Juheng Yang

Wettability Alteration by Salinity and Calcium Bridge in a Crude Oil/Brine/Rock System

Wettability alteration has been considered to be a key factor behind low salinity water effect. Though the wettability alteration is widely accepted to be determined by oil components, mineral surfaces and ions in aqueous phase, how the brine chemistry (ionic type and strength) impacts the wettability is still unknown. In this study, the auhtors conducted spontaneous imbibition, contact angle, and zeta potential measurements to investigate: (a) how the ions of the thin film of water between oil and mineral interact with oil and rock to alter the wettability of crude oil/brine/rock system and (b) the mechanism of wettability alteration behind low salinity water effect.

Hydrate slurry flow property in W/O emulsion systems

Hydrate risk management strategy has become a promising way of dealing with hydrates in subsea transportation pipelines in recent years. In this way, hydrates are allowed to form in the pipeline and are treated as a slurry flow with the help of anti-agglomerants. This work investigated the effect of hydrate formation on the flow friction factor in water in oil (W/O) emulsion systems. A series of hydrate formation and slurry flow experiments were conducted using a high pressure flow loop. Results show that the friction factor is in direct proportion to the volume fraction of hydrates formed, as it increases significantly after hydrate formation onset and then increases gradually with hydrate growing. A novel method is proposed in this work to amend the effective hydrate volume fraction and take into account the effect of hydrate agglomeration and water occlusion. In addition, it is found that the slurry flow velocity has a significant effect on the friction factor variation. As a larger flow velocity can lift the particles suspension height and cause the particles to be away from the pipe wall surface, so it gives a smaller friction factor by reducing the collisions between hydrate particles and the pipe wall surface. With the modified effective hydrate volume fraction and particle chord length distribution data, a model is proposed to estimate the hydrate caused friction factor in W/O emulsion systems, which shows a good prediction accuracy in 10% and 20% water cut conditions.

Advances in coupling thermodynamics and kinetics studies of wax precipitation-deposition and hydrate nucleation-formation

During the development of deep-sea petroleum industry, wax and hydrate are prone to form at the same time in the transportation system from reservoir to downstream equipment under high pressure and low temperature condition for the petroleum reservoir with high wax content, high pour point and high viscosity, which will increase the risk of plug or blockage and enhance the safety hazards of the system. Therefore, it is significant to investigate the characteristics of the coexistence system with wax and hydrate, which is also one of the important issues in flow assurance problems. The studies on wax and hydrate separately as well as the coupling studies in the coexistence system from aspects of thermodynamic and kinetics were reviewed and commented, combined with some initial experiments of this coexistence system carried out in high-pressure reactor and flow loop. Several thermodynamic models, like Wilson model and UNIQUAC model, are established or modified to describe wax solid phase more accurately. The classical thermodynamic models for hydrate formation prediction include vdW-P model, which is the most extensively used one, and Chen-Guo model, which is more simple and convenient to use based on a two-step mechanism. Based on the above models, the coupling study of wax and hydrate in thermodynamic aspect thus needs a roubust flash algorithm to characterize complex systems where several phases, i.e. vapor, water, hydrate, wax, liquid hydrocarbon may coexist. Mutual effects of wax and hydrate are explored by using the integrated thermodynamic model and algorithm. A lot of researches have been done on kinetics of wax deposition and hydrate formation separately. Single-phase pipe flow and multiphase pipe flow experiments have been carried out to explore the effects of such factors as molecular diffusion, shear dispersion, adhesion, flow pattern on wax deposition. The non-stoichiometry hydrate formation includes nucleation and growth. Based on experimental studies, physical modeling and mathematical modeling have been done to describe the kinetics of hydrate formation. At present, only a few studies of coupling kinetics of wax deposition and hydrate formation are reported, which are in an early stage of exploration and research. There is no systematic research achievement and no definite conclusion about the dynamic interaction between wax and hydrate. Some advanced experimental means, such as FBRM, PVM, MMF, can provide information in micro level. The main issues to be researched in the future were proposed, which should be based on the independent researches of thermodynamics and kinetics of wax and hydrate. For the study on coupling thermodynamics, a robust and valid coupling thermodynamic model should be established to understand the interaction mechanism of phase behaviors between wax and hydrate, by using the improved model for describing the non-ideality of the liquid and solid phases and focusing on the component changing in each phase. For the study on coupling kinetics, the microscopic distribution mechanism of the solid particles and emulsion phase in the coexistence system should be investigated, and the diffusion mechanism of wax, the adsorption and growth characteristics of hydrate interface should be explored, with the help of visual testing and equipment, from the two aspects of the influence of wax on hydrates formation and hydrate on wax precipitation and deposition, to obtain the interaction mechanism of kinetics behaviors between wax and hydrate.

Wax Deposition From Emulsion-water in Stratified Flow

The authors examine the wax deposition and establishes model to predict wax deposition thickness from emulsion-water in stratified flow. The deposit thickness on the top of the pipe increases first and then decreases, as the total inlet water cut decreases. In addition, the effect of the gelation becomes stronger as the emulsion water cut increases. The numerical calculation of wax deposition from emulsion-water in stratified flow is achieved considering the molecular diffusion and the gelation, predicting the deposit thickness on the top of the pipe. The predictions are consistent with the experimental results.