Gas Hydrate Formation In Pipelines Research Articles

Experimental measurement and model prediction on methane hydrate equilibrium conditions in the presence of organic carboxylic sodium salts

Gas hydrate inhibitors are employed to mitigate gas hydrate formation in pipelines. The effects of thermodynamics inhibition were evaluated by measuring the vapor - liquid aqueous solution - solid hydrate (VLH) equilibrium conditions on methane (CH4) hydrate in the presence of three organic carboxylic sodium salts (sodium formate, sodium acetate, sodium propionate) in this study. The experiments were carried out in the temperature range of 273.65 K to 281.65 K. Compared with deionized water, in the electrolyte solutions of sodium formate, sodium acetate and sodium propionate with mole fraction of 0.010 and 0.020, the VLH equilibrium pressure change (ΔP) increased by 12.93, 27.68 %; 18.78, 38.15 %; 23.51, 49.41 %, respectively. Both of the three organic carboxylic sodium salts have obvious thermodynamic inhibition effect on CH4 hydrate. The strength of hydrate inhibition is related to the carbon chain length of organic carboxylate. The dissociation enthalpy (ΔHdiss) of CH4 hydrate in three organic carboxylic sodium salts solutions remains quite uniform with deionized water, which indicates that three organic carboxylic sodium salts have not been involved in the formation of hydrate nucleus. The Chen-Guo hydrate model and N-NRTL-NRF activity model were employed to predict the VLH equilibrium conditions in electrolyte solutions. In the three organic carboxylic sodium salts solutions, the average absolute relative deviations (AARD) of the VLH equilibrium condition data between the predicted and the experimental were 0.81, 2.17, and 3.02 %, respectively. In the sodium chloride (NaCl) and potassium chloride (KCl) solutions, the AARD between the predicted and literature were 1.44, 1.69 %, respectively. The model has good universality and accuracy. Both sodium acetate and sodium propionate are food grade preservatives. Consequently, these are beneficial for the development of environmental-friendly hydrate inhibitors.

Mini review on environmental issues concerning conventional gas hydrate inhibitors

AbstractIn the offshore oil and gas fields, the formation of gas hydrates creates critical issues, and these issues or challenges become more pervasive as productive activities proceed to deep sea waters. Further, a number of chemical additives that are used to prevent gas hydrate formation in pipelines pose toxicity issues and are harmful to the environment. Commercially available inhibitors such as methanol, glycols, polyvinyl caproclatum (PVCap), and polyvinylpyrrolidone (PVP), which are being used for gas hydrate mitigation, have shown toxicity issues such as corrosion and mass loss due to their volatile nature, resulting in their high consumption. Methanol and glycols are identified as thermodynamic hydrate inhibitors (THIs), while PVCap and PVP are classified as low‐dosage hydrate inhibitiors. There has been considerable discussion in the literature on whether to use THIs or low‐dosage gas hydrate inhibitors (LDHIs) but less discussion on their toxicity and harmful effects on the environment. Therefore, in this mini review we intend to throw light on the environmental issues concerning conventional gas hydrate inhibitors used currently.

Application of statistical learning theory for thermodynamic modeling of natural gas hydrates

The gas hydrate formation in pipelines of industries and chemical plants can cause various operational damages and can increase economic risks. Hence, the knowledge of hydrate formation conditions has become a critical research study to overcome the problems arising from the formation of hydrates. In this study, we applied an algorithm to develop an LSSVM model to predict the formation temperature of natural gas hydrate for a comprehensive range of data points. Total 188 experimental data points were applied from the literature for the development of the LSSVM model. The input parameter was finalized based on the structure of hydrates by each gas species. The results obtained by the LSSVM model have good accuracy as compared with empirical correlations available in the literature. This model gave the squared correlation coefficient (R 2 ), and root mean square error of 0.9901 and 0.59974, respectively. The composition of gases may affect the phase equilibrium condition of gas hydrates. The applied algorithm revealed that the developed LSSVM model could become a good alternative for calculating the formation temperature of hydrate for the range of all data sets. The results showed that the proposed LSSVM model could be applicable for the prediction of hydrate formation temperature for all data points.

Mechanistic Model To Predict Hydrate Deposition under Stratified Flow Conditions

Gas hydrate formation in pipelines is considered as a serious flow assurance threat to oil and gas production. The severity can be realized from its rapid tendency to form plugs and impede producti...

Synergic Kinetic Inhibition Effect of EMIM-Cl + PVP on CO2 Hydrate Formation

Kinetic hydrate inhibitors (KHIs) are employed to mitigate gas hydrate formation in pipelines at low concentrations. Ionic liquids and conventional available KHIs (polymers) perform poorly at high subcooling and extended shut-in conditions. Thus, it's necessary to understand the inhibition mechanism and performance of mix kinetic inhibitors for gas hydrate mitigation in oil and gas transmission lines. In this work, the synergic kinetic inhibition effect of 1-Ethyl-3-methy-limidazolium chloride (EMIM-Cl) + Polyvinylpyrrolidone (PVP) on the induction time and gas uptake during carbon dioxide (CO2) gas hydrate formation is reported. The study was performed in a high pressure sapphire cell at a pressure and temperature of 36 Bar and 1 oC respectively using an isochoric constant cooling method. Result suggests that, the induction time of deionized water + carbon dioxide hydrate increased over 100% in the presence of pure EMIM-Cl and PVP, with PVP slightly higher than EMIM-Cl comparatively. Surprisingly, a significant reductions in CO2 hydrate inhibition performance is observed in the presence of EMIM-Cl + PVP studied synergic systems compared to their inhibition in pure state.

Efficient Hydrate Plug Prevention

A primary focus of flow assurance engineers during project development is the prevention and management of gas hydrate formation in pipelines. Historically, engineers have focused on hydrate formation prevention by injecting sufficient quantities of thermodynamic inhibitors to “shift” the hydrate stability region outside of the range of pressure and temperature operating conditions. However, as developments of hydrocarbon production occur in ever more extreme environments, the practice of complete prevention of hydrate formation may become prohibitively expensive because of the large amounts of inhibitor required. The example of high methanol dosage in equal volumes of inhibitor for water implies a cost of $84 per barrel of water produced at a methanol cost of $2/gallon. As the produced water volume increases during field life, the operators may not be able to pay for hydrate inhibition even with $100 per barrel of oil. The past decade has seen intensive research to discover strategies for transitioning f...