Increasing demand for energy has forced oil companies to resort to secondary and tertiary methods to increase the recovery from the existing reservoirs. In this paper, enhancing the recovery factor of one of Iranian reservoirs which is a naturally fractured reservoir was investigated. For this reservoir, it is estimated that 96.5 percent of oil is contained in the matrix and 3.5 percent in the fractures. The field is an undersaturated reservoir with no active gas cap and no strong water aquifer.
In this paper, injections of water, gas, water alternating gas (WAG), and infill wells on this field was investigated to increase the recovery factor. Eclipse 100 was employed to simulate the reservoir.
The simulated results showed that gas, water, and WAG injections had insignificance improvements on oil recovery. However, it was found that infill wells contribute an appreciable increase in recovery. The amount of increase for drilling five infill wells was around five percent.
Since development of existing resources contributes a major role on the supply of oil for the future oil market (around 45 percent by 2030), these results are used to screen the various methods for increasing the recovery of such reservoirs.
Introduction
Enhancing the recovery of an oil reservoir is one of the major roles of any oil company. This is achieved by development of the oilfields by employing different techniques such as infill drilling, water injection, gas injection, water alternate gas (WAG) injection, and even thermal methods. These enhanced oil recovery (EOR) techniques are implemented on mature oil fields to recover additional reserves after primary recovery methods have run their course. By increasing production efficiency, EOR methods can increase the economic life of older fields by as much as 30 years.
Among various reservoirs, naturally fractured reservoirs (NFR) exhibit one of the most complicated behaviors, because they are comprised of matrices and fractures. When secondary and EOR methods are applied to these reservoirs, fractures tend to channel injected fluids through the reservoir to production wells. This results in much of the oil in the matrix blocks being bypassed and not recovered which leads to a low recovery efficiency from fractured reservoirs. Therefore, the recovery from the matrix blocks contributes substantially to the overall recovery of such reservoirs. Matrix recovery is achieved by an interaction between the fluid in the fracture and the oil in the matrix. The fluid in the fracture is believed to act as a force displacing the matrix oil out of matrix by viscous displacement, mass transfer, or capillary displacement.1,2
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