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Gas reservoirs can be divided into two types based on the migration and accumulation processes, and distribution characteristics associated with the reservoirs: continuous accumulation that is within or adjacent to the source rocks and discontinuous accumulation that is in the reservoir rocks. Correspondingly, reservoirs can also be classified as conventional reservoirs, unconventional reservoirs and reservoirs in a transitional state. In order to demonstrate differences and regularities in the distribution characteristics and formation mechanisms of the two accumulation types, the continuous and discontinuous hydrocarbon accumulations in the Hangjinqi area of the Ordos Basin, China, is systematically analyze. Continuous accumulation (coalbed methane, shale gas, basin-centered gas, water-soluble gas) and discontinuous accumulation reservoirs (various traps) are located in the southern and northern regions of the Hangjinqi area, respectively, and they may be changed with the source rock quality, migration force, reservoir capacity and trapping condition. Several factors, such as hydrocarbon generation ability, porosity, and cap rock-trap combinations, are recognized here as essential factors for the formation and current distribution of gas reservoirs in the study area. Understanding the distribution characteristics of continuous accumulation and discontinuous accumulation can predict the potential gas reservoirs types based on discovered gas reservoirs. It is recommended to explore anticline gas reservoirs in the north of Boerjianghaizi fault, and CBM, shale gas and basin-centered gas reservoirs in the south of Boerjianghaizi fault. Though shale gas exploration activity is still lacking in the study area, we believe that the maturity and the burial depth of the marine-continental organic-rich shale in the Permian Shanxi-Taiyuan Formations are suitable for shale gas generation and preservation, indicating further research on the upper Paleozoic shale source rocks is required.

As the centrifugal pump is running, the fluid usually flows into the impeller along pump shaft, and the fluid flows out radially by the force of the impeller. The force is mutual, so the impeller is also subjected to the reaction force of the fluid, but the distribution of this force on the blades is uneven. In addition, the front and rear shrouds of the impeller are asymmetric, which are the main causes of axial force. This paper adopts numerical calculation method studying the mechanism of axial force of impeller at all stages of multistage pump at various working conditions, and exploring the formation mechanism of shroud pressure differential force and blade twisting axial force and its variation laws of similarities and differences, analyzing the steady state and transient characteristics between axial force and hydraulic property of double-casing multistage pump. The results show that the rotational angular velocity of the fluid in the front and rear pump chamber at each stage impeller is distributed along the axial direction in three regions, the regions are pump body boundary layer, core region, and impeller boundary layer. The working surface and back surface of the blade twist have the high and low axial force area, and its distribution is staggered, at the same number of stages, the greater the flow rate, the smaller the blade twisting axial force. The shroud pressure differential force with the increase of impeller stages presents a linear increasing trend, conforms to the principle of linear superposition of cover pressure differential force. The total axial force pulsation of multi-stage pump is related to the number of secondary impeller blades, its primary frequency coincides with the secondary impeller blade frequency, increasing the flow rate can reduce the multi-stage pump axial force pulsation amplitude. The pulsation period of single-stage impeller head and efficiency are related to the number of impeller blades, the smaller the number of impeller stages, the stronger the pressure dynamic, and static interference effect of the impeller inlet and outlet. Rotation of the secondary impeller causes dynamic and static interference, which is the main reason for the pulsation of the axial force coefficient in double-casing multistage pumps, the pulsation intensity is related to the periodic generation and shedding of the blade vortex. The results of the study can be used as a reference for optimizing the axial force of double-casing multistage pumps.

The axial force balancing capacity of a balance drum is a key factor affecting the life of multi-stage centrifugal pumps. At present, the traditional calculation formula of the balance force of a balance drum is mainly obtained by modifying the relationship between the last-stage impeller head and the total head through empirical coefficient, and the calculation result is less sensitive to the change of the balance drum clearance. However, many studies have shown that the increase of clearance is the main factor affecting the balance force of a balance drum. In addition, the cost of measuring the balance force of a balance drum is relatively high. Therefore, it is particularly necessary to derive the mathematical expression and to propose a simple method for measuring the balance force of a balance drum. According to the resistance equation of clearance fluid and the N-S equation under cylindrical coordinate system, the variation laws of the pressure difference along axial and radial directions in the two sides of the balance drum clearance were derived. And the mathematical formula of the balance force of a balance drum, the balance drum clearance leakage and the balance tube flow was established. The new derived formula calculation results were compared with the traditional formula calculation results and the numerical calculation results. The results show that: at nominal flow rate, the mean value of the pressure difference of a balance drum increases in a parabolic shape along the radial direction. When the clearance increases from 0.1 to 0.35 mm, the relative error of the balance force between the traditional formula calculation and the numerical calculation is 71.1%, 58.5%, 19.6%, 8.1%, −18.6% and −32.31%, while that between the new formula calculation and the numerical calculation is 3.08%, 6.21%, 4.82%, 1.17%, 3.42% and 6.58%, indicating that the new derived formula can accurately calculate the balance force of a balance drum. In addition, according to the new derived formula, the balance force of a balance drum can be measured directly by the flow rate of the balance tube, which provides a theoretical support for dynamic monitoring of the balance force of a balance drum in engineering.

Balanced drum systems are widely used in high-pressure multi-stage pump axial force balancing mechanisms. When the pump working, the fluid (solid-fluid mixture) collides with each other or rubs against the pump case, and the balance drum is affected by this situation for a long time, so wear of the balance drum gap occurs from time to time. The first is to study how the axial force of the multistage pump changes at different balance drum gap sizes in this paper. Based on the energy equation and momentum equation, and on the basis of maintaining the original balance force unchanged, a new equation of resistance pressure difference relationship is established. The corresponding relationship between balance drum gap and balance pipe orifice plate is obtained by solving this equation. The result shows that the larger the balance drum gap, the greater the balance drum balance force decreases obviously, and the multistage pump residual axial force increases in multiples. The adjustment formula of balance force can be used to obtain the radial size of the balance pipe orifice plate under different balance drum gap, when the gap increases, to keep the balance force constant, the diameter of the orifice plate should be increased gradually. After adjusting the balance force, the fluid velocity uniformity and velocity average angle of balance pipe increases, the flow pattern in the pipe becomes uniform, the gap leakage increases and the pump efficiency decreases. The pump hydraulic properties and balancing the axial force have an opposing relationship, that is, by promoting the drum balance force, the pump hydraulic properties will be reduced. Due to processing balance drum is complex, frequent replacement is time-consuming and costly, so this article provides a handy approach for enhancing the balance force of balance drum, the results of the study can provide guarantees for the balance drum system optimization and long period stable operation of the multistage pump.