Abstract

The intelligent water control sleeve can measure water cut and flow rate in real-time, remotely control the sleeve opening, and adjust the flow rate from different formation segments into the wellbore. To enhance the water control efficiency of the intelligent sliding sleeve, a multi-segment well reservoir model was established based on Well A01H in the M oilfield of the Bohai Sea. Reservoir numerical simulations were conducted for the water control process during the water-free period, low and medium water cut period, and high water cut period to study the adjustment strategies for the intelligent sliding sleeve valve opening. The results indicate that during the water-free period, targeting the liquid production profile, the duration of water-free oil production can be extended by reducing the sleeve valve opening in high production sections and increasing the opening in low production sections. During the low to medium water cut periods, with water cut as the control target, the rate of water cut increase can be reduced by decreasing the sleeve valve opening in high water cut sections and increasing the opening in low water cut sections. In the high water cut period, the focus shifts to maximizing daily oil production. Cumulative oil production can be increased by further extracting liquid production within the permissible range of production pressure difference. This study proposes control objectives and methods for each stage of intelligent sliding sleeve adjustment in horizontal wells, providing theoretical and practical guidance for water control development in CNOOC oilfields.

Abstract

Maintaining fracture conductivity in acid-fractured carbonate reservoir presents a significant challenge as the fractures tend to close due to closure pressure. A viable approach to prevent the decline of conductivity is closed-fracture acidizing (CFA). In this study, we introduce a field-scale numerical model to simulate the acid-etching pattern in CFA and its effect on the conductivity of acid-fractured fractures. The accuracy of the CFA model is validated through experiments under identical acid-etched fracture morphology. The simulation results indicate that the morphology of closed fractures determines the acid-etching patterns. When the mean fracture aperture is small (≤2 mm), roughness is high (SD>0.05), and the dimensionless correlation length is extensive (≥0.05), acid etching becomes non-uniform, forming grooves and channels. In this case, the live acid reaches farther, and the conductivity remains high under closure stress (improved 8 to 33 times compared to before acidizing). Conversely, the acid uniformly etches the fracture surface, the acid treatment distance is short, and the conductivity rapidly decreases, making the acidizing performance negligible. In short, acid tends to flow into areas with the least resistance, and ultimately affecting acid-etching patterns and conductivity.

Abstract

In this paper, the effect of near-wall distance on flow-induced vibration and heat transfer characteristics of a circular cylinder is numerically investigated. The amplitude ratio, frequency ratio, near-wake structure, and temperature distribution are analyzed. The results show that, the amplitude ratio increases with rising reduced velocity when U*≤5, and further increasing the reduced velocity leads to a transition of the cylinder’s behavior from the upper branch to the lower branch. When H=1D, the cylinder obstructs the temperature boundary layer development, resulting in reduced heat transfer, accompanied by the highest average temperature (Tmean) and the lowest Nusselt number (Numean); conversely, as the near-wall distance increases to H≥1.5D, along with a rise in wall height, heat transfer enhances, yielding higher Nusselt numbers.

Abstract

The vibration and heat transfer characteristics of two tandem cylinders with two degrees of freedom at different reduced velocities(U*) and spacing ratios were numerically investigated. The amplitude, trajectory, time averaged Nusselt number, vortex shedding, and temperature fields were analyzed. Results show that the dimensionless amplitudes of the two cylinders exhibited similar variation trends with increasing U*, first increasing and then decreasing. The trajectories of both cylinders formed 8-shaped patterns. The time averaged Nusselt number (NuA) of cylinder 1 was higher than that of cylinder 2, and both increased with increasing U*. The vortices shed from cylinder 1 covered the surface of cylinder 2, creating high temperature gradients and enhanced heat transfer on the surfaces of both cylinders.

Abstract

Reduced-oxygen air flooding can serve as an effective alternative for water injection in the development of low-permeability reservoirs. During the development process, there is a phenomenon of increased viscosity due to the mixture of crude oil oxidation and water. It is essential to clarify the impact of viscosity increase after crude oil-water mixture during low-temperature oxidation on oil recovery. This paper investigated the impact of water content on the viscosity increase of oil-water mixed fluids during air oxidation through static oxidation experiments. The results indicate that heavy components generated after crude oil oxidation can interact with water to form highly viscous fluids. As the water content increases from 0% to 70%, the viscosity of the mixed fluids initially increases and then decreases. It reaches its maximum value of 32.5 cp at a water content of 30%. The long core displacement experiment studied the impact of transitioning from water flooding to air flooding and nitrogen flooding on crude oil recovery under optimal viscosity conditions. Two sets of experiments, water flooding and gas flooding, were conducted for comparison. The results indicate that the highest oil recovery was achieved when transitioning from water flooding to air flooding. This suggests that the heavy components generated during crude oil oxidation in the air flooding process, along with the highly viscous fluid formed by interaction with water, can block high-permeability channels, exerting a localized profile modification effect. This leads to changes in gas flow channels and expands the effective gas sweep range. This leads to changes in gas flow channels and expands the effective gas sweep range.

