Calculation of tubing head pressure from reservoir pressure

[luffeman]

Some time ago I had an Excel spreadsheet which calculated the surface pressure in a dry gas well from the reservoir pressure/depth and gas composition. I have now lost it, does anyone have anything similar out there?

 

[zdas04]

No, and it is phenomenally unusual to have more confidence in your knowledge of "reservoir pressure" than flowing tubing pressure in a gas well.

The pressure traverse from the surface through the wellbore tubulars is complex, but well documented. The pressure traverse from the end of the tubing and through the near-wellbore reservoir rock is even more complex and is absolutely well/reservoir dependent. Every well has different "skin", different amounts of anisotropy, different fracture half-length, and different occurrence of natural fractures. Generalizing that into a spreadsheet seems to be the easiest part of the process--developing a generalized set of equations that has broad applicability is something that software companies have spent billions of dollars on over the decades.

Is is possible that you have substituted the term "reservoir pressure" for "flowing bottomhole pressure"? If so, the equations are well known and published in many places.

David

 

[luffeman]

Apologies what I really meant was the "maximum closed in tubing head pressure" instead of "surface pressure"

 

[zdas04]

I had a project recently where I was trying to fit a curve to the hourly build-up pressure at surface during a shut in on a group of wells. For the subset of the wells that had a smooth increase in pressure, I took the data into MathCAD and fit a curve to it. Then I extrapolated to the asymptote to estimate reservoir pressure. Took about 4 hours/well and every equation was different (more than just different constants in the curve fit, I had to change basic equations). Reservoir pressure is a really elusive beastie and I have never seen a spreadsheet approach that approximated the complexities.

David