This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 114812, "Effects of HCl Acid and Brines on Water- Swelling Packers," by A.S. Al-Yami, SPE, Saudi Aramco; H.A. Nasr-El-Din, SPE, Texas A&M University; and A.S. Al-Humaidi, SPE, M.K. Al-Arfaj, SPE, S.H. Al-Saleh, SPE, M.Z. Awang, SPE, and K.S. Al-Mohanna, SPE, Saudi Aramco, prepared for the 2009 IADC/ SPE Asia Pacific Drilling Technology Conference and Exhibition, Jakarta, 25-27 August. The paper has not been peer reviewed.
Achieving zonal isolation during well completion is critical to minimize early water production. Currently, cementing is the primary method used in Saudi Arabian fields. In horizontal sections, cementing becomes a challenge and excessive water production can occur through channeling. Another zonal-isolation method uses rubber elastomer bonded onto a base pipe. The rubber swells in water and provides a seal between the base pipe and the open hole.
Swelling packers can be used for multiple-zone openhole completions. These packers will expand when they come in contact with wellbore fluids (either crude oil or water). Swelling packers can be used in horizontal sections where cementing is difficult, in lateral zones having compartmental isolation, and in zones with large permeability variations. There are two types of swellable packers: water-swelling and oil-swelling. Contaminations in wellbore fluids can affect the swelling of the packers. An oil-swelling elastomer will swell faster in light oils compared with heavy oils. In field applications requiring acid stimulation, concentrated HCl will affect the swelled packers, but a weak acid will not.
Swelling of oil packers depends on the thermodynamic absorption process. All liquids have a solubility parameter, which is the energy required to vaporize them. These 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 fold.
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 the result of 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.
Swelling is a thermodynamic absorption process. When thermodynamic properties of the oil and packer become the same, the attraction between their molecules causes the swelling. When the viscosity of the oil increases, the time needed to swell the packer increases. A period of up to 15 days was recorded for a 22-cp viscosity oil to swell a 5.5-in. packer in an 8.5-in. hole. With a temperature as low as 70 to 90°F, the outer layer is not needed (this layer is used to delay the swelling of the packer).