Abstract
Tight sandstone reservoirs have the characteristics of poor physical properties, fine pore throats, and strong microheterogeneity compared with conventional reservoirs, which results in complicated movable fluid occurrence laws and difficult mining. Taking the tight sandstone gas reservoir of He 8 formation in Sulige gas field as an example, based on physical property test analysis, constant velocity mercury injection, and nuclear magnetic resonance experiments, an optimized gray correlation calculation model is established by improved gray correlation theory, which quantitatively characterizes the influence of microscopic pore structure parameters of different types of tight sandstone gas reservoirs on the occurrence of movable fluids, and the main controlling microgeological factors for the occurrence of movable fluid in tight sandstone gas reservoirs with close/similar physical properties are selected. The results show that the occurrence of movable fluid in Type I reservoirs is mainly affected by the effective pore-throat radius ratio, the saturation of mercury in the total throat, and the effective pore radius, and the occurrence of movable fluid in Type II reservoirs is mainly affected by the effective throat radius per unit volume and total throat mercury saturation and mainstream throat radius. Moreover, the occurrence state of movable fluids in Type II reservoirs is controlled by the throat radius stronger than that of Type I reservoirs. It has important guiding significance for the efficient development of tight sandstone gas reservoirs.
Highlights
Tight sandstone reservoirs have the characteristics of poor physical properties, fine pore throats, and strong microheterogeneity compared with conventional reservoirs, which results in complicated movable fluid occurrence laws and difficult mining
The tight sandstone reservoirs have the characteristics of poor physical properties, small pore throats, and strong microheterogeneity [12,13,14,15] compared with conventional reservoirs, which leads to complex reservoirs of movable fluids and difficult mining
Studies have shown that the recoverability of oil and gas reservoirs is mainly affected by the pore structure and the occurrence characteristics of movable fluids; the microscopic pore structure characteristics have a significant impact on movable fluids [16,17,18,19]
Summary
(1) Before Testing, Wash the Sample With Oil. e sample was washed with methanol and dichloromethane mixture in the Soxhlet extracter. E experimental method is strictly in accordance with SY/T6490-2014 “Laboratory measurement specification for nuclear magnetic resonance parameters of rock samples” [21]. E experimental method was strictly carried out in accordance with GB/T29171-2012 “Rock capillary pressure measurement” [22]. E experimental method was strictly carried out in accordance with SY/T 5162-2014 “Analytical method of rock sample by scanning electron microscope” [23]. (1) For the parameters (excluding parameters other than the effective pore-throat radius ratio) which are positively correlated with reservoir microscopic pore-throat structure characteristics and movable fluid saturation, divide directly by their maximum value. In the traditional gray correlation analysis method, the resolution coefficient is not quantified but a fixed value 0.5, without considering the distortion of the correlation degree measurement caused by the abnormal value in the data. If 0 < 1/ε < 2 that is, the normal value, 2ρ > 1, let ρ ∈ (0.8, 1), and 1 is used in this paper
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