An Analysis of Hydraulic Fracture and Mineback Data for a Treatment in the German Creek Coal Seam

Abstract

ABSTRACT A hydraulic fracture treatment in well ECC90 of the German Creek coal seam was carried out in March, 1989, at the German Creek Mine Central Colliery located in the Bowen Basin of east central Queensland to assess hydraulic fracturing of coal seams in vertical boreholes as a means of stimulating drainage of methane from the seam in advance of mining. The main goals of the project were to measure the size and geometry of the fracture formed and to test the effect that such a full-scale treatment might have on later mining operations. The plan also included dewatering the coal and producing methane from the well after stimulation. In ECC90, the German Creek seam is located 722 feet [220 m] below the surface and has a thickness of 8.3 feet [2.5 m]. During the stimulation, 80,200 U.S. gallons [303,000 1] of crosslinked gel containing about 80,500 pounds [36,590 kg] of sand were injected into the coal seam at an average rate of 30 barrels per minute [4,763 1pm]. The surface treating pressure averaged about 900 psi [6.2 MPa] and decreased slowly during the treatment except near the end of the job when it increased sharply (because of a screenout). The fracture, exposed by mining, had a large horizontal component overlying a less extensive vertical fracture. The propped width varied from zero to 7.9 inches [200 mm]. No fracture penetration into over- or underlying rock layers was observed and the mining operations were not significantly affected by the presence of the hydraulic fracture.