Underground Coal Gasification In Canada-Excavation Of The Alberta Test Site
Authors: Roehl A.A. , Brown R.A.S. , Jensen E.J. 
Published: December 2007

The underground coal gasification field test performed by the Alberta Research Council on a site performed by the Alberta Research Council on a site near Forestburg, Alberta, during the summer of 1976 is reviewed and the 1977 excavation of the test site discussed. The test comprising two burns was made in the Battle River coal seam which is overlain by 20 m of an alternating series of bentonitic shales, siltstones and sandstones. The subbituminous coal seam was 3.6 n thick and had two significant horizontal partings.

The gasification area was defined by the injection and production well pattern which was 9.1 m along the minor cleat and 18.3 m along the major cleat in the coal. Control of the rate and pressure of the air used for gasification permitted use pressure of the air used for gasification permitted use of the formation water for the reaction, producing a gas with a heating value of 3700 to 5600 kJ/m.

The region of the first burn was excavated to obtain data from the coal zone affected by the test. The visually affected zone, comprising dried, carbonized and gasified coal, was measured, photographed and sampled for laboratory analyses. photographed and sampled for laboratory analyses

Introduction

A major objective in selecting the site for the underground gasification test was to find a subbituminous seam that was shallow enough to permit excavation of the burn area after completion permit excavation of the burn area after completion of the test. A number of locations were investigated and the most suitable site was the one selected near Forestburg, Alberta. The test involved completion of 25 wells into the coal seam: four gasification wells, nine instrumentation wells and 12 water observation wells. The four gasification wells were located on the corners of a 9.1 m by 18.3 m rectangular pattern as shown in Fig. 1. Two burns were made. Burn 1 comprised the ignition of the coal in well no. 3 (cf. Fig. 1), followed by linking along the minor cleat to well no. 4 by reverse combustion and forward gasification back to well no. 3. This process lasted in excess of two weeks and produced 25 500 m of gas with an average heating value of 3700 kJ /m during linking and 169 900 m of gas with an average heating value of 5600 kJ /m during gasification.

Ignition in well no. 1 with linking by reverse combustion to well no. 2 and forward gasification back to well no. 1 comprised the first phase of burn 2. The second phase of burn 2 was an attempted line drive (forward mode) from the gasification zone between wells no. 1 and 2 to the burn 1 zone between wells no. 3 and 4. During the attempted line drive a channel from the burn 2 area to well no. 3 was established. Difficulties in maintaining lateral containment of the produced gases were encountered during burn 2 because much of the formation water was depleted during the first burn.

OBJECTIVES OF THE EXCAVATION

An understanding of the underground gasification process is possible from process data. However, at present it is not possible to confidently predict the geometry of areas which are gasified, predict the geometry of areas which are gasified, carbonized and dried in a coal seam during underground gasification. To define these zones more data are required. Additional information is also required concerning subsidence and chemical and thermal changes of the overburden bordering the gasified coal. The need for this information, a successful burn and the desire to examine and evaluate the condition of the down hole piping and instrumentation led to the decision to excavate the site.