Laminated shaly sand

Finely laminated sediments show a particular type of macroscopic anisotropy, which is created by an alternating change of permeability between coarse and fine sand layers or between sand and thin shale layers (laminated shaly sand). 

In case of laminated shaly sands, the differences in lamina properties are extreme. Sand layer permeabilities (100-10,000 md) are high permeable, but shale layers with very low permeabilities (0.001-1 md) act as an impermeable... 

For laminated shaly sand, a dramatic decrease of permeability in the vertical direction can be expected because the flow is COTitroUed by the low shale permeability, whereas in the horizontal direction, the magnitude of permeability is still controlled by the sand fraction for moderate shale content also. This creates permeability anisotropy. 

The laminated shaly sand in a layered model is composed of two components. The properties related to the individual components (layers) are the microscopic permeabilities and the volume fraction Fshaie- Th resulting macroscopic properties are the permeabilities v h-... 

Layered rocks (for example laminated shaly sands with alternating sand and shale layers) are a special case of transversely isotropy. For elastic waves with low frequency, such that the wavelength is much larger than the layer thickness, wave will see the rock as a homogeneous but anisotropic material— therefore, it is called macroscopic anisotropic ." A systematic derivation based on the Lame constants was published by Postma (1955) and Helbig (1958, 1992). The theory and model were extended for any number of components (Backus, 1962 Helbig, 1958). 

Water Bearing Rocks 313 8.6 Laminated Shaly Sands and ... 

Poupon et al. (1954) derived an equation for the laminated shaly sand conductivity using the parallel conductor model ... 

LAMINATED SHALY SANDS AND LAMINATED SANDS—MACROSCOPIC ANISOTROPY... 

Laminated shaly sand One component is a sand fraction and the other component is a shale layer. Anisotropy is created by the resistivity contrast between sand and shale. 

Track 4 compares the saturation-calculation results of a conventional shaly sand analysis using standard induction log data (which is essentially measuring horizontal resistivity) to a 3DEX- (tensor) based laminated shaly sand analysis that incorporates vertical resistivity as well. Water saturation in the pay zone has been reduced to approximately 25%. It means that an additional 40-50 ft. of pay has been identified and quantified by having vertical resistivity from 3DEX and using it in the petrophysical analysis. 

Permeability of shaly sands is controlled by shale/clay content, type of shale distribution (laminated, dispersed, stmctural), porosity, and confining stress. A general impression is given by Fig. 2.18. 

Schon et al. (2005) applied a modular model concept for electrical, hydraulic, and elastic anisotropy studies that allows a joint interpretatiOTi of anisotropic formations. The model crmsideration and analysis of real logging data show that shear wave velocities depend strongly on the shale distribution and that the difference of the velocity of shear waves with different polarization can be related to the shale distributirHi (laminar or dispersed, structural). A shear wave-based method can discriminate between laminated and dispersed shaly zones and provide an estimate of the sand reservoir properties. 

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