Lab Investigation of Oil Swelling Elastomers for Smart Well Completions

Abstract

Abstract 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 apply and result in reduced inner casing string diameter. Another method to provide zonal isolation for smart completion tools and to complete them in a 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 in 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. These oils had different viscosities, API gravities, and compositional analyses. Also, the study investigated the effect of different acids and brines on the swelled elastomers. The elastomer bonded in pipes was tested in autoclaves. The pressure drop across the pipe 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 crude oils. In addition, the elastomers swelled rapidly in some oils and slowly in others. The oil swelling elastomers showed great resistance to different acids and brines. 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 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 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