Water-Alternating-Gas Flooding in Venezuela: Selection of Candidates Based on Screening Criteria of International Field Experiences

Abstract

Water alternating gas (WAG) injection schemes have become an important strategy for improved oil recovery (IOR) technique around the world, and have been the focus of interest in recent years in Venezuela. This drainage strategy is mainly planned according to the major concerns in Western Venezuela oil fields: optimizing gas resources and improving oil recoveries in the region. As part of the support to identify those reservoirs that will be candidates to WAG flooding in this area of the country, an extensive review was carried out to describe the main reservoir management strategies implemented in WAG pilot, as well as large field projects in order to evaluate international field experiences, before expensive reservoir description, laboratory studies, economic evaluations and WAG pilot projects are carried out. This paper briefly describes part of this review and also shows some screening criteria for WAG floodings. Data from successfull and unsuccessfull worldwide projects have been analyzed obtaining relevant information about crude oil and reservoir properties as well as gas injection capacities, incremental oil recoveries, among others. All these data have been compiled and the results are presented graphically; the relationship between them is discussed and compared with data of some of the reservoirs proposed for WAG floods in Venezuela. It has been found that WAG projects must be initiated with injection pressures 24% greater than reservoir pressures unless the formation is deeper than 8000 ft. Additionally, incremental oil recoveries reported by those projects are higher for lower viscosity ratios and do not depends on injected solvent slug sizes. Finally, the authors discuss how this screening was useful as a first look to identify the actual reservoir and facilities of different fields located at the Maracaibo Lake (e.g. B-6-X.10 and VLE-305) and select them for closer investigation and planning WAG pilot projects or "WAG Field Laboratories". P. 161

EOR Advisor System: A Comprehensive Approach to EOR Selection

“…Seven parameters were short listed for the selection, namely: The interdependencies between some of the selected parameters, such as reservoir depth and temperature, are well understood, but were kept in the analysis to preserve back compatibility with the previous literature publications on EOR screening [1][2][3][4][5][6][7][8][9] . Other interdependencies such as oil gravity-viscosity and porosity-permeability follow a general trend but are still required to be defined separately to preserve the predictability of the advisory system.…”

“…EOR screening has been discussed in different levels of complexity by different authors [1][2][3][4][5][6][7][8] with different approaches postulated, ranging from applicability ranges, binary selection, data mining, and numerical simulation. Simplicity and repeatability are among the traded values during the first attempts of recog-nizing the best-suited EOR process for a given field, which of necessity, has increased the value of past experiences to guide and provide a "sanity check" for any EOR decision, particularly when dealing with scarce information.…”

Enhanced oil recovery by CO2injection in carbonate reservoirs

“…The author also mentioned that at immiscible condition with CO 2 , WAG can improve oil recovery efficiently and this experienced in some oil fields for both miscible and immiscible processes, for instance, Lick Creek, Kuparuk River, Brage and Gullfaks and in some countries (USA, Canada and recently in Norway) [11].…”

VLE WAG Injection Laboratory Field in Maracaibo Lake

“…On the other hand, the selection of the VLE field as one of the areas in the Maracaibo Lake Basin to evaluate a WAG process was based on screening criteria for WAG floodings obtained from successfully and unsuccessfully worldwide projects [1,2], analytical simulation as well as conceptual numerical simulation studies [3].…”

“…WAG has also been considered beneficial to IOR in reducing viscous fingering between the displacing gas and the oil phase and by reducing override effects caused by domination of viscous forces over gravity forces in highly heterogeneous reservoirs, as well as improved attic oil recovery in structurally complex reservoirs [1][2][3][4][5].…”