基于岩石物理参数转换模型的页岩气含气量评价新方法研究

页岩气在储层中主要以游离气和吸附气的形式存在,其含气量主要通过现场解吸和测井方法计算.由于页岩储层十分致密,并且常伴有微裂缝发育,这就造成了页岩储层的储集空间从纳米级孔隙到微米-毫米级的微裂缝并存的特殊情况.针对微孔和介孔段(50nm以内)的等温吸附方法,以及针对宏孔(50nm以上)的高压压汞方法在表征页岩孔隙结构上都存在着局限性.而核磁(NMR)T2分布本身虽然能够表征孔径分布,但是需要精确刻度横向弛豫时间与孔径的关系.本文在现有方法的基础上,结合上述方法的优势,采用拼接的方式表征页岩整体孔径分布,并将核磁T2分布刻度为孔径分布.基于横向弛豫时间和孔径的关系,结合T2-I转换模型,采用动态参数计算页岩储层含水饱和度和含气量,这为页岩储层含气量评价提供了新的可靠的方法.

Research on a new method to evaluate shale gas content based on the transformation model of petrophysical parameters

Shale gas is mainly in the form of free gas and adsorbed gas in the reservoir, the gas content of both is mainly evaluated by field desorption and logging methods. Due to shale reservoirs are very tight and often accompany micro-fractures, which leads to the special case that the reservoir space for shale reservoirs contain micro-cracks at the micrometer-millimeter scale and nano-scale pores. Both the isothermal adsorption methods for micropores and mesopores (within 50 nm) and the high-pressure mercury injection for macropores (above 50 nm) have limitations in characterizing shale pore structures. After scaled the relationship between transverse relaxation time and pore diameter accurately, the Nuclear Magnetic Resonance (NMR) T₂ distribution can characterize the pore size distribution. In this paper, we combine the advantages of the above method based on the existing methods. The overall pore size distribution of shale is characterized by splicing method, and the NMR T₂ distribution is scaled to the pore size distribution. Based on the relationship between transverse relaxation time and pore diameter, the T₂-I transformation model which can obtain the dynamic parameters are used to calculate the water saturation and gas content of shale reservoirs. It provides a new and reliable method for evaluating the gas content of shale reservoirs.