Evaluation Methods and Engineering Application of the Feasibility of “Double Sweet Spots”in Shale Gas Reservoirs

The determination of“double sweet spots”(the geological and engineering sweet spot) in shale gas reservoirs is an effective method to determine whether it economically worthy of drilling, and the quantitative study of“double sweet spots”is also conducive to the optimization of drilling and fracturing, hence improving the development efficiency of shale gas. In view of the problems of numerous sweet spot parameters and low accuracy of sweet spot evaluation, the main sweet spot parameters were optimized by using the correlation coefficient method, whereby the independent weight coefficient method was adopted to quantitatively characterize both the geological sweet spot and the engineering sweet spot. Taking the strata of Jiaoshiba Block in the Fuling Shale Gas Field as the research object, five primary geological sweet spot parameters and four primary engineering sweet spot parameters were selected. The correlation coefficient of geological sweet spot was 0.89, and that of engineering sweet spot was 0.85. The research results showed that the“double sweet spots”and fracturing ability of shale gas could be used to optimize drilling and fracturing layers, horizontal drilling azimuth and casing engineering safety management. On this basis, the positive role and advantages of horizontal drilling azimuth optimization for casing safety and large volume fracturing as well as determining fracability in shale gas reservoir were analyzed and deemed feasible.