Evaluation of Gas, Water, WAG Injections, and Infill Wells for Improving Recovery of One of Iranian Reservoirs

Abstract

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

Combined Underground Gas Storage and Enhanced Oil Recovery in a Fractured Reservoir

“…Field experience has shown that more than 15% incremental oil can be recovered from a waterflooded reservoir by updip gas injection (e.g., Johnston 1988;Carlson 1988;Shahsavari and Dabbous 1991;Langenberg et al 1995;Gunawan and Caié 1999). For high-relief fractured carbonates, updip gas injection to increase oil recovery has been used successfully in Oman and Iran (O'Neill 1988;Novinpour et al 1994;Saidi 1996;Eikmans and Hitchings 1999;Sadooni et al 2008). These field test results are supported by laboratory studies (e.g., Kantzas et al 1988;Blunt et al 1994;Øren and Pinczewski 1995;Ren et al 2003).…”