气烟囱效应——礁滩相岩性气藏的典型地震响应特征

品质良好的地震剖面上出现的地震模糊带称为气烟囱，发现和识别气烟囱是寻找大型气藏的有效方法。四川盆地东北部长兴组气藏是礁滩相岩性气藏，礁、滩作为一个独立的岩性体，与周围的地层、岩性结构差异较大，由此在构造应力场中形成力学尖点，从而产生气烟囱效应。已知的黄龙场、普光等气田，其气烟囱普遍存在。点礁通常形成下方的气烟囱，台缘礁通常在上方形成气烟囱；礁滩相在构造运动中控制了断层的发育过程，凸起的礁滩相上方可能发育对冲断层；斜坡较陡的台缘礁可能发育叠置的逆冲断层；礁、滩两侧边缘的断层一般都比较发育。断层发育加强了气烟囱效应。模拟试验验证了地震剖面解释结果。根据气烟囱地震相特征，预测黑池梁存在一个大型气藏。

GAS CHIMNEY EFFECT: TYPICAL SEISMIC EXPRESSION OF LITHOLOGIC SHOAL AND REEF GAS RESERVOIRS

An ambiguous zone on seismic profile of high quality is called gas chimney, the identification of which is an effective approach to discover large gas reservoirs. The gas reservoirs in the Changxing Formation in Northeast Sichuan Basin belong to lithologic shoal and reef gas reservoirs. As an isolated lithosome, reef and shoal facies are quite different from the surrounding rocks in respect of lithologic structures and form a mechanical spike in tectonic stress field, resulting in gas chimney effect. Gas chimney effects are common in the known Huanglongchang and Puguang gas fields. A gas chimney often occurs at the bottom of a patch reef, while on the top of a platform margin reef. Development of faults is controlled by reef and shoal facies in the process of tectonic movement, with ramps possibly occurring on the top of the upward-protruding reef, and superimposed thrusts possibly occurring on platform margin reefs with relatively steep slope. Faults are generally well developed on both sides of reef and shoal. The development of faults can enhance gas chimney effects. Simulated test verifies the interpretation on seismic profiles. Based on the characteristics of seismic facies of gas chimney, a large gas reservoir is predicted in Heichiliang area.