Investigation Of A Novel Facility Design Concept For Heavy-Oil North Sea Development
Authors: Cowie David , Schmoll J.K. , Sutton J.E. , Robertson D.S. , Robinson S.A. 
Published: October 2008

The continued cost effective production of offshore heavy oil fields will require novel facility approaches. New technologies identified in this presentation have the potential to offer more efficient oil/water separation at lower processing temperatures. These equipment options can be configured to provide an integrated production facility with weight and space requirements significantly lower than those resulting from traditional designs.

In-1ine measurement techniques were used during an offshore heavy oil trial (droplet size and viscosity) and an earlier onshore light oil trial (droplet size) to quantity the separation performance of the novel separation equipment in black oil systems under process conditions. These techniques have been beneficial to the evaluation of separation performance in traditional gravity separators as well as the novel devices.

INTRODUCTION

The size of gravitational separators on heavy oil/water separation duties is dominated by high residence times for effective crude oil dehydration. Conventionally, these residence times are reduced by the individual or combined application of heat, demulsifier chemicals or electrostatic fields to lower viscosity and/or promote water droplet coalescence.

Trials on a heavy oil, offshore discovery provided opportunities to demonstrate the separation performance and process integration of a number of novel and traditional equipment options which could substantially reduce the weight and footprint area of separators on offshore, heavy oil processing applications.

This heavy oil trial complemented previous field trials at an onshore production site. The equipment options investigated comprise:-Electrodynamic Pulsed Inductive Coalescer (EPIC)Pre-Separation Hydrocyclone (PSH)Rotary Body HydrocycloneGravity Separator

This presentation is principally concerned with the recent offshore trial using live, heavy crude oil. Results from the previous field trial are included to illustrate the development of these equipment options.

During the offshore well test, the devices listed above were assessed using live crude and produced water. These devices were used in combination with, and as alternatives to, traditional gravity separation. The effects of operating temperatures and demulsifier concentrations on separator performance were also evaluated. The results of these comparisons and assessments are presented in this report.

EQUIPMENT DETAILS

EPIC Unit

The EPIC unit functions as a pre-coalescer and works by inducing a charge on the droplets to enhance natural coalescence and promote subsequent separation of the water and oil phases in downstream separation equipment. The main variables in the investigation of the EPIC performance are the delivery voltage and the pulse frequency/duration.

The pulsed induction offers two benefits:-A higher charge delivery rate can be can be maintained. With a steady, non-pulsed delivery, the charge rate will build up slowly after initial surge. Pulsing will maintain this initial, high surge rate and reduce the duration of the slow charge build up.A relaxation period (when the pulse is oft) which will allow the charge to be stripped from the electrode with minimum resistance. This can allow more charge to be removed which will improve subsequent coalescence.