Optimizing the Utilization of Miscible Injectant at the Greater Prudhoe Bay Fields

Abstract

Abstract Miscible injectant (MI) has been injected at Prudhoe Bay and its satellite fields for over 30 years. Since 1982, more than three trillion cubic feet of MI has been injected and over 300 million barrels of oil has been produced through this enhanced oil recovery (EOR) technique. Since MI is a finite resource, the allocation of MI across all the fields in the Greater Prudhoe Bay (GPB) area, as well as the distribution of MI to various injection patterns in each field, must be managed methodically to optimize oil recovery. This paper provides an overview of all EOR projects at GPB and presents the process and methodology for MI allocation to these projects and to individual injection patterns. A new approach is used to determine the amount of MI allocated to each project based on predicted marginal MI utilization per barrel of EOR oil. The marginal MI utilization of each project is predicted using a COBRA model. COBRA is a full-field scale-up tool for predicting MI performance based on type pattern simulation model results. This paper will discuss the allocation approach used to compare the marginal MI utilization among various projects to determine the optimum MI allocation. The volume of MI allocated to each project is then distributed to the various injection patterns following a pattern ranking process. A new ranking index is proposed to combine a pattern's maturity and efficiency, so that a single indicator can be used to rank injection patterns in order to optimize the utilization of the limited MI resource.