Management of Water Alternating Gas (WAG) Injection Projects

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper summarizes the results of several successful WAG projects presented in many Improved Oil Recovery (IOR) Symposiums, indicating the main technical and operational issues considered in the development and implementation of such projects, and the management strategy for monitoring the process (Refs. 1,2,3,4). The results from these field applications will serve as useful guides and examples for improving reserves from many of our mature fields, and would lead to rethinking our strategy of reservoir development and new technology application for significant reserves enhancement in Venezuela. The paper focus on the selection of the technical aspects that must be consider in the implementation and management of the Water Alternating Gas (WAG) Injection process, providing an useable reference for the front line geoscientists, reservoir engineers, production operation engineers and technical managers who wish to obtain a technical and operational overview of the process as applied in the petroleum industry.Managing WAG injection projects requires making decisions regarding to the WAG ratio, half-cycle-slug size, and ultimate solvent slug size for each WAG injector in the field. The impact of these decisions affects the capital cost of solvent purchase, water and gas plant loads, fluid handling and lifting operation costs, and ultimate incremental oil recovery. Simulation models provide a tool for examining strategies for these decisions. However, it must be able to address operational impacts such as lift method and problems, injecting plugging, workovers and facilities operations. Project monitoring incorporating actual performance data into the reservoir models provides an excellent diagnostic tool for decision making. The technical considerations for managing WAG projects presented in this paper can be used as a methodology for monitoring projects performance at pattern and full field level, increasing understanding of the process performance, and improving decision making.

A review of gas enhanced oil recovery schemes used in the North Sea

“…It is a process whereby one gas slug is followed by a water slug (Christensen et al 2001;Al-Ghanim et al 2009). The main reason of initiating WAG in the North Sea was to improve the microscopic and macroscopic sweep efficiency (Surguchev et al 1992;Sanchez 1999;Kulkarni and Rao 2005). Water provides a better mobility ratio as most of the North Sea oil is of low viscosity.…”

“…Gas being miscible with the oil reduces the IFT which improves the displacement efficiency, and recovery of the top oil missed during water injection. Therefore, a combination of water and gas (WAG) leads to Reproduced with permission from Healy et al (1994) improved oil recovery (Sanchez 1999;Arogundade et al 2013;Heidari et al 2013;Green and Willhite 1998;Luo et al 2013;Dashti and Sheikhzadeh 2013). WAG is usually applied in reservoirs with low dip, limited gas resources, and strong heterogeneity (Christensen et al 2001).…”

“…In 1999, WAG was successfully implemented in the field as seen in Table 3. Sanchez (1999) summarised the results of successful WAG projects. It was shown that WAG could improve recovery in Statfjord by 13% above that of water flooding.…”

Water alternating gas incremental recovery factor prediction and WAG pilot lessons learned

“…Linear regression is a widely useful statistical learning method for predicting a quantitative response. Moreover, it serves as a good jumping-off point for newer approaches as many fancy Table 1 Fields used during this research study (Christensen et al 2001;Ramachandran et al 2010;Sanchez 1999 statistical learning approaches can be seen as generalizations or extension of linear regression (James et al 2015).…”

“…During the last decades, many research papers were published focusing on WAG performance (Giordano et al 1998), WAG simulation (Kohata et al 2017), WAG pilot results analysis (Christensen et al 2001), WAG process mechanisms (Afzali et al 2018), WAG hysteresis (Lazreg et al 2017), and WAG management (Sanchez 1999). However, WAG incremental recovery factor over secondary recovery is still unknown.…”