Life Cycle of a depletion drive and sour gas injection development: Birba A4C Reservoir, South Oman

Abstract

A field in South Oman discovered in 1978 is an over-pressured sour oil reservoir. Since first oil began in 1982, the field will has gone through three stages of development during its life. These can be summarized as follows; pressure depletion, pressure maintenance with sour separator gas plus sweet make-up re-injection, pressure maintenance with sour separator gas plus sour makeup gas injection from other fields The field produces from the A4C unit of the Ara Group intra salt carbonates. A carbonate reservoir totally encased in salt. No water has been produced to-date from this reservoir. The reservoir oil column is overlain by a gas cap and the reservoir fluid exhibits a strong compositional gradient which impacts the degree of richness required for a sour miscible gas. Development drilling and the construction of facilities proceeded with all well tubulars and facilities constructed out of carbon steel. Operation of the plant and wells occurs with high regard to the risks of sour, high pressure service, and with no integrity or corrosion has been observed to-date. The field produced under depletion starting in 1982 through oil and gas cap expansion mechanism. The field was shut-in in 1986 awaiting gas injection. In 1993, sour separator gas combined with sweet make-up gas was re-injected as a pressure maintenance project to keep the reservoir pressure from dropping further. Upon expansion of the production station to take production from other nearby sour oil fields, more sour gas was added to the gas injection stream in 2004. Plans are developing to change the composition of the injection gas stream to achieve higher H2S levels so that the injected gas will become miscible with the A4C oil. This is designed to further increase oil recovery. The purpose of this paper is to present the development history of this sour oil reservoir along with presenting the development approach that has been taken for injecting sour gas to increase oil recovery in this remote South Oman reservoir. Introduction The purpose of this paper is to present the development and performance history of a pressure maintenance project of a sour oil (H2S & CO2) reservoir developed in the Ara Salt in South Oman (Figure 1). This reservoir has undergone three stages of development with potential for miscible sour gas injection. These stages are as follows; pressure depletion (1982 - 1986), gas injection (1992 - 2004), sour make-up gas injection (2004 - to date). Estimated ultimate recovery is 30.6%. Modeling work has indicated that miscible gas injection will increase the oil recovery factor to 36% (Figure 9).

Injection of Acid Gas Mixtures in Sour Oil Reservoirs: Analysis of Near-Wellbore Processes with Coupled Modelling of Well and Reservoir Flow

“…Among them, the reinjection of sour or acid gas mixtures is often considered to reduce the environmental impact of field exploitation and provide pressure support for EOR purposes. For instance, the injection of sour and acid gas mixtures is a common practice in Canada (IEA 2003;Bachu and Gunter 2004) and is now applied in other regions where many sour oil and gas reservoirs are located, such as the North Caspian basin (Malik et al 2005;Abou-Saied et al 2005) and the Middle East (Miwa et al 2002;Haynes et al 2008). The conventional scheme used to reinject gas mixtures containing acid gases involves (Carroll et al 2009): the separation of acid gases from the sour hydrocarbon mixture; the multistage compression of the gas mixture; the piping of compressed gas; and the injection through suitable wells.…”

Prospects of an Acid Gas Re-Injection Process into a Mature Reservoir

“…Subsequently, larger projects emerged, including AGI initiatives at Sleipner West in the North Sea, In-Salah in Algeria, and LaBarge in Wyoming, USA [16]. Beyond these well-established sites where the injection of sour and acid gas mixtures is common practice [24,25], AGI is now applied to numerous sour oil and gas reservoirs worldwide, such as the North Caspian basin's Tengiz field in Kazakhstan [26][27][28] and the Middle East [29][30][31]. In cases of mature reservoirs containing highly soured resources that have already been produced through primary and secondary recovery, AGI presents a compelling EOR alternative that can potentially circumvent the limitations of waterflooding, as well as provide an eco-friendly option, aligning with global trends towards more sustainable and environmentally friendly industrial practices.…”

“…Subsequently, larger projects emerged, including AGI initiatives at Sleipner West in the North Sea, In-Salah in Algeria, and LaBarge in Wyoming, USA [16]. Beyond these well-established sites where the injection of sour and acid gas mixtures is common practice [24,25], AGI is now applied to numerous sour oil and gas reservoirs worldwide, such as the North Caspian basin's Tengiz field in Kazakhstan [26][27][28] and the Middle East [29][30][31].…”

Study of the impact of injection parameters on the performance of miscible sour gas injection for enhanced oil recovery

“…This research work seeks to provide insight into the impact of injection parameters on the viability of miscible flooding of a light oil reservoir by the reinjection of sour gas (Abou-Sayed et al 2004;Benham et al 1960;Christiansen and Haines 1987;Eakin 1988;Elsharkawy et al 1992;Green and Willhite 1998;Haynes et al 2008;Holm and Josendal 1974;Khan et al 2013;Lake 1989;Orr and Silva 1987;Orr et al 1982). The reinjection of a rich waste acid gas stream directly into the producing light oil reservoir for the purpose of miscible flooding enhanced oil recovery using numerical simulation was studied putting into consideration the impact of certain injection parameters on the overall performance of the recovery process.…”