Multi-Disciplinary Approach For The Journey To Unlock Secodary Recovery Potential In The Pd-48 Block

Abstract

The Greater Sirikit East (GSE) field is located in the eastern part of the Sirikit Main field in S1 concession, Phitsanulok Basin, Central Onshore Thailand. GSE_Z6 is a high petroleum potential block located in GSE area. Primary production was started in 2008. The production rate was continuously increased because more wells were drilled until it reached the peak oil production of 6,630 STB/D in March 2013. This high production rate could not be maintained since there is no sufficient pressure support from aquifer. The waterflood was started in early 2014. However, poor injection performance was encountered. Several mitigation actions such as re-perforation, stage perforation, and various injector conversions did not improve injection performance. The production then started to decline rapidly to 1,560 STB/D within 3 years. This paper presents the thorough workflow and analysis to identify root causes and troubleshooting actions to unlock the 3.6 MMSTB of secondary recovery potential from GSE_Z6 block. The GSE_Z6 waterflood was initially designed for multi-layer reservoirs with line drive-peripheral flood pattern from water level. However, most of the injectors faced zero injection rate problems. Mitigation actions including re-perforation, stage perforation, and more injector conversion were performed, but no significant improvement was observed. The satisfied injection rate from few injectors clearly indicated that it is not enough for supporting waterflood project in GSE_Z6 block. Therefore, to solve the problem, in-depth and multidisciplinary integration from injectivity test, petrophysical interpretation, geophysical analysis, and stratigraphic correlation were conducted. Finally, the integrated Facies-Thickness-Porosity maps by each individual reservoir were created to represent the subsurface models to clearly identify the root causes of injection problems together with proposed solution plans. Key results are the newly generated 63 Facies-Thickness-Porosity maps of individual reservoir. To create the net sand isochore mapping, multi-disciplinary work, which cooperates geologists, geophysicists, and reservoir engineers, was performed. The maps suggest that poor connectivity between injectors and producers is the main root cause along with the un-optimized location of drilled injectors from waterflood view point. A proposed solution is to drill new injectors at the optimized location and perform injector conversion using guidance from the updated subsurface model. Consequently, two pilot injectors were drilled in 2016 to prove the assumption. Both wells showed positive results in terms of net sand, reservoir quality, reservoir connectivity, and especially injection performance. The increasing of reservoir pressure (150-300 psi) has been observed after 3 months of injection together with the immediate oil gain of 300 STB/D. Also, 49 MSTB of additional waterflood gain has been produced after 10 months of injection. These results conclusively confirm the validity of the new subsurface models and waterflood strategy. With the successful concept proving, the development of GSE_Z6 block is more certain with higher confident. Completed detailed work of Facies-Thickness-Porosity maps is very useful for giving clearer subsurface model. Consequently, injectors were proposed at the optimum location from waterflood viewpoint using the guidance from the updated subsurface model. Ultimately, new 15 injectors which were drilled in 2017 as per new strategy also showed promising results. The long-awaited secondary recovery reserves of 3.6 MMSTB would finally be unlocked from GSE_Z6 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