Prediction of critical drawdown pressure for a gas reservoir prone to sand production in western offshore, India, and its suitability for CO2 sequestration

Abstract

Sand production is a major problem in reservoirs having moderately hard to unconsolidated rock matrix. Gas bearing Daman sandstone is one such reservoir situated in the western offshore India. Identification of sand prone zones and quantification of drawdown causing sand failure is critical in such cases as sand cuttings can severely damage equipment. Predicting sand failure is also important for the safety, environmental, operational, production, and economic reasons.Failure of sand is caused by a combination of factors viz. geology of the reservoir, properties of sand, and production conditions of the well. For wells producing with a high gas rate, sand failure is more pronounced. Depending on the amount of sand production, different methods, chemical or mechanical, are used to control sand production from the well. In the study well multiple zones were tested, of which, sand production was observed in some zones depending on the rate of gas production.Daman sandstone under study bears good porosity and permeability, as established through well productivity, core study, and micro-computed tomography. The site holds potential for CO2 injection and can be evaluated for CO2 sequestration in the long run with reservoir depletion. Present study was carried out to quantify the drawdown at which sand failure initiates. Mohr-Coulomb failure criterion was used for failure prediction. It was observed that under given stresses, sand failure occurs when the applied drawdown exceeds a certain value depending on the unconfined compressive strength of the rock. Prediction of this drawdown value, regarded as critical drawdown pressure, is vital to control sand production and mitigate hazards associated with sand failure. The study is important for preparation of a field development plan to mitigate production losses arising out of potential sand failures.