Shale gas sweet spot identification and GEO-steering drilling of Doushantuo Formation in Well Eyangye-2HF： Drilling practice and method of the world''s first shale gas horizontal well in Doushantuo Formation of Sinian

Abstract:

To evaluate the resource potential of the Lower Sinian Doushantuo Formation shale and determine the lower limit of the shale productive horizon， this study focused on the Well Eyangye-2HF. Utilizing drilling data from the nearby Well Eyangye-1 （located 18 m from the Eyangye-2HF wellhead） and integrating multidisciplinary analyses in geology， geochemistry， geophysics， and rock mechanics， the shale gas sweet spots were identified， and geological steering methods were successfully applied within a complex structural setting. The high-quality shale thickness of the second member of the Doushantuo Formation in this well is 130.5 m. Revealed a maximum total gas anomaly of 10.32% during coring， with a cumulative thickness exceeding 2% gas content measuring 105 m. The TOC peaks at 2.57%， with an average exceeding 1.5%. The maximum desorbed gas content is 2.21 m3/t， while the maximum total gas content reaches 4.82 m3/t. This high-quality shale interval is subdivided into 10 sub-layers. Based on a comprehensive consideration of gas-bearing properties， drillability， and fracturability， the Layer 7 in the second member was identified as the optimal sweet spot. By employing precise 2D seismic interpretation and geo-steering modeling， the wellbore trajectory was effectively controlled through timely adjustments during horizontal geo-steering， significantly improving the drilling encounter rate of the sweet spot. Well Eyangye-2HF is the world''s first horizontal shale gas well drilled in the Sinian Doushantuo Formation. The horizontal section spans 1410 m and was stimulated and tested in 23 stages. The well achieved a high-yield gas flow with a stable production of 55300 m3/d and an open flow potential of 198200 m3/d. This achievement effectively defines the lower limit of the shale gas production horizon and opens up new frontiers for shale gas exploration and development.