Investigation On The Phase Equilibrium Conditions Of Methane And Carbon Dioxide Hydrates In High Salinity Solutions

Hydrate formation and dissociation can cause severe problems in oil and gas exploration,production,and transportation,especially in deepwater/ultra-deepwater areas.These hydraterelated problems can affect the safety of oil and gas facilities,block equipment/pipeline conduits and increase the costs of operation.It can also clog the mud line,the surface choke line,the BOP stack and lead to wellbore instabilities in oil and gas wells.This will affect the effective management and control of the oil and gas wells.In most drilling processes,salts which are thermodynamic inhibitors are mixed with the drilling muds to reduce the freezing point of water and prevent hydrate formation.A detailed knowledge of how hydrates are formed in pure water and aqueous salt solutions is paramount to solving these hydrate-related problems.Thermodynamic models are the common tools used to predict hydrate equilibrium data but these models are complex,require several assumptions and involve rigorous analysis.They also give large prediction errors for high salinity,and high temperature/pressure systems.Thus,it is vital to develop a reliable,generalized,and simple prediction tool.In this work,new experimental dissociation data of methane and carbon dioxide hydrates in aqueous solutions of single sodium chloride,potassium chloride,and calcium chloride at high salt concentrations and high pressures are measured using the modified step-heating method.The proposed experimental method can be used to reduce hydrate dissociation time,control the volume of gas released during hydrate dissociation and manage the whole dissociation process with the use of aqueous salt solutions.A generalized correlation is also developed for accurate prediction of hydrate phase equilibrium data in aqueous salt solutions using the experimental data measured in this work and those reported by other researchers.The experimental data measured in this work show similar trends with those reported by other researchers under conventional conditions.The predictions of the commercial programs deviate from the measured experimental data in high salt concentrations and at high temperatures/pressures.Contrarily,the predictions of the correlation developed in this work show excellent agreement with the experimental data measured in this work and those in the literature at different salt concentrations,pressures,and temperatures.The predictions of the generalized correlation are also better than those of the commercial hydrate prediction tools.With this correlation,the phase equilibrium data of hydrates can be estimated using simple calculators.The exact amount of salt required to inhibit hydrate formation while drilling in deepwater environments can easily be calculated.This research work adds fundamental knowledge and tool to the prediction of hydrate equilibrium conditions in the presence of aqueous salt solutions.The real-time information(i.e.temperature and pressure profiles)of the oil and gas wells coupled with the measured data and the generalized correlation will ensure proper management and control of the oil and gas wells.