乐山—龙女寺古隆起龙王庙组储层分布规律及勘探前景

2012年在四川盆地川中地区乐山—龙女寺古隆起的磨溪地区发现了下寒武统龙王庙组气藏,地质研究成果表明,龙王庙组储层主要为颗粒滩相的孔隙型储层,局部叠加了加里东期岩溶作用形成的孔洞型储层,储层分布对气藏具有重要的控制作用。为此,该区储层预测形成了"占滩相、叠岩溶、找亮点、套圈闭"的综合预测思路。首先,根据沉积相确定其有利相带边界和岩溶作用影响范围,在精细对比储层顶、底层位的基础上,根据龙王庙组储层"亮点"地震响应特征来预测储层的有利发育区域;最后,结合储层与圈闭的有效匹配关系实现了有利勘探区带的优选。由于龙王庙组岩性和储层的横向变化,导致其顶界在地震剖面上没有统一的界面特征,对比追踪较为困难,在实际的解释过程中,便采用先寻找下伏参考层,再对比龙王庙组底界,进而对比其顶界的方法进行解释。预测成果表明,龙王庙组储层在古隆起周围区域大范围呈带状分布,勘探区主要有3大领域:①龙王庙组尖灭线附近的岩性—地层圈闭;②单独滩体形成的岩性圈闭;③古隆起北翼的构造、岩性圈闭。

Distribution rule and exploration prospect of the Longwangmiao Fm reservoirs in the Leshan Longnüsi Paleouplift,Sichuan Basin

The Longwangmiao Fm gas reservoir was found in 2012 in the Moxi area in the Leshan Longnüsi Paleouplift, central Sichuan Basin. The previous geological studies showed that the Lower Cambrian Longwangmiao Fm reservoir is mainly of porous pay zones of grain shoal facies, locally superimposed by the vuggy pay zones formed by Caledonian karstification, and the distribution of pay zones has a critical control effect on the reservoir there. To this end, the pay zones in this area were forecasted according to the following features: facies, superimposed karst, highlights, and traps. First, the sedimentary facies served as the basis for defining the favorable facies boundary and karstification influence range; on the basis of the precise comparison between the top and bottom horizons of the reservoir, the favorable development area of the reservoir was then predicted according to the "highlighted" seismic response characteristics of the Longwangmiao Fm reservoir; finally, favorable exploration areas were preferably selected according to the effective reservoir trap combination. The horizontal change in Longwangmiao Fm reservoir and lithological features resulted in the absence of uniform interface features of the top boundary on the seismic profiles and the difficulty in comparison and tracing. In the actual interpretation process, it was recommended to find out the underlying reference horizon first, then to compare the bottom boundary of Longwangmiao Fm, and finally to interpret it by referring to the method applied to the top boundary. The prediction results indicated that the reservoirs are distributed in a zonal manner in a wide range around the Paleouplift; and the exploration prospects mainly involve three fields: lithologic stratigraphic traps near the pinch out boundary of Longwangmiao Fm; lithologic traps formed by separate facies; and tectonic and lithologic traps at the north flange of the Paleouplift.