Downhole Gas/Water Separation: Engineering Assessment and Field Experience
Authors: Nichol J.R. , Marsh Jack 
Published: December 2007

Water production can curtail both the economic life and ultimate reserves recovery of a gas well. During the course of a Joint Industry Project (JIP) to study the technical and economic merits of downhole gas/water separation with water re-injection, several commercially available systems were found to be potentially viable. One of the JIP participants installed such a system, which resulted in improved gas production rates.

This paper outlines the various options available to gas well operators to manage water influx. The case history of a well with a downhole gas/water separation system is presented. The change in production rates is shown, along with the match achieved with nodal analysis. Areas requiring further investigation to advance the application of this technology are also summarized.

Introduction

Water production in operating gas wells may result in increased operating costs and reduced reserves recovery. Exploration or development gas wells which demonstrate water influx may never be tied-in. One study of a large sample of gas wells revealed that original reserves figures had to be reduced by 20% for water problems alone. The most common options available to operators in this case are:Shut-in the well.Attempt to shut off the water within the reservoir.Produce liquid to surface.Separate liquid and dispose downhole

A joint industry project has recently completed an engineering assessment of the situation with the intent of identifying cost-effective systems to separate water and gas downhole and dispose of the water within the same wellbore. Commercially available systems, which rely upon gravity separation. are generally applied to wells with relatively low gas flow rates.

Olympia Energy Inc. of Calgary, a participant in the JIP installed a commercially available downhole gas/water separation system. This provided an opportunity to examine the behaviour of wells flowing at rates higher than previously reported for this type of equipment. In addition, some new operating procedures were developed.

Subsequent modelling work was able to match the operating conditions as well as present some insights into the behaviour of this configuration. Details of the downhole separation and injection scheme are described along with some of the results of the performance model. Improvement of downhole separation efficiency is shown to be a requirement to extend the applicability of these systems.

Commercially available systems. Several commercially available configurations or devices have been reported to be suitable for re-injecting water into a lower disposal zone within a gas producing well:A conventional insert pump with a "bypass" sub.A specially designed insert pump which displaces on the downstroke.Progressing cavity pump.Electrical submersible pump.

Olympia Energy Inc. selected the "bypass" sub configuration for installation, based upon their internal evaluation of the candidate well.

Well Description

The well, Olympia et al Bittern 10–24–046–22W4, is completed in a sandstone formation (see Table 1). It is located in central Alberta, Canada. The well had produced relatively water-free for about the first 18 months after initial completion. With the onset of water influx, gas production rates began to decrease (Figure 1). While the cause of the produced water is difficult to determine because of the formation's complex fluvial environment, the presence of water influx is clearly apparent from material balance analysis (Figure 2). P. 795^