Coalbed methane (CBM) is an important unconventional energy resource, and its micropore structure has a vital impact on its exploitation. Based on the nuclear magnetic resonance (NMR) experiment, the low-temperature liquid nitrogen adsorption experiment, and the contact angle experiment, in this paper, we investigated the influence of nanofluids on the micropore structure of a CBM reservoir from many aspects. The influence of different adsorption mechanisms of TiO2 nanoparticles on the surface wettability of rock samples was analyzed. The influence of nanoparticle adsorption on the drainage and distribution of liquid in the rock sample was discussed in depth. In addition, the effects of nanofluid treatment on the micropore structure were investigated by comparing the data of low-temperature liquid nitrogen adsorption experiments, including the pore diameter, pore volume, and specific surface area (SSA). The experimental results show that the treatment of nanofluids helps to open the micropores and greatly increases the SSA, pore diameter, and pore volume of the sample. The maximum increase percentages of SSA, pore volume, and pore diameter are 228.12, 80.65, and 18.89%, respectively. It is found that the adsorption of particles is conducive to enhancing the water wettability of the pore throat surface and reducing the damage to water locks.

The evaluation of inter-well correlation is an important basis which can instruct engineers to analyze reservoir water-flooding effect, propose the adjustment suggestion. To solve the difficulties of water-flooding evaluation of carbonate reservoir, a new method is proposed based on inter-well connectivity and unascertained math. Firstly, an independent evaluation index system is established before calculating the comprehensive evaluation index weights by the analytic hierarchy process and similarity weight method. Then the Uncertainty measure model is established to evaluate water-flooding effect of well group. This method has been applied in the X oilfield, and good results are gained. The results show that different adjustments should be taken to improve water-flooding effects in different units.

According to the problems that the coalbed methane resource was rich in deep seam in China, but the economic and technology conditions were limited, it would be hard to mine with a conventional method. The CO2 capture, utilization and storage technology was provided (CO2-ECBM). The application of the technology would not only improve the methane recovery ratio from deep and unminable layer, but also put CO2 effectively in the deep layer for storage to reach a target of reducing emission. The study showed that a coal rank, coal seam pressure, coal seam permeability, injection time, injected gas types and others would affect to the recovery ratio of methane in a production mine. Therefore, before we use this technology, a rational evaluation should be conducted on the place location. So the capture and storage technology of CO2 has an important significance in protecting the natural environment.

Deposition of solid elemental sulfur may arouse severe damage to the formation and significantly affect the gas deliverability in sour gas reservoirs. As one main measure of stimulation, hydraulic fracturing always ceases to work due to the sulfur deposition in the fractures. To have a better understanding of the failure of fracture conductivity caused by sulfur deposition and learn the degree of fracture conductivity improved by acidification, an experimental was implemented and studied. In this paper, both the sulfur powder and an artificial fractured core were employed to simulate the process of sulfur deposition in the fractures. A further step was made to inject some hydrochloric acid into the blocked fracture caused by sulfur powder. The result showed that the fracture conductivity could be greatly reduced by the sulfur deposition. The fracture conductivity can be decreased by 17%~47% due to sulfur deposition. However, to some degree, acid-fracturing can improve the conductivity of fracture by eroding the surface of fracture. This means the failure of fracture blocked by sulfur deposition can be improved by acidification.

The Darcy linear equation has been widely used to describe the fluid flow in porous media. It is inaccurately used to describe the flow through preferential flowing paths which exert important influence on the performance of waterflooding reservoir. In this paper, the following two problems have been studied: (1) flow law in preferential flowing paths generated by water flooding; (2) sound nonlinear mathematical model considering special internal and external boundary conditions. The greater the permeability in porous medium becomes, the easier fluid can flow. Meanwhile the flow mechanism would change correspondingly as well. Exact solution of the nonlinear model is obtained analytically by integration. It is shown that in preferential flowing channels the flow velocity and the pressure gradient are a nonlinear relationship which is different from the traditional Darcy theory described as a straight line. Finally, the seepage characteristics of nonlinear flow and its influence are determined by analyzing the pressure gradient curve and velocity distribution between the observation point and the target well. Keywords: Preferential flowing paths; Non-linear model; Forchheimer equation; Integration method; Pressure gradient.