Assessment of SAGD heat transfer mechanism via noncondensable gas CO-INJECTION

Abstract

The favored process for extracting heavy oil from reservoirs using twin horizontal wells is called steam-assisted gravity drainage (SAGD). During this application, steam is injected into the reservoir from above well and when heated, heavy oil is mobilized under gravity to the producer lying below. Steam build-up inside the pay zone is called the steam chamber. The main problems facing SAGD are the thermal efficiency and the thermal conductivity of the heat flux at the uppermost part of the steam chamber. Moreover, the role of solution gas and injection of gas in SAGD steam chambers remains unclear, particularly issues involving heat transfer. The objective of the study is to analyze the variation of heat transfer behavior by conduction and convection on heavy oil production using heat fluxes via the co-injection of noncondensable gas (NCG) during SAGD. To evaluate this phenomenon, the field verified SAGD analytical model was modified and used to analyze the experimental results of steam with/without NCG addition at comparable volumetric injection ratios. The outcomes of the modified heat transfer study conducted during SAGD on co-injection of NCG showed that an adequately large concentration at the uppermost part of the chamber decreased the heat flow at the edge. Besides, conduction was the primary heat transfer method for steam injection only. In the modified model, there was no obvious convective heat transfer below 125 °C for steam alone and below 150 °C for cases with NCG addition. However, the convective heat flux was more dominant after 230 °C and 240 °C for the NCG addition to steam at 1:1.29 and 1:4.41 volumetric ratio cases respectively. For the conductive and convective heat fluxes, the modified model fit with the steam only case. However, the results of the addition of NCG to steam at both runs showed a tendency to decrease at higher temperatures. On the contrary, the interaction between NCG and steam at the edge of the chamber influences the flow of heat resulting in both a decreased transfer of heat to the overburden as well as to the sides of the depletion chamber and a low recovery mechanism that produces the steam and gas push (SAGP) mechanism.