Lesson learned from the application of calcium carbonate polymer for water shut-off project in a carbonate gas well, Offshore Borneo Island

Abstract

This paper provides valuable insights on the systematic engineering approach, extensive laboratory evaluation and lesson learned on the application of calcium carbonate polymer for water shut-off (WSO) project in a carbonate gas well, offshore Borneo Island, East Malaysia. Excessive water production is a well-known problem faced by petroleum industry, combine with carbonate reservoirs that are notoriously difficult to characterize and challenging to produce, the selection of suitable WSO method is vital to ensure successful and sustainable treatment. However, limited studies have been conducted to compare between various chemical WSO from the industry guidelines with the success rate and lesson learned from historical field execution particularly for carbonate gas reservoirs in Malaysia. Carbonate gas reservoirs have long been an important element of Malaysia's O&G business and as the portfolio increases to meet regional energy demand, focus on effective WSO treatment for carbonate gas wells is crucial in ensuring continuous production delivery to the customers. As a result, study was initiated to evaluate feasibility of WSO using calcium carbonate polymer in a carbonate gas field that has been producing for almost 25 years with nonuniform strong aquifer support and experiencing excessive water production. The workflow adopted for the WSO treatment involves thorough reservoir review to ascertain the water production caused, extensive laboratory testing that include core flood experiments to ascertain the chemical effectiveness, detail field historical production data analysis performance analysis (e.g. nodal analysis and network modeling), sensitivity analysis on fluid placement using CAD software (e.g. StimPro), economic evaluation that include decision risk analysis to evaluate all range of probabilistic outcome along with a structured post-job review on the failure analysis. Laboratory testing and core flooding was conducted to mimic the condition during mixing at surface, pumping into the well and the soaking in the reservoir, from 80degf at 14.7psi and to 245degF up at 1700psi. Building the model for WSO candidates requires well calibration and matching to the current well performance to ensure correct basis of evaluation, hence Prosper was used as a tool for nodal analysis for multilayer model to analyze the zone contribution, estimate the gas production gain and determine water production reduction. Chemical placement and volume were generated using StimPro considering several case scenarios that include coiled tubing placement, optimum injection rate and ideal penetration depth. Based on the laboratory test results, the calcium carbonate polymer can be pump through the CT (e.g. total gelling time of 48hrs including mixing, POOH CT & soaking). Core flooding indicate that it can be pumped into the reservoir & withstand up to 1700 psi forward pressure. Fluid placement was generated using StimPro where it was recommended to use retrievable packer to minimize the risk of calcium carbonate polymer invasion into the gas producing zone. Post-job review suggests additional test to mimic all possible scenarios on-site particularly temperature sensitivity to determine gelling time and gel stability correspond to various pumping time and rates. This paper highlighted the potential of WSO using calcium carbonate polymer for the candidate well and will be applicable as evident of practical improvement for the WSO treatment execution in the future. Change in business landscapes may be observed toward chemical WSO should the application is successful to maximize Asset value within PETRONAS that experiencing similar issue.