Geomechanical modelling of stress magnitude and orientation across fault and its relation to hydraulic fracturing

Abstract

With intense exploration around the world, easily extractable hydrocarbons are getting more and more difficult to find. Major conventional hydrocarbon accumulations have been targeted and are being produced; but increased world’s consumption has led petroleum exploration and production industry to consider exploiting targets that were not believed to be economical. Tight reservoirs include shale gas, shale oil, coal seam gas (CSG) and tight sands. This concept has changed the conventional view of shales from being source and seal rock to unconventional perception –as reservoir. These reservoirs have minimal porosity and permeability which is not sufficient to produce at economic rates. Developing these reserves may require hydraulic fracturing to create a predictable network of fractures with height of several hundred feet through which hydrocarbons can easily flow towards borehole. Even if these reservoirs are fracture stimulated at best of the knowledge and skills; production from two wells in the same field is never the same. For a successful fracturing treatment, it is necessary to understand impact of existing fractures, faults and stress regimes in the subsurface. Geologic structures influence the stress field locally and show deviation from the regional trend of stress pattern. This study utilizes geomechanical modeling with static elastic moduli to depict stress magnitude and orientation around faults. For the purpose, stress magnitudes estimated by Reynolds et al., (2006) are used. Strike-slip stress regime prevails in at the depth interval selected. A thorough study using different lithologies, σH azimuth and fault size is carried out. Stress concentrate at the fault tips on opposite quadrants of the fault tips. Fluctuation in stress magnitude increases with increase in fault size. However, the variation diminishes after fault size of 1500 meters. These models help in understanding the orientation of fractures during hydraulic fracturing and help to recognize stress barriers that may affect production from an unconventional reservoir.