Experimental Research On High-Performance Water-based Drilling Fluid For Horizontal Drilling Of Shale Gas In West Hubei

The 1^st shale gas well of Yichang,Hubei,was deployed and implemented by the China Geological Survey in May 2017.It received 60,200 m³/day and unimpeded flow of123,800 m³/day in the Cambrian Shuijingtuo Formation.The high-yield shale gas flow was the major discovery of the world's oldest shale gas reservoir in the Sinian Doushantuo Formation.The situation is expected to form a new shale gas resource base.At present,the main problems in the efficient development of shale gas in the Shuijingtuo Formation in western Hubei are listed as follows.Oil-based drilling fluid is widely used in the development of shale gas resources at home and abroad,which has problems with the high cost and high pollution.The exploration and development of shale gas resources in western Hubei is still in its infancy,and there is a lack of literature on the shale reservoirs and drilling processes of the Cambrian Shuijingtuo Formation.Therefore,it is necessary to develop high-performance water-based drilling fluid technology for the Shuijingtuo shale in the Western Hubei Province.Based on the analysis of the physical and chemical characteristics of the Cambrian Shuijingtuo shale of western Hubei Province,the factors affecting the wettability of shale are studied,and the simulation of the nanopore of shale is carried out.The selection of water-based drilling fluid agent was also discussed.Based on the electrical inhibition and wettability control methods,the formulation of SWDF high-performance water-based drilling fluid suitable for the Shuijingtu Formation shale in western Hubei Province was obtained combined with the previous research results.The thesis introduced the research purpose and significance,the research status,the research content,research objectives and research methods.Then,the mineral composition analysis,microstructure analysis and compressive strength experiments of the Shuijingtuo samples were carried out based on the information of shale rock samples,which was to lay the foundation for later shale wettability research and drilling fluid treatment agent selection.Then,the thesis explored the influence of pH,salt solution,positive gel,temperature,surfactant and shale surface roughness on the wettability of shale.The purpose was to lay the foundation for the method of enhancing the wellbore stability by controlling the wettability?specifically,making the shale exhibit hydrophobicity?.CFD?Computational Fluid Dynamics?and DEM?Discrete Element Method?method were used to simulate nanoparticle suspension on the microscopic scale to block shale pores.The motion law of the nanoparticles and the real-time blocking image could be obtained by CFD post-processing.Particle trajectory and plugging efficiency can be obtained by post-processing of the models.The UDF program was written in order to ensure the rationality of the simulation results,and the dragging force could be used to modify the standard drag curve by using experimental data and empirical formulas.The research results in this chapter can lay a theoretical foundation for the introduction of nanomaterials in the drilling fluid system.Next,screening tests were conducted to evaluate and optimize the slurry,clay,nano-materials,positive gel and fluid loss additive of water-based drilling fluid,and it laid a technical foundation for the later development of high-performance water-based drilling fluid.As a result,a high-performance SWDF for the Shuijingtuo Formation shale in western Hubei Province was obtained combined with the previous research results and based on the electrical suppression and wettability control methods.Finally,the main conclusions,innovation points and ideas for the next step was proposed.The main conclusions werec concluded as follows:?1?The shale of the Shuijingtuo Formation was mainly composed of minerals such as quartz,feldspar and calcite,with the content of 55%⁶7%.The clay mineral was mainly illite,with the content of13%²7%,no montmorillonite.Expansive formation,pores and micro-cracks on the surface of shale provided a natural channel for the intrusion of drilling fluid.There is obvious anisotropy in the Shuijingtuo shale.?2?The affecting discipline and function mechisms of pH,salts,positive gel,temperature,and surface roughness of shale on shale's wettability was investigated.The optimal value of these parameters was also determined.?3?Surfactants combination that can effectively enhance the hydrophobicity of shale was proposed.The contact angle was up to 100.7°after soaking in the composite surfactant,which played a major role in the polytetrafluoroethylene concentrate;?4?The process of simulating nanopores suspension to block shale pores on a microscopic scale was proposed with CFD and DEM methods.Particle size and concentration were the major factors influencing plugging efficiency.At particle concentration of 1 wt%and 3 wt%,a solution having a viscosity of 5 mPa·s had a blocking efficiency of 16.26%and 8.55%with respect to a solution having a viscosity of 1 mPa·s;?5?The formula of SWDF high-performance water-based drilling fluid for the Shuijingtuo Formation shale in western Hubei Province was obtained based on the electrical inhibition and wettability method and the previous research results.The comprehensive evaluation results show that the viscosity and shear force of the drilling fluid is consistent with the shale horizontal well water base.The API filter loss was only 7.2 mL,friction coefficient was 0.21.It had a low cost of 912 RMB/m³.The drilling fluid could resist 120°C high temperature,it had good inhibition and good anti-pollution ability.The main innovations are listed as follows.?1?CFD and DEM methods were used to simulate the process of nanoparticle suspension blocking shale pores on the microscopic scale,and studying the shale plugging efficiency of nanomaterial particle size,concentration and fluid viscosity.The influence has laid a theoretical foundation for the introduction of nanoparticles in the drilling fluid system.?2?On the basif of physical&chemistry?containing wettability?properties of the Shuijingtuo shale,a high-performance water-based drilling fluid for horizontal well drilling in shale gas in the region was systematically studied based on physical plugging by nanoparticles,wettability control,electrical suppression and nanoparticles sealing theory.This achievement could lay a technical foundation for the efficient development of shale gas resources in the region.In the next step,on the basis of the previous research,the on-site test of high-performance water-based drilling fluid technology will be carried out in western Hubei,and the system will be improved according to the test results.It lays a technical foundation for the efficient development of shale gas in the western Hubei and even the middle reaches of the Yangtze River.