Study On Candidate Selection And Parameters Optimization For Secondary Fracturing Of CBM

Shanxi Qinshui basin is rich in CBM resources,and it is the region with the best CBM development scale and benefit in China.Because of the characteristics of low porosity,low permeability and low pressure,hydraulic fracturing is the main technology to obtain industrial gas flow.After years of production after the first fracturing,the number of inefficient wells gradually increases,and the overall gas production decreases.Therefore,it is urgent to conduct the secondary fracturing to improve the productivity.Taking the Shizhuang south block of Qinshui basin as the target,through the study of reservoir geological characteristics,this paper proposes that the secondary fracturing is not easy to produce induced steering fractures,and temporary plugging agent should be used to make the secondary fractures turn,so as to improve the effectiveness of refracturing.Through the analysis and calculation of the parameters affecting the fracability of coal bed by using the grey correlation method,the fracability index calculation model is established.It is found that this block has good fracability,and the fracability index can be used to select the "sweet spot" for secondary fracturing Through the analysis of secondary fracturing test in the early stage,12 key parameters of candidate selection for secondary fracturing are proposed.Based on the method of hierarchical cluster analysis,a candidate selection model for secondary fracturing of CBM is constructed,and the target wells are selected.Numerical simulation of gas reservoir and fracture simulation method are used to optimize the fracture and construction parameters of secondary fracturing in the block.The oilfield application shows that the effect of increasing yield after re-fracturing is remarkable,which indicates that the method of candidate selection and the optimized design proposed in this paper is feasible.