Flow Assurance Improvement by Injecting Pour Point Depressant Chemical to Heavy Oil Well in South Mahakam Field

Abstract

South Mahakam (SMK) as an offshore field had many challenges to produce and transfer hydrocarbon by underwater pipelines. One of the challenges was the wax formation due to declining temperature in the oil production system. The production was restricted by a heavy oil well withAPI 28.6º and pour point (PP) 29ºC. The oil was thickened at arrival point of a 10 inches-6.5 km underwater pipeline. It was suspected that the paraffin content was crystallized as wax around seabed sections with lowest temperature was 24ºC. Therefore, the wax deposit should be avoided by modifying the fluid handling system. Due to the unavailability of heating process and limited dilution with additional hot liquids, the pour point depressant (PPD) injection could be one of the alternative solutions. In principle, the chemical injection should be adjusted with flowing temperature is above wax appearance temperature (WAT). Therefore, the objective of this project was to study the application of PPD in SMK for solving the flow assurance issue. Methodology: There were four main steps in the study methodology. First, the representative samples were collected at well flow line and manifold during stable condition (by monitoring flow & pressure indicators). Second, laboratory test was performed, included WAT analysis by WAT 70Xi analyzer and PP measurement by ASTM D97, to support PPD lab performance test with target PP temperature was <24ºC. Third, the PPD field trial monitored actual PP during baseline period (without PPD injection) and treatment period (with PPD injection) at each end-point pipeline sections during heavy oil stable flow. Finally, the PPD optimum dosage was determined by considering the PP value at downstream section was maintained below target temperature. Result: Based on lab test result, the WAT of well effluent was 42.9ºC and PP was 29ºC. PPD performance test showed that 1 out of 2 tested products could modify PP to 20ºC with minimum dosage of 100 ppm. The selected injection point for PPD was at wellhead considering that it has higher temperature (80ºC) than oil WAT and the chemical would be well-agitated along the pipeline. After performing 7 days of field trial, the SMK flow assurance was improved by injecting 60-100 ppm of PPD chemical continuously with the actual PP at departure point (SMK manifold) was 29ºC (similar with oil PP) and at arrival point (receiving facility) was 5ºC (below oil PP), resulting more than 1,000 bpd production without wax formation issue. Conclusion: SMK heavy oil flow assurance could be unlocked by PPD injection. The chemical operation should be continuously assessed based on actual production network that might have different target temperature and feasibility of dilution with other hot liquid. Therefore, the PPD injection could be optimized and wax issue could be controlled.