Water Shut-off Treatments-Reduce Water and Accelerate Oil Production
Authors: Thomas F.B. , Bennion D.B. , Anderson G.E. , Meldrum B.T. , Heaven W.J. 
Published: July 2010

Gel treatment applications have been used for production well WOR reduction. There have been a number of cases where conformance was very poor and, by invocation of gel treatment strategies, WOR was significantly reduced. This paper discusses both the characteristics of reservoirs and wells which result in high WOR, as well as characteristics of gel treatments which need to be designed in order to effectively minimize the produced water from a reservoir or an oil field. Examples are provided in this paper whereby, through the use of gel treatments in production wells, WOR and oil production was increased. The paper concludes that there is a significant upside to gel treatments for reservoir optimization and production well revitalization.

Introduction

A serious problem in oil-producing reservoirs is water production. As with most things in nature, fluids also tend to follow paths of least resistance which, in reservoirs, are often created by the heterogeneous nature of the rock. There are two levels to this heterogeneity. The first is microscale heterogeneity which could be represented as a simple porous feature distribution, and the second is macroscale heterogeneity which includes layering, natural or induced fractures, and high vertical and horizontal permeabilities. Both can lead to poor conformance and, therefore, need to be controlled. If conduits for water flow are available then they need to be blocked in order for production wells to continue operation. In terms of water disposal costs, approximately $1 billion is spent in Alberta alone each year.

The macroscale heterogeneities are more commonly understood and more intuitive. It is commonly known that, in some instances where fracturing operations have been misapplied or resulted in unfortunate connections to bottom water sources, the fracture permeability (100 to 1,000 times greater than the permeability of the rest of the rock) has resulted in very quick water breakthrough and very low recovery of the hydrocarbons in the reservoir. A similar response can also be observed where high permeability layers are present in certain porous media. Nevertheless, their effect is that much of the rock remains unswept.

Another form of macroscale heterogeneity, which contributes to very poor conformance is the case where poor cementing operations are present. In such cases, in order to produce anything from the well, near wellbore fluid profile modification must occur. The same applies for injection wells. For microscale conformance difficulties, often simple laboratory tests can identify problems associated with exploitation strategies. For instance, the recovery efficiency associated with a waterflood is often based on analogous reservoirs or past experience. In some cases, subtle changes in the structure of the rock can result in vast changes in the sweep associated with the flow unit even though the porosity remains about the same value. Many examples exist in the literature where permeability and porosity of reservoirs have been sufficiently high to motivate operating companies to full developmental strategies only to find out that, upon implementation, the sweep through the homogeneous flow unit is much less than the average literature numbers would have indicated.