Evaluation of sweet spots and horizontal-well-design technology for shale gas in the basin-margin transition zone of southeastern Chongqing, SW China

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.

Keywords

• Normal-pressure shale gas
• Evaluation of sweet spots
• Horizontal well design
• Wufeng–longmaxi
• Southeastern Chongqing