Optimizing hydraulic fracture spacing and lateral well spacing in tight/unconventional resource development through fully coupling stress shadowing effects and fluid flow: an integrated approach

Abstract

Development of unconventional formations was stimulated due to depletion of conventional reservoirs, and the increased energy demand all over the world. The increased demand was caused by economic development and a rising living standard. Recent successful development of shale gas/tight oil has changed energy demand and supply in the United States. Due to the extremely low permeability in tight/unconventional reservoirs, horizontal wells with multiple stages of hydraulic fractures are required in order to support commercial production. Hydraulic fracturing normally involves injection of large amounts of fracturing fluids and proppants in order to create contact area with the reservoir. Undoubtedly, hydraulic fracturing operations alter the local stress distribution, imposing influence on propagation of subsequent fractures in the vicinity. This is known as the “stress shadowing” effect, which aggravates variation between neighboring fractures in addition to those induced by reservoir heterogeneity. The developed methodology fully couples stress shadowing effects and fluid flow. The intra-fracture heterogeneity and inter-fracture heterogeneity from fracture propagation are incorporated into a reservoir model on a field scale. The methodology enables the identification and quantification of the impact of stress shadowing effects on field production and may help in optimizing fracture spacing and well spacing design. The methodology was successfully applied in a synthetic reservoir. It was found that stress shadowing effects are a function of fracture spacing, relaxation time and fracturing sequence. Fracture spacing was varied in the synthetic study, and it was found that stress shadowing effects decrease with increasing fracture spacing. For example, closure pressure increased by 28% when fracture spacing is 20 ft, while it increased by 2% when fracture spacing is 600 ft. Relaxation time variations suggest that stress shadowing effects can be reduced by adding some relaxation time between fracturing neighboring stages, and an optimum relaxation time can be found by examining changes in properties of two neighboring hydraulic fractures with relaxation time. In terms of production performance, it was found that stress shadowing effects cause production loss. The larger the treatment job size is, the larger the production loss is if fracture spacing is kept the same. For a given treatment job, more production loss is expected when fracture spacing is smaller. The methodology was used to find fracture spacing and well spacing for the synthetic study. In the end, the developed methodology was applied in a field study in the Eagle Ford and it was found that without properly capturing stress shadowing effects, the historic production of the subject well cannot be matched. This further confirmed the importance of incorporating stress shadowing effects when dealing with production from horizontal wells with multiple stage hydraulic fractures.