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Collaborating Authors
Gas-condensate reservoirs
Abstract Reservoir studies, including preparation of field development plan, are processes typically dominated by time constraints. In general, reservoir studies consist in multiple geoscience activities integrated to build a fine geological model that eventually leads to an upscaled numerical model suitable for history matching and forecast simulations. In the simulation stage, the quality and effectiveness of the activity is highly dependent on the computational efficiency of the numerical model. This is particularly true for complex, supergiant carbonate reservoirs. Often, even with today's simulators, upscaling is still needed and simplifications can be implemented to allow computationally intensive history matching and risk analysis workflows. This paper provides some real field examples where these issues were faced and successfully managed, without applying further simplifications to the geological concept of the model: principles of reservoir simulations and common sense reservoir engineering were used to adjust properties of the model and then speed-up numerical simulation. Tuning included a combination of various solutions, such as deactivating critical cells whenever possible, calibrating convergence and time stepping control, tweaking field management to prevent instability in the computation, optimization of number of cores and cells split among cores to optimize load balancing and scalability. These solutions were used on two super-giant carbonate fields, a triple porosity (matrix, karst and fractures) undersaturated light oil reservoir and a supercritical gas and condensate reservoir. The former field was described using an upscaled model of about 700,000 active cells and a dual porosity - dual permeability formulation; the latter was described by a relatively coarse model of about 400 thousand active cells using a single porosity formulation. Large speed-up, up to five times with respect to reference simulations, was achieved without simplifying the geology and losing accuracy perceivably. Benefits were achieved for both conventional and high-resolution simulators.
- Geology > Rock Type > Sedimentary Rock (0.48)
- Geology > Geological Subdiscipline (0.34)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Gas-condensate reservoirs (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Carbonate reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Simulation > History matching (1.00)
- (6 more...)
Abstract Karachaganak Field is a giant gas-condensate reservoir located in north-western Kazakhstan. The reservoir is composed of an isolated carbonate build-up of Carboniferous - Early Permian age, located on the northern edge of the Pri-Caspian Basin. The reservoir is overlain by three thick salt domes which were formed by the movement of an evaporitic sequence deposited at the end of Early-Permian. This salt tectonics has locally affected the seismic image of the reservoir and consequently makes seismic interpretation challenging. A high fold and wide-azimuth 3D seismic volume has been acquired over Karachaganak. Preliminary migrations of this new seismic volume have improved resolution of the reservoir geometry and facies. The Karachaganak carbonate reservoir is characterized by both slope and platform depositional systems, and the reservoir has undergone significant diagenetic alteration. Diagenesis has altered the original depositional rock fabric, pore and pore throat geometry. Critical reservoir properties such as porosity, permeability and irreducible water saturation at Karachaganak are influenced by of both depositional and diagenetic processes. The degree of diagenetic alteration of Karachaganak is greater than some other analogous carbonate reservoirs in the Pri-Caspian basin. This paper discusses the current reservoir model for the post-Tula Carboniferous deposits, which is based on a synthesis of understanding of the depositional and diagenetic processes at Karachaganak. The current reservoir model incorporates the results from recently drilled wells, recent interpretations of 3D seismic data and well tests. The resulting dynamic model has a good history match to observed well performance, and provides a basis for field development decisions. Karachaganak Petroleum Operating (KPO) joint-venture is conducting additional studies of the field deposition and diagenesis to provide new insights into the complex geological history of the field to improve reservoir characterization and reservoir management activities.
- Phanerozoic > Paleozoic > Carboniferous > Mississippian (1.00)
- Phanerozoic > Paleozoic > Permian (0.89)
- Geology > Sedimentary Geology (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (1.00)
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Surface Seismic Acquisition (0.75)
- Asia > Kazakhstan > West Kazakhstan > Uralsk Region > Precaspian Basin > Karachaganak Field (0.99)
- Asia > Kazakhstan > Mangystau Oblast > Precaspian Basin > Tengiz Field > Tengiz Formation (0.99)
- Asia > Kazakhstan > Mangystau Oblast > Precaspian Basin > Tengiz Field > Korolev Formation (0.99)
- (27 more...)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Gas-condensate reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Sedimentology (1.00)
Application of Pressure Transient Analysis and Rate Transient Analysis to Dynamic Evaluation on Dry-Gas Reinjection in a Gas Condensate Reservoir with Strong Aquifer Support
Yong, Li (Research Institute of Petroleum Exploration and Development, PetroChina) | Jing, Zhang (Research Institute of Petroleum Exploration and Development, PetroChina) | Yuwei, Jiao (Research Institute of Petroleum Exploration and Development, PetroChina) | Baozhu, Li (Research Institute of Petroleum Exploration and Development, PetroChina) | Jing, Xia (Research Institute of Petroleum Exploration and Development, PetroChina) | Wei, Xie (Tarim Oilfield Company, PetroChina)
Abstract For gas condensate reservoirs with high condensate content, cyclic dry-gas reinjection is usually adopted to improve recovery. But cyclic gas reinjection gradually changes the composition and distribution of reservoir fluid, which causes much more difficulties for dynamic evaluation of this kind of reservoirs, especially for the reservoirs with strong bottom or edge aquifer support. This paper presents the dynamic evaluation on dry-gas reinjection in a gas condensate reservoir with strong aquifer support. The method mainly involves pressure transient analysis and rate transient analysis (RTA). Firstly, pressure transient data are interpreted, and reservoir properties and its variation are evaluated. Then all wells are classified into different types based on well test log-log curve shape and its change. Furthermore, all producers are also analyzed based on RTA, and RTA type curve characteristics and diagnostics for different type of wells are also determined. Finally, results and understandings interpreted from surveillance data are analyzed and compared, from which reasons for well performance variation are determined. This new method has been applied to Y gas condensate reservoir in China. The massive cyclic dry-gas injection of Y reservoir started in 2001, and current gas condensate recovery is higher than 40%. A total of 145 pressure build-up tests were conducted since then. Through detailed interpretation, reservoir properties and their variation behavior, such as permeability, skin factor, aquifer distance, etc. were evaluated. Based on analysis of the results, producers are classified into four types: performance no change type, condensate banking type, aquifer influx type, and injection gas breakthrough type. Furthermore, the 4 types of producers are also identified based on the type curve diagnostic of rate transient analysis. Through detailed comparison of results from the two methods, the reasons for the difference of different type of wells are analyzed and determined in combination with other production data and surveillance data. The understandings are used for cyclic gas injection adjustment, which improves the performance of Y gas condensate reservoir. This systematic technique has been successfully applied to Y gas condensate reservoir in Tarim Basin of China, which properly and correctly evaluates the reservoir properties around both producers and injectors. It also provides a reliable method for decision making of cyclic gas injection adjustment, such as producer conversion, well infilling, etc., which is helpful for effective and economic development of this kind of reservoir.
