Evaluation of sweet spots and horizontal-well-design technology for shale gas in the basin-margin transition zone of southeastern Chongqing, SW China
Xipeng He, Peixian Zhang, Guisong He, Yuqiao Gao, Ming Liu, Yong Zhang, Dazhi Fang, Yanjing Li
Abstract
The shale gas accumulation conditions in the basin-margin transition zone of southeastern Chongqing in SW China are complex. In order to improve single-well productivity in this area, the geologic characteristics, major factors controlling the occurrence of sweet spots, and drilling/fracturing optimization were investigated in this study. The sweet spot evaluation system and criteria were established, and the horizontal-well-design technology was developed. The following three conclusions were drawn. First, the accumulation and high-productivity-oriented approaches for sweet spot evaluation are proposed and the criteria are established based on screened key indicators. Second, the horizontal well was designed based on: (1) the “six-map” method, to identify both the geology and engineering sweet spots for well locations; and (2)seismic attributes, to predict the development of fractures and cavities, and thus, avoid mud loss and improve the drilling efficiency. The target window, well-azimuth optimization, and the curvature were forecasted to improve the fracturing performances. Third, the Pingqiao anticline, Dongsheng anticline, Jinfo slope, and Wulong syncline were selected as Type I sweet spots. Currently, shale gas has been successfully discovered in the basin-margin transition zone and is being commercially developed.