel-protection synergistic effect. The molecular weight of the synthesized xanthan gum modified with pyruvic acid is 8.06×106, and the content of pyruvate in the modified xanthan gum molecule is as high as 7.9%. Compared with conventional xanthan gum, the high pyruvate xanthan gum has conformation transition temperature and thermal stability that are both significantly reduced, and has no temperature threshold, rendering the high pyruvate xanthan gum better slow-release degradation property. For the slow-release self-gel-breaking completion fluid formulated, the self-gel breaking was adjusted through the combined use of high pyruvate xanthan gum and gel-protection agents, and the time for the self-gel-breaking was controlled between 5 days and 17 days. Blocking of pores of reservoir rocks was eliminated after gel-breaking of the completion fluid, and the average percent permeability recovery of cores taken from reservoir rocks can be as high as 90.36%±0.23%, proving that the slow-release self-gel-breaking completion fluid has good reservoir protection capacity.
Study On Intelligent Gel Breaking Completion Fluid System In Offshore Oil-Gas Field
WEI Yusen, XIONG Youming, ZHOU Shusheng
2021, 38(2): 226-230. doi: 10.3969/j.issn.1001-5620.2021.02.016
For the development of heavy oil reservoirs in offshore oil and gas fields, the fish bone spur branch well technology was adopted, and the completion fluid in the branch well filling process cannot be gel-broken, so that gravel pack operation cannot be effectively implemented in the branch well. Therefore, an intelligent gel breaking completion fluid system was developed. Using the completion fluid of xanthan gum modified by succinic anhydride to solve the problem. Controlling the addition of succinic anhydride and reaction time to determine the substitution degree of succinic ester group. Alcohol hydroxyl was replaced by succinic anhydride in xanthan gum, it can reduce the ability of inhibiting oxidative free radicals, reduce the stability of xanthan gum, and solve the problem about difficultly breaking completion fluid. To achieve the purpose of intelligent gel breaking the gel-breaking time of completion fluid was regulated by optimizing the dosage of NaOH, Na2CO3 and antioxidant. Breaking time of the completion fluid prepared by XC-2 was controlled within 3-8 days. Breaking time of the completion fluid prepared by XC-1 was controlled within 5-14 days. The recovery values of reservoir permeability were all greater than 89% before and after the gel breaking of completion fluid prepared by XC-1 and XC-2, which had good protection effect to the reservoir.
Corrosion Inhibitive Cement Slurry and Supporting Techniques for Cementing the Luohe Aquifer in Changqing Oilfield
MIN Jiangben, LIU Xiaoli, WAN Xiangchen
2021, 38(2): 231-236. doi: 10.3969/j.issn.1001-5620.2021.02.017
Corrosion of the cement sheath sealing off the Luohe aquifer has caused the permeability of the cement sheath to increase, resulting in severe corrosion of the casing string in the aquifer section. Corrosion boring in the casing string has resulted in problems such as increase in the water cut of the produced fluid, low utilization of water flooding from water injectors and maladjustment of the injection and production well pattern. To solve the corrosion problem, an epoxy emulsion nonpenetrating agent and a corrosion inhibitor formulated with an anti-rust agent and a bacteria inhibitive agent, were mixed with conventional oil well cement. In this way the corrosivity and permeability of the cement slurry can be reduced, and hence corrosion to the casing string be mitigated. It was found in testing the permeability of the cement slurry samples that when a low-density cement slurry was treated with 10% nonpenetrating agent and 2% corrosion inhibitor, the permeability of the set cement was reduced from 0.075 mD to 0.021 mD. When a cement slurry of normal density was treated with 10% nonpenetrating agent and 2% corrosion inhibitor, the permeability of the set cement was reduced from 0.041 mD to 0.0009 mD. Experiment on the corrosion resistance of the set cement showed that when a cement slurry was treated with 10% nonpenetrating agent and 2% corrosion inhibitor, the corrosion resistance of the set cement was increased by a factor of 6, meanwhile, compared with the untreated conventional cement, the thickening time of the treated cement slurry and the compressive strength of the treated set cement were kept unchanged. A set of optimized operating tools and measures were used with the treated cement slurry in oil well cementing operation. The cement slurry and the supporting techniques have provided a powerful means of dealing with corrosion inhibition for the Luohe aquafer.
