Low Carbon Enhanced Oil Recovery Solution for Carbonates

Abstract

Oil production from mature fields causes significant CO2 emissions, primarily linked to the management and processing of injected and produced water. As fields age, the demand for injected water increases, increasing both costs and emissions. Similarly, in the ageing field, water production increases with time that requires to process produced water which is a costly and emission-intensive process. This thesis addresses the challenge by optimizing injection water to enhance oil recovery in carbonates with reduced water injection, decreased water production and thereby reducing CO2 emissions. The fundamentals of carbonate reservoir, oil recovery from carbonates, forces affecting fluid flow, the main mechanisms for wettability alteration in carbonates along with potential determining ions and favorable conditions for facilitating wettability alteration were discussed to help better understand the result and discussion part of the thesis. The study aimed to identify optimized injection water for wettability alteration, improving oil recovery and simultaneously reducing CO2 emissions by minimizing water injection/production. Various low-carbon Enhanced Oil Recovery (EOR) solutions including, ion-modified brines, brines with additional salts, and carbonated water, were designed, and tested in outcrop and reservoir chalk cores at high temperatures. Different oil recovery tests were performed using different injection brines to find their effectiveness in improving oil recovery. This experimental thesis work also investigates the primary reasons behind increased oil recovery and proposes a guideline for selecting representative outcrop core material that represents reservoir cores. Stevns Klint outcrop chalk core was found as a suitable analogue for North Sea chalk reservoirs for EOR and CCS studies. A 20 mM concentration of Ca2+, Mg2+, and SO42- added brine was identified as the most effective ion-modified brine. Polsulphate salts, particularly added in produced water, demonstrated superior performance in enhancing oil recovery when additional salt is added to prepare injection brine. Carbonated water also exhibited promising EOR potential including carbon storage opportunities. The presence of positive capillary forces in cores was recognized as a crucial factor for oil mobilization in carbonates.