Abstract
Steam-assisted gravity drainage (SAGD) is one efficient and mature technology for recovering heavy oil and bitumen resources. The key underlying mechanism is the growth of the steam chamber after injecting steam. However, due to the complex geological environment, the thief zones exist and have a prejudicial effect on the development of the steam chamber, thus impacting the ultimate heavy-oil recovery. In this work, our objective is to investigate the effect of a top-water thief zone (i.e., water zone overlies the oil sand) on SAGD performance and further to understand the crucial mechanisms that control the heat loss during steam injection. A large-scale three-dimensional experimental apparatus is used to carry out the SAGD process with a top aquifer. Based on the similarity criterion, the field-scale model is transformed into a laboratory elemental model. To evaluate the SAGD performance quantitatively, the dynamic growth of the steam chamber is measured using the thermal detectors and the production data is recorded. The results show that the steam chamber exhibits three distinguished stages, that is, upward spread, lateral extension, and downward development in the presence of top-water zone. The bottom-water zone has less impact on the steam-chamber growth. The existence of a confined top-water zone, however, significantly affects SAGD performance, especially the lateral expansion of the steam chamber. The lateral propagation of the steam front is hindered by the top thief zone due to the heat exchange with the top water. Once the steam chamber reaches the boundary, the accumulation of energy in the water thief zone, in turn, can reduce the remaining oil saturation along the topwater–oil interface. This study provides us some key insights into the development of heavy oil resources with top thief zones when implementing SAGD technology.
Highlights
Heavy oil and bitumen account for 2/3 of the total crude oil resources in the world
After the simulated distillation experiments, we found that the asphaltene content of the crude heavy oil is around = 13.50 wt% (n-hexane insoluble)
A preheating operation is required to establish thermal connection between the injector and producer before initiating the steam-assisted gravity drainage (SAGD) process. This operation can guarantee that the area between wells is heated thoroughly and oil can move to the bottom producer with gravity drainage in the later SAGD process
Summary
Heavy oil and bitumen account for 2/3 of the total crude oil resources in the world. The effective development of these resources is very significant to the world energy supply (Butler, 1991; Edmunds et al, 1994). The viscosity of heavy oil or bitumen is sensitive to temperature variations, a thermal process, is usually applied to reduce the viscosity, improving the ultimate recovery. The hot steam is chosen and injected into the reservoir to heat the fluids. Application of steam injection technology has been proved to be the most commercially successful EOR technique for heavy-oil reservoirs (Friedmann et al, 1994; Patzek, 1996; Gotawala and Gates, 2008; Fatemi and Jamaloei, 2011; Lyu et al, 2018). Steam can be injected in three types, that is, steam flooding, cyclic steam stimulation (CSS) and steam-assisted gravity drainage (SAGD) with/without chemical agents (Butler, 1991; Speight, 2013; Pang et al, 2018; Dong et al, 2019; Liu et al, 2019)
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