--> Abstract: The Relationship between Rank and Elastic Properties of Coal; #90063 (2007)

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The Relationship between Rank and Elastic Properties of Coal

 

Morcote, Anyela1, Gary Mavko2 (1) Stanford University, Katy, TX (2) Stanford University, Stanford, CA

 

This paper summarizes the bulk and dynamic elastic properties of five dry rock coal samples and powder from bituminous coal. The measurements correspond to one sapropelic cannel coal and four humic coals. The humic coals cover different ranks, from bituminous to anthracite.

 

The sapropelic coal presents the lowest dry density which is 1.1 g/cc. Dry density in humic coals increases with coal rank, ranging from 1.30 to 1.67 g/cc, the highest density corresponding to the highest coal rank (anthracite). Porosity of coal rock samples ranges from 1.11 to 4.9%, whereas porosity of the powder coal sample is 20%.

 

Velocities were measured at increasing confining pressure up to 40 MPa, in both loading and unloading cycles. Core plugs were taken both parallel (90°) and perpendicular (0°) to bedding planes. Coal velocities, and therefore bulk modulus, depend on both the applied confining pressure and coal type and rank. Sapropelic coal presents the lowest velocities of all samples and the smallest dry bulk modulus while velocities and bulk modulus of humic coals increase with coal rank. The dependence of velocities on confining pressure is greater at pressures up to 5 MPa, the closing pressure for most of the cleats or fractures.

 

We obtained a linear empirical relationship of Vp-Vs that covers a relatively wide range of confining pressures and coal ranks.

 

The data show that coals have significant intrinsic anisotropy at high confining pressures. This intrinsic anisotropy may be due to very fine layering and preferred orientation of coal minerals.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California