Nano-emulsions as Cement Spacer Improve the Cleaning of Casing Bore During Cementing Operations

Abstract

Nano-emulsions are emulsions where the droplet size of internal phase is less than 500 nm. Due to their small dimensions they have a high surface area and show very peculiar properties. Solvent in water nano-emulsions combine the high efficiency of the small dimensions of solvent to a low interfacial tension, due to the presence of the surfactant mixture used to prepare nanoemulsions. Solvent in water nano-emulsions used as cement spacer formulation could allow optimizing the cleaning of the casing during the cement job with a high improvement of the performances of the spacers currently in use. This methodology, based on high efficiency system with reduced chemical dosage, could also result in a considerable optimization of product cost of cement operation. The objective of this study has been the formulation of direct nano-emulsions (o/w), with a selected solvent as internal phase, in order to improve the casing -open hole cleaning and reverse the surfaces wettabitlity to allow better adhesion of slurry between casing and hole. Specific laboratory tests have been carried out to compare commercial spacers currently used in common drilling practice with nano-emulsions formulated in Eni Laboratories. Different nano-emulsions were performed in function of solvent content. The nano-emulsion efficiency was evaluated throughout different methods: Metallic Grid Test, Wettability Test, Contact Angle, Shear bond test. All tests highlight good cleaning properties of nano-emulsions and their better efficiency compared with common spacers. IntroductionCementing operations play a critical role in the drilling process of a well and mud displacement is very important for achieving a good cement bond to maintain well integrity and subsequent production performances. Pill used to separate the cement slurry from the drilling mud are termed "SPACERS". Spacers are designed in a manner such that their densities, gel strengths and viscosity are more than that of the drilling fluid and less than that of the cement slurry. In cement job the corrected application of the hierarchies of density and rheologies during the OBM displacement is necessary, but it isn't sufficient to guarantee a good cleaning of the casing-bore and reverse wettability; these properties are necessary to obtain good adhesion of slurry to casing/formation. So to avoid cement job failure a proper spacer with high cleaning properties has to be designed. Several types of spacers have been used with different degrees of success. Solvent spacers have been considered (Morris et al., 1973) and nowadays innovative spacers have been developed looking for more effective formulations (Schumacher et al., 1996;Zanten et al., 2010). In this context nano-emulsion technology could be an innovative approach in spacer preparation and could improve their cleaning performance. The object of this study was to estimate the effectiveness of solvent nano-emulsion dispersion, in OBM removal, and evaluate the oil/water (o/w) wettability of the casing-bore. Proper cleaning eliminates the oil...

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