Abstract

Alkaline Surfactant Polymer (ASP) flooding was identified as a potential field development option for a clastic field in Southern Sultanate of Oman. Extensive laboratory studies and field tests have been conducted to evaluate and mature this development option. Core floods showed that ASP can recover more than 90% of the oil remaining after waterflood resulting in remaining oil saturation below 5%. Simulation studies showed that ASP can potentially increase the field recovery factor by more than 20% over waterflood or 10% over polymer flood. A successful ASP single-well tracer test (SWCTT) and a micro-pilot in this field validated the laboratory results, confirmed the significant desaturation by ASP and the low residual oil saturation after ASP. The potential size of the prize for ASP flooding in this field alone is significant.

Upon further evaluation of ASP as a development option, significant risks and uncertainties associated with implementing ASP at field scale were identified. An ASP continuous injection pilot was designed with well-defined objectives to reduce the risks and to quantify the uncertainties. In this pilot, the ASP process was evaluated in one of the main producing zones in the flank of the field utilizing a small (75m × 75m or 1.4 acres) inverted 5-spot pattern with a total of 7 wells (4 producers, 1 injector, 1 observation well, and 1 sampling well). The short injector-to-producer distance enabled a quick response and ensured completion of the field trial within one year at the target injection rate. The pilot was commissioned in Q1 2014 with water pre-flush to establish a waterflood baseline. Injection of the 0.3 PV ASP-slug started in February 2016, followed by 0.9 PV of polymer and a water post flush that was concluded in December 2016.

A custom-built surface facility was constructed to mix and inject the required chemicals and to assess and treat produced fluids through a specialized flow loop. Dedicated Multi Phase Flow Meters (MPFM) were deployed at each producing well to provide accurate phase rates to quantify ASP incremental oil volumes. Detailed chemical analyses of injected and produced fluids were conducted throughout the pilot execution. Desaturation assessments were carried out through detailed surveillance activities in the dedicated logging observation well that involved a comprehensive suite of logs and evaluation tools, including time-lapse Nuclear Magnetic Resonance (NMR) for saturation monitoring that were used for the first time in the field.

The pilot achieved stable and safe operations with good injectivity, uptime, accurate chemical dosing, sampling and analysis as well as detailed surveillance. It recovered a significant incremental volume of oil above waterflood from decline curve analysis vs. a target of 20%, hence doubling the recovery as achieved with waterflood. Significant water cut reversal (25% - 30%) in producers and 31% reduction in oil saturation in the observation well due to ASP were observed by the time lapse NMR data. No injectivity issues were encountered with 50cP ASP and polymer chase. No scale was encountered during pilot period due to the successful and early deployment of scale inhibitor. The pilot produced saleable quality oil, free from emulsion with negligible increase in BSW over waterflood.

This paper re-iterates the pilot objectives and design, summarizes the pilot results, including well performance, chemical analysis and surveillance data, surface facility performance during pilot execution, and the dynamic simulation and analysis of the pilot performance.

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