Polymer Powder/Cement Composites for Oil and Gas Wells

Abstract

Abstract The selection of an optimal cementitious material is critical to maintain zonal isolation for the lifetime of oil and gas wells not only for primary cementing but also for well abandonment. Polymer powder/cement composites present good mechanical and durability properties since polymer latex promotes improved adhesion and flexibility to the hardened cement paste. So, for oilwell applications, which require high durability under aggressive environment, polymer powder/cement composites would be good candidates. During the well completion phase, the slurry placement strongly depends on its rheological behaviour that is studied here for polymer powder/cement composite suspensions: they present a shear-thinning behaviour in permanent shear and a transition from a gel to a liquid behaviour in oscillatory shear. The replacement of cement particles by polymer particles induces a decrease of the viscosity in the liquid state and of the storage modulus in the gel state. The good quality of the polymer particle dispersion and their high affinity for cement particles were observed by SEM and cryo-SEM. Solid state NMR (29 Si and 27Al) and DSC help to understand the influence of the polymer addition on the hydration/hardening. Depending on the temperature and on polymer chemistry, it may strongly influence the hydration reactions of the materials and their kinetics. All these results help us to understand the relations between the slurry composition, its rheological behaviour and the properties of the hardened materials. Introduction Cementitious materials used in oilwell industry have to permanently isolate the subsurface formations penetrated by the well or to durably fill up the wells when they are abandoned. Therefore they have to present good mechanical and durability properties. Polymer powder/cement composites are known to have higher flexural strength, deformability, adhesion, waterproofness and durability than standard cementitious materials [1]. For this reason, polymer-modified cements are used in the construction industry as, for example, repairing materials, anticorrosive coatings or tile adhesives. Besides, adding polymer is a way to lighten slurries without degrading their mechanical and durability properties [2]. All these reasons make polymer powder/cement composites potentially interesting materials for oilwell cementing. Many studies of the mechanical or durability properties of those composite materials can be found in the literature [3–11]. However, only a few authors [12–14] have studied the rheology of the composite pastes. Such studies are necessary for the oilwell applications since the slurries are injected in the wells by pumping. So the first matter of this work is to understand their rheological behaviour. Moreover, for the application, the setting time has to be very well-known and controlled. Some authors showed that adding latex or redispersible powder delays the hydration reactions [14–16]. We therefore performed calorimetry on the composite pastes. Besides, it has been described that adding polymer modifies the cementitious matrix: there seems to be a diminution of the amount of portlandite [16–17] and ettringite [18] due to the presence of the polymer. So we characterized the C-S-H by 29Si NMR and the aluminate hydrates by 27 Al NMR. As an example of application, we also studied the effect of polymer powder incorporation in low permeability formulation adapted to well completion.