For ensuring the safe and stable operation of waxy crude oil pipeline transportation, in this research, the molecular dynamics model was established to characterize the deposition and wall sticking behavior of waxy crude oil multiphase system pipeline transportation. The equal density interpolation fitting method was proposed to determine the wall contact angle of simulation results. Through verification, the error between the simulation results and the experimental results measured by Dos Santos et al. (2006) was less than 5%, which showed that the established model was accurate and reliable. Using the established model, the deposition and wall sticking behavior of waxy crude oil nucleated clusters was simulated. It was found that the nucleated clusters would first adhere to the wall surface to form the solidified oil layer. Then, the wax and asphaltene molecules would diffuse to the deposit layer, and the oil molecules in the solidified oil layer reverse diffused to the direction of the oil flow. With the adhering and spreading degree of clusters on the wall surface increasing, the deposit layer gradually aged, and the gelled deposit layer with a higher density and hardness would form. On this basis, the micro influence mechanism of the surface free energy was studied. It was found that the higher the surface free energy, the more hydrophilic the pipeline wall was, and the higher the adhesion degree would be. Moreover, based on the ABF sampling and the potential of mean force calculations, the selective deposition process of waxy crude oil deposited on the sedimentary layer was studied. The micro information on the deposition sites, the binding conformation, and the binding energy of different molecules in clusters deposited on different molecules in sedimentary layer were analyzed. The investigations in this study could provide theoretical support for paraffin removal and control, which could ensure the safe and stable operation of the waxy crude oil production system.
A linear combustion tube experiment with halfway fire extinguishing was utilized to reconstruct the combustion region distributions based on apparent characteristics of burnt oil-bearing quartz, temperature profile, and oil saturation field distribution between a gas injection well and a production well, etc. The gas composition and fluid composition in each region could be obtained. Following, a high-temperature-high-pressure visualization system was utilized to simulate experimentally the flue-gas flow in the crude oil. A flow characteristics simulation using such process parameters as system injected fluid composition and temperature condition based on the above test results of the combustion tube was conducted. The characteristics of each region were qualitatively described, the flow characteristics of the flue gas was visualized, and the oil bubble enhancement mechanism causing crude oil movement with flue gas was semiquantitatively determined. The results of the combustion tube simulation showed that at least five different coexistent transient regions were observed. Considering that some of the flue gas was dispersed in crude oil in the form of microbubbles, there are burnt zone, burning zone, cracking zone, oil bank, oily bubbles zone, and initial zone. On the basis of microscopic visualization experiments of flue gas flow with crude oil, the effects of flue gas composition, temperature, pressure, and crude oil viscosity on oily bubbles were investigated. The flue gas dispersed in crude oil in the form of stable microbubbles, and the oil carried by the microbubbles presented special oil incremental ability. The denser and the more stable the oily bubble is, the stronger the oil carrying capacity of the bubble is. The results show that the distribution of nitrogen bubbles is the densest, the distribution of carbon dioxide bubbles is the sparsest, and the distribution of the mixed gas bubbles is between the two. The increase of the temperature is not conducive to oily bubble development. The greater the pressure is, the more stable the oil bubble is. The greater the viscosity of crude oil is, the more stable the oil foam is. The experimental results provide theoretical support for further study of the mechanism of in situ combustion.
Since 2005, more than 250 oil spill accidents have occurred in coastal areas and rivers in China, and the risk of oil spill accidents is higher. When oil spill is occurring, it will harm the river water and even normal life of nearby residents. As such, the challenges faced in responding to oil spill of inland river water crossing pipeline merit wider discussion. The Yellow River is a very important river in China and is a high risk area for oil spill due to the leakage of crude oil in across pipeline. Based on the hydrodynamic model, 12 kinds of oil spill scenarios are simulated by MIKE21 OilSpill module, and the influence of wind, water and leakage position on the oil spill drift and diffusion pattern is analyzed. According to the simulation results and the river’s own characteristics, nine Key Sections of Emergency Disposal (KSED) in high-risk waters are obtained, and effective emergency response time of different critical sections which are given to provide technical support for oil spill emergency preparedness work. Results show that the influence of different water phases and leakage location on spill velocity is relatively large. The diffusion velocity of oil spill in flood season is much higher than that in dry season. When leakage point is in the middle position, oil spill velocity is the fastest, followed by the south bank and the North bank. The influence of wind period on the diffusion rate of oil spill is relatively weak, which has a certain effect on the shape of oil spill contaminated zone. When strong wind, flood season and middle position leakage occur, oil spill diffuses fastest with water flow drift, and oil spill emergency disposal is most difficult. According to the need of oil spill emergency preparedness, the easily accessible sluice and bridge structures are selected as the KSED treatment in the length of the river reach studied. The time to reach the KSED of the spillway front is calculated by simulation. Because of the accuracy of the simulation results of this model on key sections of emergency disposal and effective emergency disposal time, Lanzhou Petrochemical Company successfully handled a large-scale oil spill practice. These successful oil spill simulation technology and practice cases about responding to oil spill prove its feasibility. The accuracy of KSED and effective emergency disposal time will be able to provide a new promising responding method to control oil spill pollution.
Theoretical analysis and fi eld monitoring show that lateral vibration has very important effect on casing wear in deep & ultra-deep well drilling. The wear mechanism of casing under impact-sliding work conditions has been investigated and many experiments have been completed with a newly developed full-scale casing wear test machine. Test results present that adhesion wear, contact fatigue, and grinding abrasion are the main wear mechanisms under impact-sliding test conditions. The friction coeffi cient and linear wear rate of the casing rise obviously with an increase in impact load. And the larger the impact load, the rougher the worn surface of the casing. The linear wear rate decreased slightly but the average friction coeffi cient increased slightly with an increase in impact frequency under an impact load of 2,500 N. Both the linear wear rate of the casing and the average friction coeffi cient increased substantially with an increase in impact frequency under an impact load of 4,000 N. Under lower impact load conditions, grinding abrasion and contact fatigue are the main mechanisms of casing wear; under higher impact load conditions, adhesion wear and contact fatigue are the main mechanisms of casing wear.
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