Sweep Efficiency In Steamflooding

Abstract

Abstract The chief objectives of this investigation were to study, theoretically and experimentally, the sweep efficiency and oil recovery for steam injection into a five-spot pattern. Experimental runs and mathematical simulations were conducted for this purpose. The experimental models used consisted of glass bead packs simulating a quadrant of a five-spot pattern, overlain and underlain by heat-conducting formations and fitted with thermocouples to determine the temperature distribution during the steamflood. Effects of oil viscosity, saturation, injection rate, and heat losses on oil recovery and sweep efficiency were studied. The mathematical model developed was a combination of the concept of flow in channels and a formation heating model, allowing for a variable injection rate, differences in the properties of the overburden and the underburden, and variations of relative permeabilities with temperature. The mathematical model was used to simulate the experimental runs. Good agreement was observed. It was found that, for the oils tested, Sweep efficiency in steamfloods was 40 to 50 per cent, depending chiefly on the viscosity of the oil used. The oil recovery, however, was large, being of the order of 80 per cent, because of the hot waterflood ahead of the steam zone. The sweep efficiency was relatively insensitive to initial saturations and the steam injection rate. Formation thickness and steam quality were found to have an appreciable effect on oil recovery. For low-quality steam, the steamflood degenerates rapidly into a hot waterflood. Introduction DURING THE PAST FEW YEARS, pattern steamflooding has gained considerable popularity as a secondary or tertiary oil recovery method for both viscous and low-viscosity crudes. Currently, however, few methods for calculating oil recovery by a steamflood are available. Marx and Lagenheim(l), and Willman et al. did pioneering work in this area by proposing mathematical models for calculating the volume of the formation heated and the oil recovery from a radial steamflood. Davies, Silberberg and Caudle(3) proposed a method for predicting oil recover}' from a five-spot steamflood, based on the approximation of the streamlines by straight lines radiating from the injection well, and then converging to the production well. The present work proposes an improved method for predicting the performance of a steamflood in a five-spot pattern, using a combination of Higgins and Leighton's (4). Marx and Langenheim's(1), Willman et al.'s(2), and Ramey's(3) techniques adapted for a steamflood in a five-spot pattern. Also, extensive experimental results are presented, designed to test the model, and also to obtain data on pattern steamflooding, with regard to oil viscosity, distillability, injection rate, etc. Fair to good agreement was obtained between the model predictions and the experimental results. On the whole, it was found that the sweep efficiency in a five-spot steamflood is considerably lower than that in a corresponding waterflood. However, the oil recovery may not be correspondingly low, due to the beneficial effects of the hot waterflood preceding the advancing steam zone.