A Reservoir Management Tool for an Omani Fractured Carbonate Reservoir _ A Case Study

Abstract

Abstract This paper presents a case study of developing a reservoir management tool (a water coning correlation) to monitor the oil rim thickness and position in a giant densely fractured carbonate reservoir in Northern Oman. The production mechanism in the field is Gas Oil Gravity Drainage (GOGD), with crestal gas injection to maintain the reservoir pressure and dedicated aquifer pump off wells to control the oil rim position. As the field is produced from a thin oil rim in the fractures network primarily through open-hole horizontal wells, it is crucial to keep the oil rim fixed and at such depth and thickness so that coning and cusping of water and gas into the oil producing wells is minimal. In this study, two approaches; analytical and numerical were used to develop a correlation between produced water rate and distance of the measured Fracture Oil Water Contact (FOWC) from the well perforations. From the numerical simulation model, a correlation between the water rate produced from a horizontal well in a fractured reservoir and the distance between the FOWC and the well perforations was developed. The developed correlation from the simulation model couldn't be correlated with measured contacts data due to the improper fracture connectivity between the observation wells and the oil producers. However, a reasonable match was obtained between the fluid contacts from the developed correlation and the estimated contacts using the measured gas and water pressure data. The developed correlation could be further improved by incorporating the fine fracture details around the well in the simulation model. This correlation could be used on a monthly basis to estimate the location of FOWC nearby the oil producer from the tested water rate. This will yield a better oil rim management by monitoring the rim position and thickness regularly and therefore produce the field at optimum oil rate. This correlation will also minimize the need for direct measurements of the contacts using the gradiomanometer surveys and hence reduce the operational cost. Introduction Reservoir management becomes an important and challenging aspect in mature highly fractured oil field reservoirs. One of the main challenges in the management of dual permeable (fractured) reservoirs is water coning through the fractures. This issue becomes more serious in carbonate reservoirs (long open fractures) with strong aquifer support.