四川盆地下寒武统龙王庙组颗粒滩特征及分布规律

Characteristics and Distribution Rule of Lower Cambrian Longwangmiao Grain Beach in Sichuan Basin

四川盆地龙王庙组颗粒滩相沉积具有良好的天然气勘探潜力。利用盆地露头、岩心和薄片资料,结合地震解释,明确了颗粒滩相由砂屑白云岩、鲕粒白云岩、晶粒白云岩和斑状白云岩组成。颗粒滩相发育滩主体、滩翼和滩坪等微相,储层主要分布于滩主体微相。颗粒滩包含多期向上变浅的高频旋回,每期滩体厚度达2~20 m,宽0.9~1.5 km,多期滩体的叠置可形成累厚18~55 m、宽7~8 km、延伸长达百余千米的滩带;滩带主要发育在台隆区相对高部位,总体上环绕澙湖展布,受古构造和海平面变化的双重控制。这一认识有利于盆地龙王庙组滩体的预测,并有助于提高钻探成功率。

The Lower Cambrian Longwangmiao grain beach sediments are of good potential of gas exploration in Sichuan basin. Based on the data from outcrops, cores and thin sections, and combined with the seismic interpretation, it is shown that the grain beach facies is composed of doloarenite, oolitic dolostone, crystalline grain dolostone and por- phyritic dolostone in lithology. The grain beach facies includes three microfacies： the beach body, bank wings and beach flats microfacies. The reservoir mainly consists of the bank body microfacies. Grain beach contains multiple frequencies of shallowing-upward cycles. Each frequency of beach body is 2-20m in thickness and 0.9~l.Skm in width. Multiphase beach bodies are superimpo^d to form a 18~55m thick, 7-Skm wide and hundreds km long beach belt. The beach belt mainly develops in upheaval areas of the platform and distributes around the lagoon, which is controlled by ancient structures and sea-level changes. This viewpoint is useful to predicting the location of the Longwangmiao grain beach and helpful to improving the success rate of drills.