Study Of Fluid Mobility Of Medium-high Coal Rank Reservoir On Micro Scale In Eastern Yunnan And Western Guizhou

On the basis of summarizing the geological background of medium-high rank coal reservoirs in the study area of eastern Yunnan and western Guizhou,the pore structure characteristics of medium-high rank coal samples of different pore size scales were analyzed by high pressure mercury injection experiment,low temperature liquid nitrogen adsorption experiment and low temperature CO2 adsorption experiment,and the pore structure model of full pore size scale was constructed by fractal mathematics method.Nuclear Magnetic Resonance(NMR)experiments were carried out to study the fluid distribution and fluidity characteristics of medium-high rank coal samples.The results show that there are obvious differences in full scale pore structure characteristics between medium and high rank coal samples: the specific surface area and pore volume of coal samples increase with the increase of coal rank,and the pore distribution curve of the full pore size scale presents a three-peak distribution.The medium rank coal is a "high-high-high" or "high-low-high" model.The high rank coal samples are mainly "high-low-low" distribution,and the left peak corresponds to the most developed supermicro pore,especially the high rank coal.High rank coal samples have the highest degree of micropore development,while high rank coal samples have slightly lower degree of medium pore and macropore development than medium rank coal.The results of NMR experiments based on high pressure saturation show that the fluidity of low-rank coal samples is good,the water saturation of high-rank coal samples varies little during pressure saturation experiments,and the right peak of NMR relaxation spectrum is low,which indicates that the space of seepage pore is very small.Based on the experimental data of liquid nitrogen adsorption,the surface relaxation rate ?2 was calculated,and the methods of pore size conversion and saturation pore size calculation were proposed.The results show that most of the high rank coal samples have saturated water in the stage of atmospheric pressure or low pressure,and the increase of saturated water pressure has limited effect on increasing pore water content.The residual water saturation of coal samples decreases gradually with the increase of displacement pressure,and the inflection point appears at the displacement pressure of 2 MPa,then tends to be stable.The fluidity of medium rank sample water is good,and the residual water saturation is low;the fluidity of high rank sample water is poor,have more residual water.A method for calculating movable pore size in displacement process is established.The results show that the movable pore size of medium rank coal samples varies greatly,indicating that the water in the pore with larger pore size is gradually driven out,while the movable pore size of high rank coal samples varies slightly,eventually reaching an average of 18.08 nm,indicating that the water in the higher developed micropore is difficult to drive out,resulting in poorl water mobility.