Mature Condensated Gas Field Development Strategy: An Integration of Geophysics, Geology and Log for the South Sumatra Basin, Indonesia

Abstract

Since 2014 oil prices in the world have dropped 50% more that was beyond all petroleum organizations and companies imagination. The lower oil price continues to look like a new ordinary condition, putting more petroleum industrial organizations and companies under financial stress. The price slump also is forcing the companies and people to rethink their strategies how to manage the assets in the development of oil and gas resources. N field, a mature condensated gas reservoir, is located in the south Sumatra basin, Indonesia. It has served as one of the biggest suppliers to Singapore since 2005. This multi-bedded sandstone reservoir of Lower Talang Akar (L Talang Akar, LTAF) was regarded as the only target with Upper Talang Akar (U Talang Akar, UTAF) strata and granite basement (GB) at both ends. During its deposition, LTAF was not easily identified due to the onlap to GB and unclear understanding of the distribution of gas, oil and water. As more gas is needed to remedy the production decline, a cost-saving development strategy to increase production have being pushing the operator to undertake exertions and enhance the reservoir performance. This paper summarizes the latest discoveries and progress. A four-step development strategy was proposed to solve the problem under the guidelines of producing more gas with less cost. First, Improve investment efficiency by integration characterization of mature field and less risk reservoir. Five segments of U, M, L, Simpang and GB within LTAF were carefully re-identified and correlated via sequence stratigraphy based on lithology, borehole logs and geophysics data. Well logs, three dimension (3D) seismic sections, onlap boundary and impedance inversion were connected together using well-seismic ties. These characterized the structures and the sandstone reservoir, including those of L segment which were thought to have no hydrocarbon. Further investigation revealed that the local microstructure of the L segment was full of gas. The gas-oil and oil-water contacts of LTAF were studied and verified by means of Drills Stem Test (DST) data, log interpretation, pressure and daily rates. Thereupon carefully quantitative analysis, the sandstone units without productions were identified as "the potential". After 3D geometrical and property modeling, new geomodel showed a 10% increase of original gas-in-place and the future new wells were optimized by integrating the structure, reservoir and gas-oil distribution. Second, Pay attention to resource restructuring. This resulted in exploring the potential of UTAF which used to pend above LTAF. Then the UTAF gas layers will be opened up zone by zone to cover the shortage of gas supply. Third, Take GB and other relative tight and marginal reservoirs as potential hydrocarbon opportunities, which will prolong the lifetime of the reservoir or field. Finally, optimize all the available ways to improve the innovation ability for future development. The four-step development strategy suggests: 10% increase of newly identified potentials in LTAF can be produced first. Then the UTAF gas layers can be opened up zone by zone to supplement the hortage of gas supply. Fewer optimized wells could be drilled with higher production in consideration both LTAF and UTAF. Targeting the GB reservoir could be as a future source of unremitting gas. Many activities were in practice to improve the innovation for future development. This strategy provides an effective solution to the revitalisation of mature gas fields by digging the potential of whole batch of the reservoir and enhancing reservoir performance. On average 88 million standard cubic feet of gas per day is produced from LTAF and UTAF. It should be of interest to production geologists, reservoir engineers, petroleum engineers and/or anyone interested in the sustainable gas reservoir development.