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High-Performance Cement Systems consist of cement slurry designs based on engineered particle size distributions that aim to achieve improved mechanical properties and higher chemical resistance compared to traditional cement slurry compositions. The methodology used to obtain High Performance Cement Systems for Oilwells is based on the Compressive Packing Model, where higher content of solids is achieved by using materials having specific particle size distributions. With these higher solids content slurries, a lower proportion of water is required, and thus improved mechanical properties and better chemical resistance can be obtained. The High-Performance Cement Systems, also called High-Packing Cement Systems, in the present work were designed using the Compressive Packing Model, which was developed to design high performance concretes. Various systems for oilwells were designed in this work using Class G Portland Cement, Silica Fume and Hollow Microspheres. The high-performance cement system properties, such as rheological parameters, compressive strength, porosity and acid resistance are shown and compared to traditional cement systems properties. IntroductionThe influence of particle size distribution of solids materials blended with cement on the performance of concrete has been understood by the construction industry since the beginning of last century. There has been an evolution of design protocol since then, evolving from empirical methods to simplified mathematical models to more complex mathematical models in the 1990´s. Many of the models consider the materials as monodispersions or characterize each material by a single diameter (for example, the average diameter) without considering the complete size distribution.There are several models mentioned in the literature, for instance the model of Aim, which was considered as the most suitable for small particles and the model of Toufar, considered as the most appropriate for larger diameter particles [Goltermann, et al., 1997] 1 . Both models consider two classes of aggregates (fine and coarse) consisting of perfect spheres of a uniform diameter. These models optimize the packing of the aggregates only and assume the cement will occupy the voids between the aggregates.Another method described in the literature is called the Rational Method of Lee, which consists of a dynamic method for classification of aggregates, which aims to achieve a maximum density of solids by volume. This model optimizes two classes (in terms of particle size) of aggregates at a time, and considers a typical diameter for each class. If there are more than two classes, the optimization starts with the two classes of larger characteristic diameter. Then, it considers the optimized mix to be a new class of aggregate and proceeds with the optimization with a third class, and so on. The shape, surface charge and compaction of each type of material are considered, and reduced to a single factor called "porosity", which is then used to determine the optimization of aggregate blends. I...

Long‐term wellbore integrity is crucial to prevent leakage of CO2 and to ensure performance and safety of carbon geologic storage. One of the concerns is the degradation of Portland cement due to its exposure to CO2. In this study, Portland cement paste composed of three reinforced‐epoxy resins (talc, agalmatolite, and montmorillonite clay as filler) was compared to unmodified cement paste with respect to CO2 resistance. CO2 degradation experiments were conducted with aqueous CO2 at elevated pressure (50 bar) and temperature (70°C) in order to mimic wellbore conditions. Epoxy cement composites were characterized by phenolphthalein test, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and mechanical compression test. The preparation method of the composites is the parameter likely to affect the CO2 resistance than curing conditions (natural and thermal). Addition of up to 5% of montmorillonite clay reinforced‐epoxy resins provides an improvement in CO2 resistance over unmodified Portland cement paste, showing to be a promising alternative to obtain suitable materials for use in wellbores in CO2 sequestration reservoirs. POLYM. COMPOS., 39:E2234–E2244, 2018. © 2017 Society of Plastics Engineers

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Lost circulation is still today one of the most costly problems for oil and gas operators. It may occur into permeable formations, depleted zones, induced or nature fractures and cavernous formations while drilling, cementing or during workover jobs in the well. This paper focus on the evaluation of bridging and reactive systems in remediating severe losses based on their performance in a dedicated experimental facility. Laboratory apparatus commonly used to evaluate lost circulation materials generally consist in modified API-fluid loss devices using slotted metal discs, ceramic discs or natural cores. These devices are suitable to simulate permeable formations or depleted zones, but they do not simulate severe lost circulation scenarios that occur in induced or nature fractures and in cavernous formations. For that reason, a specific laboratory apparatus was built, where the performance of several materials was evaluated and classified according to different severity levels. This paper summarizes the efficiency of available commercial bridging (granular, fibers and flakes) and reactive systems in remediating severe losses according to different severity levels imposed in the developed severe lost circulation apparatus. Besides commercial products alredy used to control losses, hydrated bentonite pellets have been evaluated as bridging material.