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

Abstract

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 0.1×10−3 μm2. 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. Key words: Songliao Basin, Xujiaweizi fault depression, tight gas, sandy conglomerate reservoir, reservoir type