An Analysis of Hydraulic Fracture and Mineback Data for a Treatment in the German Creek Coal Seam
- R.G. Jeffrey Jr. (CSIRO Div. of Geomechanics) | R.P. Brynes (Capricorn Coal Pty. Ltd.) | P.J. Lynch (Capricorn Coal Pty. Ltd.) | D.J. Ling (BHP Engineering)
- Document ID
- Society of Petroleum Engineers
- SPE Rocky Mountain Regional Meeting, 18-21 May, Casper, Wyoming
- Publication Date
- Document Type
- Conference Paper
- 1992. Society of Petroleum Engineers
- 2 Well Completion, 2.5.2 Fracturing Materials (Fluids, Proppant), 1.2.2 Geomechanics, 5.8.3 Coal Seam Gas, 4.1.2 Separation and Treating, 5.6.4 Drillstem/Well Testing, 4.3.4 Scale, 3 Production and Well Operations, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 2.4.3 Sand/Solids Control, 2.2.2 Perforating, 1.6.9 Coring, Fishing, 1.14 Casing and Cementing, 1.6 Drilling Operations, 4.3.1 Hydrates
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A hydraulic fracture treatment in well ECC90 of the German Creek coal seam was carried out in Much, 1989, at the Germ: 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 alter 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 l] 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 lpm]. 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.
Hydraulic fracturing has been used in the U.S. since the mid 1970s to stimulate production from vertical methane wells, mostly for commercial production purposes although the first wells were implemented to pre-drain methane from the coal in advance of mining. Trials of hydraulic fracturing of coal seams in vertical wells were carried out in Australia in the late 1970s and early 1980s with little success. These early treatments were small compared to current practice and resulted in methane flow rates that were not sufficient to drain the gas from the seam in a reasonable period of time. In 1987, North Queensland Energy Pty. Ltd. started a pilot project in the Bowen Basin of Queens land to investigate the commercial production of methane from coal seams. Their work rekindled interest in the use of vertical wells to drain methane from coal seams around underground mines and, in response to a proposal put forward by Seamgas Enterprises Pty. Ltd. and Capricorn Coal Management Pty. Ltd., a project to test the effect of a hydraulic fracture stimulation on the mineability of the German Creek coal seam was funded by an industry-sponsored government agency that supports coal mining research projects in Australia.
Description of Project
The overall goal of the project was to assess hydraulic fracturing of vertical wells as a way of pre-draining methane from the coal in advance of mining. The project was planned to test the effect of a full-scale fracture stimulation of the German Creek coal seam on mining activities. The potential for damage, by hydraulic fracturing operations, to the rock layers overlying the coal seam was a main concern. An assessment of the effectiveness of the fracture
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