A significant number of Kharaib horizontal and deviated producers drilled over the last decade have suffered from casing leaks, with many occurring in the first two years of production due to the exposure to highly corrosive water from the overlying giant water-bearing formation known as Shuaiba formation, resulting in production losses and water dumping from Shuaiba formation into the Kharaib reservoir through these damaged wellbores. This paper investigates the impact of Shuaiba dump flooding on the Kharaib reservoir’s performance, the integrated reservoir management study that was conducted and the implementation of the study’s findings to achieve the best results. Severe casing leaks are the main production problems facing the Kharaib reservoir. A few repairs were attempted initially, however, high costs and failure rates led to a decision to cement squeeze all remaining casing leak wells, recomplete them in shallower reservoirs, and drill new replacement wells. All new Kharaib wells were designed with an extra casing to protect against the Shuaiba reservoir’s corrosive water. Although there are no longer any casing leak wells in Kharaib, their impact remains. The pre-casing leak production numbers and well counts are yet to be matched, and there is a large volume of hydrocarbons to be produced from the Kharaib reservoir. In addition, wells that are offset of old casing leak wells showed an increase in water cut, while the performance of new wells drilled down-structure of casing leak wells suffered from early water breakthrough. There is also strong evidence that the isolation in many casing leak wells, performed during the recompletion workovers, may be unsuccessful. All these factors indicate that dump flooding is likely ongoing in the Kharaib reservoir. The consequences of dump flooding have not all been negative. An increase in average reservoir pressure and a strengthening of the reservoir’s weak water drive mechanism were observed. Currently, many wells have shown an increase in oil production, while other wells have shown steady oil production with a very gentle decline which is particularly reflected in wells located up-structure of the casing leaks. As a result of the study, many wells have been drilled in carefully selected locations in order to take advantage of the flooding, and the results of the study concluded a sustained production with a low water cut. Moving forward, there are further opportunities to increase the recovery factor by mitigating the unwanted effects of Shuaiba dump flooding and utilizing the phenomenon to its best potential.
The Light Oil Steam Flood (LOSF) is proposed to increase the recovery from Mauddud reservoir in Bahrain Field. Mauddud has been on gas injection since 1938, yet residual oil saturation is still high in the gas cap due to its oil wettability. Several core lab studies were conducted confirming the high oil saturation in the gas cap. Steam flood core lab experiments were conducted recently and confirmed the residual oil saturation could reach to less than 10%. The thermal pilot project in Mauddud has gone through the following stages: The first pilot started in 2013 and operated for 2.5 years: It has one horizontal well in the gas cap, one vertical producer, four vertical injectors with three Temperature Observation Wells (TOWs) clustered around one of the injectors.First pilot performance was assessed and confirmed in reducing the residual oil in the gas cap by distillation and wettability alteration.Second pilot was designed and initiated in 2016 to assess the economic viability for full field expansion. Throughout these stages, production monitoring, logging, core studies and simulation studies have been carried to understand the LOSF mechanisms to increase Mauddud recovery from the gas cap. This paper presents the evolution of pilot design concepts and simulation of the thermal recovery in Mauddud. It also study and assess the well configurations and pilot operating strategies designed for the thermal pilots. A sector model was constructed and calibrated, then used to select a well concept for the LOSF pilots. Seventeen different pilot concepts were considered during the selection process. The well configuration and operating strategies were driven to observe a quicker steam response in the first pilot. A number of sensitivities were conducted to develop a better understanding of the effects of the various reservoir factors. A comprehensive study was then carried out to recommend a phase development approach for full-scale field development and establish a methodology for a full-field LOSF forecast. Full Field compositional model was built in thermal reservoir simulator and was then successfully history matched with seven components equations of state (EOS). A phased development approach was then proposed for full-scale field development. The initial development will focus on the mid-dip areas with higher remaining oil saturations and a thicker oil column. After establishing production in the mid-dip flanks, development could proceed to the crestal areas, which have lower oil saturations and would likely result in higher steam/oil ratios (SORs).
Nahr Umr reservoirs in Bahrain Field consist of three reservoirs (Cab, Cc and Cd) that vary from calcareous silt stones to sand stones. They are the second major producing zones in Bahrain Field and are overlain by Mauddud limestone reservoir separated by 8 - 10' shale. All these reservoirs have been on production since early thirties and Mauddud reservoir has been under gas injection since 1938. These reservoirs with diverse fluid contents and hydro-dynamically different systems communicate with each other through the extensive faulting. Based on a dynamic model, it shows significant amount of flux already had transfered from the Mauddud reservoir to Cab due to gravity drainage gas injection project in the faulted crestal part of the Mauddud reservoir. Furthermore, the high recovery in Nahr Umr Cab reservoir indicates of acting as drainage point from Mauddud supported by the differential pressure in some areas. For such mature reservoirs with a long production history, identifying by-passed oil, underperforming areas, areas under communication, locating infill wells and upgrading the reserves are challenging tasks. This paper describes the application of a practical process (1) Development of a systematic workflow for production optimization and reservoir analysis; (2) Identifying and highlighting reservoir trends, patterns and anomalies; (3) Locating the under performing wells/areas, and recommend solutions (4) Identifying essential patterns for consideration in overall development plan. The challenge was to evaluate large data sets in a short time and cost-effective manner. The technique uses a streamlined workflow of reservoir assessment processes, which require data gathering, formatting and validation through combining the data with several processes associated with both the static and the dynamic model of the reservoir. Quick interpretations of these models generate opportunity regions, re-completion candidates, and new infill potential in the reservoir. Based on the processes run in the Nahr Umr zones it was possible to understand the reservoir performance and main issues associated with field development. Utilizing these techniques, the recently completed development drilling program was suitably adopted to realize an efficient reservoir management process for developing the field with the objectives of decreasing decline rate and increasing the recovery.
Crestal gas injection started in the Bahrain Field in 1938 and since then, 1,900 Bscf has been injected in Mauddud, the main oil producing reservoir in the Bahrain Field, creating a secondary gas cap. Furthermore, since 1965, an estimated 100 MMstb of Liquefied Petroleum Gas (LPG), or 14% of the bypassed oil, has been recovered from the secondary gas cap through stripping with the remaining oil volume in the secondary gas cap being approximately 700 MMstb. Today, the remaining oil saturation in the Mauddud gas cap is estimated to be approximately 40%. This paper presents the results of an extensive study that was made to forecast the Bahrain Field associated gas compositions and potential gas-liquids production recovery. Several forecast methodologies were used including data-driven analytical models, a compositional cross-section model, and a full-field compositional history matched model. The results of these forecasts and the conclusions are presented and compared. In this study, two scenarios of different gas compositions of injected gas and their impact on gas plant liquids recovery are explored. In addition, this paper addresses the challenges and uncertainties associated in forecasting the gas compositions and ways to overcome them. The data-driven models and compositional cross-section model were initially used, however, due to their inherent uncertainties, a full field compositional simulation model was necessary. This compositional model was history matched with a seven (7) component Equation of State (EOS) to capture the lighter hydrocarbon components. Moreover, this model was used in predicting the yield and composition of the existing gas recovery plant. The results from all methods recommend doubling the capacity of the existing plant, which was commissioned in late 2018. A comparative analysis found that data-driven models can be used for gas cycling when using the same gas injection compositions. However, data-driven models over-estimate the Liquefied Petroleum Gas (LPG) yield if leaner gas is used for gas injection, which is the case for the proposed gas plant expansion.
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