Dissociation of Methane Hydrate by Hot Brine

Natural gas hydrate has been regarded as a potentially unconventional natural gas resource. It is widely distributed in the world. Many methods are proposed to dissociate hydrate, among which heat injection is one of the most effective ones. So, the investigation of production performance under different heat injection modes provides theoretical basis for actual hydrate production. An experimental study on hydrate dissociation and gas production behavior by hot brine injection was conducted with a self-designed 2D sand-packed system. Two patterns of heat injection (continuous heat injection and intermittent heat injection) are studied and the gas production, water production, and temperature variation are analyzed. Results show that the gas produced by continuous heat injection is notably more than that by intermittent heat injection; with the same heat injected, the temperature variation of continues heat injection is larger than that of intermittent heat injection; during the process of heat injection, the water production rate is slightly larger than that of water injection, which is mainly influenced by water injection rate, heat injection patterns and water production from hydrate dissociation. Under the conditions of experiment, the result of continuous heat injection is superior than that of intermittent heat injection.     

The Positive Effects of Biomass Materials as Additives on Dehydration Performance and the Pyrolysis System of Oily Sludge

The focus of the research is the minimizing amount of oil sludge via dehydration. The effects of using combination of polyaluminum chloride and biomass as additives on the possible improvement of the dehydration performance (evaluated via water content of oily sludge) of oil sludge and on the yield of pyrolysis oil at 723 K were investigated. The main influencing factors of dehydration considered in the experiment are biomass species and dosage, temperature, and flocculation time. The water content of oily sludge was significantly reduced when biomass ranging from 0.5 to 3.0 wt% on dosage ratio. The best phase dehydration performance was obtained from Apricot shell of 0.5 wt% at 313–323 K at flocculate time of 30–40 min, while the highest recovery percent of pyrolysis oil (33.54%) was obtained from Walnut shell of 1.0 wt%. The results indicate that the positive effects of the biomass in oily sludge on the improvement of dehydration performance and on recovery rate of the pyrolysis oil were observed. The main reasons that the improvement of dehydration performance may be responsible for the mixtures containing different proportions of oil sludge and biomass. The pyrolysis of the mixtures can increase the yield of pyrolysis oil and the higher heating value of oily sludge.     

Predicting on Distribution of Temperature,Pressure, Velocity,and Density of Gas Liquid Two-phase Transient Flow in High Temperature-High Pressure Wells

The authors present a predicting model concerning pressure, temperature, density, and velocity of gas liquid two-phase transient flow in high-temperature–high-pressure wells, according to mass, momentum, and energy balances. The finite difference method is used to solve the model. A high-temperature–high-pressure gas well (6,115 m deep) in Sichuan Province of China is used to check the efficiency of the proposed model and the algorithms.     

Initial Research on the Effect of Inorganic Salt on Rate of Penetration (ROP) in Drilling Fluids

The authors attempt to investigate the interaction between inorganic components of drilling fluids and sandstones as well as the influence on the rate of penetration (ROP) imposed by inorganic components. With the analysis of Zeta potential of cuttings solution, the mechanism of the experiment is initially achieved. The results show that the ROP will be enhanced by 33.7% when AlCl₃ concentration is up to 0.01 mol/L, and therefore AlCl₃ and Al₂(SO₄)₃ possess a tendency to enhance ROP. In addition, Al³⁺ enables Zeta potential of the solution containing cuttings shifted from negative value to zero, and finally to positive value by means of analyzing Zeta potential, which contributes to the significant improvement of ROP when Zeta potential is greater than ?10 mV. Higher surface free energy created by the close-to-zero Zeta potential is conducive to crushing rocks, which in turn increases the ROP and meanwhile reduces drilling costs.     

