How In-Situ Combustion Works in a Fractured System

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 117645, "How In-Situ Combustion Process Works in a Fractured System: Two-Dimensional, Core- and Block-Scale Simulation," by H. Fadaei, Institut Francais du Petrole; M. Quintard and G. Debenest, l'Institut de Mecanique des Fluides de Toulouse; G. Renard, SPE, Institut Francais du Petrole; and A.M. Kamp, SPE, Open and Experimental Center for Heavy Oil, prepared for the 2008 SPE International Thermal Operations and Heavy Oil Symposium, Calgary, 20-23 October. The paper has not been peer reviewed. Simulation of an in-situ-combustion (ISC) process was performed for a fractured system at core and matrix-block scales. The aim of this work was to predict the ISC ignition/propagation conditions, understand the mechanism of oil recovery, and provide guidelines for ISC scaleup for a fractured system. The study was of a fine-grid single-porosity multiphase multicomponent system and used a thermal-reservoir simulator. Introduction Heavy-oil recovery from fractured carbonate reservoirs (one-third of global heavy-oil resources) has been low because of the complexity of such reservoirs. The recovery mechanism and the reservoir and operational conditions at which combustion can propagate in fractured systems are not understood clearly. This study investigated ISC-propagation conditions and oil-recovery mechanisms at the fractured-core scale, and investigated the process at the block scale to address the 2D behavior of ISC at large scale. The objective was to determine the dominant processes in combustion propagation at the block scale and the characteristics of different fronts that exist. Model Four phases exist in crude-oil combustion in porous media: oil, gas, water, and solid. The oil and gas phases are multicomponent (i.e., hydrocarbon components), the water is a vapor, and the solid phase contains inert solid and coke. Reactions take place in the oil, in the gas, and on the surface of the solid phase (when coke is present). Coke is formed by pyrolysis and deposited on the solid surface. Reactions in oil and gas phases are homogeneous, but the coke reaction is heterogeneous. Simulation Oil Combustion in a Fractured System. Ignition/propagation conditions of the combustion front in a fractured system and the governing production mechanisms were studied. The simulation model is presented in Fig. 1, and the input data for the model are detailed in Table 1 of the full-length paper. A vertical core was used to mimic a top-down process. The core had no temperature losses at its boundaries, and the top row of blocks was heated with a constant heating rate. Heat injection was maintained for 24 minutes, until ignition occurred. This time was considered to be approximately that used in a nonfractured core.