柴达木盆地东部石炭系致密灰岩孔渗特征

碳酸盐岩储层孔隙系统复杂。对空隙结构特征、渗流机理的研究直接影响到油气资源的勘探和开采。本研究选取了柴达木盆地东部地区ZK5-2钻井中石炭系的5块致密灰岩样品，通过XRD、XRF技术对灰岩的矿物成分、化学成分进行定量测试；利用氦气双室法与孔径分布实验（包括压汞法、氮气吸附法、二氧化碳吸附法）确定灰岩的孔隙度与空隙的孔径分布;用CH4、N2、CO2、He四种气体进行渗流实验确定灰岩的表观渗透率。研究结果表明:致密灰岩的表观渗透率与其孔隙度没有明显的关系。表观渗透率由达西流、滑脱流与扩散流三部分组成，表观渗透率大小按CH4、N2、CO2、He的顺序依次增加，其中He所测得的表观渗透率明显高于其他三种气体。滑脱流对表观渗透率的贡献受到分子平均自由程与孔径的双重控制，当气体分子平均自由程与岩石内集中出现的孔径接近时，在这些相近孔径的孔隙中会出现明显滑脱现象，此时滑脱流将对表观渗透率产生较大的贡献。分子平均自由程较大的气体在致密灰岩中主要以扩散的形式运移。岩石孔径小于分子平均自由程的孔隙所占比例越大，扩散流对表观渗透率的贡献度越高。 

Porosity and permeability characteristics of compact Carboniferous limestone in the eastern Qaidam basin

The pore system of carbonate rock reservoirs is complex. The study of the pore structure characteristics and flow mechanism has a direct impact on the exploitation of oil and gas resources. This work analyzed five tightly consolidated Carboniferous limestone samples taken from the borehole ZK5-2 in the eastern Qaidam basin. The mineral and chemical compositions of these samples were analysed using X ray diffraction (XRD) and X ray fluorescence (XRF) techniques; and the porosity and pore structure characteristics were further studied respectively using helium double chamber method and aperture distribution tests (using the mercury intrusion, nitrogen adsorption and carbon dioxide adsorption methods). Four kinds of gases, i.e. methane, nitrogen, carbon dioxide and helium, were used in the seepage experiments to measure the apparent permeability of each sample. The results show that there is no direct connection between the apparent permeability and porosity of these limestone samples. The measured values of the apparent permeability, which are jointly governed by the Darcy, slip and diffusion flows, increase in the order of CH4, N2, CO2 and He. The apparent permeability values measured using He are significantly higher than other gases. The contribution of the slip flow to the apparent permeability is controlled by both the molecular mean free path and the pore size. When the molecular mean free paths are close to the pore size of the rock, there will be a significant slippage in these pores and the slip flow will make significant contribution to the apparent permeability. Gases with large molecular mean free path flow mainly by diffusion in dense rock. The contribution of diffusion flow to apparent permeability increases with the proportion of rock pores that are smaller than the molecular mean free path.