Optimizing Water-Injection Design in a Shallow Offshore Reservoir

Abstract

Summary Water injection is commonly used to improve oil recoveries in depleting reservoirs. However, insufficient injectivity can result in water-injection projects being limited in injection rates, which can sometimes make them uneconomic. Implementing water-injection projects requires a multidisciplinary approach to optimize water-injection rates for reservoir-performance, cost, and well-design considerations. The costs for the surface facilities are dependent on the required water quality, water temperature, and other operating parameters that are linked to the injectivity of water. A work flow including quantitative assessment of the injectivity development as a function of the operating parameters as well as the uncertain geomechanical and reservoir parameters can be used to improve the surface-facility design. Such a work flow was applied to a shallow offshore field. The results showed that the base-case design of the facilities should be modified to avoid an increase of the flowing bottomhole pressure (BHP) above the minimum stress of the caprock. The effect of the various parameters on the BHP was investigated, and the sensitivity of the BHP to uncertain input parameters under different operating conditions was tested. The results indicated that the BHP does not exceed the BHP limit, and hence the injectivity is expected to be high enough for a sufficiently long period of time under a wide range of conditions.