Development and Management of a Reservoir with Gas Cap and Water Drive

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This thesis aims to provide reservoir management strategies to enhance oil production from a mature oilfield with a very low recovery factor (RF) after producing oil for over 40 years. The oil field under study contains a medium-sized gas cap and a large aquifer. Gas coning, the most critical challenge in this oilfield, was investigated by using Addington correlation and an improved correlation. The correlation was validated through the field data. The current status, future development and management plan of an IOR scheme in the field can be improved by use of the new correlation. Some classic techniques, such as production performance analysis, decline curve analysis, and material balance calculation were carried out in the study. Based on the preliminary simulation study, it was found that the gas coning is a common problem in the reservoir. Addington correlation (1991) has been widely accepted as one of the fundamental correlations for coning issues. Yang and Wattenbarger (1991) and Benamara and Tiab (2001) followed Addington’s steps and extended the application range. The improved correlation proposed in this thesis shows the limitations of previous theories. Based on the results from the improved gas coning correlation and reservoir history match simulation results, multiple prediction plans were further proposed, and an optimized reservoir management plan was recommended. An improved gas coning correlation, derived from Addington correlation (1981) and reservoir production performance, was proposed to help understand gas production and breakthrough behaviors in the mature oilfield. Upon comparison of production history data and calculated critical oil rate, the improved correlation provided the guidance for optimizing the field production rates. For instance, after several years of production, W3 shows a gas coning phenomenon with 85.3 sm3/d oil rate while the critical rate calculated by Addington correlation is 97.4 sm3/d and the critical rate calculated by new improved correlation is only 35.7 sm3/d. These results show that the new correlation estimates a more reliable critical oil rate. Applying the new correlation in case of a previously perforated well, critical oil rate was determined, which helped to define the optimized flowing bottomhole pressure (FBHP). The FBHP of well W11 was limited to 202 bars to meet the 72.2 sm3/d critical oil rate calculated via the improved correlation. In an infill well, based on an optimal critical oil rate, the perforation intervals and the distance between GOC and the top of perforations were estimated. The improved correlation was generated by a multiple-well numerical model instead of a one-well radial model. The production history was taken into account to adjust dimensionless parameters in the correlation. Compared with Addington correlation, the modified one improves the accuracy of critical oil rate estimation.

reservoir management and development, gas coning, gas cap, production analysis, material balance