Rapid Producibility Evaluation of Thin, Sand-shale Laminated Reservoir - A Case Study in South China Sea

摘要

Laminated sand-shale reservoir poses many challenges in formation evaluation and hence risks on decision making such as oil testing or completions, particularly for offshore. This paper presents a new approach of NMR based rock typing, permeability characterization and rapid production prediction for thin sand-shale laminated reservoir, conducted in an offshore field of South China Sea. The method is validated through a study integrating logs, formation tester and drill string test (DST) data, to build a generally applicable approach. It was used for rapid producibility evaluation right after openhole logging, in order to facilitate the decision making of the consequent completion and production test. Based on a quick yet reliable answer, operators can decide whether the well should be completed and where should be tested in order to achieve the lowest cost and HSE impact and better time efficiency for exploration and appraisal. The major challenges facing are: highly laminated sand/shale sequences, strong heterogeneities, complex porosity-permeability relationships, and different scales of different measurements. We set up an improved method using NMR measurements to evaluate effective properties within a depth frame of thin beds in order to overcome the resolution challenge because the individual lamination thickness is about centimeters or even thinner, which is much below the resolution of logs. Comparing with DST results, the accuracy of predicted producibility is in an acceptable range, giving great confidence of the reliability in the study result. This case study has demonstrated the applicability of the new NMR based method, and set up a rapid producibility evaluation approach for thin, sand-shale laminated reservoir; and this new NMR method and the approach applied are not limited to this specific field but applicable to other fields with similar geological settings and formation types in this region.