Normally we only hear of announcements of procedures started or finished. This time (Monday 10 Dec12 ann) it is very refreshing to get the real data that is still open to interpretation. What would you observe and then deduce from this micro-seismic diagram? It is worth poring over. We can but try.
Prelim technical note:
The nature of the stimulation is such that water penetrates the pre-existing micro-fractures under high pressure, prises them apart (by Pascal’s Principle) yielding lots of micro-seismic pings, whereupon a slight lateral shift (horizontal) of the rock layers across one another is likely, so that even after the relaxation of pressure the rock granules cannot precisely re-engage and a small permanent sheet crack remains.
Hab 3, right next to Hab 4, was previously stimulated so that relatively few ‘pings’ would be received from that ‘old’ area. Nevertheless, the pressure would be transferred undiminished through the water to the old boundaries.
Keep in mind that the diagram is actually in 3-D although the total thickness is only about 100m.
Some observations:
• The colour coding enables seeing the gradually fracturing front advancing over the two weeks (blue to red). [It’s a bit like slowly tearing apart the pages of a book that have become wet and are partially stuck together.]
• The advance seems to be occurring very noticeably in the Northerly direction.
• The software has been modified (from a few years ago) to show the intensity of the seismic ‘pings’ as in the size of small spheres. The diagram appears to indicate that the fracture stimulation was still progressing into new areas (North) right up to the time when the test was stopped.
• The question arises, if the test had been continued, whether the stimulated area could have increased still further. Increasing the total effective area is one of the prime goals.
• In the Easterly direction there seems to be a definite barrier either to fluid penetration or to stimulation of the matrix. There is also a barrier to the West but not quite so pronounced.
• The grey dots to the South, and some to the West are those from the earlier stimulations of HAB 1 and HAB 3 printed under the new coloured ones. This raises a bit of a puzzle in that one might expect the fluid to immediately push to the old boundaries and begin to stimulate (and open) new areas from there. But that didn’t appear to happen.
• A theoretically possible explanation would be that there are two distinct fracture systems that have been developed one just above the other, less than 100m apart. It would also mean that the connectivity between them is low (which is hard to accept).
• My estimate the size of the new stimulated area is 2.1 km2
When HAB 5 is drilled it will have its own stimulated patch which will be arranged to overlap with that of HAB 4 so that we have a pair of production and reinjection wells with good flow connection through the heat reservoir. What additional inferences would you make?
Higgybooboo,
You ask why do I look forward to the third flow test? The event just completed was the major stimulation occurring at high pressure over an extended period of time ending 3 Dec. The intent was to maximise the effective area of the heat exchanger and to increase the gap width. It is really only the first flow test after the major pressurisation and therefore becomes a critical test. I would therefore expect a significantly higher flow rate than the 38 litres per sec obtained in November.
We usually tend to think of geological rock structures as hard and inflexible. However the forces generated by the stimulation and transmitted through the incompressible water are colossal so that the Earth does heave and flex (by tiny amounts). It means that for some time (days to weeks) afterwards the fine fractures will continue to progress and generate pings until an equilibrium state is reached.
The micro seismic activity (pings) is of very small amplitude so that on the ground surface you would not know that it is occurring. Peak amplitude of pings is about magnitude 3 on Richter scale which is harmless. Magnitude 4 you might just feel as a vibration such as that a heavy passing truck might generate on a road surface. (Richter scale is logarithmic so that each magnitude change means an energy increase of 10x.
I hope this adds to your thinking.
Juke
RNE Price at posting:
12.0¢ Sentiment: LT Buy Disclosure: Held
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