Clastic and Carbonate Formation Evaluation Case Study: East Asia

Abstract

Proving a hydrocarbon bearing zone has a significant impact on appraising a well. Pressure gradient and fluid sampling are typically used to identify fluid type in exploration phase. In addition, to confirm if the field is viable for oil & gas production, there is a need to ascertain volume of hydrocarbon from petrophysical evaluation. Aside from this evaluation, reference to adjacent development wells occasionally become common for the operator to aid in reservoir study and plan for development.This work is based on a case study on a Sarawak Basin field, drilled with Water Base Mud, which has three reservoirs of interests stretching across Clastics and Central Luconia Carbonate on the bottom zone. The poor quality sand and tight upper zone are challenging for reservoir evaluation. This has called for the application of multi-frequency dielectric tool for fluid saturation and advanced downhole fluid analyzer to obtain PVT equivalent fluid analysis in real time.With the dielectric tool showing the presence of hydrocarbon in both clastic and carbonate formations, downhole fluid analysis was planned to verify the mobile formation fluid and successfully guided the identification of oil and water in clastic formation and gas in the carbonate reservoir. The presence of water in clastic formation was not expected since the water producing interval is located at about 100 m down dip from a nearby development well that is producing gas. Dispute in results, in addition to tight nature of the reservoir has triggered the need for larger scale testing. A DST was initially planned by the operator after the well has been cased. With cost and time consideration, the decision was changed to run the formation tester dual packer module to perform interval pressure transient testing (IPTT). This paper will present the results of IPTT, fluid analysis and dielectric tool to demonstrate the methodology used in this case study field evaluation.