Wednesday, 6 October
Optimistic about Salamander-1 Well
Earlier this year, Panax had reported problems in achieving the estimated permeability
in its Salamander-1 tests. A study conducted by Down Under Geosolutions (DUGEO)
estimated the transmissivity in the open hole section of Salamander-1 well to
range from 6.7 Dm to 13.5 Dm. The Panax production tests failed to achieve these
numbers.
Subsequently, Panax commissioned SKM-New Zealand to conduct a Well Productivity
Index (PI) testing program on Salamander-1. Five production/discharge tests
and one injection tests were carried out by Panax under the supervision of SKM
engineers. All pressure, temperature and flow data (the latter is also known
as spinner data and are collectively known as “PTS” data) collected during the
tests, were analysed by SKM. The results, as announced by Panax in a ASX press
release yesterday, turned out to be similar to earlier Panax measurements. In
other words, the SKM-measured well transmissivity was also significantly below
the estimated 6.7 - 13 D-m range. However, the SKM advised Panax that the test
results may be reflecting the status of the well itself, rather than the quality
of the intersected target reservoir rocks. The significance of this point is
that, by adopting appropriate well completion techniques/methods, the Salamander-1
well has the potential to be developed into a production well.
Panax suggests that the problems encountered in the Salamander-1 well are not
dissimilar to the problems experienced by the coal bed methane (“CBM”) industry
in the 1980s and 1990s. Many of the original pioneers in this field used standard
petroleum drilling methods, but did not succeed in producing economic flows.
These “well completion problems” have since been resolved by adopting new well
completion techniques. Panax is now planning to tap into this experience to
develop a suitable well completion program for Salamander 1.
The rest of this blog is part of the educational mission of this blog, where
we will try to unpack some of the technical concepts in the above paragraphs.
What is a "good" permeability?
The key parameters of a geothermal reservoir are illustrated in the following
figure.
I copied this figure (and most of the following analysis) from a paper by Hugh
Murphy, Don Brown et al in Geothermics 28 (1999) 491-506. The paper is
on EGS but the figure applies to both HSA and EGS. One operational parameter
of great interest is the flow impedance, Z, defined as the difference between
the injection and production wellhead pressures, divided by the produced flow
rate. It is required that Z < 1 MPa s/l if the power required to pump water
through the reservoir is not to exceed a substantial fraction of the power produced
by the reservoir. The Murphy paper quotes an earlier estimate by Parker that,
if economic development of a commercial reservoir is the target, Z would have
to be 0.1 MPa s/l or less. In
an earlier blog (27 May 2010), I converted the Panax estimate of 6.7 Dm
to the metric impedance units. A transmissivity of 6.7 Dm corresponds to about
0.03 MPa-s/l, which three times better than this economic threshold specified
by Parker, and the higher end of the DUGEO estimate, 13.5 Dm, correspond to
0.015 MPa-s/l, which is six times better than the Parker limit.
Panax of course has only one well at this stage and the production tests supervised
by SKM would reflect the values around the well.
Instrumentation?
Panax reports that pressure, temperature and the flow rate were logged during
the tests. The following downhole tool might have been used in these tests.
This is a Schlumberger downhole tool that contains pressure, temperature and
flow sensors and, according to Schlumberger, was used in geothermal wells with
bottom hole temperatures as high as 650 oF or 343 oC.
The flow rate was measured by using a spinner. This is an impeller-type
flow meter as shown above on the right (copied from a Schlumberger presentation
to the USGS Geothermal Conference ):
Click here for the rest of the blog