They had a similar issue in Unit 3 and in the other reservoirs 1A and 1B. One had cement blocking the fractures, the other had excessive mud cake. Both these issues impacted the ability to flow and the flow rate.
One of the risks with open hole completions - is they need to overcome blockages caused by the drilling mud cake. Given the highly fractured nature of the reservoir, drilling mud invasion is likely to be extensive and maybe there was not enough formation pressure to "push out" dislodge the filter cake in the fractures. They would be in a position to assess this by looking at mud loss ad correlating it to the FMI logs.
The Alameda section is behind casing, so they will have to perforate. Maybe they run some bigger charges to punch through any filter cake and this issue may not present itself in the Alamdea tests.
This is where brains and experience is going to have to come into play. Once they solve the problem, it will open up all the reservoirs, so it is essential they spend the money and time to solve the riddles. Whatever the case, maintaining lamellar flow conditions when producing will be a key issue and it will be very tricky, as we have seen. Permeability in an open fracture could be in Darcies, whereas in permeability in the porous/vugghy sections could be in millidarcies. This will cause anisotropy in flow and it can be problematic - my view is comingled production over a wide interval is not a good solution. Another consideration is that the fracture aperture (and therefore permeability) will be directly proportional to the pressure of the fluids they contain. So if you rapidly depressurise the near well bore formation, you could end up "closing" the productive fractures in the vicinity of the well bore.
They may be better served to focus production from narrow zones, so as to better control flow lines to the well. Another solution is to "frac" the formation so as to open up new conduits to allow formation fluids to bypass the mud impacted fractures.
The long and short of it is...this will take time.
MAY Price at posting:
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