Does well head pressure blow reservoir fracturing pressure

[10815L]

Hi,
Can some one advice on fracturing pressure and well head pressure because of produced water is being injected in injection well and planing section give maximum well head pressure value but they never give fracturing pressure.
What complications will be faced if pressure is more than reservoir fracturing pressure.
Thanks
10815l

 

[zdas04]

Parting pressure or "fracturing pressure" of a reservoir is a characteristic of the rock in that reservoir. Some rocks like coal fracture at a very low pressure, some fracture at a very high pressure. I'm not certain that I understand your question.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[10815L]

Hi David ,
The question is regarding the water injection (flooding) for keeping the reservoir pressurized. The problem is how to determine the maximum operating pressure. I think I can't go more than the reservoir fracturing pressure because of high pressure can damage the reservoir characteristics.
Thanks
10815l

 

[zdas04]

Generally, for any injection well you do a step rate test to to determine parting pressure. In this test you inject water at a specified rate and monitor pressure. Then you increase injection rate some defined increment and inject at that rate for a set time. Repeat until you see the reservoir break or you reach the maximum rate your pumps can give you. From an analysis of the pressure data you can see if you reached parting pressure and can set a safe injection pressure. In most jurisdictions you have to do this test before you can get a permit to start injecting.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[dcasto]

Fracking pressure in most cases is assumed to be 1 psi per foot of depth. This pressure can be found experimentally for each and every rock on earth at what expense. So when the regulations says your maximum surface pressure (tubin preesure) is XXX.X psig, with saturated brine as the column in the tubing, they have either done a test or assumed the 1 psi with a de-rating of typically 70% to 80% of the 1 psi per foot of depth.

A 10,000 injection well will have a frack pressure of 10,000 psi. With an 80% derating, the maximum allowable pressure is 8000 psi at the bottom of the hole. saturate brine with a .52 psi per foot (10.0 pound brine)creates 5200 psig. so 8000 - 5200 = 2800 psig at the surface.

 

[zdas04]

That rule of thumb does not match with my experience. I've found that every formation breaks at a very different place. Coal will break at something like 0.1 psi/ft gradient. Shales can exceed 1 psi/ft by a fair bit. Generalized rules of thumb always have one thing in common--they are wrong at least as often as they are right.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[dcasto]

I hope they are not injecting into coal or a "tight" sand formation, they better be injecting into a nice high porosity high permeable rock that fractures at a nice pressure, that's why the rule of thumbs work and states have rules that depend on them else every well would become a science experiment and the cost would go to the moon.

 

[zdas04]

dcasto,
Have you seen where we inject in the San Juan Basin? In Colorado it is the Mesaverde which is classed as "tight gas" interbedded with several shale members. In New Mexico it is the usually the Entrada which is just about as tight as sandstone gets. Mostly they don't let us use "high porosity high permeable rock"

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[10815L]

Hi,
we have two types of injection wells, one is -tive pressure (Vaccume) and other is positive pressure and maximum well head pressure is 700 psig. I would like to determine operating pressure as my company decided to replace the existing corroded aged pipeline(40 year old). my problem is that, no ready information is available on the previous design conditions.
To set up new design basis, I want to understand the reservior fracturing pressure so i can determine the maximum operating pressure.
Thanks for sahring valueable information and updating my knowledge.
101815L

 

[zdas04]

I would go to your company geologists for that information. There is so much variability in rock properties across the world and across the spectrum of a given formation that generic data is pretty worthless.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[dcasto]

just do the hydraulics to determine bottomhole pressure. Then there is an EOS that will predict the bottomhole pressure at new conditions of flow, viscosity and density.

 

[zdas04]

Determining the static or flowing bottom hole pressure is the easy part. Determining the parting pressure of the reservoir is the tough part. Generally it is done with a step rate test. If someone is not willing or able to do that test, then ask a geologist.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[SomeCrazyGuy]

Yes, if your bottom hole pressure is greater than the zone frac pressure you can cause the water to channel to a producer. This will obviously increase the water cut at the producer, often to 100%. If you are injecting enough rate for long enough to wash out the fracture this damage can become permanent, effectively rendering the injector useless.

Talk to your geologist and they will give you the expected formation fracture pressure either based off of a step rate test from that well or from offset data. You should be able to get a decent idea of what the operating pressure used to be based on the specs of the old pipeline, pumps and pop valves.

In an older field your reservoir pressure is likely significantly lower than the frac pressure, so it probably won't even be an issue.