Downhole Oil/Water Separator Development
Authors: Peachey B.R. , Matthews C.M. 
Published: March 2010

A feasibility study and subsequent equipment prototype design work completed by the Centre for Frontier Engineering Research have led to the development of some novel downhole oil/water separator systems for improving the economics and recovery of oil from conventional and heavy oil reservoirs. The basic concepts and driving forces behind the systems that have been developed are based on several ideas and technologies which were brought together with the objective of producing a lower cost alternative for handling production and reinjection of water from maturing, high water oil ratio (WOR) reservoirs. These systems are currently in the prototype development phase in preparation for field testing.

The downhole oil/water separation systems have the potential to achieve large, perhaps order of magnitude, savings in lifting costs through significant reductions in the volume of water that must be produced to surface. In most cases, these cost reductions would be accompanied by increased revenue, through reactivation or increased production from wells that are currently shut-in or constrained by the limits of the current lifting system or surface facilities. Other potential benefits include reduced exposure to environmental liability from high volume water spills or contamination of fresh water aquifers. The main requirement for application of these systems is that a suitable water disposal zone be accessible from the producing wells.

Introduction

Numerous conventional oil wells, especially in North America and Southeast Asia, are becoming less economic due to high lifting costs and reduced recoveries. Much of the cost increase is in managing the ever increasing volumes of water that must be lifted to surface, separated, treated, pipe lined and reinjected back into the formations. Meanwhile ultimate recoveries are being eroded by shutting off production from specific reservoir zones through recompletions to reduce wafer inflow and by the eventual early abandonment of wells which leaves much of the original oil in place. The downhole separation project was initiated to help operators keep wells on production longer, economically producing more oil from existing mature reservoirs.

A review of field production data showed that most rod pumped wells were being shut-in at WOR's of between 10 to 15 m3 of water per m3 of oil, which is reflected in overall field WOR's of 10 or less. Figure 1 shows the production history for the Leduc D-3A pool which is almost exclusively on rod pump and where the oil leg is reduced to the point where conventional water shut-off techniques are relatively ineffective. However, oil reserves in this pool are almost three million m3 of oil per meter of oil zone, so there is a strong incentive to implement a production method that is capable of economically producing the oil leg down to the last few centimetres.

FIGURE 1: Leduc D-3A production. (Available in full paper)

Figure 2 shows the production history for the Redwater D-3A pool where there is less of a discrete oil zone and most wells are produced with electric submersible pumps, which circulate high volumes of water to sweep the dispersed oil to the wellbore.