Summary Acid fracturing is widely applied to enhance production from oil, gas, and geothermal reservoirs in fractured carbonate formations. Because acid preferentially flows along natural fractures, accurate prediction of acid-etched fracture behavior is essential. However, existing acid-etching models fail to account for fracture deformation under in-situ conditions, particularly the thermal effects prevalent at depth. To bridge this gap in this study, we develop a new model that can simulate the spatiotemporal evolution of contact asperities on fracture walls under coupled thermal-hydrological-mechanical-chemical conditions. The model is validated against acid coreflooding experiments, and the results show that closure stress compacts fractures, forms closed regions, and hinders acid transport, yet ramified, channel, and uniform dissolution patterns still develop. The closure area evolves in two stages: an initial dissolution-driven decrease followed by a deformation-driven increase, whereas uniform dissolution remains stable in the later stage. A higher injection rate enhances acid transport but narrows fracture width; higher closure stress strengthens deformation and reduces transport, with uniform dissolution being the most sensitive and ramified dissolution being the least. In multimineral fractures, quartz and dolomite mitigate closure-stress-induced fracture width loss and increase the effective acid-penetration distance. Compared with uniform dissolution, ramified and channel dissolution are less sensitive to temperature in their final etching patterns. This study advances acid-etching modeling for fractured carbonate rocks, provides insights into reactive flow in narrow fractures, and supports the efficient development of subsurface energy resources.
Summary Effective operation of low-rate electric-submersible-pump (ESP) wells often requires intermittent or alternating-frequency control, particularly in mature fields where installed ESP capacity exceeds the current sustainable reservoir inflow, and a full workover is not economically justified. In such wells, gradual loss of tightness in the downhole tubing check valve above the ESP discharge can cause back-drainage from the tubing during nonproducing intervals, distorting shut-in pressure recovery and restart conditions, and reducing production efficiency; under sufficiently strong reverse flow, the pump may also enter a pump-as-turbine (PAT) regime that further changes the hydraulic response of the system. While not every ESP completion includes a check valve, analysis of ESP workover records for a large sample of ESP wells across Western Siberia fields confirms that this is a common and recurring operational condition rather than a rare edge case. This paper extends a reduced-order transient model of ESP wells to account for leakage through the downhole tubing check valve above the ESP and for reverse-flow pump behavior during alternating-frequency operation. The proposed extension preserves computational efficiency while improving the model’s ability to reproduce nonstationary pressure and fluid-level dynamics. The model is integrated into automated adaptation and optimization workflows and tested on field cases from Western Siberia. The results show improved agreement with observed shut-in recovery behavior, substantially reduced cycle-to-cycle variability in production and power relative to baseline intermittent operation, and more robust selection of operating schedules for wells affected by leakage. The proposed approach can be used for diagnostics, model adaptation, and optimization of both individual wells and well groups operating under intermittent or alternating-frequency conditions.
Summary Excellent temperature and salt resistance are essential performance indices for high-temperature cementing fluid loss additives, which dominate the construction safety of deep well cementing operations. To address the insufficient temperature and salt tolerance of traditional fluid loss additives, a high-performance high-temperature cementing fluid loss additive was fabricated via a stepwise polymerization strategy based on the stability design of amphoteric polyelectrolytes and multielement cyclic structures. Alternating oligomers were first synthesized in aqueous medium by virtue of the approximate reactivity ratios of acrylonitrile (AN) and N-vinylformamide (NVF) monomers. High molecular weight terpolymers were further prepared by copolymerization with the salt-resistant 2-acrylamido-2-methylpropanesulfonic acid (AMPS) monomer. Ultimately, cationic five-membered amidine ring structures were formed from the alternating units of terpolymers through acidic amidination reaction to obtain the target additive. The observed outstanding temperature and salt resistance of the additive are consistent with the synergistic effect of the antipolyelectrolyte behavior of amphoteric ions and the structural stabilization of cyclic skeletons. The cement slurry doped with 1.2 wt% additive presents a high-temperature and high-pressure fluid loss lower than 25 mL at 220℃ and exerts no negative impact on the thickening performance of cement slurry, satisfying the technical requirements of 220℃ high-temperature cementing. Field application in Daqing Oil Field verifies that the additive can achieve superior cementing quality and desirable field application effects.
Summary Supercritical CO2 is prone to induce pitting corrosion during pipeline transportation, leading to pipeline perforation failure. At present, most studies only consider the corrosion of pipelines under a single effect and ignore the influence of bidirectional mechanoelectrochemical coupling. However, under actual operating conditions, bidirectional mechanoelectrochemical coupling may complicate the pitting corrosion behavior. Focusing on X80 steel pipelines, this study incorporates the corrosion expansion theory and the regulatory mechanisms of stress on anodic equilibrium potential and cathodic exchange current density into the constitutive equation to establish a bidirectional mechanoelectrochemical coupling pitting evolution model. The spatiotemporal evolution of stress corrosion, electrochemical corrosion, and product film corrosion of pitting under bidirectional mechanoelectrochemical coupling was analyzed, and the expansion rules of pitting in horizontal and vertical directions were further explored. Additionally, the influence of bidirectional mechanoelectrochemical coupling on pitting was quantified. The results show that temporally, the stress, current density, and product film thickness in the defect area increase gradually with time. Spatially, the closer to the pitting center in the defect area, the greater the stress, the smaller the current density, and the thicker the product film. Pitting corrodes outward and downward in the horizontal and vertical directions over time, with the displacement increasing gradually and the rate of change first increasing and then decreasing. The corrosion parameters under bidirectional mechanoelectrochemical coupling conditions are 9.42–11.61% higher than those under simplified conditions, and the corrosion-induced stress promotes pitting corrosion. The research results provide theoretical support for pipeline corrosion prevention and control as well as safety optimization.
Summary Accurate production evaluation is critical for optimizing operational parameters in oil fields, yet it remains challenging because localized production bottlenecks are controlled by multiple dimensions, including reservoir properties, wellbore integrity, and artificial lift performance. To address these limitations, an integrated dual-scale multicriteria evaluation (DME) framework is proposed in this study, integrating macroscale fieldwide benchmarking with microscale single-well diagnostics. The framework serves as a fieldwide screening and prioritization tool, enabling engineers to rapidly identify underperforming wells requiring intervention and to further localize limiting dimensions and indicators. At the macroscale, a hybrid weighting scheme was developed to harmonize professional expertise with data-driven regularities, effectively mitigating the biases inherent in single-weighting approaches. Furthermore, the selection of multicriteria decision-making (MCDM) models was informed by Kendall’s coefficient analysis to improve the robustness and consistency of dimension-specific evaluations. At the microscale, data envelopment analysis (DEA) incorporating slack variable analysis was used to identify potentially limiting indicators. The practical applicability of the DME framework was examined in a reservoir block of China’s G oil field containing 90 sucker rod pump (SRP) wells. Leveraging the optimized MCDM rankings, five underperforming SRP wells were identified. Following the implementation of targeted interventions based on the proposed framework, the ensemble ranking and artificial lift subdimension ranking of these low-efficiency wells improved by up to 52% and 73%, respectively, relative to preintervention levels. These measures also yielded maximum increases in liquid production of 18.05 m3/d and oil production of 2.59 m3/d. The consistency between slack-variable analysis results and post-intervention production responses provided field-based support for the practical utility of the proposed framework. Overall, this study establishes a practical data-driven framework for production diagnostics and intervention prioritization, offering a decision support tool for enhancing development efficiency in complex reservoir environments.
