考虑压裂影响的低渗气藏高压平面供气机理探讨

Discussion on the mechanism of high pressure plane gas supply in low permeability fractured gas reservoir

采用高低渗区“串联”方法开展了考虑压裂影响的高压(最高为45MPa)平面非均质供气机理渗流实验,研究了配产、物性、压裂改造等对供气能力的影响,通过建立单井平面非均质渗流数值模型对实验结果进行了论证。结果表明,配产越高,稳产期越短,总采收率越低;生产初期高渗区贡献率从60%左右逐渐降低,高低渗区最终贡献率受各区储量控制;渗透率级差越小,基质渗透率越高,相同配产下采收率越高,低渗区动用程度越高;压裂后近井高渗区压差变小,更有利于提高低渗区压差,高低渗分区采收率和总采收率均提高,储层平均渗透率越低,压裂后采收率提高幅度越大;当渗透率级差大于50倍时,近井高渗“甜点”并不能有效激活远井低渗储层,储层总体采出程度低。本文研究成果对高效开发低渗非均质气藏有重要的生产指导意义。

The “series” method in the high-low permeability zone was used to conduct seepage experiment of heterogeneous gas supply mechanism at high pressure plane (up to 45 MPa) while considering the effect of fracturing. It studied effects of gas distribution,physical properties and fracturing transformation on gas supply capacity. The experimental results were demonstrated by establishing a single well plane heterogeneous percolation numerical model. The results showed that the higher yield may cause shorter stable yield period and lower total recovery efficiency. In the initial stage of production,the contribution rate of high permeability zone decreased gradually from about 60 %,and the final contribution rate of high and low permeability zone was controlled by the reserves of each zone. The smaller permeability difference may indicate the higher matrix permeability,and the higher recovery efficiency may be obtained under the same production,and producing degree may be higher in the low permeability zone. After fracturing,the pressure difference decreases in the high-permeability zone near the borehole,which is more conducive to increasing the pressure difference in the low-permeability zone. The recovery efficiency and the total recovery efficiency in both high and low permeability zones are improved. The lower average permeability of the reservoir may cause greater recovery enhancement after fracturing. When the permeability difference is more than 50 times,the near-borehole high-permeability “sweet spot” cannot effectively activate the far-well low- permeability reservoir,and the overall recovery of the reservoir is low. The research results of this paper have important production guiding significance for the efficient development of low permeability heterogeneous gas reservoirs.