The Qiwu Mine is located in the Ten Xian coal field of Shandong province.It experienced repeated volcanic activity,after the coal beds formed,where magma intrusion was significant The effect of coal reservoir porosity after magma intrusion was studied by analysis of regional and mine structure and magmatic activity.Experimental methods including maceral measurement under the microscope and mercury porosimetry were used for testing the pore structure.The authors believe that magma intrusion into low-rank bituminous coal causes reservoir porosity to gradually increase：the closer to the magmatic rock a sample is,the less the porosity.The pore size distribution also changes.In the natural coal bed the pore size is mainly in the transitive and middle pore range.However,the coal changes to anthracite next to the magmatic rock and larger pores dominate.Regional magma thermal evolution caused coal close to magmatic rock to be roasted,which reduced the volatile matter,developed larger holes,and destroyed plant tissue holes.The primary reason for a porosity decrease in the vicinity of magmatic rock is that Bituminite resulting from the roasting fills the holes that were present initially.
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.
