Geomechanical Evaluations of Deep Shale Gas Reservoir in Sichuan Basin,Western China

摘要

A large shale gas reserve has been discovered in the deep Longmaxi reservoir in Sichuan basin,western China,which is anisotropic,tectonically stressed,largely naturally fractured,and under complex geological structure.Successful development of the deep shale gas resources relies on placing suitable hydraulic fractures right into the reservoirs.To achieve this,the application of geomechanics plays a critical role in determining the anisotropic mechanical properties and subsurface stress field,identifying favorable stimulation intervals for landing,optimizing stimulation of horizontal wells,and predicting dynamical behavior of the natural fracture network during drilling and stimulation.To gain an in-depth understanding of the anisotropic mechanical properties and in-situ stresses of the deep shale gas reservoirs and to best serve the need for field applications,comprehensive geomechanical evaluations were conducted.As the fundamental first step,systematical geomechanical core laboratory tests were carried out to investigate the anisotropic mechanical behavior of the reservoir formation at core scale under in-situ condition.The description of the anisotropic mechanical behavior obtained from the laboratory tests was used to derive the correlations required to determine anisotropic mechanical property profiles along wellbores,which are at log scale by using wireline and LWD sonic logs.Based on the wireline and LWD sonic logs and the correlations derived from the geomechanical core laboratory tests,the anisotropic mechanical property profiles were determined for more than 20 wells.Based on the anisotropic mechanical property profiles,more accurate horizontal stress profiles were obtained.The reliability of the completed geomechanical models was validated through comparison between wellbore stability predictions from the models with observation of borehole failure from the borehole image.This paper shows that the extensive geomechanical evaluation,from core to log,revealed the key characteristics of the anisotropic mechanical properties of the deep shale gas reservoirs in Sichuan basin.This work,through filling the knowledge gap on the anisotropic mechanical properties of deep shale gas in Sichuan basin,provides an opportunity to unlock this deep shale gas reservoir toward commercial development.