Study and Application of Evaluating the Performance of Cement Slurries Under Dynamic Complex Pressures
LI Zhiheng, ZHANG Xiaocheng, XIE Tao, LI Jin, ZHANG Yuchen
2021, 38(2): 237-242. doi: 10.3969/j.issn.1001-5620.2021.02.018
A comprehensive method for evaluating the anti-channeling performance of cement slurries under dynamic complex pressures was developed for the purpose of improving the job quality of cementing adjustment wells under dynamic complex pressures and satisfying the requirements of performing well cementing without interrupting water injection job nearby in the Bohai oilfield. This evaluation method involves three devices, which are a self-developed device for evaluating the performance of resisting dynamic water dispersion, a device for evaluating the anti-channeling performance of interfaces between cement sheath and casing string/borehole wall, and a device for measuring the volume of plastic materials. This method can be used to evaluate the performance of a cement slurry aimed at dealing with difficulties such as disordered and complicated pressure system, low quality of pay zone cementing job and poor isolation between different pay zones. A new anti-channeling cement slurry was developed based on the evaluation and optimization of anti-dynamic water dispersion agents, expanding agents, toughness enhancers and cement retarders etc. The development of this new cement slurry was aimed at dealing with problems encountered in cementing wells affected by the dynamic pressure system in the Bohai oilfield. Compared with the cement slurries used in this oilfield, the set cement of the new cement slurry had compressive strength that was increased by 18.6%, bonding strength increased by 28.7%, pressure to resist water channeling increased by 60.8%. This new cement slurry has also been used in four wells in the Penglai oilfield, and the well cementing job quality was enhanced by 22.3%-37.5% over the job quality of cementing performed previously. Field application of the new anti-channeling cement slurry has indicated that it has excellent anti-channeling capacity, and is able to greatly improve the well cementing job quality of adjustment wells drilled in formations with complex pressure system. This new cement slurry helps realize well cementing without interrupting water injection operation, and has broad prospects of application in the future.
Damage Evaluation of Perforated Cement Sheath and Study on Fracture Propagation Law
ZHANG Xiaocheng, LI Jin, HAN Yaotu, ZHANG Qilong, LIU Peng
2021, 38(2): 243-248. doi: 10.3969/j.issn.1001-5620.2021.02.019
In order to further improve the mechanical integrity of cement sheath in the process of perforation, fracturing and filling completion or hydraulic fracturing, and meet the requirements of completion and stimulation operation for cement sheath integrity. Aiming at the damage of cement sheath under perforating impact, perforation shooting test is carried out, and the relationship between perforation cement sheath damage and perforator and cement sheath performance under simulated temperature and pressure conditions is analyzed. Combined with the structure of perforating charge, the numerical model of cement sheath damage under perforating impact load is established. The cumulative plastic strain rate and maximum deviator stress are taken as the key indexes to form the quantitative evaluation technology of perforating cement sheath impact damage. Based on the fluid solid coupling theory and fracture propagation mechanics theory, a numerical analysis model for fracture propagation of cement sheath with non-mean characteristics is established. The damage of cement sheath and fracture propagation law during fracturing are studied according to the four states of initial crack of perforated cement sheath. The research conclusion can provide feedback guidance for perforation parameter optimization, cementing design optimization and fracturing completion operation optimization, and improve the mechanical integrity of cement sheath in reservoir perforation section, which is of great significance to ensure wellbore safety and prolong the life of oil and gas wells.
