Experimental Study Of Seepage Law Of Fractured Carbonate Gas Storage Injection And Production

Fractured carbonate reservoir always has dual structure characteristics and the fluid seepage law is complex. Therefore, building underground gas storage (UGS) based on the fractured carbonate reservoir is difficult. For now, physical simulation of fractured carbonate gas storage mainly includes two parts:microscopic visualization and core. The article takes the S UGS in north China as the research object, having carried out research of reservoir microscopic characteristics, gas water seepage mechanism and injection-production running simulation of UGS, having revealed the high-speed seepage mechanism and main control factors affecting the operation efficiency of UGS, optimized capacity parameters of UGS. The main research results are summarized as follows:1. Based on the comparative analysis of capillary pressure curve and T2 spectrum in nuclear magnetic resonance, the characteristics of the pore throat structure in the carbonate reservoir is studied; by researching the gas-water two-phase relative permeability curve with non-steady state method, gas-water two-phase percolation law in the micro-crack carbonate reservoir is analyzed. The research shows that the S carbonate condensate gas reservoir has the characteristics of developed micro-fracture, narrow pore throat and concentrated distribution, the gas seepage characteristics are various in different layers.2. The seepage law of UGS is very complex because of its complex pore-throat structure, strong heterogeneity and different degree of water invasion. Since it is difficult to obtain the representative core of microfissure-pore carbonate reservoirs, microfissures have been produced through fracturing on cores that without cracks and then began water-gas mutual flooding experiments. The research shows that the relative permeability curve of fractured model is similar to "X" and remained largely unchanged after several gas water mutual flooding, two phase region of core model curve become narrow after several gas water mutual flooding; the contribution rate of fracture in the reservoir storage space is high, reservoir with fractures has high utilization effect of the reservoir storage space and utilization effect of reservoir without fractures become lower and tends to be stable.3. According to the vertical distribution of gas-water two phase before a gas reservoir converted into gas storage, UGS can be simplified as a model of two parts, which are pure gas zone and transition zone. Experiment simulation of sensitivity analysis about rate and water intrusion and evaluation of a multi-cycle injection and production have been carried out to evaluate the pore space utilization analysis of gas storage during the operation of production. The research have shown that:multi-cycle injection and production rate and water intrusion are the main factors of the utilization of the pore space, injection speed is the most significant; the pure gas zone has a decrease in the pore space utilization and not been fully used during the high speed injection and production process, the effect of injection and production rate on the micro-fracture model is greater than the fracture model; due to the Jiamin effect and gas flowing around in transition zone, there are a certain dead space and lots of gas have been lost, pore space utilization in transition has decreased and the effect of water intrusion on micro-fracture model is more obvious.