坑壁破壊から見た応力場変動と石油鉱業への応用

抄録

Stress analysis based on borehole failures is becoming a common procedure to evaluate not merely in-situ stresses but fault seal and fluid flow, to maximize the success rate of exploration and production capability. The mechanics of borehole failures, breakouts and drilling induced tensile fractures (DITFs), can be explained by stress heterogeneity generated around the wellbore as an open space in the stressed rock mass. The natural stress field is constrained by the Coulomb frictional sliding, and the rocks break when the stress condition fulfills an appropriate failure criterion. Thus the characteristics of the borehole failures and rock strength can be used to calculate the in-situ stresses. The stresses sometimes fluctuate around discontinuity surfaces, such as faults and fractures, suggesting that these planes may be tectonically active and can be conduits of fluids.