Feasibility of the Steam-Assisted-Gravity-Drainage Process in Offshore Heavy Oil Reservoirs with Bottom Water

Abstract

Due to the water-coning problem, cycle steam stimulation (CSS) in the heavy oil reservoirs with bottom water is often less effective, and the oil recovery is even below 10%. Steam assisted gravity drainage (SAGD) is the oil-producing process with a constant pressure-drop (about 0.30 MPa), and it is a potential technique for this reservoirs. Through the implementation of SAGD, bottom water could be effectively controlled. Aiming at the LD heavy oil block in Bohai offshore oilfield, the SAGD performance in heterogeneous heavy oil reservoir with bottom water was numerically studied in this paper. In these simulation models, the water was broken into three components (connate water, injected water and bottom water) to study the water producing in SAGD process. Thus, the influences of startup approach, oillayer thickness, water thickness and the distance between well-pair and bottom-water on the water rising were all simulated. Thereafter, a set of numerical simulations were performed to assess the shale issues in SAGD process, e.g. the vertical and horizontal position of shalebarriers, the shale distribution range, the barrier permeable condition and the macroscopic vertical permeability.Results indicated that bottom water reduced the ultimate recovery of SAGD process by about 10% of the OOIP. The startup by steam-circulation was much suitable for the bottom water heavy oil reservoir instead of CSS approach. The bottom water tremendously reduced the startup pressure-decline rate, and thus the startup-time was prolonged. The distance between well pair and water zone had a great influence on the SAGD performance, and a small distance would delay the beginning time of the steam-chamber rising. For reservoir heterogeneity, the vertical and horizontal heterogeneity have great influence on the drainage process, especially the shale cases. It tremendously decreased the recovery rate by about one time. This investigation could be used as a tool for the successful design of SAGD process in heavy oil reservoirs with bottom water.

Numerical Simulation Study on Steam-Assisted Gravity Drainage Performance in a Heavy Oil Reservoir with a Bottom Water Zone

“…Figure 8 reveals that the oil recovery factor and cumulative energy injected into the oil reservoir without a bottom water zone are lower than those occurring in reservoirs with a bottom water zone due to the bottom water augmenting the expansion process of the steam chamber in the oil pay zone, as indicated in Figure 9. This result is opposite to that of the previous study [26], which showed that the oil recovery factor is reduced by 10% with the bottom water zone. This difference occurs mainly because, in the previous study, no solution gas was considered in the heavy oil so that the heat transfer rate would not be reduced and the steam chamber could extend freely [26].…”

“…This result is opposite to that of the previous study [26], which showed that the oil recovery factor is reduced by 10% with the bottom water zone. This difference occurs mainly because, in the previous study, no solution gas was considered in the heavy oil so that the heat transfer rate would not be reduced and the steam chamber could extend freely [26]. Therefore, the pressure in the steam chamber was not maintained, and the steam could be injected continuously.…”

“…Therefore, the pressure in the steam chamber was not maintained, and the steam could be injected continuously. When the steam chamber reached the bottom water zone, heat loss occurred and negative effects occurred [26]. However, in this study, solution gas was considered in the heavy oil, and the gas bank reduced the heat transfer and kept the steam in the inner part of the steam chamber.…”

An Empirical Correlation to Predict the SAGD Recovery Performance

“…Preheating phase aims to create thermal interconnection between producer well and injector well. There are three approaches, including cyclic steam stimulation, steam circulation and fracturing (Liu 1998;Dong et al 2014). In this model, the CSS preheating method is adopted.…”

“…They considered the steam channeling phenomenon among vapor chambers. Dong et al (2014) numerically studied the SAGD performance in a heterogeneous heavy oil reservoir with bottom water. Using CMG-STARS thermal simulator, Hashemi-Kiasari et al (2014) studied the effect of operational parameters on SAGD performance in a dip heterogeneous naturally fractured reservoir.…”