Reservoir simulations of H2S production during a SAGD process on a meandering fluvial reservoir taking into account both the aquathermolysis effects and the thermal conductivity.

Abstract

Nowadays, EOR methods such as thermal techniques are widely used to recover the viscous hydrocarbons from heavy oils and bitumen reservoirs. One of the thermal methods is the Steam-Assisted Gravity Drainage (also called SAGD) consists in injecting steam through the injector well into the reservoir to melt the viscous oil and allow its mobility. The melted oil falls by gravity and is produced by the production well. The hot steam injected, in contact with heavy oils/bitumen, creates chemical reactions called aquathermolysis reactions. These reactions generate gases such as the hydrogen sulfide (H2S) or carbon dioxide (CO2). The H2S is known to be a highly toxic and corrosive, therefore, it needs to be given a particular attention when it is produced at the surface. Reservoir models have been built to simulate thermal effects during a SAGD but only few publications in the literature deal with the aquathermolysis reactions occurring in the reservoir where steam is injected.

This report will focus on building a reservoir simulation model in order to forecast the H2S production. This model is built based on a PVT description of the heavy oil/bitumen and on a new sulfur-based kinetic model. A literature study was performed to build up the general understanding of the physical and chemical mechanisms occurring during a steam injection process. A description of the heaviest components found in heavy oils/bitumen is made through a SARA analysis. A new sulfur-based kinetic model recently developed was presented and used in the reservoir model to reproduce the aquathermolysis reactions.

A large part of this thesis is dedicated to the topic of building a PVT model for heavy oils. Throughout this chapter, the PVT (Pressure-Volume-Temperature) model is built based on correlations specific for heavy oils. This PVT describes the behavior of the fluid (oil) used during reservoir simulations.

Then, a chapter presents the reservoir models used for the simulations. Reservoir simulations were run using both the 2D and 3D models in order to compare the simulation results. A 3D reservoir model is presented to get to know the main characteristics of this heterogeneous reservoir. This model reproduces the Hangingstone heavy oil field in Canada.

Finally, these simulations results are then presented, such as the oil and gas productions, the steam injection, the Steam-Oil Ratio as well as the H2S production. A sensitivity analysis was also performed in order to see how some parameters, such as the pressure/temperature (at the saturation conditions) of the steam injected or the rock conductivity, would affect the H2S production or the oil production.

The different simulations presented in this report show consistent results in terms of H2S production at surface for different steam injection pressures. This shows that the fluid description and the kinetic model used in the study are relevant for acid gases prediction in the context of steam injection reservoir simulations.