FIGURE 13.- Individual hole gas flows; hole 3. 3 2 WATER FLOW, gpm GAS FLOW, 1,000 ft3/day Hole 4 250 200 150 100 50 100 FIGURE 14. When all the holes were completed, the initial total gas flow, the in situ pressure, and total water flow after the first 24 hours of operation from the five 3-1/2-inch-diam holes were 994,000 ft3/d, 18 lb/ing, and 2.95 gal/min, respectively. Waterflow averaged 0.6 gal/min/hole. Initial measure ments were influenced by the long drilling period. Gas Analysis The methane gas is of pipeline quality and is not expected to require remedial treatment for acceptance into the gas company's supply line (table 1). Table 2 summarizes the comparative data on the degasification holes at the 18-foot shaft and the multipurpose borehole. Table 1 shows a comparison of gas composition from the multipurpose borehole and the 18-foot shaft. At both locations the gas emitted contains about 9 pct carbon dioxide. Gas compositions are comparable at these sites, about 2.6 miles apart. Average gas flow per 100 feet of hole (table 2) is higher at the 18-foot shaft than the multipurpose borehole. This is to be expected. Seven holes were drilled from the bottom of the multipurpose borehole, and because of the length of the holes (average length 618 feet), gas flow from any one hole is soon affected by the adjacent holes. This effect is called "interference." One hole robs gas that would flow into the adjacent holes which are interconnected by the fracture system of the coalbed. The interference effect is more pronounced on adjacent holes drilled at an angle of 25° or more to the face cleat. |