Experiments on Steam-Assisted Gravity Drainage with Coinjection of Noncondensable Gases during the Middle and Later Stages of Its Development in Super-Heavy Oil Reservoirs

Abstract

Summary The problems of oil/steam ratio (OSR) and oil production decline are prominent during the middle/later stages of steam-assisted gravity drainage (SAGD) in superheavy oil reservoirs. Using noncondensable gas (NCG) by SAGD can reduce heat loss to the overburden and reduce carbon dioxide (CO2) emissions. However, to date, laboratory experiments have mainly been conducted to simulate NCG coinjection with steam in the early stage of SAGD. There has been limited research on the NCG coinjection into the mature SAGD steam chamber. For this study, five sets of 2D physical simulation experiments are introduced and designed based on NCG coinjection with steam into the sand-packed model. The influencing factors of steam-assisted and gas push (SAGP) are analyzed through experiments, including different NCGs [methane (CH4), CO2, and nitrogen (N2)] and coinjection of NCG at different times (i.e., during the lateral expansion and descending stages of the steam chamber). The results indicate that the mechanism of SAGP includes reducing the steam consumption, maintaining the pressure balance of the steam chamber, reducing the partial pressure of the steam, maintaining the quality of the steam, and improving the displacement efficiency of the steam during the lateral expansion of the steam chamber. In addition, the top gravity displacement is the primary mechanism during the later stage of pure gas injection, which manifests that the residual oil at the bottom of the steam chamber is further recovered by using the residual heat of the the steam chamber. Compared with SAGD, the recovery of CO2-assisted SAGD (CA-SAGD), CH4-assisted SAGD (MA-SAGD), and N2-assisted SAGD (NA-SAGD) increased 6.8%, 5.4%, and 4.4%, respectively. The NCG coinjection effect was better during the descending stage of steam chamber, and the oil recovery was 4.7% higher than that during the lateral expansion stage. The selection of NCG and coinjection timing plays a crucial role in improving the ultimate oil recovery and OSR during the middle and later stages of SAGD in superheavy oil reservoirs.