Experimental Research of Critical Condensate Saturation and Flow Characteristics of Gas Condensate Reservoir

The critical condensate saturation is a key parameter to reflect condensate flow capacity. The authors propose an experimental method to determine the critical condensate saturation and analyze the flow characteristics of gas condensate by coreflooding and chromatography. Using this method, they perform two sets of experiments with real-core of a gas condensate reservoir and a binary mixture fluid of methane and n-pentane under 84°C. Experimental results show that the critical condensate saturation is 3.04% and 4.66% when irreducible water saturation is 40% and 27%, respectively. The results also indicate porous media will raise the dew point pressure. The irreducible water and capillary number effect is conducive to the flow of condensate. Based on experimental researches, the authors theoretically analyze the distribution and mobilization characteristics of condensate. Although critical condensate saturation is low, it doesn't mean the condensate will be able to flow freely when it achieves the value, and condensate saturation will continue to increase. Compositional simulation is performed to demonstrate that the critical condensate saturation is low, which is important for the high effective development of a gas condensate reservoir.     

Properties and Field Application of LFW (Low Free Water) Drilling Fluid

Wellbore instability is known to be a significant problem that has plagued mud engineers for many years. In order to solve this problem, mud engineers have studied on pressure control, increasing inhibition of drilling mud, and plugging the formation, but the relationship between flowing state of free water in drilling fluid with wellbore instability has been always ignored. The authors discuss the properties and field application of the low free water (LFW) drilling fluid in more than 10 wells drilled in China. It is a new kind of drilling fluid, which has less free water contrasting with counterparts. In addition, it is also a new concept to solve wellbore instability. Field application shows that LFW drilling fluid can increase bearing capability of the formation, decrease the density of drilling fluids when finishing drilling, and shorten the drilling time.     

Oxygen Diffusivity in Asphalts and Mastics

Determination of oxygen diffusivity in binders was made by comparing the oxidation rates at the surface and at a solid–binder interface of an asphalt film of known reaction kinetics. For neat asphalts, oxygen diffusivities (D _{O 2} ) ranged from 10^?10 to 10^?11 m²/s, with log(D _{O 2} /T) varying linearly with log(η _o *) for both base asphalts and polymer-modified binders (PMBs). For asphalt mastics, oxygen diffusivity was observed to decrease as the filler volume fraction increased. Quantitatively, this effect follows a theoretical estimate of the effect of a dilute suspension of spherical inclusions on diffusivity.     

Wax Deposition in Pores and the Permeability Change for High-wax Crude in a Sandstone Reservoir

Wax deposition in pay zone is an important factor that influences well productivity for high-wax crude oilfield. Taking Hongze oilfield as an example, rheological property of the crude and effective flow permeability at different temperature was measured. Flow pattern and process of wax deposition in porous medium was studied. Experiment results show that seepage flow of high-wax crude is significantly sensitive to temperature. It is non-Darcy flow and there exist threshold pressure gradient when temperature is lower than wax appearance temperature. According to experimental data, seepage flow and deposition patterns were proposed.     

The High-Pressure Physical Property of Gas With CO2 in the Changshen Gas Reservoir

The natural gas in Changshen gas reservoir has high CO₂ content. There are no conventional methods to calculate the physical parameters of natural gas. In view of this specificity, the physical parameters are determined and analyzed by PVT laboratory experiments. Experimental studies show that, below 20 MPa, the compressibility factor, volume factor, density, and isothermal compressibility have strong sensitivity to pressure, but the steam content contributes little and the absolute viscosity maintains strong pressure sensitivity. The compressibility factor, density, absolute viscosity, and steam content increase violently stronger than volume factor with the increase of CO₂, and the isothermal compressibility is not sensitive to CO₂. The variations of the high-pressure physical properties of Changshen gas reservoir depend on pressure and CO₂ content, which should be considered in the reservoir development.     

Modeling Asphalt Oxidation in Pavement With Field Validation

A model for asphalt oxidation in pavement was developed based on fundamentals of oxygen diffusion in the mastic and reaction with asphalt. Diffusion depth, a concept different from the conventional film thickness, defined the oxygen diffusion region in the mastic. A field calibration factor accounted for the factors not considered in the model such as the effect of small aggregate particles on oxygen diffusion. Carbonyl area and viscosity of binders recovered from field cores were measured and were used for model calibration and validation. Results demonstrated that the proposed model estimates carbonyl growth over time in pavement, layer by layer, quite well.