Analysis of Microscopic Main Controlling Factors for Occurrence of Movable Fluid in Tight Sandstone Gas Reservoirs Based on Improved Grey Correlation Theory

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.

Study on microstructure influence mechanism to mechanical behavior of OGFC asphalt mixture

Microstructure characteristics of OGFC (open graded friction course) asphalt mixture are closely related to the mechanical behavior. To study the microstructure influence mechanism to mechanical behavior of OGFC asphalt mixture, the digital image processing technology is used to process the specimen’s fault images and obtain the microstructure parameters of the OGFC asphalt mixture with different gradation. At the same time, the microstructure influence on mechanical behavior of OGFC asphalt mixture is explored by using the Grey correlation theory based on the experimental results of mechanical performance and the microstructure parameters. The influence of four key sieve passing percentage (1.18, 2.36, 4.75, and 9.5 mm) on the microstructure was discussed by using the Grey correlation theory, and the influence mechanism to mechanical behavior of OGFC asphalt mixture was further revealed. The results show that with the increase of air void content, the total void area, the equivalent pore diameter, and the number of big voids (here, “big” means voids with an area greater than 10 mm2) increase, the length of void and corresponding void area increase synchronously, the drainage performance is enhanced, and the mechanical performance is decreased. With the increase of nominal maximum particle size, the average area of single void, the percentage of number of big voids, and the equivalent diameter increase, and the drainage performance, anti-skidding performance, and mechanical performance of pavement are enhanced. It is considered that the key sieve passing percentage affects the mechanical behavior by influencing the microstructure of asphalt mixtures. The influence degree of microstructure parameters on mechanical behavior and the influence degree of the key sieve passing percentage on microstructure parameters were obtained. The research results have a certain reference value for the optimization of mechanical behavior of OGFC asphalt mixture.

Mean-Square Non-Local Stability of Ship in Storm Conditions of Operation

The purpose of the paper is to create a method for studying nonlocal stability in the mean and in the mean square of the ship, positioned on the beam of an intensive wind–waves mode, which is based on the use of the correlation theory of random functions close to continuous Markov processes. With the help of this method and the integral formula of event probability, a method for determining the reliability indicator of the ship in respect of the existing wind–waves excitations of the operating area is formed. An example of investigating the nonlinear motion of the ship, determining its local and nonlocal stability in the first approximation of the theory of considered random functions, is given. Such approximation uses correlation theory with models of acting excitations represented by the generalised derivatives of the Wiener process. Moreover, special attention is paid to reflecting the connection of the proposed methods for investigating the ship stability under constantly acting random excitations with the traditional methods of studying ship stability at small and large inclinations. The established connection defines the proposed methods as a development of the traditional methods of ship stability deterministic theory during the transition to its formation in the class of random functions, with the addition to these methods of the missing link of determining the level of reliability of ships towards the acting wind–waves excitations of the operation area.