Sensitivity Analysis of Hydraulic Parameters on Contaminant Intrusion in Transient Conditions

Hydrodynamic Features of Two-Phase Oil–Gas Flow in Pipelines

The results of the experiments on the transport process of fluid flow through a pipeline under temperature gradient conditions between the internal and external environments, and on continuous gas generation at the contact boundary of the transported media, are presented in this paper. The test results showed that under non-isothermal flow conditions, a slippage effect will impact flow velocity and pressure, as well as the temperature distributions in variable cross-section pipes. Laboratory experiments were conducted in order to study the effects of the gas nucleus at the pipe walls on the hydrodynamic characteristics of the fluid flow. It is shown that the throughput capacity of the pipe is affected by the temperature difference between the oil and the pipe walls. The test results also demonstrated that at certain temperature gradients on the border layer, the pipe’s capacity reaches its maximum value. Quantitatively, the hydroconductivity of Q/ΔP increased from about 1.45 × 10−5 m3/(s·MPa) under relatively isothermal conditions to a maximum value of approximately 2.04 × 10−5 m3/(s·MPa) with a temperature difference in the oil–pipe-wall zone of about 3–5 K, which corresponds to an increase of about 41%. With a further increase in the temperature difference, the hydroconductivity decreased to about 1.64 × 10−5 m3/(s·MPa) at 10 K and then stabilized in the range of (1.60–1.64) × 10−5 m3/(s·MPa). This non-monotonic behavior is explained by the temperature-induced release of gas and the formation of a gas-saturated wall zone, which initially reduces the effective resistance of the wall and creates an apparent sliding effect. At high temperature differences, gas accumulation, thermal insulation of the wall area and two-phase flow disturbances limit this effect, which leads to the decrease and subsequent stabilization of the pipe capacity.

On solving the problems of maximizing the development of oil reserves in the drainage zone of wells and reservoirs

A new experimental finding regarding the violation of Darcy's law during the flow of liquids in a microcrack with an opening less than its critical value h<hcr, i.e., the manifestation of the "microcrack-fluid" effect is observed, which is the reason for the violation of Darcy's law. It has been revealed that when liquid moves in fractured and low-permeability media with an opening of h<hcr, an additional force arises due to the "microcrack-fluid" effect, which prevents the movement of liquid and this is the reason for the low oil recovery coefficient. The effect in the “microcrack-fluid” system is the reason for changes in the mechanical properties of fluids in microcracks and equivalent ultra-low-permeable porous media. It was revealed that when a one-parameter viscous fluid flows through a crack with an opening h<hcr, it becomes a two-parameter fluid, i.e. it behaves as an anomalous fluid. When the fluid flows through a crack with an opening h≥hcr, it restores one-parameter properties. The anomalous behavior is accompanied by an increase in the rheological constants of the model. Based on the developed methodological guidelines, rheological parameters of filtration systems and crack opening under reservoir conditions are determined. According to the research data, the proposed technique makes it possible to estimate the effective crack opening and the corresponding permeability of the porous medium of the bottomhole zone with sufficient accuracy for practice under steady-state well conditions without interrupting well operation. Therefore, to attract residual oil to the well faces, it is necessary to develop measures that allow deposits to be transferred from the h<hcr state to the h≥hcr state and ensure well flow. Keywords: microcrack opening; Newtonian fluid; structural viscosity; "microcrack- fluid" effect.

Volume of fluid-based CFD study of triggering and eruption in urban storm sewers

Geyser eruption in urban drainage is a high-velocity discharge of an air–water mixture driven by intense air–water interactions. It is sudden, destructive and strongly non-linear, and is often associated with air entrapment, surcharge flows during intense rainfall and transient hydraulic processes, posing risks to drainage assets and surface infrastructure. A representative horizontal main pipe–vertical riser configuration is modelled using a volume of fluid (VOF) two-phase framework and a systematic numerical study is conducted of the inlet pressure head, dimensionless initial entrapped air index, Ia0, and the initial water-column height. Results identify a distinct eruption threshold: under the fixed geometry and boundary conditions considered in this study and within the tested parameter range, geyser eruption is triggered when Hin/H0 ≥ 1.33 andIa0 ≥ 3.20. As the free surface enters the upper riser, pronounced pressure spikes at PT4 and PT5 can serve as precursors. For a given inlet pressure head and the initial entrapped air condition, increasing the initial water-column height leads to higher eruption velocities, highlighting its control over eruption intensity.

Study on the Factors Affecting the Stability of Drainage Foam in Coastal Power Plants and the Aeration Pattern of the Overflow Weir

Coastal power plants draw seawater from the open ocean through their cooling-water circulation systems. The cooling water falls over an overflow weir inside the siphon well, entraining large quantities of air, and generates a foam pollution plume upon discharge to the sea. By combining physical model experiments with numerical simulation, this study investigates the key factors governing foam stability and the aeration behavior of the water downstream of the siphon-well overflow weir. The principal conclusions are as follows: among the three single-factor variables tested in controlled laboratory conditions—temperature, salinity, and shellfish-flesh suspension concentration—the biological substance proxy showed the strongest effect on foam stability; when the shellfish-flesh suspension concentration reaches 20% (mass/volume basis, independently prepared), the foam volume and half-life increase by factors of 1.4 and 3.36, respectively, relative to the 4% baseline condition. When the dimensionless aeration depth z/z90 < 0.75, the air-concentration profile rises relatively slowly with depth, whereas it increases more rapidly as the free surface is approached. Within the investigated viscosity range of 1.0–8.3 mPa·s (1.0 mPa·s for the pure-water control and 1.5–8.3 mPa·s for the measured viscosities of the 4–20% shellfish-flesh suspensions), the cross-sectional mean air concentration shows an overall decreasing trend as the liquid-phase viscosity increases, and the total bubble number density decreases correspondingly. The findings provide a laboratory-based indication of the mechanisms that must be addressed in the development of physical foam-suppression technologies; confirmation against field discharge water is required.

Water hammer study in rigid and viscoelastic pipelines with sensitivity analysis of overpressure and damping

Hidden Risks to Sustainable Operation of Water Systems: Suffosion Process Triggered by Pipe Leakage

Failures and leakages in water distribution pipelines affect the sustainable operation of water supply systems. While water losses caused by leaks are widely recognized, their impact on soil stability and internal erosion processes remains insufficiently investigated. This study examines water flow velocity distributions in soil around leaking water pipes regarding suffosion risk. Numerical simulations were performed using the FEFLOW software for four scenarios combining two pipe diameters and two internal pressure levels. Each scenario assumed circumferential leakage with continuous water outflow into the surrounding soil. The numerical model was validated through field experiments conducted on four experimental setups. The simulation results showed that flow velocities near the pipe exceeded critical values in all scenarios, indicating a risk of suffosion. Although hydraulic pressure and leakage area significantly affected local flow velocities, their influence on the extent of the potential suffosion zone was negligible. In all cases, the zone where critical velocities were exceeded extended more than 1.5 m from the leakage location. The results highlight the importance of considering suffosion risk in the operation and risk assessment of sustainable water supply systems. They also indicate that this hazard should be taken into account during the design stage, particularly when selecting pipeline routes and assessing ground conditions.