Abstract
Both the characteristics of pore structure and movable fluid are significant properties in controlling the flow regularity in pores in tight sandstones. However, the governing factors that affect the fluid flow features will still be a myth. In our research, the western area of the Sulige gas field was chosen as the research region, and various kinds of experiments were conducted. Three reservoir groups, including intergranular-dissolved pore type, dissolved-intercrystalline pore type, and pore plus microcracks type were identified on the basis of pore development features. The results suggest that the intergranular-dissolved pore type has a more prominent influence on the high movable fluid saturation and larger pores. Both large throat sizes and homogeneous pore-throat degree demonstrate high movable fluid saturation. The increment of the thickness of water-film resulted from hydrophilic enhancement, indicating that an increased hydrophilic will decrease the movable fluid saturation and block the throats. The reservoirs of different pore combination types are closely related to the gas content of the reservoir.
Highlights
As the representative of the unconventional gas reservoir, tight sandstone reservoir is being paid attention to by researchers with the progress of exploration and exploitation and the depletion of conventional reservoir [1,2,3,4,5]
The core samples from the Lower Shihezi group and Shanxi group of Sulige gas field are tested using casting sections and scanning electron microscope (SEM) to observe the characteristics of the pore-throat structure, clay minerals content and porethroat structures parameters are determined on the basis of X-ray diffraction (XRD) and mercury injection data, a comprehensive study is carried out with nuclear magnetic resonance (NMR) technique to study the characteristics of movable fluid saturation, and an experiment is conducted with gas-water relatively permeability technique to elucidate the wettability
The NMR test and other experiments results show that the tight sandstone reservoirs of the Sulige gas field can be divided into three types based on pore types: reservoirs with the intergranular-dissolved pore type (RIDP), reservoirs with the dissolved-intercrystalline pore type (RDIP), and reservoirs with pore plus microcracks (RPPM)
Summary
As the representative of the unconventional gas reservoir, tight sandstone reservoir is being paid attention to by researchers with the progress of exploration and exploitation and the depletion of conventional reservoir [1,2,3,4,5]. In addition to physical property analysis, rock core observation and so forth, casting sections (TS), scanning electron microscope (SEM), drainage and imbibition tests, small-angle and ultrasmall-angle neutron scattering (SANS and USANS), and other techniques were applied for pore-throat structure analysis purposes in tight sandstone reservoirs for several decades [15,16,17,18,19]. The core samples from the Lower Shihezi group and Shanxi group of Sulige gas field are tested using casting sections and SEM to observe the characteristics of the pore-throat structure, clay minerals content and porethroat structures parameters are determined on the basis of X-ray diffraction (XRD) and mercury injection data, a comprehensive study is carried out with NMR technique to study the characteristics of movable fluid saturation, and an experiment is conducted with gas-water relatively permeability technique to elucidate the wettability. The effect of porethroat characteristics on the movable fluid percentage is discussed in the end
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