Utmost deposited in a very low- energy environments”

Utmost shaly sand calculation
approaches involve the awareness of the volume of shales and the way they
impact several measurements.  Pettijohn
(1975) gave a definition that “shales are mixture of clays minerals and other
fine-grained particles deposited in a very low- energy environments”

The shaly-sand evaluation remains a challenging task, and due to
this, there has been over thirty models developed to interpret Shaly-sand
reservoirs in more than fifty years (Adeoti et
al, 2014).

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The challenges confronting shaly-sand interpretation do come up each
and every time there is an high content of clay minerals present in a Shaly-sand
formation. The clay minerals add to the rise in the general conductivity.  When in much quantity, the conductivity turns
out to be as vital as the conductivity of the formation water (Kurniawan,
2002). Shaliness do affect the formation features and the logging tool
response.

 

Apart from the effects
of shaliness on permeability and porosity, the electrical properties of
reservoir rocks, subsequently their saturation are impacted negatively by the presence
of shale. The way shaliness impact log responses is subject to the amount of
shale, the shale physical properties, and how the distribution is in the host
layer. Shale materials are distributed in the host layer in three ways (laminar,
structural, and dispersed). These may happen concurrently within same
formation. Nevertheless, when shale appear more
in a single form or predominanlty in a reservoir, a more simplified models will
give realistic porosity and water saturation( Schlumberger, 1967; Clavier et
al, 1977; Hilchie, 1982, Worthington, 1985, Oil field review, 1989, Saner et
al, 1994 Hamada, 1999,)

The existence of shale in reservoirs do leads to inaccurate
values of porosity and water saturation when computed from well-logs. Consequent
the porosity value from log is calculated from Total porosity which consist two
parameters (shale porosity with shale volume and effective porosity). So, to compute
the effective porosity of a shaly sand reservoir, the volume and porosity of shale
need to be well-defined properly (Hamada, 1999). There is always inaccuracy in measurement
or estimation of volume when electrical resistivity logs are used to estimate the
volume of  conductive and non-conductive elements
existing in pore space of sediments due to the presence of clays  in the reservoir (Lee and Collett, 2006).

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