Low temperature and high pressure conditions favor the formation of gas clathrate hydrates which is undesirable during oil and gas industries operation. The management of hydrate formation and plugging risk is essential for the flow assurance in the oil and gas production. This study aims to show how hydrate management in the deepwater gas well testing operations in the South China Sea can be optimized. To prevent the plugging of hydrate, three hydrate management strategies are investigated. The first method, injecting thermodynamic hydrate inhibitor (THI) is the most commonly used method to prevent hydrate formation. THI tracking is utilized to obtain the distribution of mono ethylene glycol (MEG) along the pipeline. The optimal dosage of MEG is calculated through further analysis. The second method, hydrate slurry flow technology is applied to the gas well. Pressure drop ratio (PDR) is defined to denote the hydrate blockage risk margin. The third method is the kinetic hydrate inhibitor (KHI) injection. The delayed effect of KHI on the hydrate formation induction time ensures that hydrates do not form in the pipe. This method is effective in reducing the injection amount of inhibitor. The problems of the three hydrate management strategies which should be paid attention to in industrial application are analyzed. This work promotes the understanding of hydrate management strategies and provides guidance for hydrate management optimization in oil and gas industry.

A stability criterion for gas-hydrate slurry stratified flow was developed. The model was based on one-dimensional gas-liquid two-fluid model and perturbation method, considering unstable factors including shear stress, gravity, and surface tension. In addition, mass transfer between gas and liquid phase caused by hydrate formation was taken into account by implementing an inward and outward natural gas hydrates growth shell model for water-in-oil emulsion. A series of gas-hydrate slurry flow experiments were carried out in a high-pressure (>10 MPa) horizontal flow loop. The transition criterion of smooth stratified flow to other flow patterns for gas-hydrate slurry flow was established and validated and combined with experimental data at different water cuts. Meanwhile, parameters of this stability criterion were defined. This stability criterion was proved to be efficient for predicting the transition from smooth to nonsmooth stratified flow for gas-hydrate slurry.

As oil/gas exploitation moves into deep water, hydrate formation and plugging in flowline have been a main concern of the flow assurance engineers. A series of experiments were conducted in a gas-emulsion multiphase flow system using a high pressure flow loop. The properties of hydrate agglomeration and deposition in different flow patterns were investigated. First, based on the hydrate chord length distribution and the changes of slurry density, several methods were proposed to quantitatively estimate the hydrate agglomeration degree and deposition degree. Second, typical results in each flow pattern were analyzed, and the plug formation mechanisms in each flow pattern were proposed. Then, after comparing the results in each flow pattern, it was found that the order of hydrate agglomeration degree from high to low is slug flow, stratified flow, bubble flow, and annular flow; and the order of hydrate deposition degree from high to low is annular flow, slug flow, bubble flow, and stratified flow.

Hydrate deposition is a major concern in the oil and gas industry. This paper studies the hydrate deposition mechanisms in water-in-oil (W/O) emulsion systems using a high-pressure flow loop. The experimental results indicate that the hydrate deposition process can be divided into four stages: the initial formation and deposition, deposit sloughing, secondary formation and redeposition, and deposit annealing. For the first time, a method to quantify hydrate deposits is proposed. The results show that a low temperature, high pressure, high additive concentration, and low water cut decrease the amount of hydrate deposits. The hydrate deposition amount first increase and then decrease with an increasing flow rate. The experimental results demonstrate that the hydrate deposition process is affected by the hydrate formation driving force, wall surface properties, adhesive water amount, mass-transfer coefficient, and flow shear force.

As the oil & gas industry moves into deep water, hydrate has been a major hazard to the deep sea flow assurance. The objective of this work is to study the hydrate formation kinetics in a gas-emulsion multiphase flow system. A series of experiments were carried out with different gas/liquid flow rates using a high pressure flow loop. Results showed that the experimental data were remarkably reproducible in the flow loop system. It was found that as the gas flow rate and liquid flow rate increased, the hydrate formation induction time increased and the critical supercooling degree decreased. The gas/liquid flow rates exhibited little effect on the hydrate formation amount. As the liquid hold-up increased, both the induction time and the critical supercooling degree increased at first and then decreased. In addition, the hydrate formation amount remained almost constant when the liquid hold-up was higher than 20%.

A new modified EOS-GE model is developed for the highly asymmetric paraffinic systems, where the volume translated Peng-Robinson EOS is adopted coupled with the LCVM mixing rule. In the new modified EOS-GE model, the original UNIFAC is replaced by a newly established UNIFAC where the nonlinear calculation of the segment fractions of molecules in γC (the combinatorial activity coefficient) is introduced to modify the traditional assumption that “all groups are isotropic in solution”. A total of 956 vapor-liquid experimental bubble points in highly asymmetric paraffinic systems including binary systems, ternary systems, quaternary systems and multiple systems are used to test the new developed EOS-GE model. Results show that the original UNIFAC and the improved UNIFAC both perform well if the molefractions of light components (CH4 or C2H6) are low; however, with the increase of the light components, the improved UNIFAC is remarkably superior to the original UNIFAC.

The topic of hydrate formation and blocking in offshore petroleum industry has attracted more and more attentions, which is known as one of the flow assurance issues. A new technology has been proposed to avoid the occurrence of hydrate blockage in multiphase transportation system, which is hydrate slurry flow technology, also named as cold flow technology. The low dosage hydrate inhibitor of anti-agglomerate was added into the flow systems to allow hydrate formation in the liquid phase while it prevented the aggregation of hydrate particles. Thus these particles were evacuated with the liquid phase as pseudo-fluid like slurry. In this work, an inward and outward hydrate growth shell model coupled with two phase flow hydrodynamic model was applied to investigate the characteristics of gas-hydrate slurry stratified flow. The inward and outward hydrate growth shell model considered the kinetics, mass transfer and heat transfer process of hydrate formation, which could predict the hydrate formation rate and the released heat. The two phase flow hydrodynamic model included mass, momentum and energy equations. A case for an inclined pipeline was simulated using the combined models. The results showed that once the kinetic requirements for hydrate crystallization was satisfied, hydrates would form quickly at the initial stage and then hydrate formation rate would decrease obviously due to the limitation of mass transfer and heat transfer. Meanwhile, the flow characteristics, such as the liquid holdup and pressure drop, were predicted by the model, which also provided an acceptable results about the state of hydrates (onset time of formation, formation rate, volume fraction, etc.) in multiphase system for the operation engineers in the field. The key parameters of the inward and outward hydrate growth shell model were determined by referring to the literatures. To investigate the reliability and influence of these set values on the results, a sensitivity analysis of the key parameters of the shell model was implemented. Further works should be done, such as the flow mechanism in other flow regimes as well as the influence of particle aggregation.