Hydrocarbon gas flooding is one of the most applied miscible EOR processes in the oil industry. The process becomes extremely challenging in heterogeneous carbonate reservoirs. An inverted four-spot hydrocarbon (HC) gas injection pilot has been under execution since 2016 to address these challenges, in a heterogeneous multi-layered Oolitic carbonate reservoir in West Kuwait. The pilot consisted of a pre-flush phase of water injection (2016-19) followed by a gas injection phase (2021-2022). This paper describes modelling and history matching of pre-flush waterflood phase and forecasting ahead of gas injection phase. The pre-flush waterflood was carried out sequentially into four target layers, injecting a range of pore volumes in each layer and gathering wealth of pilot data including Inter-Well Tracer Test (IWTT), PLT/ILT, time-lapse saturation logging, coring, and VIT to assess the impact of heterogeneity on the displacement process. Integrated review of the acquired dataset was conducted leading to better understanding of the reservoir performance. Model calibration was challenging as variable tracer arrival and concentration profiles indicated high heterogeneity. Detailed compositional simulation studies were undertaken on hybrid sector models of the pilot area created from full-field models, incorporating newly drilled well tops, reservoir properties and full-field fluxes. High-level experimental designs were conducted leading to dynamic sector models calibration, by identifying layer connectivity and baffle introduction as the main modelling gaps. The results showed baffles to vertical flow play a key role in reservoir and fluid flow performance. The knowledge gained from the pre-flush pilot data review and modelling were instrumental in forecasting the pilot gas injection performance. Activities undertaken to forecast the gas injection pilot performance include a two-pronged strategy of using calibrated hybrid sector model realizations and simple box models. The box-models captured range of gas injection phase outcomes on a simplified finer resolution of injector-producer models, testing gas injection strategy sensitivities without any dependency on history match quality, while the calibrated hybrid sector models offered pilot gas injection outcomes accounting for pilot area wells interaction and full-field streamline fluxes, testing gas injection programme robustness. The approach tremendously helped with the surveillance programme design of the pilot gas injection phase. Novel integrated modelling workflows, history matching techniques and forecasting approaches were used in this study of a complex heterogeneous multi-layered carbonate reservoir. Results of which assisted KOC to plan and successfully implement the pilot gas injection phase and formulate a robust surveillance programme to capture the effects of gas injection process. Further, it will help in designing a road map for commercial deployment of gas injection on a field scale.

Umm Gudair Minagish Oolite is a highly heterogeneous reservoir with intermittent micritic units forming low permeability barriers to fluid flow. Based on screening/lab study, the polymer or surfactant-polymer flooding was proposed using normal 5 spot injection pattern. KOC decided to test only polymer flooding because of cost considerations. This study is to design fit for purpose long-term polymer injectivity (LTPI) pilot using produced water (salinity 230000ppm) with the objectives of testing injectivity, adsorption, breakthrough, resistance factor and response time within 6-12 months. Numerical simulation and economic modelling was used for this evaluation to explore various novel strategies. Various parameters were optimized to design Fit for Purpose LTPI pilot configurations using high salinity produced water. The laboratory experiments were conducted in conjunction with reservoir simulation to confirm the technical viability of polymer flooding using high-salinity water. In this study, we discuss existing challenges and how the same was transformed into opportunities by optimizing various parameters such as number of wells, well spacing, well location, perforation layer for injectors and producer and the economics to meet pilot objectives. The simulation results show that normal 2-spot injection pattern (2 injectors and 1 producer) with 80m well spacing and perforation in B-zone is a suitable solution for LTPI pilot within given time. Based on the above plan, one injector was drilled near the existing producer. The recent gyro survey demonstrated shifting of the sub-surface locations of both the producer and injector, thereby altering the well spacing. Further simulation incorporating the new locations indicated that the pilot would not meet the objectives within the piloting duration of 6 months because of shifting. Surface constrains hindered the shifting of drilling location for the second injection well to maintain 2-spot injection pattern. To overcome this challenge, additional simulation works performed to plan and drill the second injector well near another existing producer at 80m well spacing in a different area to test different rock types. Both LTPI pilot designs show higher incremental cumulative oil over water flood, faster polymer breakthrough (∼1 month), faster polymer response and oil peak within 6 months. In addition, using high salinity produced water for polymer flooding is expected to reduce piloting cost and increase operational efficiency by reducing operational problems associated with treatment and handling of less saline water.

The matured field is located in the Sarawak offshore, Malaysia. Discovered in 1968, the field is an anticlinal structure with vertically stacked reservoirs deposited in a shoreface environment. The brown field has been producing under active aquifer drive with a very high recovery factor. The field is currently producing with more than 85% WC and has significant levels of uncertainties with respect to oil-water contacts, flank structure, depth of spill points, production allocation, SCAL and residual oil saturation.Major challenges were observed in building fine static models for further dynamic simulation work. A coarse mega model were built covering all reservoirs to capture the STOIIP uncertainties in the field as well as to support an integrated conventional approach to locate the remaining oil and estimating the potential infill reserves. A robust workflow were developed to identify the infill opportunities by integrating material balance study, case hole logs information, water diagnostic plots, decline curve analysis and many more. The comprehensive LTRO methodologies applied has been successful in identifying the location of the remaining oil as well as estimating the potential reserve. This approach has also managed to accelerate field development plan and afforded the team efficient resource optimization by avoiding the more time consuming re-cycling the conventional static-dynamic modeling approach.

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CO2 flooding is known to be one of the most applied miscible EOR process in E&P industry given its ability to mix with reservoir oil and form a miscible flood at relatively low reservoir pressures. CO2 EOR pilots' locations selection, configurations and design are key for success of an EOR piloting scheme. This goes without withstanding detailed compositional simulation to replicate components exchange under the MCM process as well as potential implications on existing well completions and surface facilities.A structured workflow was established to rank and prioritize all reservoir units in terms of their suitability for miscible EOR. A thorough scrutiny of pilot locations, configuration as well as pilot design as a whole was undertaken. This was aimed to short-list preferred pilot locations and configurations that address most of remaining uncertainties. It was also intended to establish a list of expected deliverables from the pilots. Numerous pilot configurations were analyzed and ranked based on the size of EOR prize, uncertainties reduction as well as capturing synergies and common objectives across the reservoir units.Detailed compositional simulation studies are being undertaken. This included one-dimensional models for the purpose of examining the displacement process; 2D mechanistic models to assess the impact of heterogeneity on the displacement process as well as fine grid pilot models for the purpose of optimizing the pilot design. A probabilistic production forecast of each pilot is also considered aiming to capture a range of possible outcomes and identify key uncertainties to be acted upon.A tailored monitoring program is being designed to acquire key performance data including production and saturations monitoring, fluid sampling and pressures. This will feed inputs to sector model calibration as well as the evaluation of pilot performances.Results from this study are expected to assist ADCO to plan and implement the EOR road map while accounting for all related issues such as flow assurance and asphaltene deposition, reservoir pressure maintenance, CO2 strip-out and re-injection as well as its impact on existing facilities.