Cyclic Water Injection Simulations for Evaluations of its Potential in Lagocinco Field

Abstract

Abstract Cyclic Water Injection (CWI) has been proposed as a technique to improve water sweep in stratified and fractured reservoirs. This recovery process takes advantage of the pressure transient response in regions of different permeability, leading to forced imbibition of the lesser permeable layers, in the case of stratified reservoirs. A process such as this is expected to yield an additional recovery between 2 and 7% over continuous waterflooding and a significant reduction in watercut, reason why it has been proposed as a zero cost EOR process, wherever facilities for water injection are already available. Several mechanisms have been attributed the additional oil production, among which are listed pressure differences between layers with limited communication and hysterisis of the capillary pressure and relative permeability curves. Here we have taken a full-field model of an extensively investigated reservoir of Western Venezuela, the VLE-305, located in the Lagocinco field to analyze some of the critical variables of the process and determine the potential for cyclic water flooding. The reservoir has been proposed as a candidate for immiscible WAG injection and a successful pilot test has been carried out. This deep, stratified sandstone reservoir meets the characteristics sought in cyclic water injection projects. In recent work, it was shown that some potential exists for water cyclic injection in the WAG pilot area. Production history of the field has been used to help with the analysis of critical variables of this process, including injector-to-producer well distance and reservoir pressure relative to the bubble point pressure, among others. Additionally, a recently developed analytical model of the process was also tested to determine its potential as a fast evaluation tool for CWI. Results show that permeability trends, reservoir pressure, well distance and water saturation at the startup of the process have high impact on the potential additional recovery, leading to recommendations for the application schedule of the process. Introduction An issue in IOR planning is the startup timing of a recovery process, especially when revamping of large infrastructures is required. In production areas where waterflooding facilities are available, life extension of these projects by means of well-conformance or pattern re-arrangement become desirable to delay investments or better yet allow companies the time to deploy other IOR strategies. In this sense, Cyclic Water Injection (CWI) has been proposed as alternative for waterflooding optimization in fractured or heterogeneous reservoirs1. In the case of Venezuela, oil production is characterized by a long exploitation history of the prolific reservoirs, since the beginning of the 20th century. The Lake Maracaibo basin, located in western Venezuela, has numerous accumulations that include some of the largest heavy-oil fields to date, to deep light-oil reservoirs, being in all, one of the richest oil provinces in the world. This region has been under exploitation, mainly by primary recovery methods and steam injection (for heavy-oil fields), and gas injection and waterflooding, to a lesser extent. However, much of the original oil in place still remains in the subsurface, as the recovery factor (RF) is of the order of 30% for waterflooding and 40% for gas injection, being even less for primary production schemes, in average2. This situation demands the use IOR strategies to sustain oil production, because, although new discoveries had been made in the last 20 years, Lake Maracaibo reservoirs have contributed with the major share of the Venezuelan production in the last decades. However, the decision-making for IOR processes exhibits certain complexity because of the state of maturity of these reservoirs and the lack of hydrocarbon gas for injection3.