试论致密砂岩气藏中的夹层控气作用——以川西大邑须家河组气藏为例

Application of Interlayer Controlling Gas Accumulation in Tight Sandstone Gas Reservoir:A Case of Xujiahe Formation Gas Reservoir in Dayi,West Sichuan Basin

夹层主要是指储层内部不渗透或低渗透,能够对油气的流动、运移或聚集产生控制作用的条带。在天然气运移过程中,若夹层的毛细管突破压力小于下部储层的毛细管饱和压力,天然气会在下部储层还未达到含气饱和的时候通过夹层向上部储层运移,造成下部储层含有可动水。夹层与储层相互叠置会形成多个不饱和含气储层。此类气藏要形成纯气藏的重要因素是圈闭足够高大,进而增加气对原始地层水的排驱压力。大邑地区须家河组储层致密,非均质性强,须二段及须三段均含有不等厚致密夹层,气藏高度大于圈闭高度,夹层控气作用造成大邑气藏无边底水、气水过渡带长、高含水饱和度、普遍气水同出、含气丰度偏低、地层压力接近常压等特点,在此基础上对大邑地区须家河组气、水分布规律进行初步分析。

Interlayer is the bands of impermeable or low permeability within the reservoir and effects of oil-gas flow,migration and accumulation.During gas migration the movable water in the lower reservoir occurs when the gas below the gas saturation in the lower reservoir migrates up to the upper reservoir through the interlayer,if the capillary breakthrough pressure of interlayer is less than the capillary saturation pressure of low permeability.There are a lot of unsaturated gas reservoirs when interlayer and reservoir overlay each other.The formation of the pure gas pool needs the larger closure height for increasing the displacement pressure from gas to original formation water.The gas pool of Xujiahe Formation in the Dayi is characterized tight reservoir and strong heterogeneity,unequal thickness tight interlayer and height of gas bigger than closure′s of T3x2 and T3x3,the interlayer controlling gas accumulation cause the gas reservoir with no edge and bottom water,wide gas-water transition zone,high water saturation,gas-water coproduction,low gas bearing abundance,formation pressure approaching to normal pressure,since.Based on new understanding above,we discuss the gas and water distribution in the Xujiahe Formation of Dayi.