Gas Flow at two different pressure injection points
Gas Flow at two different pressure injection points
(OP)
Hi,
Let's say there is a gas lift compressor handling 2 mmscfd and it is to inject the gas to two different wells, with different pressures. One well is 3500 psig, and the other one is 2000 psig. I know the well with the lowest pressure will take the most of the flow but, how can I calculate how much this difference will be? There is no regulator valve installed and I would like to know how'd the system behave, how much of the 2 mmscfd would the 2000 psig take letting the physics on its own. I assume I should use both Bernoulli's and Continuity eq's, would like to have a path to develop a solutionm though.
Thanks
Let's say there is a gas lift compressor handling 2 mmscfd and it is to inject the gas to two different wells, with different pressures. One well is 3500 psig, and the other one is 2000 psig. I know the well with the lowest pressure will take the most of the flow but, how can I calculate how much this difference will be? There is no regulator valve installed and I would like to know how'd the system behave, how much of the 2 mmscfd would the 2000 psig take letting the physics on its own. I assume I should use both Bernoulli's and Continuity eq's, would like to have a path to develop a solutionm though.
Thanks





RE: Gas Flow at two different pressure injection points
You need to describe your system much better and look at flow and pressure drops and how the downstream system reacts to gas flow.
From the info provided it is not possible to arrive at a solution.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Gas Flow at two different pressure injection points
Remember, the goal is to provide the energy that each well needs, the goal is NOT to just inject gas. Far too often surface guys lose track of the goal.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Gas Flow at two different pressure injection points
We are getting the regulator valve for the lowest pressure well to keep a fixed flow rate for it, preventing that way the well from taking all the flow, also measurement system for each one (this time based on orifice plate), the lead time is long, though. I was just trying to figure out how would the gas flow behave on its own. For example, our client is requesting us to inject 1.0 MMscfd to each well, one at 3500 psig, the other one at 2000 psig, I'm curious on whether the whole 2.0 MMscfd would go to the lowest pressure well (assuming the well can accept it, eventhough this could mean the well to decrease its production), or would it be just some more than 1.0 MMscfd, considering there is a single discharge line coming from the compressor and spliting into two equal diameter lines, one for each well. I'm trying to get the escenarios with calculations rather than hunches. Also I started studying Fluid Mechanics and want to apply this in my job. I'm aware dealing with compressible fluids is much more complex.
RE: Gas Flow at two different pressure injection points
The problem with the regulator is that the well requirements change second to second and the regulator is not up to the task.
All of the arithmetic you will be looking at for this flow is incompressible, not compressible. As a rule of thumb, as long as the pressure at the foot of a pipe is more than about 90% of upstream pressure we assume that the change in density is immaterial. Trying to do this calc with compressible flow calcs would give you very wrong answers (the correlations for low-velocity compressible flow don't work very well).
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Gas Flow at two different pressure injection points
For the flow meter, a crude temporary setup would be a restriction orifice and a DP guage - that should keep things going for a while - required flow is constant, and pressure upstream is also constant from the compressor.
RE: Gas Flow at two different pressure injection points
Any of you know the model of equations I should use for branching piping pipes like this?
RE: Gas Flow at two different pressure injection points
Ask an instrumentation engineer to size and set up the RO for you; keep the beta ratio on the RO at higher than 0.2, and select a DP guage to suit the dp produced at the RO. A DN50 globe valve should be okay for now.
RE: Gas Flow at two different pressure injection points
RE: Gas Flow at two different pressure injection points
If the pressures you quote are the wellhead pressures, then until you get to 3,500psig at that point, you won't have any flow in that branch.
If the 2000 tree can accept your 2mmscfd without getting to a point where the friction losses amount to 1500 psig (seems unlikely) ALL flow will go that route.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Gas Flow at two different pressure injection points
And thanks LittleInch, your explanations makes the point clear to me. I was uncertain on whether it would be a Zero/All flow to each branch or Most/Less. Now it is clear that ALL the flow will go to the lower pressure branch, not just a significant part.
RE: Gas Flow at two different pressure injection points
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Gas Flow at two different pressure injection points
Compressor stated to be for "gas lift"?
RE: Gas Flow at two different pressure injection points
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Gas Flow at two different pressure injection points
So the LP pressure stage would deliver the flow (2000psig @ 2+2 MMSCFD) to the 1st well and then the MP stage would feed the next well (3500 psig @ 2 MMSCFD). So it is basically an extraction.
Or does the compression unit already exist and the delivery pressure fixed ?
With gas lift I've often seen two stages compressors LP/MP but with dehydration unit in the interstage.
Problem is your pressure is quite high and I would tend to call this service injection instead of gas lift...just a thought.
RE: Gas Flow at two different pressure injection points
I've seen a lot of gas lift, but people only tend to use dehydrated gas when they are doing off-site compression. When the compressor is on the same site (or relatively close) then there are some major improvements in economics (with no corresponding reduction in performance) by using raw gas.
This situation (multiple injection pressures) is really common. I saw one stream used for a 23 wells with over 2000 psi spread from the lowest to the highest injection pressure. The only way we were able to get it to work is with high quality pressure regulating valves (we used Fisher V-Cones) and measuring each stream. My client took a half dozen shortcuts before they gave up and hired me to make it work. I got rid of the short cuts and we got control of the process. We were able to inject exactly what we needed into each well (and the injection pressures changed dramatically from hour to hour). After about 3 months of hitting all of our injection targets we shut the gas lift down because with high quality data it became clear that the underlying technology was the wrong way to operate these wells. We couldn't determine that until we got reliable, repeatable performance.
With the extreme variability that any natural reservoir will present you with, the idea of taking interstage gas for some wells and final gas for the rest has failed repeatedly. The volume requirements just swing too much to allow the final (usually third) stage to perform properly. Starving or flooding the third stage on a 1500 hp compressor is a really good way to break something expensive.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Gas Flow at two different pressure injection points