One of the major unsolved complex problems confronting the petroleum and chemical industries at present is the untimely deposition of heavy organic and other solids dissolved or suspended in the fluid flow systems. The production, transportation, and processing of petroleum can be significantly affected by flocculation and deposition of such compounds in the course of industrial processing systems, including transfer conduits, reactors, and refineries and upgrading equipment, with devastating economic consequences. Heavy organics such as paraffin, wax, resin, asphaltene, diamondoid, mercaptdans, and organometallic compounds can precipitate out of the crude oil solution due to various forces causing blockage in the oil reservoir, well, pipeline, and in the oil produc-

Hydraulic fracturing is vital in the stimulation of oil and gas reservoirs, whereas the dynamic process during hydraulic fracturing is still unclear due to the difficulty in capturing the behavior of both fluid and fracture in the transient process. For the first time, the direct observations and theoretical analyses of the relationship between the crack tip and the fluid front in a dynamic hydraulic fracture are presented. A laboratory-scale hydraulic fracturing device is built. The momentum-balance equation of the fracturing fluid is established and numerically solved. The theoretical predictions conform well to the directly observed relationship between the crack tip and the fluid front. The kinetic energy of the fluid occupies over half of the total input energy. Using dimensionless analyses, the existence of equilibrium state of the driving fluid in this dynamic system is theoretically established and experimentally verified. The dimensionless separation criterion of the crack tip and the fluid front in the dynamic situation is established and conforms well to the experimental data. The dynamic analyses show that the separation of crack tip and fluid front is dominated by the crack profile and the equilibrium fluid velocity. This study provides a better understanding of the dynamic hydraulic fracture.

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Consideration of initial stress state after cement hardening provides a vital basis for the prediction of cement failure, which has been overlooked in previously published methodologies partly due to the difficulties in examining this problem rationally. In the present study, the hoop stress at casing-cement interface during cement hardening is investigated experimentally based on the full-scale casing-cement sheath-formation system (CCFS) facility, which is equipped with the real-time stress-strain measurement capability. The hoop stress at casing-cement interface during cement hardening drops sharply, rather than equating with the initial annulus pressure of cement slurry. It presents a higher drawdown under higher annulus pressure and thinner casing, and a lower drawdown under elastic cement slurry and thicker cement sheath. Furthermore, an analytical model taking the effect of cement hardening into account is developed to predict the integrity of cement sheath. Reliability of the model is verified by comparison with field observations. Excellent agreements are observed. The results illustrate that the tensile cracks are likely to occur at the inner cement (inner surface of cement sheath) by the effect of cement hardening, since the hoop stress at inner cement during cement hardening drops greatly and even becomes tensile. A detailed sensitivity analysis illustrates that an elastic cement slurry with a lower elastic modulus works more effectively, which can resolve the SCP problem in shale gas wells.

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