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The north fringe of heavy crude represents the main source of Cuban hydrocarbons. Gas and oil seals of Cuban Northern Province are represented by a series of orogenic formations consisting mainly of terrigenous rocks with clay components. For seal quality evaluation of these formations, petrography and mineralogical characterization are essential. The primary sealing elements of Cuban northern province are clays, which are defined as the fundamental object of this research. They are distinguished by having a lower crystallinity than carbonates, effect that is caused by crystal imperfections: crystallite size, structural disorder and stress, while carbonates have a chemical composition that includes a smaller number of chemicals that showing clays. For this characterisation it was applied the infrared spectroscopy and x ray diffraction techniques. For this purpose samples were taken from clays and carbonate rocks of drill cores and geological outcrops. The application of these techniques allowed the determination of the composition of the rocks, characterized by the complex mixture of: illite, smectite, chlorite and hydromica (hydromuscovite) accompanied by their respective interlayereds. [ABSTRACT FROM AUTHOR]

The oil reservoirs in the Northern Heavy Oil Province of Cuba are characterized by the presence of unstable clay formations when they come in contact with water based drilling fluids. Such a phenomenon leads to undesirable events that hinder the advance of the drilling process. The clay mineral hydration constitutes the main cause which determines the increase of its original volume and its dispersion in the drilling fluid. The selection of a fluid which minimize such conditions represent a challenge for science and technology. This paper shows the results achieved in studies performed in order to select a suitable fluid formulation, using sodium silicate as an additive. Other conventional additives and formulations were tested with montmorillonitic clay samples and other clays characteristic of Vega Alta geological formation that constitutes the reservoirs seal of the northern gas - oil province of Cuba. The results obtained from swelling and dispersion test, rheological analysis and fluid composition allowed the selection of a suitable fluid formulation for a successful well drilling in a located in an area with unstable clay formations. [ABSTRACT FROM AUTHOR]