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Gas-condensate reservoirs (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Gas-injection methods (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management (1.00)
Understanding a Complex Overburden to Deliver Safe & Productive Wells at the Giant Shah Deniz Gas-condensate Field, Offshore Azerbaijan
Price, Gavin R (BP Exploration (Caspian Sea) Limited) | Hall, David (BP Exploration (Caspian Sea) Limited) | Kaiser, Karl (BP Exploration (Caspian Sea) Limited) | Tranchina, Enrico (BP Exploration (Caspian Sea) Limited)
Abstract The stage 2 development of the giant Shah Deniz gas-condensate field (SD2) represents an investment in excess of 45 billion USD and requires the drilling of 26 subsea development wells. Significant well cost reductions may be achieved by minimising the amount of ‘non-productive time’ (NPT) during drilling. NPT associated with subsurface geological characteristics may be minimised by careful pre-drill well planning, robust subsurface interpretation and data integration, application of learnings from previous Shah Deniz drilling and clear communication of subsurface risks to all parties involved in designing and executing the well. To achieve this, a dedicated team exists to provide an Integrated Subsurface Description (ISD) of the overburden and reservoir section at Shah Deniz. A three year plan describes the key ISD products designed to influence NPT and contribute towards the safe and efficient drilling of wells. These ISD products include an ‘ever-green’ geological model of the field, with overburden, reservoir and aquifer descriptions, plus 3D models of stress and pore-pressure. Such is the complexity of the pore pressure story at Shah Deniz that this represents one of the biggest risks to safe delivery of the wells required for SD2. Delivery of a detailed overburden ISD is enabled by comprehensive interpretation and integration of all well and seismic data acquired over the past 18 years. This paper will focus on some of the tools and techniques used to enhance understanding of the overburden geology at Shah Deniz, types of overburden products generated and how they are used in well planning.
- Asia > Middle East > Iran > Caspian Sea > Southern Caspian Basin (0.99)
- Asia > Azerbaijan > Caspian Sea > South Caspian Basin > Shah Deniz PSA > Shah Deniz Field > Balakhany Formation > Fasila Suite Formation (0.99)
- Asia > Azerbaijan > Caspian Sea > South Caspian Basin > Shah Deniz PSA > Shah Deniz Field > Balakhany Formation > Balakhany VIII Interval Formation (0.99)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Gas-condensate reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
Abstract The paper illustrates the approach to the formation of technological and instrumental base for selection of the optimal strategy to prepare the field for full-scale development and planning program of exploration plan/ experimental program, based on the example of multilayer field, including oil and gas condensate layers, differing in state of knowledge, conditions of sedimentation, reservoir properties, fluid properties, initial thermobaric conditions. Several exploration wells were drilled on the field, the area is covered with 3D seismic, the set of well logs was carried out (including modern methods), the core was picked and analyzed, the wells were tested using exploration plan and experimental program. The main purpose is to estimate geological and technological uncertainties and risks, and associated with them possible ranges of reserves and production levels. An algorithm for solving this problem included: review of the various options of geological structure, taking into account identified uncertainties, estimation of various development scenarios, taking into account technological risks separately for oil and gas reservoirs, and for the field as a whole. Peculiarity of the work is the aggregation of modern technologies of modeling variability of the geological structure, filtration processes, estimation of key risks calculatingly of technical and economic indicators for each of the scenarios. As a result, against the background of negative economic indicators of field development, obtained according base scenario of development, it was detected that it is possible to use of current uncertainties and risks on the field as a tool to find alternative scenarios of economically viable development plans. Such approach, in case of confirmation in each scenario of hypotheses leads to increase of overall efficiency of the project. Based on the probability of confirmation of such scenarios, the strategy of exploration plan and experimental program of the field is formed, including the drilling of exploratory wells, their research, analytical and laboratory works. The program is presented in the form of a decision tree, allowing to see the course of events on "a step forward", depending on the result. An integrated approach has allowed to optimize the program of exploration plan and experimental program: the amount of information needed to make decisions, received with fewer new exploration wells, that allowed to reduce the capital expenditures on the exploration plan and experimental program.
- Reservoir Description and Dynamics > Reserves Evaluation (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Gas-condensate reservoirs (0.52)
- Management > Asset and Portfolio Management > Field development optimization and planning (0.40)
- (4 more...)