Water Shut-Off in Oil Production Wells - Lessons from 12 Treatments
Authors: Fulleylove R.J. , Morgan J.C. , Stevens D.G. , Thrasher D.R. 
Published: December 2007

Water Shut-Off in Oil Production Wells - Lessons from 12 Treatments.

In the past few years water shut-off treatments in production wells have started to become accepted as part of standard well service work. The benefits from a successful treatment can be large and immediate; often the "pay-back" time for a water shut-off job is just a few months, weeks, or even days. This paper details the lessons learnt from BP's first twelve "modern" production well water shut-off treatments in Alaska and the North Sea, carried out over the last three years.

Three types of treatment will be discussed:–Near well bore, total shut-off of an isolated zone. Here one entire section of well bore is being abandoned in order to allow production from other zones.–Injecting a relative permeability modifier, full well bore, into all perforated zones. In this case it may not be possible to identify the specific water producing zone, or there may be no barriers (such as shales) beyond the near well bore region to provide fluid control (of both the treating fluid and subsequent produced fluids).–Dual injection treatments.

In this final category, a single, discrete, reservoir zone is targeted (for either total shut-off or relative permeability modification), but mechanical well bore control of fluid placement is not available.

Detailed, example, case studies will be presented for each category of treatment, together with a discussion of how to apply the treatments to a range of reservoir conditions.

Introduction

Water Shut-Off (WSO) treatments in production wells are a routine part of standard well service work. We now use cement squeezes or mechanical isolation methods with high success rates for "straightforward" WSO targets. By contrast, the perception of chemical treatments such as polymer gels for WSO has been one of relatively high risk. Therefore we have tended to use gel-based methods as a final option (short of side-tracking the well) for WSO when standard methods are obviously inapplicable or have already been tried without success. These target wells have been complex, and some had mechanical limitations due to long-term shut-in or failed previous WSO attempts using plugs or cement. We have often been exploring new territory, and have had to consider many issues.

Despite this, our experience since we restarted using gels in late 1993 has been very positive. The first six applications were all technical and economic successes. The conclusion so far is that with care a high success rate can be obtained with gel-based WSO, and this approach can often hit the parts other WSO methods cannot reach. As with any developing method, there are some potential problem areas. Some are chemistry-related, some are well-related and some reservoir-related. This paper deals with lessons learnt during design and application, and precautions and short-cuts we have found helpful. The lessons are drawn from 12 treatments, most of which (but not all) are mentioned specifically. These treatments were completed in collaboration with operating groups in BP Exploration and ARCO Alaska, Inc. There is still no comprehensive, how-to-be-safe manual as yet, but this at least brings together a partial check list.

However, this is certainly not a comprehensive check list. In particular, other oil companies and service companies have been enjoying recent success with very different versions of the same gel system, and with different chemistries altogether. Our job designs are conservatively based on systems that we know well enough to control. Other options might well be simpler, cheaper or technically more robust than the ones we have used for some of our targets. As users and adapters, rather than inventors, we will undoubtedly pick up new designs, especially for some of the non-conventional well targets on the horizon.

By discussing all we can think of in the way of job notes and alternative options we are aware that we may make the gel approach look complex and full of potential pit-falls. This comes from dealing with many very different intervention objectives. several chemical systems, and a vast range of well/reservoir conditions. The reality can be quick and easy.

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