Abstract

Achieving net-zero emissions and curbing the long-term increase in global warming requires large-scale carbon dioxide (CO2) sequestration through various techniques. Among the plethora of options for large-scale CO2 storage, geological storage stands out as the most promising, given its expansive storage capacity and minimal environmental impact. Deep saline aquifers, in particular, have emerged as frontrunners due to their vast storage potential and broad global availability. In saline aquifers, various trapping mechanisms, including structural and stratigraphic trapping, residual or capillary trapping, solubility trapping, and mineral trapping, work synergistically to store CO2. The displacement dynamics of CO2-brine two-phase flow in pore-scale dictates the structural and residual trapping of CO2 in subsurface formations. In this regard, a highly heterogeneous porous microchannel was used to investigate the impact of salinity and porous heterogeneity on CO2-brine displacement dynamics. A computational fluid dynamics (CFD) simulation based on the volume-of-fluid (VOF) method was used to study the immiscible two-phase flow dynamics under deep reservoir extreme temperature and pressure conditions. Microfluidic experiments, conducted under a high-resolution digital microscope with different brine salinities, provide pore-scale flow visualization and quantification of trapped CO2. Meanwhile, CFD simulations on the same porous media consider thermophysical property changes for CO2 and brine under high-pressure and high-temperature conditions, elucidating their impact on CO2 trapping or storage. The observed unstable finger-like displacement pattern in the microchannel, attributed to very low capillary number (Ca) and viscosity ratio (M) values, results in CO2 channeling with limited water displacement, thus restricting CO2 saturation at around 50 %. Along with viscous fingering, small pore-throats pronounce the snap-off effects at the micro-scale, which increase the residual trapping of CO2 in the porous media. An increase in brine salinity increases viscosity, interfacial tension, and contact angle, leading to a more vertical sweep of water and increasing the CO2 storage capacity of a saline aquifer. Under reservoir conditions, the comparatively higher density of CO2 and increase in contact angle resulting from the adsorption of CO2 increases CO2 trapping in porous channels. This combined approach of microfluidic experiments and CFD simulations provided valuable visualization and insights into CO2-brine dynamics at the pore-scale, which would contribute significantly towards efficient, enhanced, and secure storage of CO2.

Abstract

The supercritical carbon dioxide (s-CO2) Brayton cycle is one of the recommended power cycles for next generation high efficiency power plants. An additional benefit of using this working fluid is the miniaturised moving parts when compared to conventional Rankine or Brayton cycle. However, one of the challenges is the
miniaturised design of heat exchangers used in gas cooler, gas heater and regenerators. This can be achieved by reducing the hydraulic diameter of fluid flow channel. However, heat transfer coefficients for supercritical CO2 flow through such miniaturised channels are yet to be studied. In any heat exchanger, the decrease in hydraulic diameter of the channel leads to a higher heat transfer coefficient at the expense of higher pumping power. This study deals with the comparison of a large-diameter single-channel type (SCT) heat exchanger and a small hydraulic diameter multichannel type (MCT) heat exchanger using s-CO2. A numerical investigation is done on a tube-in-tube type heat exchanger, and the effect of mass flow rate and channel diameter at the given inlet temperature and pressure is depicted. At 3 different mass flow rates, such as 1 kg/hr, 3 kg/hr, and 4 kg/hr, the percentage enhancement in the rate of heat transfer for MCT is found to be higher w.r.t. SCT, by 33.4%, 30.34%, and 25%, respectively.

Abstract

Catering to variable load has been a big challenge for large chillers for air-conditioning and process cooling applications. Traditionally chillers were designed for catering to peak capacity with hot-gas bypass being the most common technique for capacity control in fixed speed operation. In more recent applications variable speed compressors have been the preferred choice. In this study we propose a novel hybrid system which combines the mechanical and thermal compression techniques for producing chilled water. The mechanical compression caters to steady load whereas the adsorption based thermal compression caters to variable load. The refrigerant used in this study is R134a with coconut shell based activated carbon as the adsorbent. The adsorber connects to evaporator under peak load operation whereas it regenerates during low load condition thereby keeping the chilled water outlet temperature nearly constant. Experiments are conducted on a lab-scale 1 RTon system. The proposed operational strategy has the potential to handle up to a 26% variation in refrigeration load on the evaporator for maximum regeneration temperature of 850C for the adsorbent.

Abstract

During load cycling processes of coal-fired power plants, the MPS pulverizers system’s response time dominates the power unit’s operation flexibility. Reducing the effect of the delay and inertia of the pulverizing system is urgent. This study established and validated a complete pulverizing system model, which included six coal mills, coupling with an established coal-fired power plant model. A revised fuel demands control strategy based on the main-auxiliary coordination was proposed. The results show that by implementing the revised control strategy, the absolute pulverized coal output deviation was reduced by up to 216 kg, 126kg, and 116kg, respectively, with three operating modes. When four coal mills were operational, the reduction constituted 0.09% of the pulverizing system’s output during the load transition. The new control strategy enhanced the matching of the main and auxiliary systems in coal-fired power units.

Abstract

In this study, methanol has been produced from biomass feedstocks using Aspen Plus simulation tool. The proposed system is a combination of gasification plant, syngas cleaning facility and methanol generation plant. Hydrogen rich syngas was generated using steam biomass gasification facility. After extensive gas cleaning the syngas was fed to the methanol generator system. Five different biomass feedstocks, viz. wheat, barley, rice husk, food waste and date pits were used for the analysis. Among all the feedstocks, date pits yielded the highest amounts of hydrogen (52.52%) and carbon monoxide (34.29%). It was observed that the methanol yield for date pits was the highest (0.82 kg/kg of biomass).