Abstract
A high CO2 carbonate gas field offshore Sarawak, Malaysia, is scheduled for development. Fines migration has been identified as a potential risk for a sustained and stable production for this field, triggering this investigation. The reservoir investigated (subdivided in S3, S2, S1 formation) has an average 8% clays, of which over 50% are migratory illites and 15% migratory kaolinite. This paper discusses the laboratory findings and factors contributing to fines migration for this reservoir. We conducted core flood tests to determine critical flow rates for the onset of fines migration of high CO2 hydrocarbon gas and CO2-saturated brine within the production gas zone. In addition, we measured total suspended solids during each incremental rate stage and performed scanning electron microscopy–energy-dispersive X-ray (SEM–EDX) analysis on the effluents collected. We also performed mineralogical analysis of formation rocks to determine clay types, amount, and morphology. Core floods performed with CO2-saturated brine on S3 and S2 cores showed damage at a critical flow rate of 10 ml/min with permeability recovery of 65–75%. This shows that CO2-saturated brine tends to mobilize the fines such as illite and kaolinite. Core floods performed with high CO2 hydrocarbon gas showed permeability recovery of 93–96% at rates up to 10 ml/min. SEM analysis on effluents collected showed presence of silicate and carbonate particles with size of 5–50 μm. A combined salt dropout and fines mobilization core flood showed a higher degree of formation damage due to fines mobilization with 74% permeability recovery compared to baseline permeability compared to core floods with high CO2 hydrocarbon gas. However, the formation damage due to fines mobilization for this experiment was reversible. Overall, the results indicate that a high potential for fines migration in this type of carbonate system exists for CO2-saturated brine flow with significant less potential for dry CO2 flow.
Highlights
The increase in C O2 as a greenhouse gas in the atmosphere has triggered efforts to reduce greenhouse gas emissions and significant research efforts, one of them being CO2 sequestration, which foresees the injection of CO2 into the subsurface
The results demonstrate that fines migration in carbonates can be an issue
The core floods with CO2–N2 gas showed no sign of formation damage at increasing rate stages;
Summary
The increase in C O2 as a greenhouse gas in the atmosphere has triggered efforts to reduce greenhouse gas emissions and significant research efforts, one of them being CO2 sequestration, which foresees the injection of CO2 into the subsurface. Malaysia is considering carbon capture and storage (CCS) as a possible way to reduce its greenhouse gas emission footprint. In this respect, it is critical to prove that the (re-) injection of CO2 does not have any adverse impacts (e.g. Kashim et al 2019). It is well known that fines migration can cause significant permeability reduction in subsurface formations associated with oil and gas as well as water production (Civan 2014). This formation damage may require massive stimulation
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