Abstract

Achieving successful zonal isolation during well completion is critical to minimize early water production. Currently, cementing is the only method used in Saudi fields to provide zonal isolation. However, in horizontal sections, cementing becomes a challenge and water flows can occur due to channeling. Another method for zonal isolation is to use a rubber elastomer bonded onto a base pipe. The rubber swells in water and provides a seal between the base pipe and the open hole.

This paper will outline the step-by-step qualification testing that was carried out in Saudi Aramco facilities in an attempt to improve zonal isolation in horizontal and multilaterals wells.

In this study, we present lab evaluation of elastomers at 190ºF using brines of different ionic strengths and pH values. The evaluation involved examining the effect of salinity and pH on the rate of swelling of elastomers. Also, the study investigated the effect of 15 wt% HCl acid on the swelled elastomers. To the best of the authors' knowledge, no previous work was done to examine the impact of these factors on the swelling mechanisms.

The elastomer bonded in pipes was tested in autoclaves. The pressure drop across the pipes was measured as a function of time. The influences of fluid density and viscosity were also investigated using elastomer samples. Swelling was related to volume of the samples and fluid characterstics.

Water swelling elastomers withstand pressures up to 5,000 psi at 190ºF after placing the elastomers in salinities up to 200,000 mg/l. However, the swelled elastomers shrink in 15 wt% HCl. This paper discusses the advantages and limitations of swelling elastomers and gives recommendations for successful field applications.

Introduction

Swelling packers can be used for multiple-zone open-hole completions. These packers will swell when they come in contact with wellbore fluids (either crude oil or water). Open-hole completions become attractive because they require fewer trips and no cementing near-wellbore which can cause formation damage.

Swelling packers can be used for any of the following reasons:1 Horizontal sections where cementing is difficult, lateral zones with compartmental isolation, and zones with large permeability variations. There are no operational difficulties in running the swelling packers. There are two types of packers; water-swelling and oil-swelling. Contaminations in the wellbore fluids can affect the swelling of the packers. Oil swelling elastomer will swell faster in lighter oils compared to heavier ones. In field applications where acid stimulation is required, the swelling packers will be exposed to acids. Hydrochloric acid is commonly used to matrix acid carbonate formations. Concentrated HCl acids will affect the swelled packers, but not the weak ones.1

Swelling of oil packers depend on thermodynamic absorption process. All liquids have a solubility parameter, which is the energy required to vaporize them. The packers have two components; a polymer and a flexible material. When the polymer is immersed into a liquid with a similar solubility parameter, a strong affinity between the polymer and liquid will cause swelling of the polymer and, as a result, the flexible material will expand and the volume of the packer will increase by several folds. 2

Swelling will continue until equilibrium is reached. The time to reach equilibrium will be reduced at higher temperatures. When swelling reaches equilibrium, the mechanical properties and volume of the packer remain constant. If further expansion is reached, it will be due to thermal chain degradation of the polymer. When expansion is limited by the wall of the hole, the packer will not reach equilibrium and will continue to swell until it does.2

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