Simulation Studies of Steam-Propane Injection for the Hamaca Heavy Oil Field
Authors: Venturini G.J. , Mamora D.D. , Moshfeghian M. 
Published: March 2010

Simulation studies were performed to evaluate a novel technology, steam-propane injection, for heavy Hamaca crude oilfrom Venezuela's Orinoco Basin. The oil has a specific gravity of 1.005 (9.3 ° API) and a viscosity of 25 Pas (25,000 cp) at 50 ° C. Two types of studies were performed: a simulation study to history-match laboratory results and a reservoir simulation study of steam-propane injection in a 5-spot pattern.

A 1D 48 grid-cell model was used to describe the sand mix in the injection cell. A ten pseudo-component oil model for Hamaca oil was developed based on composition up to C10 that gave a satisfactory history match of experimental results. Components in the C7 - C10 range appear to play a significant role during steam-propane injection and therefore need to be described in greater detail. The pseudo-component oil model was subsequently used in the reservoir model.

The reservoir model represented a symmetry volume that is one-eighth of a 10-acre 5-spot pattern. A 9 ? 5 ? 10 3D Cartesian model was used to describe the symmetry volume, with one axis (x-axis) oriented parallel to the injector-producer direction. Simulation results indicate the following. First, oil production acceleration of 15﹪ was observed with a propane-steam mass ratio (PSR) of 0.05 compared to pure steam injection. A substantial gain in discounted revenue and savings in steam injection cost would be realized. Second, unlike the experimental results, the oil production rate peak with steam-propane injection, 175 m3/d (1,100 STB/D), is significantly higher than that with pure steam injection, 110 m3/d (690 STB/D). Third, oil production acceleration increases with increasing propane content. And finally, oil recovery (at the end of the five-year forecast period) increases from 2.3﹪ OOIP for pure steam injection to 7.0﹪ OOIP for steam-propane injection with a PSR of 0.05.

Both experimental and simulation studies indicate that steam-propane injection is a very promising technology. Further research, followed by field tests, are recommended to better understand and verify the process under actual field conditions.

Introduction

In 1991, Butler and Mokrys(1) described a variation of the steam-assisted gravity drainage (SAGD) called VAPEX. Propane is injected with steam into a horizontal well, forming a vapourfilled chamber within the reservoir. The vapour dissolves in the oil around the chamber and the oil drains by gravity to a horizontal producer near the bottom of the reservoir. Subsequent work by Butler and Mokrys(2, 4) showed VAPEX resulted in partial in situ de-asphalting and a reduction of heavy metals in the produced oil. The resulting oil can be of a higher quality and better suited for direct refining.

The basic mechanisms of steam injection with additives are z thought to be swelling of the oil, viscosity reduction, and solution gas drive. It is observed that the additives tend to exist primarily at the boundary of the steam chamber where they expand the size of the steam chamber but lower the steam temperature (because of partial pressure effects). It is also in this region where significant partitioning into the oil and water phases occurs.