Kinetics of Methane Oxidation Inside Sandstone Matrices
Authors: Chu Chieh 
Published: December 2007

The kinetics of methane oxidation bas been studied in both empty and sandstone-Packed vessels. Crushed Berea sandstone was used in most of the work; however, some tests were conducted with crushed Torpedo sandstone and consolidated Berea sandstone. The temperature levels covered were from 700 to 900 degrees F, and the pressures ranged from 100 to 400 psig. The methane concentration in the feed gas varied from 4 to 14 percent, whereas the oxygen concentration was percent, whereas the oxygen concentration was from 9 to 21 percent. The superficial molar velocity was 0.481 gm mol/(sq cm)(hour) in most of the experiments. Sandstone was found to have a catalytic effect on the methane oxidation reaction. Different samples of sandstones have different catalytic effects on the reaction. An equation describing the reaction rate inside the crushed Berea sandstone matrix was developed by use of the method of steepest descent. This equation takes into account both the homogeneous and heterogeneous reactions. Such an equation will help predict or explain the ignition, maintenance or extinction of the combustion of gas inside reservoirs.

Introduction

In the in-situ combustion process for oil recovery, natural gas is generally burned in the initial stage to establish a high temperature zone around the injection well. In certain reservoirs where fuel deposition is not high enough to support combustion, the use of natural gas has been suggested to alleviate this deficiency. Also, bottom-hole heating with an air-gas mixture is sometimes used for stimulating production. Because of the practical significance of the methane oxidation reaction inside sandstone matrices, the reaction kinetics was studied in this work. The kinetics of the methane oxidation reaction taking place in an empty reaction vessel has been studied by many investigators. As a result of their work, various rate equations have been proposed. Norrish and Foord used a nonflow system to study the slow oxidation of methane by observation of the change in total pressure in gas mixtures at constant volume and specified temperature. The temperatures used were 480 degrees to 720 degrees C and the pressures ranged from 50 to 300 mm Hg. They suggested that the surface of the reaction vessel influenced the reaction rate according to the expression

(1)

where p and denote partial and total pressures, respectively, the subscript o indicates the initial value; D is the diameter of the reaction vessel, and A is the surface activity per unit area. Hoare and Walsh studied the effect of vessel surfaces on the combustion of methane by using a silica reaction vessel pretreated in four different ways; namely HF-treated, aged, heat-seated and PbO-coated. They used temperatures from 500 degrees PbO-coated. They used temperatures from 500 degrees to 750 degrees C and pressures up to 1 atm. They expressed their results in terms of the rate equation,

(2)

where the values of x, beta and gamma vary with the vessel surface employed and are within the ranges a = −1.0 to 2.4, beta = 1.2 to 3.0 and gamma = 0.3 to 0.9. Karadlova et al. used a quartz reaction vessel which had been washed with HF. The temperatures ranged from 423 degrees to 513 degrees C and pressures from 117 to 325 mm Hg. Aside from changes in the total pressures, they also determined the concentrations pressures, they also determined the concentrations of the various components in the reactive mixture, after the reactions had been arrested by quenching.

SPEJ

P. 145