The first field scale Polymer flood project in the Middle East region is being implemented in an oil field of Sultanate of Oman from early 2010. The oil field discussed here containing viscous oil (90 cp) was discovered in 1956 and is located in eastern part of South Oman Salt basin. First commercial production started in 1980 from this field. The field has gone through different development phases in its 30 years of history prior starting tertiary recovery phase by polymer flooding. This field scales Polymer flood project comprising 27 patterns as Phase-1 covers about one third of the total field IOIP (initial oil in place). It is worth mentioning that whole field is under water flooding and water injection was going on prior to initiation of Polymer flood in all these 27 injectors. Further extension in phases to full field polymer flooding is under evaluation. Till now this Polymer flood project has successfully completed 3 years of good performance contributing to significant oil gain. This paper describes briefly about the principles involved in polymer flooding, planning of this polymer flood project, field implementation and field examples of polymer response. In addition, a few practical aspects of managing key issues in polymer flooding like- fracture growth in injectors, shear degradation of polymer solution, pattern conformance and back produced polymer has been covered in this paper.
A field in Southern Oman has been identified as a potential target for Alkali-Surfactant-Polymer (ASP) flooding. Experimental investigations showed that ASP flood recovers more than 90% of waterflood remaining oil saturation. Simulation study showed that ASP increases the field recovery factor by more than 20% over waterflood or 12% over polymer flood. The potential size of the prize by ASP in this field alone is significant. The successful ASP single well chemical tracer test (SWCCT) and micro-pilot in this field validated the lab experimental results and demonstrated the significant desaturation by ASP and the extremely low oil residual after ASP. The ASP pilot was designed and initiated to de-risk and underpin the financial investment decision for a full-field implementation. The ASP pilot is designed as a small 1.4 acres (75m × 75m) inverted 5-spot pattern. It ensures completion of the field trial within one year of ASP flood. The pilot was commissioned in Q1 2014 with water pre-flush and the first ASP injection is anticipated for Q1 2016. A dynamic model was constructed and simulation was carried out. A comprehensive surveillance program was included in the pilot design and is being executed successfully. Surveillance data provide critical information to understand pattern communication, fluid flow path and reservoir characteristics. This paper will describe the results and analysis of some waterflood surveillance data and the integrated workflow of history matching. During the ASP pilot drilling campaign in 2013, an unexpected fault was encountered crossing the well pattern. This introduced an element of uncertainty regarding pattern communication. Pressure data and a passive tracer test confirmed the connectivity between the injector to 4 producers and that the fault is non-sealing. Initially the sector model was built with one fault across the pilot area, but the fluid communication in the pattern revealed by analysis of tracer suggested possible different geological realizations than the initial model. Therefore several static geological models were generated to reduce the uncertainties on history match. Well conformances were determined by PLT and DTS/DAS and were incorporated in the dynamic model. The time-lapse NMR log in the observation well provides insights on sweep, desaturation and micro displacement efficiency. Establishing and building a waterflood baseline is the foundation for the next phase of ASP implementation. This paper will share the analysis, learnings and practical implications of the pilot to date.
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.
A field in southern Oman has been identified for conducting an alkaline surfactant polymer (ASP) pilot project to enhance oil recovery. The potential benefit from ASP flooding had been estimated to be significant, based on coreflood investigations and single-well tests. The ASP pilot was initiated to derisk and support the financial investment decision for full-field implementation. The vertical saturation estimates were obtained through state-of-the-art nuclear magnetic resonance (NMR) technology in the observation well, which was completed with fiber-reinforced plastic (FRP) casing and located midway between the injector and a producer of the pilot. Laboratory ASP flood experiments demonstrated that NMR response is insensitive to the chemistry of ASP/polymer solutions. The tool response provides salinity-independent inference for saturation profiling. These characteristics of NMR technology make it a suitable saturation monitoring tool for fields applying chemical enhanced oil recovery (EOR). The pilot was executed with several phases, starting with pre-ASP waterflooding. This was followed by ASP slug injection, which, in turn, was followed by polymer chase and, ultimately, by chase water injection. The base vertical saturation profile was established during the last stage of the pre-ASP waterflooding phase. The time-lapse vertical saturation profiles facilitated estimation of incremental desaturation during and after every stage of the injection phases. The dedicated multiphase flowmeters for each producer have also provided realtime oil production profiles to quantify the incremental oil production. During the ASP pilot, NMR indicated the formation of an oil bank and desaturation due to ASP. This paper discusses the results of NMR during ASP pilot and the insights that NMR brings into understanding of subsurface performance and vertical sweep due to ASP.
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