In-Situ Combustion in a Thin Reservoir Containing High-Gravity Oil
Authors: Hardy W.C. , Fletcher P.B. , Shepard J.C. , Dittman E.W. , Zadow D.W. 
Published: December 2007

A project in the May-Libby reservoir of the Delhi field of Louisiana has demonstrated that the in-situ combustion process can be successfully employed to recover crude oil having a gravity as high as 40 degrees API. A two-dimensional computer program is used to evaluate field performance in response to this thermal stimulation.

Introduction

In-situ combustion, or in-place combustion, is an oil recovery process in which air is injected into an underground reservoir for the purpose of displacing crude oil and sustaining an exothermic reaction. Through the injection of air, a moving heat source or front and propagated through the reservoir, driving oil into strategically located producing wells. During the past two decades the in-situ combustion process has been demonstrated in a number of field projects. During, this time, considerable effort has been devoted to laboratory studies directed toward defining and evaluating the process variables that control the in-situ combustion process.

Although the in-situ combustion process is not completely understood, several excellent papers have shown it to be dependent upon the quality and quantity of fuel deposited in the formation and upon the type of rock that contains the reaction.

Characteristic temperature distributions, unique to the forward in-situ combustion process, have been shown to be dependent upon heat transfer by conduction and convection within the reservoir and upon the heat losses by conduction to the surrounding rock masses.

A modified form of the in-situ combustion process, designed to increase its thermal efficiency, has been demonstrated in the laboratory and applied with limited extent in the field. In this modified in-situ combustion process, water is injected simultaneously with the air process, water is injected simultaneously with the air for the purpose of absorbing heat in the burned zone and transporting it to the cooler regions of the formation down-stream of the moving combustion front.

The Reservoir Geology

The May-Libby reservoir (Fig. 1) is located approximately 1 mile southwest of the town of Delhi and falls within portions of Sections 22 through 27, T17N-R9E, Richland portions of Sections 22 through 27, T17N-R9E, Richland Parish, La. The reservoir is Upper Cretaceous in age, Parish, La. The reservoir is Upper Cretaceous in age, and is contained within the lower Tuscaloosa formation. Structurally, the May-Libby reservoir is a sand lens that appears to be isolated by shale. It is roughly 2 1/2 miles long, 1 mile wide, and has a dip of approximately 250 ft/mile perpendicular to its major axis.

Reservoir Properties

The May-Libby reservoir has an average thickness of 4.4 ft and lies at a depth of approximately 3,400 ft. An isopachous map of the reservoir is shown in Fig. 2.

Core analyses indicate that the May-Libby reservoir has an average porosity of 31.2 percent. Permeabilities of recovered core material ranged Permeabilities of recovered core material ranged from 20 to 2,900 md, with an average value of 1,069 md. Mineral analyses indicated that the core material contained 76 percent medium-to coarse-grain sand, 13.5 percent silt and 10.5 percent clay. The clay fraction is predominantly kaolinite but does contain some montmorillonite, illite and chlorite.

JPT

P. 199