Reservoir Characterization As The Clue To Unlock Field Potential And Maximize Oil Recovery – A Case-Study In The Remote Off-Shore North Pattani Field

Abstract

The offshore North Pattani fields lie in the northeast of the Pattani basin, have been in production since 1999 and have produced over 200 MMBOE of oil and gas from hundreds of fluvial and lacustrine sands, drilled by hundreds of deviated and horizontal wells. The main reservoirs consist of stacked, amalgamated fluvial sands, with variable degree of distribution and connectivity; typically, OOIP for each sand ranging from few thousands to millions of MMBOE. Depending on the location in the regional structural trend, the fields show very strong aquifer support and related high recovery factors, or minimal aquifer support, where severe depletion after some production leaves significant amounts of hydrocarbons in the subsurface. The North Pattani field is one of these zones: currently a mature area developed by wells drilled in different years, the main present challenge is to enhance the ultimate oil recovery, and identifying the remaining oil accumulations in a complex structure and stratigraphic setting. Waterflooding is often used in the North Pattani fields as part of an overall strategy to extend the fields' life by optimizing the oil recovery where water injection pipelines are present. For platforms located in remote areas, waterflooding is implemented thanks to the mobile sea water injection units (SWIMS) design, which permits the injection of sea water into sands at high rates while still maintaining stable displacements, helping to execute IOR projects in areas without water injection pipeline. The detailed work focused on a thorough static and dynamic reservoir characterization of a small oil reservoir penetrated by 3 wells: seismic mapping, formation pressure data collection, material balance, static modeling and reservoir simulation were used to define the size of the opportunity and to estimate the time of execution of the waterflood project. A robust SA&O plan was put in place, including control on the production conditions, gathering reliable well tests and water samples to evaluate the chloride content. This allowed to monitor production trends, to better understand reservoir connectivity and sweep, and eventually to observe clearly the water breakthrough after the increase in the chlorides content, a natural and cheap tracer. Waterflood response was observed aligned with the simulation prediction, with a pronounced increase in the oil rate and pressure. As a result of the water injection, recovery factor was increased significantly. This case-study will be presented together with the different approaches in seismic and subsurface characterization performed to capture the reservoir architecture. The production results and waterflood lookback of this successful case will be shared along with the valuable lessons learned, best practices and future opportunities. This Platform remains a focus area for asset development due to substantial remaining resources.

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