Study On Fracturing Technology Of Coalbed Methane Well In Leping Formation Of Dianqianbei Depression

Coalbed methane reservoirs in China have the characteristics of low gas saturation,low permeability and low pressure because of the strong structural damage and the development of structural coals after the period of coal-forming.Because coalbed methane reservoir not only has relatively high in-situ stress,but also has a very strong heterogeneity,it is necessary to adopt stimulation treatment to achieve the value of commercial exploitation.Based on investigations of a large number of literatures at home and abroad,this paper aims to analyze the geological characteristics of the target field,optimize the fracturing fluid system,figure out the fracturing technology of the target field and investigate the reusability of the produced water.The main achievements and understanding are as follows:(1)The rock of Leping coal Formation in southern Sichuan has strong hydrophilicity and well-developed fractures,and thus there are potential risks of water-sensitive,velocity-sensitive,alkali-sensitive and acid-sensitive damage.It is found that pulverized coal particles are easy to migrate and have strong speed sensitivity.And it is also found that coal powders have a significant negative effect on the conductivity of proppant filling layer.The three direction geostress is closer to the target layer,and there is an inclined crack state which changes horizontal cracks to vertical joints.In the six blocks that we have been studied,the gas prodcution in the area of Wu De block is lower than that of other blocks.(2)Foam fracturing fluidwith the characteristics of less liquid content,less filtration,good proppant carrying performance and strong flowback capability is suitable for coalbed methane wells.However,natural macromolecules,polymers as well as cationic surfactants can not be used in the coalbeded methane.The fracturing fluid had no side effect on the isothermal adsorption performance of the coal powders.The potassium chloride had the best anti swelling effect on bentonite but had little effect on the swelling resistance of pulverized coal.The employment of pulverized coal dispersant is better in the field and deserves to be used.(3)According to the fracturing operation data of the target well area,the fracturing technology,operation parameters and drainage production data of the connected area were analyzed carefully.And summary table for the fracturing technology,operation parameters and drainage production data of each well were drawn.By comparing and analyzing the area,well type,fracturing mode,pad fluid ratio,maximum fluid displacement,sand proportion,average sand ratio,maximum sand ratio,fracturing operation curve type,fracture pressure gradient,pump shutdown pressure gradient,drainage gas breakthrough time,the effect of 0.6+fracturing aid used in the general fracturing well was relatively good and the effect of 2013 mode fracturing used in separate pressure production well proved to be quite good.(4)By qualitatively and quantitatively ananlyzing the ion species,amount,impurities,scaling tendency and other factors,measuring water quality,doing data analysis and scaling trend prediction for backflow liquid,the results are as follows:there is calcium carbonate scaling in the backflow fluid,but there is no calcium sulphate scaling.If water would be reused in the formation,the procedures of pre precipitation and two stage fine processing are necessary to reduce the risk of scaling.Based on the analysis of engineering geological characteristics,reservoir protection technology of Leping formation coalbed methane,the evaluation of fracturing operation,the performance of post-fracturing and fracturing effect in coalbed methane wells,systematic and comprehensive evaluation research and design optimization for coalbed methane well fracturing technology in Leping formation were completed.It provides technical support for fracturing reconstruction,material selection,fracturing fluid compatibility and evaluation and later drainage of coalbed methane reservoir.And it also provides coal seam fracturing technology for the exploration and development of CBM in Yunnan Guizhou Sichuan Basin,which has important application value and practical significance.