Reactive elastomeric composites: When rubber meets cement Agathe Robisson a,⇑ , Sudeep Maheshwari b , Simone Musso a , Jeffrey J. Thomas a , Francois M. Auzerais a , Dingzhi Han a , Meng Qu a , Franz-Josef Ulm c a Schlumberger-Doll Research, 1 Hampshire St., Cambridge, MA 02139, United States b A.T. Kearney, 7 Times Square #36 New York, NY 10036, United States c Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, United States article info Article history: Received 27 June 2012 Received in revised form 30 October 2012 Accepted 21 November 2012 Available online 5 December 2012 Keywords: A. Particle-reinforced composites A. Oxides B. Mechanical properties C. Elastic properties D. Dynamic mechanical thermal analysis (DMTA) abstract This paper describes a novel reactive composite material comprised of hydrogenated nitrile butadiene rubber (HNBR) compounded with slag cement. The composite initially looks and behaves like rubber, but when exposed to water it simultaneously swells and stiffens due to hydration of the cement compo- nent. The material eventually reaches a stiffness that is intermediate between that of HNBR and hydrated cement, while maintaining a relatively large ductility that is more characteristic of rubber. This behavior, which is ideal for sealing applications, differentiates this material from conventional swellable materials that become less stiff upon swelling. The development of this new type of material was motivated by the requirements of oilfield zonal isolation, where alternatives to cement are needed for some challenging sealing applications. A mechanism for the swelling and stiffening of the reactive composite is proposed: water diffuses into the HNBR matrix and is converted to bound water through hydration reactions with the cement, causing the effective solid filler content of the composite to increase. A model is proposed that treats the composite as a cellular solid with a continuous filler phase (hydrated cement). This model is able to reproduce the observed increase in the elastic modulus with time during exposure to water. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Zonal isolation, defined as sealing of the wellbore against un- wanted movement of fluids, is a significant challenge for safely extracting oil and gas from offshore and deepwater reservoirs, and has become one of the most important environmental con- cerns for the oilfield industry [4]. In the worst-case scenario, oil or gas moves vertically upward from the reservoir along the bore- hole and escapes into the surrounding land or seabed. In particular, zonal isolation is a significant challenge for producing shale gas reservoirs due to the stresses generated in the wellbore by hydrau- lic fracturing, which can damage the isolation material. The standard approach to zonal isolation is to pump cement slurry into the annular space between the formation and produc- tion casing and allow it to harden in place. Ensuring long-term zo- nal isolation requires a durable material with low permeability and reasonably high compressive strength that completely fills the annular space. Another approach to sealing, widely used in the automotive and aerospace industries and increasingly used in the oilfield, is to utilize gaskets, O-rings and packers made of elasto- mers. For these applications, the seal provides a localized block against fluid flow. The maximum differential pressure that the seal can sustain is primarily determined by the contact stress between the seal and its confinement, and by the modulus of the seal mate- rial [13]. In some cases, the seal relies on its swelling [7,2,3,12]. The ability to seal is crucial to the functioning of diverse components (from a refrigerator or a car to a space shuttle) and sealing failures are responsible for a significant fraction of mechanical break- downs, leading sometimes to catastrophic results [17]. While pre- dicting seal performance and potential failure are complex tasks [1], improvements in elastomer sealing performance can be achieved, in some conditions, through modulus and strength opti- mization during service life, i.e., in situ. This was the motivation for the development of the material discussed here. Swellable elastomer seals are increasingly used to replace ce- ment as elements of zonal isolation under challenging oilwell pro- duction conditions. For example, standard oilwell cement provides inconsistent sealing results behind a production casing that is sub- jected to repeated temperature and pressure cycling. Poor sealing is often related to the tendency for the cement to debond from the casing or rock formation. As a result, over the past decade, there has been growing interest in the use of swellable elastomer seals for downhole applications such as openhole completions, in- stead of cement. With these seals, no mechanical compression is needed. Instead, a state of compression is developed through the 0266-3538/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compscitech.2012.11.012 ⇑ Corresponding author. Tel.: +1 (617) 335 6476; fax: +1 (617) 335 2384. E-mail address: agathe.robisson@gmail.com (A. Robisson). Composites Science and Technology 75 (2013) 77–83 Contents lists available at SciVerse ScienceDirect Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech