Rod Burgass

Visual observation of gas-hydrate formation and dissociation in synthetic porous media by means of glass micromodels

Visual observation of gas hydrates at the microscopic scale in synthetic porous media provides unequivocal visual evidence that clathrates can form in systems without the presence of a free-gas phase. Hydrates were formed from a soluble liquid hydrate former (tetrahydrofuran, C 4 H 8 O), from free gas (CH 4 ), and from dissolved gas (CO 2 ). Clathrates were found to form within the center of pore spaces, rather than on grain surfaces. Cementation of grains only occurred in regions of a small grain size, or where a large proportion of pore space was filled with hydrate. However, even at high clathrate saturations, a thin film of free water persisted on grain surfaces. The results have important implications for the potential cementing effect of hydrates on sediments, and thus for sediment permeability, slope stability, and seismic interpretation of hydrate-bearing sediments.

Gas Hydrates in Oil Systems

Extensive studies have been conducted on hydrate formation in gaseous systems; however, little information is available on hydrate risks in oil systems. This is partly due to difficulties in measuring the hydrate stability zone in oil systems, as well as problems associated with compositional representation of such systems. Furthermore, it is reported that hydrate formation pose less risks in oil systems than gas systems, partly due to the presence of natural inhibitors, formation of water in oil emulsions, and possibly oil wet pipeline walls. However, little is known of the nature and mechanism of the natural inhibition and the response of the system to an increase in the water cut. In this communication, we present details of two experimental set-ups specifically designed to study the hydrate risks in oil systems. They include a visual high pressure kinetic rig for measuring the hydrate stability zone, crystal size, distribution and the rate of hydrate formation and dissociation, and a glass micromodel for visual observation of hydrate formation / dissociation in micro-scale. We report some of the recently obtained experimental results using the above experimental equipment. The results show that the existing techniques should be revisited for generating reliable data in oil system. We also demonstrate that proper characterization of the heavy end and taking into account the possibility of wax formation may play a role in improving the reliability of predictive techniques. The results provide better understanding and evaluation of risks associated with hydrate formation in pipelines carrying oil.

Effect of water chemistry on asphaltene stabilised water in oil emulsions - A new search for low salinity water injection mechanism

Although most of the investigations report that the injection of low salinity water (LSW) can improve oil recovery, the effect ion content/valency could be more significant than ion concentration in LSW injection. In this study, the impact of aqueous phase ionic strength and ionic content on formation of water microemulsions in model oil with f=0.005 g.g-1 asphaltene content were investigated using state of art petrographic optical microscope. Various salt concentrations of NaCl, CaCl2 and MgCl2 in water are prepared to determine the role of water salinity and ion valency on creation of asphaltene stabilised water in oil (W/O) microemulsions, their stability and morphology. The results reveal that at low ionic strength conditions in presence of divalent cations more W/O microemulsions can be observed. Furthermore, this study shows that the effect of the ion valency of salts on the emulsion stability follows MgCl2 > CaCl2 > NaCl, and Mg2 plays a crucial role in the stability of water-in-crude oil microemulsions, leading to more stable emulsions in comparison with Ca2 followed by Na . These new findings elucidate how large a role, the asphaltene and water chemistry play in the observed W/O microemulsions behaviour in LSW injection.