Abstract
Oso 1-Y1 is a large, mature condensate field located in OML 70, about 45 km from shoreline in the southeastern part of Nigeria. Several geoscience studies for this complex deltaic have assessed Original-Condensate-In-Place (OCIP). Over 63% of the OCIP has been recovered, primarily through miscible crestal gas injection combined with sound reservoir management practices.
In 1987, MPN carried out a pre-production simulation study of the Oso field with the primary objectives of determining the condensate recovery factor, the optimal placement of wells and to obtain an insight into the reservoir behaviour under gas injection. The results indicated that the highest recovery factor (70%) would best be obtained by miscible gas injection. Additional simulation results post-production also estimated recovery efficiency of 72%. Actual production performance indicates a 74% recovery versus 55% average usually obtainable for gas-condensate reservoirs.
Although crestal miscible gas injection is the main recovery mechanism, different tools that use real-time production performance have also been concurrently utilized to continually optimize and update the depletion plan as required/necessary. These tools include adequate pressure monitoring to determine pressure trends and track efficiency of gas injection while monitoring miscible gas front movement and ensuring optimum contact closure. In addition, Integrated Production Model (IPM) updates are done periodically to confirm condensate remaining-in-place and recoverable volumes, assess infill opportunities and optimize production. The main objective of these tools is to reduce unswept condensate, condensate lost due to retrograde condensation and hence improve recovery.
This paper will focus on how the application of various reservoir management practices have been integrated to develop an ever-green depletion plan in order to optimize production and achieve world class recovery from a structurally and stratigraphically complex condensate field.
