咸化湖盆高效基岩气藏储层中基质孔隙的发现及意义

近年来,柴达木盆地东坪地区天然气勘探获得了重大突破,已累计产气超过2×108 m^3。通过钻井岩芯观察、偏光显微镜鉴定、物性分析以及场发射扫描电镜研究发现,东坪地区基岩由变质岩和花岗岩组成,平均孔隙度为4.72%,平均渗透率为1.71×10^-3 μm²。除裂缝和少量溶蚀孔外,岩石中基质微孔广泛发育,主要包括花岗岩中发育于铁镁质矿物的微孔以及片麻岩中的云母片晶间孔两类,其孔径极小且连通性差,多为数百纳米至数微米,为东坪地区基岩重要的天然气储集空间类型。大量石膏充填于上部基岩的孔缝中,为上覆地层路乐河组和干柴沟组沉积时咸水流体下渗沉淀、胶结所致,盐类矿物的封堵作用为大气田的形成起到了重要作用?这种发育于基岩中的“二元结构”的首次发现对指导咸化湖盆基岩油气勘探具有重要意义。

Discovery of Matrix Pore of High Efficiency Bedrock Gas Reservoir in Saline Basin and Its Significance

There is a major breakthrough on gas exploration in Dongping area of Qaidam Basin in recently years. The cumulative gas production is more than 2×108 m3. According to the drilling core observation, polarizing microscope identification, physical property analysis and field emission scanning electron microscopy, the bedrock in Dongping area is made up of metamorphic rock and granite with the average porosity of 4.72% and the average permeability of 1.71×10-3 μm2. In addition to crack and a small amount of dissolved pore, matrix micropores widely develop in rocks, including micropore developed in femic mineral from granite and mica sheet intercrystalline pore in gneiss. These pores have tiny radius and poor connectivity, and the sizes are from hundreds of nanometers to several micrometers. They are the important types of gas reservoir space of bedrock in Dongping area. A lot of gypsum fill in the aperture of the upper bedrock, because there are saline fluid infiltration, precipitation and cementation when the overlying Lulehe Formation and Ganchaigou Formation deposit. Plugging effect of saline mineral has an important role on the formation of a great gas field. The first discovery of “two-unit structure” developed in bedrock has an important significance on guiding the petroluem exploration in bedrock of saline basin.