Fractures shales

Coral reef. Dolomite. Fractured shales. Lost Circulation. Withdraw tooU slowly to prevent swabbing action. 

As much as two-thirds of conventional crude oil discovered in U.S. fields remain unproduced, left behind because of the physics of fluid flow. In addition, hydrocarbons in unconventional rocks or that have unconventional characteristics (such as oil in fractured shales, kerogen in oil shale or bitumen in tar sands) constitute an enormous potential domestic supply of energy. 

An SVE pilot test was conducted at a service station site that had experienced a release of gasoline. Some LNAPL had been removed, but high concentrations of vapor persisted across the site. The site was underlain by silty clay, which overlies weathered and highly fractured shale at a depth of approximately 7 ft. The water table occurs within the upper portion of the shale at a depth of approximately 11 ft. 

FIGURE 1.3 (See color insert) Pictorial example of bedrock core obtained near the experimental site showing the interbedded fractured shale (black) and limestone (white/gray) that dominates the saturated zone. 

Jardine, P.M. et al., Quantifying diffusive mass transfer in fractured shale bedrock, Water Resour. Res., 35, 2015, 1999. 

McKay, L.D., Sanford, W.E., and Strong, J.M., Field scale migration of colloidal tracers in a fractured shale saprolite, Ground Water, 38, 139, 2000. 

McCarthy, J.F., McKay, L.D., and Bruner, D.D., Influence of ionic strength and cation charge on transport of colloidal particles in fractured shale saprolite, Environ. Sci. Technol., 36, 3735, 2002. 

Price, L. C. LeFever, J. A. 1992. Does Bakken horizontal drilling imply a huge oil-resource base in fractured shales In Schmoker, J. W., Coalson, E. B. Brown, C. A. (eds) Geological studies relevant to horizontal drilling examples from western North America. Rocky Mountain Association of Geologists, Denver, Colorado. 

Damage mechanics principles have been applied extensively for well stability problems, especially for hard, brittle and fractured shale rocks. Constitutive models using damage concept, coupled with hydro-chemical swelling models, have been developed based on experimental results, and applied for design of drilling fluid density, combined with FEM methods (Liu, 1995). 

Borehole instability arises mainly in geochemi-cally sensitive smectitic (S) shales, usually of higher porosity (>10%), and in low-porosity (<10%), highly fractured, quartz-illite (Q/I) shale. These rocks are encountered in most deep drilling operations in both tectonic and non-tectonic situations. The origin of the fractured shales is of geological and practical interest. 

Not only are stresses altered, but fabric is also massively and irreversibly changed. The blocky nature of the fractured shale creates a scale issue larger diameter boreholes are more likely to experience sloughing of the shale chunks (Fig 3). 

The conservative strategy is to place an intermediate casing string seated at the boundary between ductile and fractured shales, having drilled the ductile shale with oil-based drilling fluid, then converting to a water-based fluid to drill out of the... 

Heat flow is purely by conduction in all but intensely fractured shales, therefore a pure thermal problem can usually be treated as uncoupled. However, a change in temperature directly affects all other transport properties. Increased temperature reduces water viscosity (Darcian), increases Browian motion (Fickian), increases stresses (microfissuring with k increases), reduces water layers (increased kinetic energy), and accelerates all chemical reaction processes. 

OBM alone is ineffective in coping with fractured shales because the fracture aperture is sufficient to allow the oil to penetrate the wall, equilibrating the pressures and destroying the support effect. 

So far we have performed detailed studies for flow over isolated bodies, for example, curved fractures, shale arrays, and fractured boreholes. Here we will focus on steady and transient-compressible reservoir-scale flows produced by multilateral well systems. Because their topologies are not simple, we turn to computational methods. We will highlight problems that arise in reservoir simulator development, and importantly, we will describe a recently developed, three-dimensional algorithm that is very robust, numerically stable, exceptionally fast, and extremely accurate, and now available to the user community. Engineering implementation is an objective of the work oil companies want practical solutions that optimize operations, profits, and time value of money. The model provides tools that evaluate what if production scenarios, infill drilling strategies, and waterflood sweep efficiencies. In addition to being accurate, the solutions require minimal hardware, software, and costly human resources. 

Laboratory scale experiments performed under well-controlled conditions represent a complementary approach towards the characterization of the chemical containment of radionuclides in the undisturbed and fractured shales. Sorption isotherms of Cs for the shale matrix and for calcite are provided in Fig. 6. Batch experiments were carried out in gloveboxes under N2 atmosphere and with synthetic fracture water which approximate in situ and far-field conditions. The liquid/solid ratio was 5mlg . The results show the weaker retention of Cs by calcite fillings than by the shale matrix. Interstrati-fied I/S have strong affinities for many radionuclides (Milton Brown 1986), whereas calcite is known to have small laboratory values for... 

Mazurek, M., Alexander, W. R. Mackenzie, A. B. 1996. Contaminant retardation in fractured shales matrix diffusion and redox front entrapment, Journal of Contaminant Hydrology, 21, 71-84. 

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