Reservoir Engineering in Coal Seams: Part 2—Observations of Gas Movement in Coal Seams

Abstract

Summary This paper, the second of two concerning the movement of gas in coal seams, covers observations of seam fluid pressures and flows in mines in northern and central Queensland, Australia. Techniques based primarily on underground measurement rather than measurements from surface primarily on underground measurement rather than measurements from surface boreholes were used to gain information on the seams. The techniques used for in-seam studies are described because they differ substantially from conventional oil and gas surface borehole techniques. The paper demonstrates the importance of cleats and joints in the control of fluid movement and records flow increases consistent with increasing permeability with production. Methods Pressure Measurement. Pressure measurement was Pressure Measurement. Pressure measurement was conducted in seam by two basic techniques. In the first, a hole approximately 50 mm [2 in.] in diameter was drilled in seam and then the drill rods were withdrawn after a predetermined length, typically when 10 to 80 m [33 to predetermined length, typically when 10 to 80 m [33 to 262 ft], had been reached. Following this, a 1- to 2-m [3.3- to 6.6-ft] -long packer was installed as quickly as possible on the end of the conduit string, leaving 2 to 10 possible on the end of the conduit string, leaving 2 to 10 m 16.6 to 33 ft] of open hole ahead of the packer. The packer was inflated with water through a synthetic braid packer was inflated with water through a synthetic braid hydraulic hose. Packer inflation pressure typically was raised to that required to expand the packer to borehole size plus I 1/2 times the fluid pressure being measured. Ocasionally, this packer pressure may have led to some problems because it may have approached or exceeded problems because it may have approached or exceeded total in-seam stress and therefore tended to open the cleats (fractures) within the seam, thus promoting leakage around the packer. The pressure within the zone at the end of the packer was measured through a 4.8-mm [0. 19-in.] -OD nylon tube leading to the borehole collar and connected to either a pressure gauge or a chart recorder. The coal permeability was normally sufficiently low that no significant leakage occurred around the packer into the borehole, and reasonably reliable pressure measurements could be obtained. By repeating the procedure outlined above, it was possible to gain an understanding of the pressure possible to gain an understanding of the pressure distribution that existed within the coal along the line of a borehole. Up to five tests at 10-m [33-ft] intervals could be conducted in a 7-hour shift with this technique. Attempts were made to extend the use of packers to permanent pressure measurement. A single packer was permanent pressure measurement. A single packer was considered inadequate to measure the overall pressure distribution along a borehole, and therefore multiple packer assemblies were constructed containing pressure measurement ports between the packers as described by Lama et al. These were expensive and difficult to maintain.

Influence of basement structures on in situ stresses over the Surat Basin, southeast Queensland

“…The coals within these basins are of significant interest for coal seam gas exploration and production, particularly within the “Walloon Fairway” (Figure ). Viability of coal seam gas production is partially dependent on the intersection of production wellbores to reservoir (coal seam) fracture and cleat permeability, whereas primary porosity plays a diminished role [ Gray , , ]. Furthermore, the ability of these fractures and cleats to transmit fluid is partially in situ stress dependent, with fractures that are critically stressed being more likely to be effective fluid conduits than those that are not [ Barton et al ., ; Zoback , ].…”

Review on desorption-diffusion-flow model of coal-bed methane

“…众所周知, 煤层气割理-裂隙系统中充满水 [17][18][19] , 但是关于煤基质孔隙中是否存在水, 若存在水的分 布如何却存在争议. 在澄清煤储层的孔隙分类的基 础上, 为了判别煤层解吸气在不同尺寸基质孔隙中 的运移方式, 仍需研究煤储层的原始气水分布.…”

Monitoring and modelling of gas dynamics in multi-level longwall top coal caving of ultra-thick coal seams, part I: Borehole measurements and a conceptual model for gas emission zones

“…Based on these validation studies, the gas emission curves were modified to eliminate the observed over-and underestimates of emissions and produced the British Coal Firedamp Prediction Method as it is known today. Building upon the understanding of how a longwall panel and the surrounding strata respond to progressive coal extraction, gas emission patterns associated with conventional mechanised longwall mining have been extensively studied in the past few decades (Barker Read and Radchenko, 1989;Durucan, 1981;Gray, 1987;Karacan et al, 2011;Lunarzewski, 1998;Noack, 1998). Whittaker (1974) described dynamic stress changes and the formation of stress abutments in a longwall panel ahead of an advancing longwall coal face.…”