Study and Application of a High-Performance Salt-Resistant Cement Slurry
DAN Meihan
2021, 38(2): 249-254. doi: 10.3969/j.issn.1001-5620.2021.02.020
High-pressure salt and gypsum beds prevail in the Missan Oilfield in Iraq. In well cementing, tight hole resulting from the creeping of salt layers, increasing salinity of cement slurries from hole washout and salt dissolution, narrow drilling window and reduced displacing efficiency pose challenges to the well cementing jobs. Cement slurries formulated with semi-saturated NaCl solution and 3%-5% KCl solution are widely used presently and have the shortages of low compressive strength of set cement and poor bonding between casing string and cement sheath and between cement sheath and bore hole wall. To solve these problems, a cement slurry was formulated with a slat solution containing 25% NaCl and 5% KCl, and other additives of choice, such as filter loss reducer, dispersant and retarder. As a high-performance salt-resistant cement slurry, it is free from the high rheology and high thixotropy previously encountered when cement slurries are brought into contact with salt. Laboratory study showed that this cement slurry is able to inhibit the dissolution of salt. A cement slurry of 2.39 g/cm3 can be made with only 30% hematite at a minimum, which not only saves money, but also greatly improves the compressive strength of the set cement. The 24-hour compressive strength of this cement slurry is 48 MPa, almost doubling the compressive strengths of the set cement of cement slurries presently in use. The 24-hour compressive strength of the cement slurry being contaminated is still greater than 14 MPa. These characteristics of the new cement slurry satisfy the needs of cementing the salt and gypsum beds in the Missan Oilfield, Iraq, making the cement slurry worth spreading in this oilfield.
A New Weakly Acidic Drag Reducing Viscosity Reducer
AN Shaohui, LU Haichuan, TIAN Dongcheng, FENG Wangsheng, GAO Jichao, LIU Yanjun, YAN Yubo
2021, 38(2): 255-258. doi: 10.3969/j.issn.1001-5620.2021.02.021
Synthetic polymers, because of their high temperature resistance, high salt-resistance and versatility, have long been the leading material of cement additives. Cement slurries treated with high molecular weight polymers generally have high consistency and their rheology is difficult to adjust. Conventional drag reducers are unable to deal with this high rheology effectively. To solve this problem, a new weakly acidic drag reducing viscosity reducer was developed based on microstructure design and selection and compounding of raw materials. Laboratory evaluation of the drag reducing viscosity reducer showed that it can significantly reduce the viscosity of cement slurries treated with synthetic polymers as the main additives; the percent reduction of the apparent viscosity was at least 40%, significantly improving the rheology of cement slurries and imposing no negative effects on the thickening and strength development of cement slurries. Cement slurries treated with the viscosity reducer have ratios of thickening time of 1.0-2.0, and ratios of compressive strengths at least 0.9, demonstrating good general performance.
Study on Neutral Integrated Slick Water System for Acidification and Fracturing
YAO Erdong, WU Guodong, ZHAO Longhao, MELJEM Guli Anweier, LIU Yanchi, ZHOU Fujian
2021, 38(2): 259-264. doi: 10.3969/j.issn.1001-5620.2021.02.022
After conventional fracturing operations, acidification is usually used to relieve the damage of the reservoir. There are many operating steps and poor economic performances. The development of a liquid system that can realize both fracturing and acidification has practical significance. In this paper, a class of neutral and water-soluble lipids with the ability to produce H+ ions were selected. The effective generating H+ concentration and the carbonate dissolution rate of these self-generating acids under different temperature and concentration conditions were measured. Then the optimized self-generating acid was combined with slickwater to form a new neutral integrated slickwater system with acidification function. The frictional drag tester and pressure conduction experiment are used to study the drag reduction, scale inhibition and damage relief capabilities of the system respectively. The research results show that self-generating acid does not generate acid at room temperature, and has obvious slow-rate acid generation capacity at reservoir temperature. The final generating acid concentration is as high as 8% equivalent hydrochloric acid, and the ability of dissolving carbonate rock is 0.41 g/mL. The compatibility of optimized self-generating acid and slick water is good, and the drag reduction rate reaches 72.3%. The pressure conduction experiment shows that traditional slickwater produces 34.8% of the reservoir damage. In striking contrast, this new fracturing fluid not only produced no damage, but also improved permeability of the treated core as high as 29.9%. The new fluid proved the obvious integrated stimulation effect of acidification and fracturing.