The Effect Of Production Well Open Interval On Steamflood Performance

Abstract

Abstract Completion intervals at production wells can be used to control steam conformance to a certain extent and thus, improve recovery. This approach differs from the general concept of applying an open interval over the entire pay zone to obtain maximum flow potential as in many conventional oil reservoirs. The reasons are that bitumen and connate water at initial reservoir conditions are practically immobile where injectivity relies on small flow channels such as fractures and, that steam has a tendency to override, resulting in poor vertical sweep efficiency. This paper presents results on the effects of production well open interval on steamflood performance in oil sand reservoirs. Two parameters, namely aspect ratio, defined as pay thickness to well spacing, and percentage of open interval, were investigated using a commercial thermal reservoir simulator. Results indicate that oil steam ratio can be improved by limiting the length of open interval of the production well, at the bottom of thick reservoirs in a steam override case. For a small aspect ratio a larger open interval is preferred; however, the oil steam ratio is less sensitive to open interval in this instance. For the case of steam underride, the oil steam ratio is insensitive co open interval. This relationship was explained by the relative magnitude of the two driving forces, gravity drainage and pressure gradient, in steamflood projects. Introduction One of the long-standing uncertainties associated with oil sands reservoir engineering is determining what interval of the pay zone should be completed for a particular well spacing when steamflooding a reservoir. One argument for a large open interval at a production well is to allow a large fluid flow potential. This is particularly true for piston-like displacement processes. Hence, a large open interval is preferred for favourable mobility ratios such as waterflooding conventional oil reservoirs, As well, with a large open interval, the fluid velocity is lower, which tends to reduce sand production problems. However, steamflooding oil sand reservoirs with negligible initial fluid mobility, with initial mobility through small flow channels, with adverse mobility ratios and with gravity override of the steam, the piston-like displacement assumption is not valid. These factors cause the steamflood process to be difficult to control. Because oil recovery in a steamflood depends on the size of the steam zone, the open interval would seem to provide a method to improve steam conformance. A literature search indicates that very little work in this area has been published. Gomaa et al.(1) discussed completion interval and pay thickness as sensitivity parameters in a steamfood but did not correlate the two parameters. In this paper, the effectiveness of using open interval to improve Steamfood performance is discussed in terms of the aspect ratio of the reservoir and the location of the communication path. The improvement in the oil steam ratios for different open intervals at a given aspect ratio is compared. Approach This paper discusses the effect of open interval on steamnood performance using Computer Modelling Group's ISCOM 3.0 numerical simulator.