The Influence of Crack Geometry on Production of Hydraulically Fractured Shale Gas Reservoirs

Abstract

Shale formations are the source rock for many of the oil and natural gas reservoirs. However, shale layers reflect extremely low permeability and porosity so that water, natural gas, and oil cannot easily move through these layers. Recently, innovative methods have been introduced to extract some of the largest resources of the natural gas and oil existing in shale layers by employing horizontal wells together with hydraulic fracturing technology. Using hydraulic fracturing and horizontal wells, fractures can be extended over a large area in shale layers providing several flow paths with relatively high permeability. In addition to the creation of hydraulic fractures, existing natural fractures are connected to the hydraulic fractures producing an extensive fracture network system. The highly-conductive fracture network system makes it feasible to economically extract the oil and gas from shale layers. It is known that different formation and operation conditions bring about different hydraulic fracture geometry. Considering geomechanical features of shale layers, hydraulic fractures geometry plays a vital role in the production of shale reservoirs. Therefore, an efficient production strategy necessitates the optimization of geometrical parameters of hydraulic fractures, namely fracture spacing, fracture distribution pattern, fracture length, and fracture angle. Also, geomechanical stress field has considerable influence on the production performance, particularly in naturally fractured shale reservoirs. In this research, a sensitivity analysis was carried out on the production performance of shale gas reservoirs as a function of geometrical parameters of hydraulic fractures, geomechanical stress field and geological features of shale layers. To conduct the sensitivity analyses, numerical models were developed based on finite difference and distinct element method to analyze the gas flow in fractured shale layers coupled with the geomechanical stress field. The sensitivity analyses demonstrate that, considering geomechanical effects, the production of shale gas reservoirs is highly affected by the fracture geometries, e.g. lateral and central fracture length, number and spacing of the fractures and fracture distribution pattern. Finally, it can be concluded that economical gas production in shale reservoirs requires an optimization of hydraulic fracture geometries considering geomechanical effects.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016