Risk Mitigation Strategy Improves Drilling Performance of Shale Gas Horizontal Wells

摘要

The shale revolution has extended the life cycle of the oil and gas industry,promoted the growth of global oil and gas reserves and production,and changed the energy's strategic pattern of various countries.At present,the national shale-gas demonstration area of PetroChina Changning and Weiyuan is in the stage of large-scale production.Horizontal well and hydraulic fracturing are two key technology that have proven to provide an effective way to economically develop medium to high maturity shale gas resources.However,due to geological complexity of the shale-gas demonstration area,and the lack of robust analysis and research on overpressure mechanism and wellbore instability characteristics,drilling events such as stuck pipes,lost circulations and inflows occurred frequently during horizontal well drilling.These nonproductive events greatly restricts the wellbore construction cycle time and the production of shale gas reservoir.A comprehensive geomechanical study was carried out from which the three pressure profiles required for drilling,i.e.,pore pressure,collapse pressure and fracture gradient,are established.The study also clarified the spatial distribution of overpressure across the field.The improved pore pressure and geomechanical understanding of the field provides the necessary inputs for an integrated,multi-disciplinary approach carried out during pre-drilled analyses,real-time monitoring and post-drilled evaluation to manage the stability of horizontal wells.The safe mud weight window derived from geomechanics provides the basis for mud weight and mud formulation designs that can be continuously optimized to improve wellbore stability and reduce drilling risks.The integrated approach has been applied for 4 horizontal wells in Weiyuan's shale gas field.One of the wells,Wei202-H34-3,has the horizontal section length of 2500m,making it the longest horizontal section recorded in the block.Drilling performance analyses of the well showed that the overall drilling risk,the wellbore construction time,and the drilling costs were substantially reduced by optimizing the drilling operations through geomechanics integrations and applications.The experience and knowledge obtained from this integrated workflow will provide guidance and serve as reference for the efficient development of unconventional oil and gas reservoirs in China.