裂缝—孔洞型凝析气藏不同开发方式的长岩心实验

A long-core experimental study of different development schemes on fractured cavernous gas condensate reservoirs

柴达木盆地塔中Ⅰ号气田裂缝孔洞型碳酸盐岩储层表现出“双孔双渗”特征，凝析油反蒸发机理不同于砂岩凝析气藏，国内外对如何提高裂缝孔洞型凝析气藏采收率的研究还比较少。为此，首先取得无裂缝的碳酸盐岩岩心进行孔隙度和渗透率测试（平均孔隙度6．5％，平均渗透率1mD），然后进行造缝（裂缝渗透率5～10mD），并将岩心组合成长岩心（105．8cm），最后采用塔中Ⅰ号气田凝析气（凝析油含量533g／m3）进行了注气、吞吐和脉冲注气实验，优选出提高凝析油采收率的开发方式。实验结果表明：露点压力以上注气凝析油采收率最高，其次是最大凝析油饱和度下注气或脉冲注气；与低渗透砂岩凝析气藏不一样，注气吞吐提高凝析油采收率效果最差。该实验对裂缝孔洞型储层高含凝析油型的凝析气藏的合理开发提供了技术支撑。

The fractured cavernous carbonate reservoirs in the Tazhong-I Gas Field,Tarim Basin,present the characteristics of dual-porosity and dual-permeability,and the retrograde vaporization mechanism in this kind of reservoir is different from that in sand gas condensate reservoirs,and few studies have been found at home and abroad on how to improve the recovery of fractured cavernous gas condensate reservoirs.In this paper the porosity and permeability of the non-fractured carbonate cores were first measured(the average porosity was 6.5% and the average permeability was 1 mD),then fractures were generated in the cores(the fracture permeability was 5-10 mD) to be combined into a long core with the length of 105.8 cm.After that,the Tazhong-I condensate gas(the condensate oil content is 533 g/m3) was used to perform gas injection,huff and puff and pulsed gas injection to select the best development mode of improving the condensate oil recovery.Experimental results indicate that the best way is gas injection above the dew point,the second is gas injection under the largest condensate oil saturation or pulsed gas injection.Unlike low permeability sand gas condensate reservoirs,huff and puff performs the worst in improving the condensate recovery.The results of this experimental study provide great guidance for the development of fractured cavernous carbonate gas condensate reservoirs with rich condensate oil.