(99f) Separation of Heavy Oil Emulsions

As the conventional light oil is replenishing, the focus has been shifted to the recovery of heavy oil. Almost half of the world's reserves are classified as heavy or extra-heavy. For better understanding of the heavy oil recovery process, it is important to understand the gravity separation process using heavy oil system. Heavy oils have density typically in the range of 10-30 API causing much lower separation rate than conventional crude oil due to very low density difference between two immiscible liquids i.e. oil and water. To enhance the separation rate and achieve similar processing throughputs as observed in conventional crude oil processing, water droplet-droplet coalescence and droplet-homophase coalescence should be maximised. Thus it is important to understand droplet-droplet and droplet-homophase interactions. In a typical industrial process, much of the droplet-droplet coalescence occurs within the process pipeline leading into the gravity settler. However, there is still great uncertainty regarding droplet-droplet coalescence during separation. Aim of the current study is to understand these coalescence mechanisms in the continuous gravity settler and also, to study the droplet-droplet and droplet-homophase interactions independently in the microfluidic cell.

Laboratory scale vertical gravity settlers (height: 1m, diameter, 0.075m) have been constructed to study the coalescence mechanics during separation. To reduce the number of variables that are to be considered, model emulsions have been developed using mineral oil and de-ionised water, stabilised by Span 80. Also, some experiments have been carried out using asphaltenes instead of SPAN80. For the heavy-oil emulsion investigation, mineral oil is premixed with Halocarbon oil (ρ = 1.95g/cc) to increase the oil density to 0.94g/cc. To allow for measurements under steady state conditions a closed loop set-up has been utilised. The droplet size distribution and the emulsion density are measured along the length of the column at the steady state. From the drop size distribution it is possible to track the changes in size as a function of position. Such information is important when trying to understand coalescence mechanics. Through a combination of both measurements, and measurement of the water retrieval flow rate, a coalescence rate at the emulsion-water interface can be inferred. The experimental program considers both the separation of light-oil and heavy-oil systems as a function of surfactant concentration. At steady state, water outlet in the gravity settler corresponds to droplet-homophase coalescence rate. It is found that, this water outlet decreases with increase in surfactant concentration.

Microfluidic setup is used to generate water droplets in the range 20-100 microns in oil using flow-focusing geometry made up of PDMS using soft lithography. In order to understand how droplets interact with each other, droplets are brought into contact with the range of different velocities and surfactant concentrations (Capillary number). Nature of interaction and interaction time is recorded to get a broad spectrum of data. Such data is relevant in the sedimentation zone of the gravity settler where droplet-droplet interactions are predominant. For droplet-homophase interactions, generated droplets are brought in contact with the pool of water homophase at T-junction and droplets are stacked at particular pressure over the pool of water homophase. Such kind of interactions is observed near the packed bed-homophase interphase in the gravity settler.