Stress Reorientation Around Horizontal Wells

Abstract

Abstract The production and injection of fluids in a reservoir results in reorientation of stresses. This phenomenon has been supported by field studies and micro-seismic observations. This paper presents a study of stress reorientation around horizontal wells. Stress reorientation has been calculated for different scenarios and patterns of horizontal injection and production wells. Horizontal wells are increasingly being used for production and waterflooding. Long-term injection into these wells can result in the creation of fractures that grow over time. The effect of fractures on reservoir sweep and on problems such as early water breakthrough is largely controlled by fracture / stress reorientation. A systematic study of stress reorientation around horizontal wells and well patterns will allow an operator to (a) select candidate wells for fracturing (b) choose appropriate operating conditions to avoid early water breakthrough and achieve better reservoir sweep (c) choose the right time window for fracturing (d) improve the design of multiple fractures in single horizontal well. Poroelastic simulations show that the maximum stress trajectories tend to align along injection wells and across production wells. The extent of stress reorientation varies depending on the injection rates, reservoir pressure, production rates, in-situ stress contrast, distance between wells and orientation of the wells with respect to the in-situ maximum/minimum stress. Some general rules of thumb are derived about stress reorientation around horizontal wells and conditions favoring/opposing the reorientation have been analyzed in detail. Implications for waterflood sweep efficiency are discussed.