Reservoir Productivity Assessment Using Advanced Formation Evaluation, Image Logs and Formation Testing and Sampling Methods: A Case Study

Abstract

Saka Indonesia's primary objective of drilling an appraisal well offshore North-East Java was to accurately assess productivity of the three main reservoirs discovered by the exploration well drilled in the Pangkah Block. This paper details the integration of advanced formation evaluation procedures and interpretation of image logs with novel formation testing methods, which were used to plan and optimise drill stem tests (DST) conducted across the three reservoirs. Deployed on wireline, formation evaluation and electrical borehole image logs were acquired in open hole of the exploration well. Nuclear magnetic resonance (NMR) and image logs were processed simultaneously in near real time to facilitate the planning of the subsequent formation pressure testing and fluid sampling program. Using the recently introduced advanced formation testing technology, reservoir deliverability was accurately established, in addition to characterising fluids insitu and obtaining reservoir fluid samples. Interpreted results of data acquired on wireline from different logging runs were integrated and consequently used to optimise the well testing program across the intercepted heterogeneous and low permeability limestone reservoirs. In addition to determining porosities, free fluid volumes and the range of permeabilities, Drill Stem Test (DST) zones were confidently defined using the free water levels ascertained by constructed vertical pressure profiles. As a result, DST measurements matched the permeability and productivity estimations across the three pay zones. The integrated approach of formation evaluation, textural analysis and permeability and productivity measurements enabled the evaluation of three complex limestone reservoirs discovered in this field, which included secondary porosities and interconnected vugs. These results were ultimately verified and confirmed by the well tests conducted across the three reservoirs.