Gas Injection into the Tengiz oilfield began in January 2007 with sweet gas injection as Phase 1 of the SGI pilot project. Phase 2 of the project, sour gas injection, began in October 2007, but was interrupted due to initial injection start up problems. Continuous sour gas injection began in January 2008. As part of the SGI Surveillance Plan, a variety of reservoir measurements are routinely acquired to monitor the progress of the flood. The SGI project has four signposts for success: Compressor reliability, Injectivity, wellbore durability, and reservoir performance. The sour gas compressor at Tengiz was the first of its kind and has had greater than 90% availability when SGP has been operational. Injectivity has exceeded expectations and wellbore durability has also been excellent. The fourth area is reservoir performance and all indications are that the reservoir is performing as expected. The SGI project consists of seven inverted five-spot patterns. To expedite data acquisition, the SGI well patterns were designed to include one "super-spot" pattern (twin injectors 100 m apart providing dedicated injection support to different geologic layers) and three short-spaced producers (producer-injector spacing approximately 1/3 of the standard spacing). Tracers, pulse tests, multiphase meters, gas saturation logging, and production and injection are used to monitor and understand reservoir performance. A specialized simulation model (Monitoring Model) was constructed which uses local grid refinement in the SGI pattern area. On August 22, 2008, gas breakthrough occurred in Well T-318, the first of the short-spaced producers. This breakthrough was predicted with the Monitoring Model. Predictions from Monitoring Model suggest most likely breakthrough is near top of reservoir, and this was substantiated by logs. The gas injection project will continue to be closely monitored to improve our understanding and reservoir forecasts.
Sour gas injection operation has been implemented in Tengiz since 2008 and will be expanded as part of a future growth project. Due to limited gas handling capacity, producing wells at high GOR has been a challenge, resulting in potential well shutdowns. The objective of this study was to establish an efficient optimization workflow to improve vertical/areal sweep, thereby maximizing recovery under operation constraints. This will be enabled through conformance control completions that have been installed in many production/injection wells. A Dual-Porosity and Dual-Permeability (DPDK) compositional simulation model with advanced Field Management (FM) logic was used to perform the study. Vertical conformance control was implemented in the model enabling completion control of 4 compartments per well. A model-based optimization workflow was defined to maximize recovery. Objective functions considered were incremental recovery 1) after 5 years, and 2) at the end of concession. Control parameters considered for optimization are 1) injection allocation rate, 2) production allocation rate, 3) vertical completion compartments for injectors and producers. A combination of different optimization techniques e.g., Genetic Algorithm and Machine-Learning sampling method were utilized in an iterative manner. It was quickly realized that due to the number of mixed categorical and continuous control parameters and non-linearity in simulation response, the optimization problem became almost infeasible. In addition, the problem also became more complex with multiple time-varying operational constraints. Parameterization of the control variables, such as schedule and/or FM rules optimization were revisited. One observation from this study was that a hybrid approach of considering schedule-based optimization was the best way to maximize short term objectives while rule-based FM optimization was the best alternative for long term objective function improvement. This hybrid approach helped to improve practicality of applying optimization results into field operational guidelines. Several optimization techniques were tested for the study using both conceptual and full-field Tengiz models, realizing the utility of some techniques that could help in many field control parameters. However, all these optimization techniques required more than 2000 simulation runs to achieve optimal results, which was not practical for the study due to constraints in computational timing. It was observed that limiting control parameters to around 50 helped to achieve optimal results for the objective functions by conducting 500 simulation runs. These limited number of parameters were selected from flow diagnostics and heavy-hitter analyses from the pool of original 800+ control parameters. The novelty of this study includes three folds: 1) The model-based optimization outcome obtained in this study has been implemented in the field operations with observation of increased recovery 2) the hybrid optimization of both schedule and operation rule provided practicality in terms of optimization performance as well as application to the field operation 3) provides lessons learned from the application of optimization techniques ranging from conventional Genetic Algorithm to Machine-Learning supported technique.
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Tengizchevroil (TCO) has had up to 20 years of experience in industrial Waste Water Disposal (WWD) into the subsurface. TCO industrial waters cannot be recycled or utilized for any other purposes, hence, malfunction of any component of WWD system (especially wells) can lead to production curtailment. Therefore, TCO has identified the WWD wells as "critical" wells in the business unit. Waste water is injected into three disposal wells; there are six monitoring wells that provide important information about reservoir pressure, the change in chemical composition of water samples, the fluid level and wellhead performance. Regular surveillance is a key to get data, such as reservoir pressure, temperature, downhole samples, reservoir connectivity, etc. This is important to build the correct reservoir model, both static and dynamic with immediate interest in identifying the water front movement and eventual water breakthrough wells. In the light of expected operational activities, optimization projects and commercial oil growth, WWD activities are planned to be expanded. Drilling new wells is proposed to add spare injection and monitoring capacity to the project. Additional services, surveillance steps, well geometry and completion design optimization is considered for all new wells. Cross-functional efforts of subsurface earth scientists and petroleum engineers, lab technicians/facility engineers/environmental specialists/regulatory teams are critical to achieve technical excellence, and hence to fulfil regulatory requirements. Third party involvement in lab analyses and results interpretation strengthens confidence in the operator's efforts to maintain and protect the environment according to official agencies vision.
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