Influence of Supercritical CO2 Fracturing Fluid on the Permeability of Shale Reservoir and Mechanism Analysis.

Reduction of the reservoir permeability during supercritical CO2 fracturing caused significant reservoir damage, which directly affects the crude oil recovery rate. This investigation explored a novel thickener for supercritical CO2 fracturing fluid, this CO2 thickener not only effectively improves the viscosity and rheological properties of CO2 fracturing fluid but also contributes to reduce reservoir damage and improve permeability. The research results indicated that the synthesized CO2 thickener (3 wt %) can increase the apparent viscosity of supercritical CO2 fracturing fluid to 7 mPa·s, and a 9% matrix permeability damage rate and a 0.5 mD permeability decrease value are shown in a 3% CO2 fracturing fluid. However, 3 wt % of commercial CO2 thickener only increases the apparent viscosity of supercritical CO2 fracturing fluid to 3 mPa·s, while the reservoir damage rate increases to 13%. Two thickeners exhibit completely different damage capabilities to the reservoir, and the synthesized CO2 thickener shows excellent characteristics of reducing reservoir permeability and is also conducive to protecting shale reservoirs. Furthermore, supercritical CO2 fracturing fluid containing synthetic thickeners has better temperature and shear resistance compared with commercial thickeners. This may be because the synthesized thickener and the micro grid formed by supercritical CO2 reduce the adsorption in shale crevices, but a large amount of commercial thickeners can adsorb on the surface of shale.

Characterized Functional Groups of Temperature- and Salt-Resistant Copolymers and Surfactants and Their Relationships.

As the physical properties of newly discovered oil and gas reservoirs become more complex and the requirements for field development effectiveness continue to increase, the performance of polymers and surfactants, which are commonly used as chemical agents in oil field development, is facing great challenges. The determinations of temperature and salt resistance of anti-temperature and anti-salt viscosity-enhancing copolymers and low-interfacial-tension surfactants in recent years have been reviewed. The mechanism of temperature and salt resistance of distinct functional groups was discussed, and the common functional groups of temperature- and salt-resistant viscosity-increasing copolymers and temperature- and salt-resistant low-interfacial-tension surfactants were pointed out. An outlook on the molecular structure design of a new temperature- and salt-resistant oil displacement agent is presented.

Testing and Evaluation of the Emulsifying Properties of Compound Oil Displacement Agents.

Aiming at the phenomenon that the emulsification degree of the composite oil displacement agents affects the recovery factor, composite oil displacement agents of the P/S binary system and the A/S/P ternary system were taken as research objects. Emulsion particle size and stability were tested and evaluated, and the effects of the surfactant and alkali content on the emulsification degree of emulsion were investigated. The concept of the emulsification stability index and its measuring method were put forward, and a method was used to test and evaluate the emulsification stability of the emulsion. The results showed that the emulsion formed by the ternary system had the smallest average particle size, the best stability, and the best emulsification stability. The binary composite system was second, and the polymer solution did not form an emulsion. The emulsification stability index method could effectively quantify the emulsification degree of the emulsion. Within a certain range, the increase of the surfactant and alkali content in the composite oil displacement agent was beneficial to the improvement of the emulsification degree of the emulsion.

Spontaneous Imbibition of Capillaries under the End Effect and Wetting Hysteresis.

The phenomenon of spontaneous imbibition is widely present in the development process of tight oil/gas reservoirs. To further explore the spontaneous imbibition behavior of capillary tubes to provide theoretical and methodological references for the study of microscopic porous media imbibition phenomena, the capillaries that can be observed with the naked eye on the order of 10-100 µm were selected as research objects. Based on the theory of interface chemistry, the capillary end effect, and wetting hysteresis, the influence of the additional pressures generated by the two-phase interface on the spontaneous absorption of the horizontal capillary was studied. Some of the capillaries were processed for wettability, and then the water wettability of different capillaries was measured by the introduced concept, which is the conversion height of the self-absorption phase in the capillary. The capillaries were horizontally placed in the liquid for a spontaneous imbibition experiment, and the air-liquid two-phase menisci behavior was observed at the same time, and then the influence of water wettability, surfactant, and capillary diameter on spontaneous imbibition was discussed. It was found that in the equal diameter capillaries, the spontaneous air-liquid imbibition behavior of capillary tubes with different water wetting properties is different in sensitivity to surfactants and tube diameters; when surfactants are used to improve capillary water wettability to increase spontaneous imbibition efficiency, the initial water wettability of the capillary and the comprehensive changes in the capillary pressure caused by interfacial tension should be considered.

Endonasal endoscopic repair of cerebrospinal fluid rhinorrhea in a series of 69 patients.

We presented our experiences in treatment of Cerebrospinal Fluid (CSF) rhinorrhea with an endoscopic endonasal surgery approach, and showed the severe postoperative complications and failures we experienced, in order to outline some of the characteristic problems that can occur. We performed a retrospective analysis of all of the patients with CSF rhinorrhea. All of the patients were managed with an endonasal endoscopic procedure. Data collected included the site of leakage, the surgical interventions, and the postoperative complications. Sixty-nine patients (33 females and 36 males) were included in this study. All patients underwent an endoscopic repair approach with a multilayer reconstructive technique. The success rates of the first attempt in our study were 89%. Four patients presented with postoperative meningitis and brain abscess and one of these patients died of the brain abscess. Our results indicate that an endoscopic endonasal surgery approach provides a wide, safe, and direct route for treatment of CSF rhinorrhea. The precise location of leakage prior to surgery and proper patient selection, eliminating those with large leakages, are helpful in ensuring a successful endoscopic CSF repair with minimal mortality.

[Anesthesia selection in hypophysectomy by endoscopic transnasal sphenoidal approach].

OBJECTIVE: To explore the anesthesia selection in resection of pituitary neoplasms by endoscopic transnasal sphenoidal approach. METHOD: Fifty-six cases with pituitary tumor underwent transnasal sphenoidal endoscopic surgery . Among the 56 cases, 8 cases accepted general anesthesia and 48 cases accepted local anesthesia and sedation. RESULT: All patients had no complains of surgery. 48 cases who accepted local anesthesia and sedation were completed surgery successfully, without graining and struggling during the operation. CONCLUSION: Local anesthesia and sedation is a simple, safe and good selection for resection of pituitary neoplasms by endoscopic transnasal sphenoidal approach.

[Anatomic study of pterygopalatine fossa under endoscope].

OBJECTIVE: To provide endoscopic anatomic bony structures of pterygopalatine fossa for skull base surgery. METHODS: The bony structures of the pterygopalatine fossa were observed in ten dry skulls under endoscope. RESULTS: The pterygopalatine fossa showed a long and narrow cleft composed of the body and pterygoid process of sphenoid bone, the lamina perpendicular of palatine bone, and the posterior wall of maxillary sinus. The pterygopalatine fossa is (21.4 +/- 0.8) mm x (5.2 +/- 0.3) mm x (3.2 +/- 0.3) mm, with seven paths communicating with nasal cavity, mouth cavity, pharynx, orbit, infratemporal fossa and middle cranial fossa. Under endoscope,the whole pterygopalatine fossa could be observed. CONCLUSIONS: Endoscopic anatomic study of the pterygopalatine fossa is important to endoscopic endonasal skull base surgery. Under endoscope,the whole pterygopalatine fossa can be observed.