Thursday, 27 May
News from Panax Penola Project
It has been over a week since Panax issued a news release on the results of the Salamander-1 drilling. So the following is not exactly news hot off the press. But I suppose late is better than never.
Panax results are important not only for Panax but also as the first HSA result in Australia, for future of Hot Sedimentary Aquifer developments.
The temperature measured at the bottom of the hole is 171.4 oC, which means the prediction by HDRPL was spot on (they apparently had a prediction of 171 oC based on their modelling -- clap your hands loudly for Graeme Beardsmore and the good people of HDRPL).
The above image shows the Panax planning for future development in this project. The production from the two-well project will of course depend on the transmissivity of the medium between the two wells. The same Panax press release also provides transmissivity estimates. These were provided by Down Under Geosolutions (DUGEO) based iin Perth. DUGEO estimates that the transmissivity in the open hole section of Salamander-1 well range from 6.7 Dm to 13.5 Dm.
To put these numbers into perspective, let me provide a bit of background on reservoir transmissivity. Please skip the rest of the blog if you are not interested to learn about different ways to express geothermal reservoir transmissivity.
At least for a first pass analysis, it is common practice, to simulate the fluid flow through a geothermal reservoir as a problem of fluid flow through an idealised porous medium of packed granular material as shown in the following sketch.
This is the so-called Darcy flow problem. Darcy tested (1856) the flow of water through a bed of sandy material and, based on his tests, he developed the following expression for the pressure gradient across a porous plug in a pipe:
The above equation was the original equation reported by Darcy. The effect of viscosity was later incorporated into this equation by other people to obtain the equation which has become the Darcy's Equation:
which is usually expressed as
Here, K is called the permeability for the porous medium. In SI units, it is m2 but it is usually expressed in terms of D or darcy (1 darcy = 9.87 x 10-13 m2).
The viscosity of water is highly dependent on the temperature as shown in the following chart:
Let us take the viscosity of the water at the bottom of the Salamander - 1 hole as roughly 0.2 cP. The cP or centipoise is a unit of viscosity and can be converted to SI units as 1 cP = 0.001 N-s/m2. Substituting this into the above equation and recognising that the flow through the reservoir is Q=uA, where Q is the flow rate and A is the flow area, we get
The first term in brackets on the right represents all the known unknowns about the reservoir: the permeability (K), the flow area(A), and the length of the flow path( &Delta x). This term is sometimes referred to as the K-h factor for the reservoir and its unit in SI units is m3 but it is cooler to refer to it as darcy-meter. One darcy-meter is of course 9.87 x 10-13 m3, following on the definition of darcy given above.
After this background information, we can now comment on the transmissivity values reported by Panax. A range of 6.7 Dm to 13.5 Dm was reported, let us say it is 10 Dm. If we substitute KA/ &dDelta x = 10 x 9.87 x 10-13 in the above equation, and after some manipulation and further unit conversion, we should get
This means that to get 1 liters/s from the production well, we need to have a pressure forcing of 0.02 MPa. This is from the virgin reservoir with no stimulation yet. For stimulated EGS reservoirs, this ratio is known to change between 0.1 and 1 MPa-s/l. For the Cooper Basin hot rock resource, it was reported as 0.71 (Wyborn, 2009 AGEC, Brisbane). We will report on future progress as more reports come out of Panax. Watch this space.
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