In any sequence of new developments, particularly when they work well, the ideas brain usually leaps ahead, "How can we maximize the use of this bit", etc. Despite the technical hitches, the principles of Cooper Basin project have really worked as a textbook model. It is magnificent. We need to be careful that a new idea is not interpreted negatively. As each segment is understood it is tested with the intent of exploiting it to the full. This in fact increases the value of the project.
Some past examples of valuable systematic development:
1. Can we build an underground reservoir with one well? Is it possible to determine the size and shape of this thing?
Yes, with the fraccing process and suitable placement of geophones a 3D picture of the stimulated fracture was obtained. The elliptical pancake shape was so clear that the data was collated as a movie and sent as a DVD to all shareholders. It enables rather precise estimation of the volume of the reservoir surrounding a well.
2. Can we get a connection (pressure correlation) between two wells 500m apart?
A stepped pressure sequence was tested between Hab 1 and Hab 2 about three years ago resulting in some delightful graphs being printed in the Q reports. There were no ambiguities just as might be predicted. The pressure changes were clearly transferred with the anticipated build ups, time delays, etc.
3. Can we get a fluid flow between these two wells?
The open loop flow test in March this year demonstrated conclusively that adequate mass flows could be obtained.
4. Can we control the flow between these wells?
Since stimulation can be repeated at varying pressures the fracture gap is a controllable parameter. Fluid flows thus can be adjusted. This can be done at any time during the life of the system.
5. Can we optimize the underground interface heat transfer for energy extraction purposes (as distinct from just bulk flow)?
This is a function of the contact area, nature of surface, flow rate, temperature difference, viscosity of fluid, etc. Some of these parameters are interconnected but choosing judiciously can improve heat transfer. There is considerable scope for further engineering innovation here.
6. Can we produce multiple paths for fluid flow? (This is where we are at now.)
In any heat exchanger the fluid normally branches to finer capillaries for maximizing the surface contact of the working fluid. Where these are the same diameter the collected fluid will have equal temperatures at the aggregation points.
In the Jol 1 experimental extension to 4911 m over 120 drilling breaks occurred in 1100 m. A significant number of these are potentially natural fractures that, with some differential stimulation, could produce a flow. Since scores of wells will be drilled GDY is looking for a practical control methodology that can rapidly isolate specific sections, to stimulate such zones, and thereafter to keep the fracture gap at predetermined values. A think tank with wide expertise is investigating this. Many standard techniques available from the oil industry can be used (eg placement of presized ceramic propants for equal gap spacing.)
7. Can we reduce costs by drilling fewer wells for the same output? i.e. fewer per square km.
Yes. Hab 1, 2, and 3 are separated by 500m based largely on the early precedent set at Soultz. The 50 MW array will be targeted at a 1000m spacing. (The savings were discussed in a post here several weeks ago.) This decision is possible knowing that artificial stimulation works so well in this geological structure. However for the same power output at the greater inter well distance the flows would have to increase. For that reason (among others) the wellbore had to increase to 8.5 ins dia.
8. Can flows through a one sheet fracture provide sufficient energy?
Possibly. The projected 50MW from a 9 hole unit array implies a 10 MWe/ well requirement. An experimental peak production of 40 kg/sec occurred briefly and continuous flows of 20 kg/sec were maintained at 27MPa through a 14 mm choke. While flows could be doubled with further stimulation it is the rate of interface heat transfer that is the critical issue and this is yet to be tested and optimized.
9. If this were so, why have multiple fractures?
Consider again, if the flows through each fracture layer can be kept the same as above, then adding (or stacking) stimulated fractures multiplies the energy flow without adding extra wells (and their cost). All that is required is a slightly deeper well, perhaps an extra 300 m. If (say) 5 such fractures can be utilized simultaneously it might save drilling 8 extra wells (4 pairs). It is such induced fractures and numbers that have to be investigated for optimum effect. (Referred to as technology acquisition.)
Multiple fracture stimulation may therefore not be an absolute requirement for geothermal energy to be successful but is highly desirable for the next phase of increase in efficiency and reduced cost. Note that the word ’model’ may be variously used for the idealised construct for segments of the project or for the whole.
10. No doubt further new ideas will be considered and tested. They are not necessarily restrictions but enhancements. That is the very reason why we had an innovations thread here a few weeks ago.
Keep thinking and questioning.
Juke
RNE Price at posting:
86.0¢ Sentiment: Buy Disclosure: Held
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