基于多尺度数字岩石的煤储层气相流动控因机理OA

[Background]Deep coal reservoirs exhibit highly heterogeneous pore-fracture structures.However,limited by a single imaging resolution,conventional digital rock techniques struggle to characterize complex pore-fracture net-works across multiple scales.This poses significant scientific challenges for the fine-scale characterization of deep coal reservoirs and the investigation of their seepage mechanisms.[Methods]This study investigated deep coalbed methane(CBM)reservoirs in the north-central Qinshui Basin.The pore-fracture structures of coal samples were characterized by integrating X-ray computed tomography(CT),mercury injection capillary pressure(MICP),and scanning electron mi-croscopy(SEM).Digital rock models incorporating multi-scale pores and fractures were then constructed by integrating physical experiments with numerical reconstruction.Using the lattice Boltzmann method(LBM),single-phase seepage in deep coal reservoirs was simulated.Based on the simulation results,key factors influencing the seepage capacity of the reservoirs were analyzed.[Results]The method combining physical experiments with numerical reconstruction con-strains fractures using CT,corrects pores through MICP experiments,and characterizes structural anisotropy with SEM.Using this method,digital rock models incorporating multi-scale pores and fractures were constructed,enabling the in-tegrated characterization of fractures and multi-scale pores.Compared to experimentally derived reference porosities,the reconstructed models showed total porosity errors ranging from 0％to 0.08％.Furthermore,the volumetric proportions of pores at varying scales and the trends in pore size distributions in the reconstructed models were generally consistent with the MICP experiment results.These findings demonstrate a high degree of consistency between the models and ex-perimental results in terms of pore volume and pore scale distribution.The seepage simulation results reveal pronounced anisotropy in gas flow in deep coal reservoirs.Preferentially interconnected channels were more likely to develop paral-lel to bedding planes,with permeability ranging from 0.28×10-3 μm2 to 2.33×10-3 μm2.In contrast,lower permeability was observed perpendicular to bedding planes,ranging from 0.29×10-3 μm2 to 0.82×10-3 μm2.Across all the samples,interconnected porosity was positively correlated with permeability,with a correlation coefficient(r)of 0.192.In con-trast,pore-fracture tortuosity and channeling index exhibited relatively strong negative correlations with permeability,with r values of-0.742 and-0.745,respectively.These results reveal the mechanisms underlying the coupled control of multi-scale pore-fracture structures on permeability.Rather than being solely determined by the number of pores,the dif-ferences in permeability are governed by a two-stage controlling mechanism.Specifically,pore mterconnectivity determ-ines the occurrence of effective flow,whereas the channel architecture governs the flow efficiency.In other words,inter-connected porosity governs the formation of effective flow pathways;after interconnection is established,tortuosity and the degree of channeling further regulate the fluid transport efficiency.[Conclusion]The developed digital rock models incorporating multi-scale pores and fractures preserve actual fracture frameworks using CT,constrain multi-scale pore distributions through MICP,and characterize structural anisotropy with SEM.These models enable the integrated char-acterization of actual fracture structures and trans-scale pores,thereby overcoming the limitation associated with a single imaging resolution and addressing the insufficient fidelity of numerical reconstruction alone.Furthermore,the de-veloped models provide an approach to revealing the mechanisms controlling gas flow in deep coal reservoirs.