Winning Over the Production Threat: An Innovative Petrophysical Approach for Sand Grain Size Prediction and Rock Strength Evaluation

Abstract

Majority of producing reservoirs in Malaysia come from sandstone accumulation with varying properties, rock fabrics and qualities. Being one of the major culprits in development and production spectrum, failure to take proactive measures for early prevention and detection of sanding issue has proved to be an expensive lesson learned especially during the mature production stage and late field life. High cost, increasing risk and intervention complexity and massive revenue loss are among the consequences due to this failure. This paper will highlight the challenges faced in sand prediction and monitoring and the proposed solutions at various field stages incorporating subsurface analysis, technology and brilliance at basics. The same approach will be used in rock strength evaluation for field subsidence analysis. Subsurface data such as logs, cores, drill cuttings and downhole well configuration can offer a tremendous insight at early stage of sanding issue. During field exploration and appraisal phase, information on reservoir compaction, barrier and heterogeneity, grain size, clay types and fines accumulation are usually investigated to give the overall reservoir potential and productivity overview. More comprehensive study could be conducted if core is available such as compressive strength, pore volume compressibility, elastic properties and even flooding test to simulate formation damage and factors affecting sand production. In area where limited core data is available, logs can be used to predict and generate sanding parameters such as grain size and other rock strength properties, hence driving the completion optimisation efforts and sand production preventive measures. Once production commences, sand count and particle size mapping should be updated frequently to complement the monitoring program. Leveraging on technology and collaboration, downhole logging acquisition to locate sand producing interval, chemical based sand consolidation treatment and core-driven sand screen selection and gravel size design are among the common scenarios taking place to help with production revival. Results generated from subsurface study will be input to the early formulation of field development plan and production strategy especially for downhole as well as surface sand control mechanism. In addition, integrated grain size and rock strength prediction workflow had been formulated based on logs to provide a competitive framework for time and cost optimization. Case studies presented in this paper will demonstrate a holistic and integrated approach at each stage of field life to win over the sand production hurdle as well as minimizing threat to production sustainability. Banishing the emerging threat through comprehensive subsurface study, strategic planning, execution and monitoring become the main agenda to protect well integrity as well as safeguarding the production.