Study And Application Of Shale Gas Fracuring Fluid In Changning Weiyuan Of Sichuan

Shale gas has gradually become the main contributor to the natural gas produCion growth in China.It plays an important role in alleviating the supply-demand contradiCion of natural gas,adjusting and optimizing energy struCure,and guaranteeing the sustained,healthy and high-speed development of national economy and social environment.In 2010,the state launched the first round of shale gas exploitation in Changning-Weiyuan shale gas development demonstration area.Because the shale gas wells in Sichuan are mostly located in densely populated hilly and mountainous areas,where land and water are short,it is difficult to realize large-scale economic development and there are no former experiences both domestically and internationally.Therefore,this dissertation focuses on the research and application of fraCuring fluids for the development of Sichuan Changning-Weiyuan shale gas resources,and carrying out the study based on the charaCeristics of Sichuan shale gas reservoir.Successful stimulation of shale gas formation requires injeCing a large number of fraCuring fluids with low viscosity at high pumping rates,which tends to form turbulent flow without a drag reducer.In this study,polyacrylamide drag reducers with viscosity-average molecular weights in the range of 1.5×106?1.7×106 were synthesized throggh free radical polymerization and solution polymerization.By incorporating the drag-reducing technology of the drag-reducer,micro-emulsion surfaCant technology,anti-swelling technology,and baCericidal technology,a slick water system was formed,together with a complementary guar fraCuring fluid system and a conventional acid system developed.The developed slick water can be continuously mixed and used with different surface water and groundwater in Sichuan.The drag reduCion efficiency is 73%-78%.In view of the great difference between the laboratory friCion data and the field operation,the laboratory can not guide the field operation,a modified praCical pipe diameter model has been firstly established in the world.The model shows,when the slope of reff and v ratio measured in the laboratory versus that measured in the field is between 0.02704 and 0.05093,the modified praCical pipe diameter model can prediC the drag reduCion efficiency,and the general formula for prediCing the drag reduCion rate is DR=0.94 mvn.In view of the technical bottlenecks of large-scale volume fraCuring,such as the large volume of flowback water,difficult water treatment process,and the supply shock of water resource,a low-cost and easy-to-operate recycling process of flowback water has been formed.When the salinity is?3×104mg/L,local ponds and sewage tanks in the field are used to settle the impurities in the discharged liquid through a long period of static storage.Then the supernatant is taken to mix with fresh water and treated with additives to make the performance of the flowback water meet the requirements of slick water.When the salinity of the flowback water is<3×104mg/L,the supernatant is direCly treated with additives for slick water reuse.Because Sichuan shale gas resources are located in mountainous areas and water resources are scarce,waterless fraCuring fluid has been widely used in the field abroad.It is necessary to carry out research on waterless fraCuring fluid.The formulation of high temperature resistant liquefied petroleum gas fraCuring fluid and the performance evaluation method of liquefied petroleum gas fraCuring fluid were developed for the first time in China.The LPG fraCuring fluid shows good heat and shear resistance performance,the maximum resisting temperature is up to 134.1?,The viscosity is 200mPa·s,when the LPG fraCuring fluid is heated to 90?,and sheared at 170s-1 for 1.5h.Using sodium acetate as gel breaker,liquefied petroleum gas fraCuring fluid can be completely brokel into liquid at 90?.LPG has little damage to shale core,the permeability regain is 96.97%.The evaluation method of liquefied petroleum gas fraCuring fluid rheological properties,damage performance and gel breaking performance has been formed.The work accomplished in this dissertation have developed and improved the theory of fraCuring fluids for shale gas stimulation,which is of guiding significance for fraCuring this kind of reservoirs.The slickwater,cross-linked gel,linear gel,and conventional acid system were used in 11 wells in Changning-Weiyuan National Shale gas Demonstration Area.The cumulative wellhead test produCion reaches 123.23×104m3/d.