A Log Based Analysis To Estimate Mechanical
Properties And In-situ Stresses In A Shale Gas
Well In North Perth Basin
Author(s)
S. Archer & V. Rasouli
Abstract
In drilling operation the design of a proper mud weight to avoid any instability’s
is important. A low mud weight may cause breakouts around the borehole
whereas a high mud weight can fracture the formation. Mud weight design is
based on two main factors: the mechanical properties of formations being drilled
and the state of in-situ stresses in the field. While drilling in soft formations are
thought to be more prone to drilling related issues than hard formations, there are
several cases where opposite observations have been reported. This is indeed due
to a high stress anisotropy which can apply a large shear stress to the rock to fail
it. As it is seen, in order to define the stable mud weight windows for drilling it is
important to not only have a good understanding about the mechanical properties
of formations but also a good estimation of the state of stresses in the field.
In this study we used a log based methodology to extract rock elastic and
strength properties as well as the magnitude of stresses including vertical and
maximum and minimum horizontal stresses. This is based on the fundamental
relationship between physical properties of rocks as captured in petrophysical
logs (such as sound velocity or density) and mechanical properties, such as
uniaxial compressive strength. Due to rapid increase in developing
unconventional reservoirs, in particular in Australia, in this study we applied the
log based analysis as a case study to a shale gas well drilled in the North Perth
Basin. Continuous logs of elastic and strength properties were extracted using
available correlations and were calibrated at some depths where the triaxial lab
tests results were reported on some core samples. The pore pressure and stress
profiles were estimated using poro-elastic relationships. Pore pressure profile
was calibrated using MDT data, the minimum stress profile was calibrated
against the leak-off test data and maximum stress curve was fixed in a way to
Keywords
mechanical earth model, in situ stresses, mud weight window
Related Book
Other papers in this volume
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