Results of Proactively Managing a Heavy-Oil Waterflood in South Oman Using Streamline-Based Simulation

Abstract

Streamline simulation is an ideal reservoir management tool for mature waterfloods since it can identify unswept reserves, quickly evaluate multiple forecast scenarios, and provides novel information like well-pair interactions. The identification of well-pair interactions is particularly useful as it allows for pattern surveillance, quantifying offset production with injection volumes, and identifying efficient vs inefficient areas of injection. The Thuleilat heavy-oil field consists of 120 wells and is geologically complex with stacked reservoirs, multiple oil-water contacts, and numerous faults, making it difficult to identify well interactions and areas of unswept reserves. However, being a dead oil reservoir with the majority of production a result of injection, it is ideally suited for streamline simulation. Several opportunities were identified based on the streamline simulation. These opportunities, which generally apply to all waterfloods, could be divided into well rate target recommendations, pattern optimization, producer-injector conversions, and infill locations. Pattern optimization opportunities resulted in a 10% gain in the offset oil producers. In one of the pattern optimization activities three water injectors were identified for injection rate increase, followed by optimization activities in the associated oil producers which resulted in a significant oil gain. Other pattern optimization activities were to close in high gross rate wells and diverting the flow toward offsets oil producers. One of the trials was to close-in one of the producers in the central area for one week, which resulted in a measurable oil gain in 3 offset oil producer wells. The second activity was closing another producer in the northern sector for two weeks which resulted in an oil gain in 5 offset oil producers. Further use of the streamline model includes the assessment of unswept reservoirs for infill locations and the estimation of water cuts for development locations. Introduction Numerous authors have already shown the possibility of building complex history match streamline models for waterfloods.1–7 Many of these authors have also used their streamline models in a manner similar to finite-difference (FD) models for waterflood management, such as forecasting, testing infill locations, and identifying bypassed oil. Recently Thiele & Batycky9 showed how to use the novel information of well-pair connections from streamline simulation to improve flood performance. Specifically, alter well rates to increase oil production and reduce fluid cycling. However, there is little if any documented results of altering well rates based on streamline identified well-pairs, and what the outcomes were. The purpose of this paper is to show the results of implementing well rate changes to the Thuleilat field, based on a streamline model, and what changes to production actually occurred. The Thuleilat field is located on the eastern side of the South Oman basin approximately 200 km NE of Salalah Figure 1. This is a heavy oil field that has a STOIIP of some 96 Mln m3, and has been on production since 1987. Details of the geology and production of the field are described below.