Abstract
Steam injection is the major method of thermal recovery for heavy oil reservoirs. Due to the severe steam channeling caused by viscosity fingering and gravity override, pure steam injection may not be sufficiently efficient to develop heavy oil. The use of high-temperature gel is to block the channeling path and divert the following steam to the areas rich in residual oil, so that the sweep range of the oil layer is expanded.
In this paper, the performance of the high-temperature gel was firstly studied with three indexes: salt resistance, temperature resistance and scouring resistance. Then, a two-dimensional visible physical simulation was used for studying the effect of high-temperature gel on the improvement of steam flooding. An image acquisition system was adopted to compare the images prior and posterior to high-temperature gel injection. Meanwhile, the whole process of steam channeling in steam flooding for heavy oil development was tracked, as well as the sweep situation of steam flooding layer posterior to high-temperature gel injection. Accordingly, the micro-mechanism of high-temperature gel for improving steam flooding was also studied.
The results of evaluation on high-temperature gel showed that after gelling in distilled water or formation water with a salinity of 8×104mg/L, apparent viscosities of the gel were both about 35000mPa·s. And after aging for 20 hours at 200°C, the gel still presented stable gel state. The residual resistance factor of the gel blocking agent was more than 120 after scouring by steam of 10PV. So, the high-temperature gel had good salt resistance, temperature resistance and scouring resistance. The results of visible experiment indicated that in the process of steam flooding for heavy oil reservoir, steam channels tended to form between the injection and production wells due to different pressure gradients. Steam resulted in fingering phenomena in oil layers, thus reducing the sweep range of steam, leading to a large amount of residual oil on both sides of steam channels. The gel solution firstly flowed into the channeling path, and occupied large intra-particle pores. Gel had a good plugging performance on channels with high permeability. The following steam bypassed the mainstream channels for further residual oil flooding. Oil flooding results showed that posterior to gel solution, the final sweep efficiency could reach 70.44%, and the ultimate oil flooding efficiency was 60.45%, higher than that of pure steam flooding by 22.35% and 15.17% respectively.
This paper adopts a visual method to study the effect of high-temperature gel on improving recovery percentage of heavy oil by steam flooding from both macroscopic and microscopic aspects. The results of this study are of significance for the application of high-temperature in the development of heavy oil reservoirs.
