A pilot water flood was carried out in the Marrat reservoir in the Magwa Field. The main aim of this pilot was to allow an assessment of the ability to sustain injection, better understand reservoir characteristics. A sector model was built to help with this task.An evaluation of the injectivity in Magwa Marrat reservoir was performed with particular attention to studying how injectivity varied as injected water quality was changed. This was done using modified Hall Plots, injection logs, flow logs and time lapse temperature logs.Data acquisition during the course of the pilot was used to better understand reservoir heterogeneity. This included the acquisition of pressure transient and interference data, multiple production and injection logs, temperature logging, monitoring production water chemistry, the use of tracers and a re-evaluation of the log and core data to better understand to role of fractures.A geological model using detailed reservoir characterization and a 3D discrete fracture network model was constructed. Fracture corridors were derived from fractured lineaments interpreted from different seismic attribute maps:A sector model of the pilot flood area was then derived and used to integrate the results of the surveillance data. The main output is to develop an understanding of the natural fracture system occurring in the different units of the Marrat reservoir and to characterize their organization and distribution. The lessons learned from this sector modeling work will then be integrated in the Marrat full field study.The work described here shows how pilot water flood results can be used to reduce risk related to both injectivity and to reservoir heterogeneity in the secondary development of a major reservoir.
Interference testing is the oldest but still the most effective way of establishing communication between wells and determining the reservoir transmissibility. However, data can be difficult to interpret and the results can be misleading. Fortunately, simple steps can be performed to validate the data and obtain first estimates of the formation parameters. We demonstrate this methodology for an interference test performed in the Greater Burgan field in Kuwait.A pilot project was started to understand how to successfully inject water in the Wara reservoir. Seven wells were drilled in an area away from the existing wells: one injector at the center of a 250 m-radius hexagon formed by six producers. An interference test was performed between the injector and the producers. The main objective of the study was to evaluate the transmissibility between wells and the permeability anisotropy in the formation. In five of the producers, the target sands were oil bearing, whereas surprisingly, the same sands were water bearing in the sixth well. Consequently, a second objective was added to the study: to check whether the sixth well was in communication with the other wells and to determine the origin of the water.The tests showed that all wells responded to the pressure pulse, including the sixth well, thus refuting the assumption that a fault was isolating it. The fall-off analysis of all the wells highlighted the presence of boundaries, a finding that was consistent with the fluvial depositional environment. Moreover, the analysis showed that the channel was narrowing near the sixth well. Therefore, we could hypothesize that the sixth well had been drilled in a zone with perched water trapped by the channel boundaries. A few weeks after the test, the oil cut started to increase in that well, confirming our hypothesis.The findings from this pilot project proved the efficiency of waterflooding as secondary recovery method and were used to design the pressure maintenance program.
Greater Burgan in Kuwait is the second largest field and the largest clastic reservoir in the world. Discovered in 1938, the production initially came from Wara sandstone and soon followed by other underlying Burgan clastic reservoirs. Burgan reservoir mainly consists of three reservoir units namely Wara, Third, and Fourth sand. The Wara Water Flood Pilot Project is the first clastic waterflood pilot in Kuwait. Reservoir pressure in Wara has been falling below the bubble-point in many parts of the reservoir. This would ultimately result in free gas evolving from the oil and significant loss in reserve recovery. This pilot was designed with the objective to obtain information in the areas of:Long-Term InjectivityReservoir ConnectivityWater Breakthrough Time and DirectionWater-Cut DevelopmentProductivityOperational Experience The Wara pilot pattern is of inverted seven spot with one injector, six producers, and one water source and was designed to inject 5,000 to 10,000 bwpd into a single injector and to produce from six producers drilled around the injector. Each well is 250 meters apart and the producers are equipped with ESPs to produce even after water breakthrough. The project has been in the operational phase for the last two years and the main objectives of evaluating long-term injectivity and the reservoir response to water injection in the Wara reservoir were achieved. Results from this pilot were needed to reduce subsurface uncertainty and to support the design of future Wara waterflood projects. This will ultimately help in the decision of whether to build a permanent water flood project to maintain astable reservoir pressure in the Wara reservoir. This paper highlights the challenges and accomplishments in designing, completing, and operating of this successful water flood pilot project which could benefit other similar projects around the world. 1. INTRODUCTION The Greater Burgan field is located in the South-Eastern part of Kuwait as shown below and is producing most of the oil for the state of Kuwait. The Burgan reservoir mainly consists of three reservoir units namely Wara, Third, and Fourth sand. The Third and Fourth sand members have excellent reservoir characteristics and are prolific producers. At this time the Third sand is the major producer and contributing around 60–70% of the total present production of the Greater Burgan field.
Accurate and timely welltest data is critical to evaluate well performance and for effective reservoir management. In Kuwait Oil Company's Burgan South and East areas, the standard method of welltesting in the past has been through test separators and test tank. Because of the flow rate stabilization time and minimum volume required in the test tank for accurate reading of fluid level, welltest duration can range from 10 to 24 hours, especially for low volume wells. This is an operational challenge from the standpoint of acquiring accurate data and meet welltest frequency targets. In an effort to meet these goals, KOC has installed a new system of well testing with Coriolis meter and AGA Gas flow meters in its gathering centers (GCs). The coriolis meter, an online mass and density flow meter, can measure well flow rates with reasonable accuracy within 1–2 hours. This study has compared "simultaneous" well tests results of different categories of wells - high and low flow rate, dry and wet and high GOR using the Coriolis meter, GC test tank and portable test separator at the well. The performance and accuracy of this technology of well testing under different flow conditions are reported. Introduction Well testing is one of the most important data gathering activities that occur throughout the life of a field or a reservoir. The data collected impacts every aspect of work planned and performed in a field/reservoir. This data is a key component of the well surveillance program which effects capital and operational decisions in an oilfield. Therefore, every effort should be made to ensure that this data be accurate and is generated at regular intervals. For a well test to be considered accurate, the fluid rates (oil, water & gas), temperatures and pressures measured should reflect the normal flowing conditions of the well. It calls for appropriate metering equipment and methodology for well testing and correct reporting of the data in the database. Accurate analysis of field performance and timely remedial actions also necessitate data acquisition at appropriate frequencies. Frequent well tests are important in order to be able to identify well problems when they occur and to establish consistent production (oil, water & gas) trends. Any deviation from an established trend may indicate a well problem, which may require corrective measures. The desired frequency of well testing depends on the type of reservoir and maturity of the field. Early stage of development of a reservoir may require low well testing frequency, if minor changes are occurring in production rates, water cuts and GORs. However, with the field maturing, reservoir and production characteristics may change rapidly which will require higher testing frequency to better understand reservoir performance and changes as they occur. Thus, there is no general rule to define "appropriate" well test frequency as it depends upon multitude of factors prevailing in a field. In Kuwait Oil Company (KOC), the short term target for well test frequency has been fixed at 4 accurate well tests per string per year (1 welltest per string per quarter). The long term objective is to acquire one test per string per month.
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