Reservoir depletion and its effect on wellbore stability evaluation

Abstract

Abstract Production from hydrocarbon reservoirs can lead to decreases in the pore pressures, of up to 60 MPa, over the lifetime of the field. This depletion results in changes of the horizontal stresses acting in the reservoir. Field data are reviewed and new data presented which define linear decreases of the minimum stress with pore pressure, for reservoirs which have undergone pore pressure reductions of 1.8 MPa to 56 MPa. The depletion responses cannot be accurately predicted using the most commonly used linear elastic relationship, due to either inappropriate boundary condition assumptions, or incorrect input values. Relationships for three different boundary conditions and two material, responses, are presented which can potentially be used to describe the minimum stress-depletion response of reservoirs. The significance of the change in the horizontal stress anisotropy with depletion for different boundary conditions is also discussed. Finally, the impact of the stress-depletion response on wellbore stability is assessed for inclined wells, focussing on openhole production wells, whose stability can significantly decrease with depletion.