The paper was presented at the SPE/DOE Unconventional Gas Recovery Symposium of the Society of Petroleum Engineers held in Pittsburgh, PA. May 16–18, 1982. The material is subject to correction PA. May 16–18, 1982. The material is subject to correction by the author. Permission to copy is restricted to an abstract of not more than 300 words Write: 6200 N. Central Expwy., Dallas, TX 75206.

Abstract

Occidental Research Corporation has for the past five years been actively engaged in a research past five years been actively engaged in a research program of draining methane gas from the Pocahontas program of draining methane gas from the Pocahontas #3 coal seam. This work is being conducted in Island Creek Coal Company's deep mines in the Virginia Pocahontas Division. The technique consists of drilling long horizontal inseam holes in advance of mining. The initial objective of the program was to reduce methane emissions in mine program was to reduce methane emissions in mine workings in order to improve mine safety and productivity. As the research program evolved, potential productivity. As the research program evolved, potential for commercial scale production and utilization of the gas resource became apparent. Current research activities include production and capturing of the gas and utilization at the mine plant for drying the coal. To date 27 horizontal holes have been drilled in three mines for an aggregate depth of over 6,400 meters (21,000 feet). The longest hole is 835 meters (2,740 feet). Over 18.4 million cubic meters (650 MMCF) of pipeline quality gas has been drained and transported safely to the surface through a network of underground pipelines. Coal dryers have been retrofitted with gas burners to replace #2 fuel oil and pulverized coal for drying coal.

Introduction

Island Creek Coal Company is a major coal producer and much of its production comes from producer and much of its production comes from underground mines. Seven of its mines located in southwest Virginia are deep and gassy with the maximum depth exceeding 800 meters. The gas content of coal in place approaches 19cc/gm (600 SCF/ton). It has long been recognized that the presence of methane gas in coalbeds poses a safety hazard and therefore hinders productivity and increases mining costs. The gas contained in the company's coal reserves has been recognized as a significant resource as well. Total gas reserves contained in the coal beds and associated carboniferous rocks in the U.S. are estimated to exceed 28 trillion cubic meters (one quadrillion cubic feet). In the present environment of high priced energy supplies present environment of high priced energy supplies exploitation of this gas as an energy source is becoming economical in its own right.

The deep mines of Island Creek Coal Company's Virginia Pocahontas Division present favorable conditions for exploitation of this resource because the Pocahontas #3 seam is very gassy and the mines provide easy underground access to the coal bed. provide easy underground access to the coal bed.

DRAINAGE CONCEPT AND OBJECTIVE

The methane drainage concept applied by Occidental Research Corporation consists of drilling deep horizontal inseam holes into the Pocahontas #3 seam in advance of mining, The gas draining from these holes is captured and piped to the surface through an underground piping system. Two variations of the horizontal hole drainage concept, namely shielding and depletion are employed: In one case drainage holes are drilled parallel to the working sections to shield the active workings from gas. The second approach involves drilling into virgin areas far in advance of mining and draining the gas for several years to deplete the reservoir. The "shielding" approach produces quicker results in the form of reduced gas emissions in a mining section. The "depletion" approach sustains production of significant quantities of gas for production of significant quantities of gas for longer periods of time. Both approaches serve a dual purpose of draining gas for improved mining productivity and at the same time supplying gas for productivity and at the same time supplying gas for utilization.

DRILLING AND COMPLETION

Since inception of the program a total of 27 horizontal holes have been completed for an aggregate depth of over 6,400 meters (21,000 feet), This includes an extensive exploration project which has been initiated to determine gas drainage characteristics in all mines in the division. Targeted depth for any production hole is about 600 meters (2,000 feet). However, the longest hole drilled so far was 835 meters (2,740 feet) deep (Figure 1). An average drilling rate of 61 meters (200 feet) per shift and a maximum of 130 meters (420 feet) per shift have been achieved.

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