Mature Field Revitalization: Analysis of Wellhead Compression to Enhance Productivity from a Mature Retrograde Reservoir

Abstract

Sajaa gas field is one of the oldest fields in the Northern Emirates operated by Sharjah National Oil Corporation (SNOC) where Petrofac currently holds accountability for the Sajaa asset operations until November 2015. Since 1982, this mature asset has experienced increasing gas recoveries with declining reservoir pressures subsequently leading to condensate banking and liquid loading problems. Many techniques had therefore been adopted including drilling of multilaterals, plant inlet compression and foamer, but the effects were short lived as the reservoir pressure declined further. This paper deals with the latest production enhancement technique involving field wellhead compressors applied on the asset to increase its deliverability and longevity.This project involves the installation of 12 Well head compressors which effectively aim to include the entire inlet from the field through these units. A total of 18,600 HP of compression has been introduced throughout the field with these fuel gas powered reciprocating compressors, including a primary separation unit on each skid. They have principally been able to reduce the flowing WHP to as low as 15 Psig associated with a reduction of DeltaP across the wellbore, thereby reducing the effect of liquid loading and aiding to an increase in the primary condensate and water recovery. The scope of this paper is the analysis of the Full field compression (FFC) project providing an overview of the installation methodology, performance of the wells and the incremental effect of the project which exceeded the forecasted gain, along with troubleshooting from a subsurface point of view. Finally using the Integrated Asset Model to link the subsurface performance to the surface gain and forecasting the increment of reserves associated with the FFC in a mature retrograde carbonate reservoir environment. An insight into the factors influencing the compressor performance and the optimization techniques employed during the 2 year long project is also presented.