Successful Parallel Appraisal and Development in a Complicated Gas Cap Field, A Case Study

Abstract This paper demonstrates successful application of parallel appraisal and development in G field, Niger. G field is a complicated stacked light oil reservoir with gas cap in its E2 major pool. After current operator's takeover in 2008, the government required realization of 10 KBOPD in this field within 3 years, leaving only 1 year for appraisal and development as field construction in this landlocked country at least takes 2 years. Whereas there was only 2D seismic and one well data (G-1) with RFT and testing, parallel appraisal and development strategy must be adopted and following 2 major challenges were identified: 1) Limited data and great uncertainties in gas-cap and well productivity; 2) development decision-making along with appraisal process. Appraisal and development have been optimized by following approaches: 1) RFT and wireline data were fully studied to identify oil-gas-contact in E2 pool and indicate possible oil in E3 pool; 2) appraisal wells placement based on new 3D seismic; 3) identify key uncertain development parameters and combine into appraisal campaign targets to gradually reduce uncertainties. Appraisal well G-2 confirmed the separation of block G-1 and G-2. The second appraisal well G-3 confirmed oil-gas-contact, encountered oil zone in lower E3 pool. The third appraisal well G-8 encountered oil zone in E2 and further firm up gas-cap area, laying firm foundation for subsequent development well placement.6 producers were placed out of gas cap and appraisal wells were transferred to development wells, all successfully commissioned in 2011, achieving desired production target. Conclusions drawn from successful parallel appraisal and development application were:1) utilization of all data available contributed to correct appraisal decision-making; 2) Combining 3D and appraisal well findings help reduce geological uncertainties; 3) Identify and reduce key development uncertainties during appraisal speed up appraisal process. For complicated fields at appraisal stage, the methodology in this paper is of strong reference value.