Advanced Fracture Diagnostics by Utilizing Over 250 Fracture Diagnostic Tests in Indian Volcanic Tight Gas Reservoir

Abstract

Abstract This paper documents the basis of fracturing diagnostic test design and analysis methodology adopted while fracturing one of the few commercial volcanic gas reservoir in the world. More than 10 distinct types of diagnostic tests were performed with each having specific objective. These tests were primarily conducted to: Reduce the uncertainty while fracturing Improve reservoir & hydraulic fracture understanding to enhance production Validate qualitative sources of information These tests included standard pre-frac injection tests, post injection surveys as well as innovative modifications which significantly helped to enhance operational efficiency and improved production results. To achieve maximum net pay coverage with minimum number of frac stages, limited entry fracture technology best suited the economics of this field. Since limited entry technique was selected even with its inherent uncertainties with respect to diversion in individual fracture cluster, the overall performance of this field heavily depended on its effectiveness. To maximize the probability of success, uncertainties & risks were evaluated and a workflow was designed. This workflow consisted diagnostic tests with specific deliverables such as DFITs to calibrate mechanical earth model (MEM), Step rate tests to estimate the efficiency of fluid diversion, temperature surveys to validate fluid distribution, production logs to confirm production performance. These standard tests were also modified to minimize cost/time implication while ensuring specific information was acquired as expected from these tests. Fracture model calibration was achieved by a combination of injection tests, post injection test/fracturing temperature surveys, along with a consistent method for fracture history matching. Final verification was obtained using a series of production logs. Over 13 Diagnostic Fracture Injection Tests (DFITS), 63 Step Rate Tests (SRT), 80 Step Down Tests, 58 post SRT/Fracturing Temperature Surveys, over 50 production logs are incorporated in this study. All of this augmented reservoir understanding and helped to save operational time and reduce cost. These tests further helped to increase from 3 clusters per frac to 6 cluster per frac, thus increased net pay coverage with same frac stages. The contribution of 6 clusters was also validated from production logs. Completion improvements have resulted in productivity and Estimated Ultimate Recovery (EUR) increases of 80% and 20% respectively. Screen out rates have dropped from 33% in the very first campaign to 5% in the most recent campaign. Detailed analysis and key engineering findings from all of these tests. Representative case histories including, DFITS, Step rate tests, Mini Fracs, Temperature surveys and production logs to back up the results. The results from these learnings are summarized in this paper.