Summary
Permeability is one of the most important petrophysical parameters for
reservoir characterization, but also one of the most difficult to obtain. Logs
provide a good estimate of porosity and saturations, but the accuracy on
permeability derived from nuclear magnetic resonance (NMR) is rather poor. So
far, reliable values of permeabilities are obtained only from laboratory
measurements on core samples for local measurements and well testing for a
larger scale-averaged determination.
We present an original method for measuring the permeability of drill
cuttings without any specific laboratory conditioning (cleaning, coating,
etc.). A volume of approximately 100 cm3 of cuttings is placed in a pressure
vessel. The cell is then filled with a viscous oil. The process of oil invasion
into the cuttings always traps a certain amount of gas. When a pulse of
pressure is applied on the cell, the oil enters into the cuttings thanks to the
gas compressibility. The permeability is then derived from the dynamic of the
oil invasion by using a simple model.
The method was tested by using various crushed-rock samples of known
permeability. Excellent reproducibility and good agreement between cores and
cuttings permeabilities were found for many decades of permeabilities. This
method presents many advantages. The measurements can be performed in a few
minutes, leading to the possibility of operating on site during drilling. The
limitations of the method are related mainly to the size, the representativity
of the drill cuttings, and the absence of the confining stress.
In developing this method, our purpose is not to replace core analysis but,
rather, to provide additional quick and inexpensive information on reservoir
characterization.
Introduction
When a new well is drilled, the main concern of operating companies is to
answer quickly two key questions: what are the reserves (porosity, saturation),
and what is the well deliverability (permeability/viscosity ratio)? Most of the
time, the logs provide a good estimate of porosity and saturation along the
well. The viscosity value can be known either from existing
pressure/volume/temperature (PVT) studies or by estimation, but its value is
often considered as uniform within the reservoir, at least in the early stages
of reservoir evaluation. In this paper, we will focus on the evaluation of the
permeability profile, which is much more difficult to obtain because this
parameter refers to a flowing property of the reservoir rock. We present an
original method to perform a direct measurement of permeability from cuttings,
which may be suitable during the drilling operation.
© 2005. Society of Petroleum Engineers
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History
- Original manuscript received:
21 April 2004
- Revised manuscript received:
17 March 2005
- Manuscript approved:
22 March 2005
- Version of record:
15 August 2005
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