Good morning/evening Greyhairs, old chap...
Sorry, I don't mean "old" - it's just an expression.
I'm having great fun with this. Of course I'll keep debating.
Maybe when we critique spelling & grammer, we are splitting those annoying shoulder-blade hairs (yucky!!!). <ggg>
I have to belabour the sphere issue.
I admit that I'm getting in a little deep and have no references at the Oman wellsite here, but here goes...
Let's take away the Earth's gravity and talk about, for sake of argument, 1 cubic km of rock around the 17' of open wellbore (bad example as the corners of the cubes will have different properties to the centres of each face, but bear with me). When we extract fluid from around that wellbore, then, all other things being equal, we will have a draw-down in equal proportions from all directions, i.e. in the shape of a sphere. I see no fault in this argument, which is what I was originally gettting at. Please enlighten me if I am wrong.
Now, other factors may come into play, as you say (porosity, perm, etc...). I was trying to relate the concept of "coning", as I understand it, to the SI members, not specifically relating to this well. That is to say, under ideal conditions.
The Earth's gravity has a HUGE influence on the cone. If it weren't for gravity, our fluids wouldn't arrange themselves in cute little layers in the first place.
Again, all other things being equal, without the Earth's gravity, the fluids would be relying on their own tiny gravitational fields and arrange themselves densest at the centre and lightest at the perimeter (notwithstanding the rock's contribution, of course).
18,000 psi...
I believe it was a representative of one of the oil companies (Mr. Aidan Walsh comes to mind, but I may be wrong) who stated that it would require a minimum 15,000psi at the Temblor to both cause the blow-out and cause the geyser.
You're absolutely right about "cautionary reading". I am working from memory here, but time will tell (hopefully a short time!!!).
One thing is for sure - we are dealing with a highly overpressured reservoir.
Again, you misunderstood my meaning - probably my bad grammer <ggg> - regarding choking the well back.
What I was getting at was this:
Say we have the Temblor at 17,600', with a lithostatic pressure of 18,000psi, and we have a water zone at 13,000' with a lithostatic pressure of 6,000psi. The wellbore with the BOP at the surface operating normally and penetrating the Temblor should have a pressure in equilibrium with the Temblor, as it is a closed system. Everything is fine.
Suddenly, we blow off the BOP assembly and now have an open system. The pressure in the wellbore drops drastically (by how much I have no idea) to, say, 3-4,000 psi. The fluids somewhere in the geyser are now at atmospheric pressure (more or less - I don't know the elevation of ELH).
If there is communication between the water zone and the wellbore, water will flow to the area of lower pressure, i.e. into the well & up.
I was saying that if we repressure the wellbore by choking at the surface, just enough to maintain equilibrium with the water zone at 13,000', it might hold back the water and allow us to produce only from the Temblor. I agree that Temblor production would fall also, but was saying that this might be a good test to see if we do have uphole water or not.
I have no idea if this would work in reality. Any thoughts?
"The problem child grew increasingly problematic each day but now it is becoming more submissive. <ggg>"
This child has a lot of pent-up anger, but has recently found an outlet to vent it's fury. It went too close to the iron and got burned.
I do have some idea of how the blow-out occurred. This information came from a person at the ELH wellsite. It is third party information, but the source has been reliable in the past, so I believe him.
They did lose the mud column to the Temblor. A drilling break occurred somewhere around 17,300', and after approximately three hundred feet of faster drilling, the mud went south. They realised at that time that they were underbalanced, due to very high formation pressures and weighted up the mud system to 19.8lb mud. Something, possibly a fracture, caused them to lose the mud column.
After packing off and regaining circulation, the decision was made to run casing, for safety reasons. As you probably know, seating casing in a porous zone is not the preferred situation, as your cement tends to go sideways and, as you say, a poor cement bond is the result.
This process all took about 6-7 weeks, spanning the month of October, which is why no news came out in October - not much was happening.
They resumed drilling on the Thursday prior to the blow-out, drilling out cement over Thurs. & Friday. Saturday they began to drill new formation using a lighter mud weight (I don't know the #) and made 17 feet before realising that they were underbalanced again, i.e. the well was flowing in on them.
Sunday and part of monday were spent circulating and weighting up the mud system, when the bit plugged and they lost circulation. Gas came up through the annulus and they could not hold it back. The guys on the rig had a short time to escape, knowing what was going to happen, but unable to do anything about it as they could not circulate. The well blew out, leaving the drill-pipe in the hole, which is the way it sits today.
As I say, this is unofficial, but I believe it to be true.
I do know that we initially penetrated the upthrown side of the fault, which prompted the decision to pull back and side-track. We are now in the down-thrown side, which is why we have the overpressure. The huge sheet of overthrusted rock (see www.hiltonpetroleum.com) is a recent event, exerting added pressure beneath it - on the Temblor and beyond.
What remains to be seen is if we are anywhere near the top of the structure. A knowledgeable source on seismic interpretation told me that a very small difference in signal arrival time, combined with processing techniques can alter the shape of the seismic map quite a lot. We could conceivably be 2-300 feet off the top of the anticline - alternatively, we could be right in the top - your guess is as good as mine. Just food for thought.
Here endeth this chapter of waffle.
Rick. |
