Performance Investigation of Asphaltene Adsorption at a Carbonate Rock Surface: Spectroscopy Experiment and Molecular Simulation.

Investigation of asphaltene adsorption at rock surfaces plays an important role in enhanced oil recovery (EOR) for the petroleum industry. In this work, the interaction performances of asphaltene adsorption at carbonate dolomite and calcite surfaces are investigated based on experimental and simulation insights. On the one hand, macroscopic interaction performances were investigated by spectroscopy experiments to obtain the Langmuir thermodynamic model and pseudo-second-order (PSO) kinetic model. The results indicated monolayer molecular asphaltene adsorption for both dolomite and calcite, while they showed 'slow adsorption-slow desorption' for dolomite but 'fast adsorption-fast desorption' for calcite. Meanwhile, dolomite showed a higher adsorption capacity with qm(dol 1) = 5.35 mg/g > qm(cal 1) = 1.28 mg/g and a stronger adsorption spontaneity with ΔGm(dol 1)θ = -7.76 kJ/mol < ΔGm(cal 1)θ = -4.76 kJ/mol. On the other hand, microscopic interaction performances were investigated for three asphaltene molecules by molecular dynamics simulation (MDS) with ∼8 Å distance-placing and 500 ps time-running. According to the results, dolomite showed higher system stability than calcite with a lower final energy of ΔEdol-cal = -58 kJ/mol, and archipelago asphaltene showed higher adsorption stability with the smallest equilibrium energy of Earch(dol) = -147 kJ/mol for albite and Earch(cal) = -89 kJ/mol for calcite. The model of molecular orientation and force dominance was proposed as the interaction mechanism for asphaltene adsorption, which "lie sideways" at low concentrations but "stands upright" at high concentrations. This work allows the performance investigation and mechanism illustration of asphaltene adsorption at rock surfaces, which can help gain a fundamental understanding of the EOR during reservoir exploitation.

The safety profile of preoperative administration of heparin for thromboprophylaxis in Chinese patients intended for thoracoscopic major thoracic surgery: a pilot randomized controlled study.

BACKGROUND: Patients undergoing major thoracic surgery especially for cancers are at a high risk of perioperative thromboembolism. Current guidelines recommended either heparin sodium (unfractionated heparin) or low-molecular-weight heparin (LMWH) for those patients at high risk of deep vein thrombosis (DVT). However, the rational timing of starting heparin has not yet been well established, because DVT can be caused by not only surgery but also comorbidities as well as prolonged hospital stay, and thoracic surgeons always concerned about heparin-related increased risk of intra- or post-operative bleeding. Therefore, this study aimed to establish the safety profile of preoperative administration of heparin for thromboprophylaxis in Chinese patients intended for thoracoscopic major thoracic surgery. METHODS: From June to August 2016, patients intended for thoracoscopic lobectomy, esophagectomy, and thymectomy were randomly assigned into two groups: the case group (starting heparin sodium 5,000 U, bid preoperatively upon the admission into our department) and the control group (starting heparin sodium 5,000 U, bid postoperatively from postoperative day 1). The baseline data including demographic data and preoperative conditions were collected. The end points included operation time, intraoperative bleeding volume, postoperative chest tube drainage volume and duration as well as lab coagulation function data. RESULTS: A total of 58 qualified patients were randomized into case group (29 patients) and control group (29 patients), and after excluding 6 conversion patients, the case group and control group each had 26 patients for analysis. The baseline data of the two groups were comparable. Operation time (P=0.368), intraoperative bleeding volume (P=0.231), postoperative drainage days (P=0.466), and mean drainage volume per day (P=0.108) were not significantly increased in case group compared with those of control group. Moreover, there were no significant differences of perioperative coagulation function between these two groups. CONCLUSIONS: Preoperative administration of heparin for thromboprophylaxis in Chinese patients intended for thoracoscopic major thoracic surgery was safe and feasible. TRIAL REGISTRATION: NCT02940444 (https://register.clinicaltrials.gov/).