Lab Investigation of Oil Swelling Elastomers for Smart Well Completions
Authors: Al-Yami Abdullah Saleh , Nasr-El-Din Hisham A. , Al-Saleh Salah , Al-Humaidi Ahmed S. , Al-Arfaj Mohammed Khalid 
Published: October 2008

Achieving successful zonal isolation is critical to install smart completion tools. Currently, cementing and mechanical packers are the only conventional methods used in Saudi fields to provide zonal isolation. However, these techniques are difficult to operate and result in reduced inner casing string diameter. Another method to provide zonal isolation for smart completion tools and to complete them in single stage is to use a rubber elastomer bonded onto a base pipe. The rubber swells in oil 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 by Saudi Aramco facilities in an attempt to improve zonal isolation for smart completions.

In this study, we present lab evaluation of elastomers at 190°F using six different oil samples. The evaluation involved studying the effect of oil viscosity and API gravity. Also, the study investigated the effect of acids on the swelled elastomers. To the best of the authors' knowledge no previous work was done to investigate 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 effects of other factors were investigated using elastomer samples and fluid characterization. The oil swelling elastomers withstood pressure up to 5,000 psi at 190°F after placing the elastomers in some crude oils. In addition, the elastomers swelled rapidly in some oils and slowly in others.

Introduction

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

Swelling packers can be used for any of the following reasons:1 Horizontal sections where cementing is difficult, lateral zones with compartmental isolation, and large permeability variation zones. 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. Common acid used in carbonate formations is HCl at various concentrations. Higher concentrations of HCl acid will affect the swelled packers, but not the weak ones.1

The swelling packers depend on thermodynamic absorption process. All liquids have solubility parameter which is the energy required to vaporize them. The packers have two components which are polymers and flexible materials. When the polymer is immersed into a liquid with similar solubility parameter, a strong affinity between the polymer and liquid will result. These affinities will cause swelling of the polymer and as a result the flexible material will expand. The result of this is that the packer will swell in some cases to several 100% by volume. The swelling will continue until equilibrium is reached. The time to reach equilibrium will be reduced with increase in temperature. When swelling reaches equilibrium, the mechanical properties and volume remain constant. If further expansion after equilibrium is reached it will be due to thermal chain degradation in 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