An experimental study on the imbibition characteristics in heterogeneous porous medium

Focusing on problems of rapid production decline and poor development effect after volume fracturing of the shale oil reservoir, a production method of SC-HNP (surfactant slug assisting CO2 huff and puff) was proposed. Taking CQ block (CQ, the reservoir block name) as an example, laboratory experiments were carried out using typical oil samples and core samples, and a numerical simulation model of SC-HNP was established based on the experimental results. The production performance and oil recovery mechanism were analyzed, and the oil production by SC-HNP of a typical well was predicted. The results showed that (1) the oil recovery degree of the surfactant imbibition experiment is 34.5%, showing good imbibition oil recovery effect. CO2 has good swelling effect and viscosity reduction ability to the oil. (2) SC-HNP combines the effects of the surfactant and CO2, and it has the best replenishing formation energy ability and the highest oil production level. Its improved recovery degree is about 2.4% (one cycle), showing the best development effect. (3) Compared with SF-HNP (surfactant huff and puff), SC-HNP can improve the oil displacement effect in the far-well fractured area, and compared with CO2-HNP (CO2 huff and puff), SC-HNP can improve the oil displacement effect in the near-well fractured area. (4) Using SC-HNP, it is predicted that the oil recovery degree of well CQP-32 (CQP-32, the well name) can be increased by 1.84%, which significantly improves the development effect, and the CO2 storage percent is about 32%.

Surfactant slug assisting CO2 huff and puff in enhancing shale oil reservoir recovery

Xia,

Yin,

Wang

et al. 2024

Optimizing extreme limited entry design for lateral heterogeneous reservoirs

Wang,

Liang,

Deng

et al. 2024

Extreme limited entry (XLE) method can enhance hydraulic fracture uniformity by elevating wellbore pressure to overcome reservoir heterogeneity. However, it increases surface pressure and decreases hydraulic fracturing efficiency. In this paper, the effects of stress shadow and heterogeneity of the lateral breakdown pressure on fracture propagation are numerically studied, from which an optimization method is proposed for the XLE design with the minimal requirement of fracturing pressure. Initially, the unconventional fracture model is applied to analyze fracture propagation in formations with homogeneous geomechanical parameters and various perforation designs. Fracture length distribution is correlated with perforation friction, revealing insights into the influence of geomechanical parameters and fracture spacing. Then, the uniformity of fracture propagation is assessed for different XLE designs by varying lateral breakdown pressures. Simulation results are utilized to develop a cross-plot of fracture length distributions vs normalized perforation frictions for optimizing an XLE design. In homogeneous reservoirs, decreasing perforation spacing and increasing perforation hole erosion rate slow down the reduction in the fracture length distribution span with perforation friction, necessitating a higher perforation friction for uniform fractures. In all simulated cases, a similar trend is observed when the distribution of fracture lengths is plotted vs the normalized perforation friction to the difference of breakdown pressure within one fracturing stage. It is recommended that this normalized value be maintained above 2 in an XLE design. This new plot makes the conventional horn-shaped plot more applicable to reservoirs with heterogeneous lateral breakdown pressures.

Numerical study of a composite cooling method for hypersonic aircraft

Chen,

Tian,

2024

Thermal protection is a crucial issue for a long-flying hypersonic aircraft. In this work, a composite cooling method is proposed and implemented on a hypersonic blunt cone. The composite cooling method combines impinging and convective cooling at the cone head with transpiration cooling employed downstream to produce an overall cooling effect of the cone. Using computational fluid dynamics, the influences of the cooling gas and different attack angles on the cooling effect are examined. The results indicate that the combined cooling method can effectively reduce the overall outer wall temperature of the cone. In particular, with the combined cooling method, an increase in mass flow rate of the cooling gas has been observed in numerical tests, which results in a decrease in the head temperature. The maximum temperature decrease can reach 77.0% on the wall when the mass flow rate of the cooling stream is 1.1 kg/m2 s. The cooling performance on the leeward side can be better than that on the windward side for a fixed cooling gas mass flow rate. This gap in cooling performance between the two sides can be further amplified by a larger attack angle. Quantitatively, when using the combined cooling method, the temperature difference between the windward and leeward sides increases from 106 to 270 K when the attack angle increases from 4° to 8°. The numerical results in this study could provide theoretical and statistical guidance for the design of novel active thermal protection methods for hypersonic aircraft.