Joint Optimization of Oil Recovery and Carbon Intensity in a Middle-East Oil Field Under Miscible Water Alternating Gas

Abstract

Abstract This work investigates how the green-house gas (GHG) emissions of a producing oil field can be reduced through adaptation of the reservoir management, i.e. the injection and production guidelines. Indeed, the world’s energy production must be decarbonized as far as possible, and this includes minimization of the emissions associated to the oil and gas extraction itself. An additional decision criterion for oil and gas projects is the hydrocarbon carbon intensity, which is the emissions total divided by the production total, expressed in kgCO2eq/boe. The reservoir management strategies now attempt the joint optimization of all the following dimensions: net present value, short-term production, final recovery, and now oil carbon intensity. In some WAG fields, several controls are available even after the development is finalized: flow rates of both gas and water in each injector, duration of injection of each phase, possible conversion from WAG to water injection. A method has been devised to perform the joint optimization: a reservoir simulator is coupled with a surface model containing GHG emissions equations for compressors, pumps, turbines according to their throughputs. In brown fields, this emissions model can be calibrated on historical profiles and energy consumption per machine, while in green fields, a synthetical model can be built from theoretical operating curves and calibrated a posteriori. In this work, the method was applied on a giant Middle-East carbonate oil field under Miscible WAG injection. Numerous reservoir management scenarios were run, resulting in new production and injection profiles, together with their associated GHG emissions profiles, without the need for time-consuming loops between subsurface and development or exploitation teams. All scenarios were ranked in recovery and carbon intensity simultaneously. For the selected field, it was found that reservoir management actions can be strong levers to reduce the carbon intensity of the produced oil, where required – typically by 10% or more. The most efficient reservoir management actions for GHG reduction were those that reduce the gas injection rate and therefore the associated gas compression requirements. The actions did not impact the short- and mid-term oil production but lead to a reduction of one point of ultimate recovery. Reservoir management decisions must consequently be compromises between ultimate recovery, carbon intensity and net present value. The integrated production and emissions prediction tool proves extremely helpful to identify the relevant reservoir management scenarios, perform informed arbitration or enforce hard-fixed carbon intensity constraints.