Heavy-Oil Recovery by In-Situ Combustion - Two Field Cases in Rumania
Authors: Cadelle C.P. , Burger J.G. , Bardon C.P. , Machedon V. , Carcoana A. , Petcovici Valentin 
Published: December 2007

Cadelle, C.P., Inst. Francais du Petrole Burger, J.G., Inst. Francais du Petrole Bardon, C.P., Inst. Francais du Petrole Machedon, V., Research and Design Inst. for Oil & Gas Carcoana, A., Research and Design Inst. for Oil & Gas Petcovici, Valentin, Research and Design Inst. for Oil & Gas

Laboratory and field results are presented for two Rumanian fields: Suplacu de Barcau and Balaria. Insitu combustion is in the industrial stage at Suplacu de Barcau (38 air-injection wells), and the Balaria project (now 5 air-injection wells) is being expanded. Data given include air injected, oil produced, cumulative air/oil ratio, and composition of gas produced. These data, with measurements of temperature and thickness burned, have been used to follow and control the process.

Introduction

The depletion of easily producible oil resources is giving increasing importance to the considerable accumulations of heavy oil scattered throughout the world. Recovery using conventional production techniques is limited, however, and laboratory research and field testing have been conducted in an effort to develop more efficient recovery methods - mainly steam injection and in-situ combustion.A cooperation agreement was signed in Sept. 1969 between the Inst. Francais du Petrole (IFP) and the Ministry of Mining, Petroleum, and Geology of Rumania, representing the Research and Design Inst. for Oil and Gas (ICPPG), to carry out joint research and development on thermal recovery methods.Since this agreement was signed, IFP and ICPPG have studied the various aspects of oil recovery by insitu combustion. They have conducted laboratory work and field applications in a wide variety of reservoirs containing heavy or conventional oil, thereby gaining broad experience in the use of the insitu combustion technique.This paper outlines and describes their joint endeavors, concentrating particularly on two in-situ combustion field operations under way in Rumania.

Feasibility of In-Situ Combustion

Screening criteria have been developed through theoretical research and laboratory experimentation to determine the suitability of a given reservoir for insitu combustion. It has been found that shallow reservoirs containing heavy oil are often promising candidates. Once a reservoir is chosen, in-situ combustion is carried out in three phases, as illustrated in Fig. 1: ignition, process implementation, and measurements and interpretation.Specific field applications have been conducted by ICPPG and IFP on the basis of this methodology and are described, along with the base studies, in this article.

Ignition

If sufficient heat is released by the oxidation of the oil under reservoir conditions, spontaneous ignition will occur a few days after air injection is begun.To determine the probability of spontaneous ignition, the oxidation rate of the oil under reservoir conditions was measured in the laboratory.Oil/sand mixtures are placed in a cylindrical vessel with a metal screen so that the oxygen in the surrounding gas has easy access to the crude. The vessel is placed in the pressure cell (Fig. 2). The oxidation rate, calculated from the change in the oxygen content of the air in the cell, is determined at temperatures between 50 and 140 degrees C (122 to 284 degrees F) and at pressures between 3 and 10 MPa (435 to 1,450 psia).A numerical model then is used to calculate the temperature changes vs. time and the space coordinate when air is injected into the formation. The ignition delay is considered as the time required for the maximum temperature in the investigated zone to reach the ignition temperature (210 degrees C or 410 degrees F). It appears that spontaneous ignition is likely to occur when the reservoir temperature is above 55 to 60 degrees C (131 to 140 degrees F).

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