Screening of Field Development Options by Simulation Study To Improve Recovery From Lower Southern Units of Complex Carbonate Reservoir

In the paper, we will briefly review the pilot design and demonstrate the utility of applying the EM imaging to the pilot. We will also show the benefit of the optimized casing material on the resolution of the crosswell EM resistivity images and describe the methods employed for monitoring the fluid flow and show preliminary results of the modeling process. This crosswell EM technique which has been successfully employed and proven in other geographical areas is being implemented first time in UAE. The EMI technology is being deployed in southern part of a complex carbonate reservoir in the middle-east where an uneven flood front advance has been observed in different reservoir units. It has been observed that water front has advanced much faster in the highly permeable upper reservoir units as compared to lower reservoir units. In order to understand the horizontal and vertical fluid flow behavior, an inverted 5-spot water injection pilot pattern is being implemented. The pilot will address the issues of the uneven sweep efficiency, bypassed oil and effectiveness of stylolites across different units. The pilot results and observed data will be used in the simulation to design an optimum development scheme for the lower reservoir units in the southern part of the field. The current dynamic simulations predicted that the injected water will reach producers after 7 to 10 years. However, the decision on field developments have to be taken early enough to avoid the slumping of water from upper to lower units and loss of reserves in the lower units. Early imaging of the injected water from the injection well into the reservoir is paramount in assessing the success of the pilot and future field development issues. It is anticipated that this tomographic Cross-well Electro-magnetic (EM) resistivity technique will provide sufficient imaging information to track the water flood movement between wells. The most favorable conditions to acquire reliable formation resistivity distribution information, EMI require at least one kilometer distance or separation between wells. Prior to the field deployment, simulations were run to confirm the applicability of the technique and define the parameters for the survey with objectives; 1) to check the sensitivity of EM technique to the reservoir conditions and injected fluids, and 2) to carry out actual EM tool simulation and check the quality of tool response. The study concluded; 1) cross-well EM resistivity technique is well suited for tracking the water front in the current reservoir conditions, 2) the injected fluids create enough resistivity contrast to be easily picked up by the technique, and 3) the flood front progress can be captured by conducting the surveys in a time-lapse mode. As part of this project, lab tests were conducted to choose a material that would limit the attenuation at high frequency as much as possible at source and receiver locations. Introduction Peripheral water flooding as pressure maintenance method was commenced within few years of the discovery of the giant complex carbonate reservoir in the middle-east region. Although initially quite successful, the field has experienced uneven distribution of water flood front, vertical and lateral sweep due to reservoir complexity. Detailed simulation modeling was performed to delineate optimum strategy for maximizing reserves in the lower two oil bearing units of reservoir thereby controlling the process at a more local level (Ref. 1). The benefits of this process are more efficient and faster recovery. The potential drawbacks are greater costs and higher local pressures which could induce uneven flows.

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Tracking Interwell Water Saturation in Pattern Flood Pilots in a Giant Gulf Oil field

Bhatti

Mansoori

Sembawy

et al. 2008

Abu Dhabi International Petroleum Exhibition and Conference

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Peripheral water flooding has been the preferred pressure maintenance tool for many gulf carbonate reservoirs over the past 30 years. Due to uneven sweep and pressure distribution, this technique has given way to pattern floods in several gulf fields. As these new floods are established, it is important to understand the water saturation between wells to properly manage the sweep and recovery. In 2007, ADCO initiated water injection (WI) and WAG pilots to test the recovery strategy. The pilot employs advanced geophysical and modeling tools to measure formation properties at the wells and between wells; this paper discusses the WI pilot. Among the novel techniques applied is the crosswell electromagnetic method, which measures the interwell resistivity distribution between observation wells at the pilots. Interwell resistivity data can be used to infer the water saturation distribution because of the sharply different electrical resistivity between injected water and oil bearing reservoir rock. By allowing an evaluation of the water distribution long before the injected fronts reach producers or observers, a better and more rapid understanding of the pilot arises from the crosswell electromagnetic technique. In this paper, we briefly describe the pilot design, describe the detailed geological model and show results from the initial set of baseline and time lapse EM data sets from the water injection pilot. The images highlight the influence of background geological constraints on the flow. Introduction Applying peripheral water flooding for pressure maintenance was commenced after few years of the discovery of field A, a giant complex carbonate reservoir in the middle-east. Although this strategy has been successful, there is evidence of an uneven sweep due to reservoir complexity. These complications have led to the introduction of pattern-based flooding technology and the establishment of the water injection (WI) and WAG pilots in the underswept lower units of the reservoir. The benefits of pattern flooding are more efficient and faster recovery. The potential drawbacks are greater costs and higher local pressures which could induce uneven flows. Detailed pattern flood modeling helped develop an optimum strategy for maximizing reserves and production, especially in the lower two oil bearing units of the reservoir (Ref. 1). Consequently, WI pilot has been implemented in the lower units of the reservoir. A detailed multi-year and multi measurement monitoring plan has been established to determine the pilot performance which includes deep reading technologies like electromagnetic surveys. The main objectives of the WI pilot project are:determine sweep efficiency in the target reservoir units,qualitatively assess the impact of injected fluid fluxes vertically across low permeability sub-units within the reservoir, anddetermine pressure support due to pattern injection. The pilot will also address the issues of uneven sweep, bypassed oil, and residual oil saturation. The acquired field data will be used to calibrate the simulation model for production, injection, saturation and pressure data in order to design as an optimum field development scheme for the lower reservoir units in the southern part of the field. (Ref 2)

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Screening of Field Development Options by Simulation Study To Improve Recovery From Lower Southern Units of Complex Carbonate Reservoir

Cited by 7 publications

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Optimum development options and strategies for water injection development of carbonate reservoirs in the Middle East

Optimum development options and strategies for water injection development of carbonate reservoirs in the Middle East

Imaging Injected Water flood Fronts between Wells in a Complex Carbonate Reservoir: Designing Completions to Optimize Image Resolution

Tracking Interwell Water Saturation in Pattern Flood Pilots in a Giant Gulf Oil field

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