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This paper describes planning, implementation, and results of chemical gas tracers used in a gas injection pilot study in a heterogeneous multilayer reservoir, onshore Kuwait. The use of tracer for waterflooding is a common practice to understand and improve field performances. In contrast, tracing injected gas with chemical tracers is applied less frequently. This study presents the first implementation of gas tracers in a pilot study in Kuwait and is an early adaptation of tracers to investigate gas-based EOR in the Middle East. The pilot comprises of one injector completed in three target layers and seven producers, completed in similar or other different layers. Unique gas tracers were injected into isolated layers independently at different times to evaluate the injector-producer connectivity in each layer. The producers and re-injected gas were sampled for one year to evaluate gas tracers return. The recovered tracer masses were evaluated against the injected amount to provide information on connectivity and sweep efficiency. The main revelation from the gas tracer study is their distinct difference from what could be expected from a consideration of the water flow itself. A likely explanation for the difference is that the water and gas behave differently in the reservoir, which in turn leads a conclusion that gas enhances the production of oil by replacing oil in the reservoir volumes.
This paper describes planning, implementation, and results of chemical gas tracers used in a gas injection pilot study in a heterogeneous multilayer reservoir, onshore Kuwait. The use of tracer for waterflooding is a common practice to understand and improve field performances. In contrast, tracing injected gas with chemical tracers is applied less frequently. This study presents the first implementation of gas tracers in a pilot study in Kuwait and is an early adaptation of tracers to investigate gas-based EOR in the Middle East. The pilot comprises of one injector completed in three target layers and seven producers, completed in similar or other different layers. Unique gas tracers were injected into isolated layers independently at different times to evaluate the injector-producer connectivity in each layer. The producers and re-injected gas were sampled for one year to evaluate gas tracers return. The recovered tracer masses were evaluated against the injected amount to provide information on connectivity and sweep efficiency. The main revelation from the gas tracer study is their distinct difference from what could be expected from a consideration of the water flow itself. A likely explanation for the difference is that the water and gas behave differently in the reservoir, which in turn leads a conclusion that gas enhances the production of oil by replacing oil in the reservoir volumes.
A hydrocarbon gas injection pilot was successfully conducted in a heterogeneous multilayered Oolitic carbonate reservoir in Kuwait. The pilot strived towards de-risking technical and commercial feasibility for field-scale deployment of miscible CO2 WAG EOR development. The aim was to generate reliable unambiguous pilot performance results on remaining oil saturation, inflow profile and sweep efficiency to better quantify risks and uncertainties. This paper describes design, execution, and results of this pilot and its challenges and opportunities. The pilot was an inverted four-spot, consisted of a pre-flush water injection phase (2016-19), drilling and coring two fiberglass cased observation wells, followed by a gas injection phase (2021-2022). The phases were carried-out sequentially in three target layers, injecting a range of pore volumes in each layer. The pre-flush surveillance program included Inter-well water tracer test (IWTT), time-lapse saturation logging, coring, PLT/ILT, VIT, PGOR and ESP monitoring of the pilot wells. The gas injection phase surveillance in addition constituted gas tracers, pressure transient data and time-lapse saturation logging in the two observation wells to monitor the gas flood front movement. The immediate impact of this miscible gas injection pilot was the bolstering oil production increase and water-cut reduction in several pilot wells in relatively short pilot duration, persuading the management to high-grade CO2 full-field development as in-plan firm project. An integrated analysis of all the gathered data was conducted, providing an insight on reservoir de-saturation, inflow and sweep for the pre-flush and gas injection phases along with the achieved oil gain, assisting better understanding of the implications for future CO2 Water Alternating Gas (WAG) Enhanced Oil Recovery (EOR) full field pattern development. Detailed integrated static and dynamic modeling of the pilot area were conducted using compositional simulation models, incorporating pre-flush and gas injection phase data, history matched to production, injection, GOR, water-cut, pressure, tracer production concentration and arrival time, ILT/PLT and time-lapse saturation logs. This detailed assessment revealed the impact of heterogeneity including horizontal baffles and barriers on the displacement process. The water and gas tracer analysis provided a unique opportunity to conduct Residence Time Distribution (RTD) analysis to assess, quantify, and compare heterogenous flow patterns and swept volumes for both water and gas transport between well pairs in different reservoir layers. Novel integrated workflow consisting of robust surveillance techniques, reservoir modelling workflows along with tracer analysis techniques were used in this complex heterogeneous multi-layered carbonate reservoir study in understanding pore scale and reservoir scale sweep efficiency and its impact on oil recovery. The immediate increase in oil production in pilot and surrounding wells has provided KOC the much-needed opportunity in designing a road map for commercial deployment of CO2 WAG in this world class field.
EOR pilot initiatives, integral to the company's strategy, are conducted within limited areas, typically less than ∼5 acres, to assess the commercial feasibility of selected EOR methodologies for specific reservoirs. This study examines subsurface challenges encountered throughout the execution of EOR projects, focusing on geological uncertainties. It proposes pragmatic remedies by addressing constraints in geological data and devising risk mitigation strategies during the pilot implementation phase. Drawing upon insights gleaned from EOR pilot initiatives, various strategies are employed to mitigate geological uncertainties within and surrounding the pilot zone. These encompass the acquisition of directional surveys in pilot and adjacent monitoring wells, as well as the collection of core samples, RFT data, fluid specimens, CBL logs, FMI, and VIT data in a minimum of two pilot wells to facilitate correlation. Additionally, comprehensive analyses such as complete core CT scans, sedimentological assessments, XRD analyses, and petrographic studies are conducted. Surveillance during the pilot phase involves obtaining baseline and time-lapse data through methods like HPT-SNL, PLT, induction resistivity, and pulse neutron logging. Furthermore, interwell tracer data is acquired at least twice and integrated with geological correlations. In the first case study, a three-well pilot comprising two injectors and one producer, alongside an existing central producer, was initially designed. The first injector well was drilled based on the predetermined plan. Subsequent analysis of the most recent deviation surveys revealed alterations in the target subsurface distances between the injector and central producer wells, prompting adjustments to the design to align with the updated surveys. In the second case study, the acquisition of cores from multiple wells within a conventional five-spot chemical EOR pilot proved instrumental in accurately determining the depths and widths of highly permeable zones in each well. This core data was then correlated with HPT-SNL logs to delineate the extension of permeable layers within the pilot area. Furthermore, insights derived from formation mineralogy aided in understanding issues related to siderite precipitation resulting from chemical injection, particularly in zones with large perforation intervals. The third case study involved a miscible gas EOR pilot, cores from pilot wells aided in avoiding weathered zones for perforation. VIT, guided by FMI and openhole logs, identified six lithological barriers; unexpectedly, only two were leak-free. These findings shed light on gas breakthroughs and guided perforation strategies. The study focus lies on tackling geological uncertainties and suggesting solutions like thorough data acquisition. Adaptation of pilot designs using deviation surveys, accurate zone identification through core data, and employing Vertical Interference Testing (VIT) for lithological barrier assessment in miscible gas EOR projects are highlighted as essential insights.
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