Discussion on Low-Cost Drilling Technologies of Normal Pressure Shale Gas in the Outer Margin of the Sichuan Basin

The shale gas reservoirs on the outer margin of the Sichuan Basin have a pressure coefficient of 0.90-1.20,which belongs to the normal pressure shale gas reservoirs and are developed by high-pressure shale gas drilling technology.The cost of per unit gas production is high,which hinders the economic development of shale gas.Therefore,according to the analysis on the differences between the drilling of normal pressure shale gas and high pressure shale gas reservoirs,the low-cost drilling technologies were discussed taking into consideration the casing program,wellbore trajectory design,wellbore trajectory control,drilling fluid and cementing processes.The low-cost drilling technologies and associated measures (i.e.,optimizing the tri-section casing program into the dual-section one,designing the wellbore trajectory with dual-2D model,controlling the second section wellbore trajectory with rotary steering technology,using the low oil-water ratio oil-based drilling fluid,and adopting the low-cost supporting technologies and measures like production casing cement top optimization,etc.) were proposed to provide technical supports for the economic development of normal pressure shale gas reservoirs in the outer margin of the Sichuan Basin.