The pore-fracture system properties of coalbed methane reservoirs in the Panguan Syncline,Guizhou,China

The Panguan Syncline contains abundant coal resources, which may be a potential source of coalbed methane. In order to evaluate the coalbed methane production potential in this area, we investi- gated the pore-fracture system of coalbed methane reservoirs, and analyzed the gas sorption and seepage capacities by using various analytical methods, including scanning electron microscopy （SEM）, optical microscopy, mercury-injection test, low-temperature N2 isotherm adsorption/desorption analyses, low- field nuclear magnetic resonance and methane isothermal adsorption measurements. The results show that the samples of the coal reservoirs in the Panguan Syncline have moderate gas sorption capacity. However, the coals in the study area have favorable seepage capacities, and are conductive for the coalbed methane production. The physical properties of the coalbed methane reservoirs in the Panguan Syncline are gener- ally controlled by coal metamorphism： the low rank coal usually has low methane sorption capacity and its pore and microfractures are poorly developed; while the medium rank coal has better methane sorption capacity, and its seepage pores and microfractures are well developed, which are sufficient for the coalbed methane＇s gathering and exploration. Therefore, the medium rank coals in the Panguan Syncline are the most prospective targets for the coalbed methane exploration and production.

Morphological complexity and azimuthal disorder of evolving pore space in low-maturity oil shale during in-situ thermal upgrading and impacts on permeability

In-situ thermal upgrading is used to tune the pore system in low-maturity oil shales. We introduce fractal dimension(D), form factor(ff) and stochastic entropy(H) to quantify the heating-induced evolution of pore morphological complexity and azimuthal disorder and develop a model to estimate the impact on seepage capacity via permeability. Experiments are conducted under recreated in-situ temperatures and consider anisotropic properties—both parallel and perpendicular to bedding. Results indicate that azimuthal distribution of pores in the bedding-parallel direction are dispersed, while those in the bedding-perpendicular direction are concentrated. D values indicate that higher temperatures reduce the uniformity of the pore size distribution(PSD) in the bedding-parallel direction but narrow the PSD in the bedding-perpendicular direction. The greater ff(> 0.7) values in the bedding-parallel direction account for a large proportion, while the dominated in the bedding-perpendicular direction locates within 0.2-0.7, for all temperatures. The H value of the bedding-parallel sample remains stable at ~0.925 during heating, but gradually increases from 0.808 at 25℃ to 0.879 at 500℃ for the beddingperpendicular sample. Congruent with a mechanistic model, the permeability at 500℃ is elevated~1.83 times(bedding-parallel) and ~6.08 times(bedding-perpendicular) relative to that at 25℃—confirming the effectiveness of thermal treatment in potentially enhancing production from low-maturity oil shales.