The Effective Seismic Techniques For Tight Carbonates And The Application Of Matured Naung Nuan Oil Field, Gulf Of Thailand

Abstract

Palaeozoic carbonates are widely distributed in the world. Even they are tight in matrix due to long time diagenesis, there are still high productive large cavities (such as vugs and caves) in tight matrix. Exploration and development on such type of tight carbonates often has following problem related to the high heterogeneity. • High uneven distribution of reserves with high productive wells very close to dry holes • High uncertainty in drilling results without understanding of the heterogeneity • High cost and NPT in drilling due to large mud-losses • Low recovery rate due to early water-breakthrough • Large potential left in mature fields and assets Many E&P operations on tight carbonate plays are under performed due to the knowledge on quality reservoir limited to fracturing, dolomitization and reefs. Technical approaches are same as on clastic reservoirs, without effective characterization on heterogeneity. Based on our new insight on carbonate heterogeneity from deposition to production, we have developed an effective workflow and associated approaches to improve E&P operations on carbonates, which is especially efficient for development of tight carbonates. • High density seismic acquisition • Heterogeneity-targeted seismic reprocessing and interpretation • Cavity connectivity and network mapping • Property trapping and flow-unit delineation for fluid prediction • Accurate delineation of sweet-spots for drilling locations • Drilling optimization to minimize the cost and maximize the productivity • Production optimization under the guidance of reservoir modelling and simulation Part of the workflow has been applied to Nang Nuan Oil Field at concession block B6/27, Chumphon Basin, Gulf of Thailand. The procedure and result consist an excellent showcase on how efficient seismic technique on carbonate reservoirs could add value to a mature field, which has not only revealed large remaining potential for development and exploration in this block but also provided valuable references on the large potential and effective approached for tight carbonate plays worldwide. Nang Nuan Field was discovered with well NNN-A01 in 1987. The subsequent appraisal and development drilling illustrated the high uncertainty in results. With total five wells drilled, three had high flow rates and two were dry. Total Cumulative 5.86 million barrels of oil was produced with 90% from Well NNN-B01. The production started in 1988 and suspended in 2007 due to high water-cut. The step-out exploration drilling effort was failed with an expensive dry hole. The operational results in this block demonstrates the extremely high reservoir heterogeneity and the typical E&P operational performances on tight carbonate plays but without proper knowledge and approaches on them. To evaluate the remaining development potential of the Nang Nuan Oil Field and the associated exploration potential of B6/27 Block for decision if to return or keep the B6/27 Block, the seismic techniques mentioned above has applied, as an advanced subsurface reservoir characterization project, from targeted seismic reprocessing to identifying potential areas for future exploration. The result reveals that the main controlling factor for well productivity is the large cavities (caves) in Permian carbonates. The production well NNN-B01 with 5.3 MMBO is associated with large cave features while the dry hole NNN-B02, deviated from NNN-B01 is far away from cave features. The two wells provide the key QC on cavity-targeted seismic reprocessing. Many previously-unrecognized subtle cave features are revealed with optimizing parameters in several reprocessing steps. Direct cave interpretation and cave-network mapping characterize the strong uneven-distribution of cavernous reservoir. The flow-units separated NNN-B01 has been delineated based on mapped cavity-connectivity and carbonate top. Large remaining potential with low uncertainty is identified in three areas at north part of the field. In addition, high prospective areas are identified to the north and east of Nang Nuan Field for step-out exploration in this block.

AAPG Datapages/Search and Discovery Article #90331©2018 AAPG Asia Pacific Region GTW, Back to the Future – The Past and Future of Oil and Gas Production in the Asia Pacific Region, Bangkok, Thailand, September 26-27, 2018