致密砂砾岩气形成主控因素与富集规律——以松辽盆地徐家围子断陷下白垩统营城组为例

Formation and accumulation of tight sandy conglomerate gas: A case from the Lower Cretaceous Yingcheng Formation of Xujiaweizi fault depression, Songliao Basin

以油气钻探实践为基础,应用地质、地球物理和地球化学相结合的方法,以松辽盆地徐家围子断陷深层下白垩统营城组致密砂砾岩气为例,探讨致密砂砾岩气形成主控因素及其富集规律。营城组致密砂砾岩气主要受储集层物性控制,储集层具有先致密后成藏的特点;气藏具明显的干气特征,各类储集层具有不同的产能,储气层孔隙度下限为2.5%,渗透率下限为0.1×10-3μm2;构造背景对致密气的分布影响不大,气层"甜点"分布宏观上受气源岩发育状况、储集层沉积相带展布以及断裂带发育部位等因素综合控制,三角洲前缘亚相储集层物性相对较好,其中营城组砂砾岩储集层和下伏气源岩有走滑断裂沟通的条带状区域是致密砂砾岩气勘探的有利地区。

Based on oil and gas drilling data, the main control factors and accumulation rules of tight sandy conglomerate gas in the Lower Cretaceous Yingcheng Formation of the Xujiaweizi fault depression in the Songliao Basin are discussed by combining geology, geophysics and geochemistry. Tight sandy conglomerate gas of the Yingcheng Formation is controlled by the reservoir properties and hydrocarbon accumulation happened after the formation was compacted tight. The gas reservoir mainly produces dry gas, and various reservoirs, different in productivity, have a porosity lower limit of 2.5% and a permeability lower limit of 0.1×10^3μm2. Structural setting has little effect on tight gas distribution. Gas-bearing ＂sweet spots＂ are controlled macroscopically by gas source rock development conditions, reservoir sedimentary facies belts and sites rich in faults. Reservoirs in delta-front subfacies are fairly good in physical properties. The strip zone where strike-slip faults connect sandy conglomerate reservoirs and underlying gas source rocks is the favorable area for tight sandy conglomerate gas exploration.