元坝地区须三段天然气富集控制因素

 结合层序地层学理论、岩心观察、岩心分析实验结果及钻井测试资料等,分析了元坝地区须三段的层序地层特征、储层岩性特征、储层微观特征及天然气富集的控制因素。目的层储层岩性复杂,以西部发育钙屑砂岩,东部发育岩屑石英砂岩为主要特征。岩心分析实验表明:目的层储层物性差,属于特低孔-低渗次生致密砂岩储层;须三段上部3 个砂组天然气相对富集,在富气砂组内有利岩性带、砂体厚度是天然气聚集的基础条件,储层内部发育裂缝和溶蚀孔组合是天然气富集的关键因素。

Formation,sedimentary characteristics and natural gas enrichment control factors in the 3rd member of Xujiahe formation in Yuanba area

This paper analyzes the sequence stratigraphy feature, lithology facies distribution, reservoir features and the distribution and control factors of the 3rd member of Xujiahe formation in Yuanba area, on the basis of the theory of high resolution sequence stratigraphy and core observation results. The target zone has been divided into one long sequence and five short sequences, corresponding to five sand groups. The experimental analysis of cores reveals that the reservoir belongs to low porosity and low permeability tight sandstone reservoir due to its poor physical properties, and this type of tight sandstone reservoir belongs to secondary tight reservoir because the efficient pores were formed during diagenesis procedure. Well test data confirm that the gas wells' productivities are very different and the upper three sand groups of the 3rd member of Xujiahe formation are relatively rich areas for natural gas. However, the distribution of gas in these three sand groups is still not uniform, which indicates that even in the same sand group, the gas performance varies dramatically from well to well. In order to find the reasonable explanation for this phenomenon, we conducted careful calibration between wells and logging curves to identify the reservoir features such as fissures and dissolution pores as well as analysis of influences of microfacies, lithologic belt, and sand body thickness. We draw a conclusion that favorable lithologic belt and sand body thickness are basic conditions for natural gas accumulation, and fissures combined with dissolution pores are key factors.