Bottom Hole Pressure, Methods & Importance 1

[emandems]

I am presently trying to find out how bottom hole pressure is directly measured (not calculated)(ex. equipment, methods, etc.). I also need to know the importance of the bottom hole pressure. I surmise it has to do with production capabilities and reservoir size. I am located in the Illinois Basin, and have access to several shut-in wells that are located on a potential lease. The wells are approximately 780 feet deep. Everyone I have consulted with, want to "blow the wells" and measure the pressure (quality also is a given). Does this method get me what I need to present to a professional for analysis of the reservoir? I am new to the industry and am trying to get my feet on the ground. Thanks!

 

[quadtracker]

Use a wireline service company, they will lower a pressure recorder down the tubing to record bottom hole pressure with the well shut-in over 24 hrs (longer if you like).You will want to leave it in for 24hr to stabilize the well, get a more realistic reading. The recorder is pulled out and downloaded into a computer. Most often downhole pressures are higher than surface pressure even if you blowdown the well and its liquids. Over 24hr you can see how rapid the reservoir pressure builds and recovers. You can also record the bottom hole pressure drop when doing a 24hr flow test. Contact your local wireline service people more detail, I am sure they'll explain the program in more detail.

 

[DrillerNic]

A Build Up Test, as Quadtracker describes will give you the reservoir pressure- ie the pressure in the reservoir away from the well bore. This is very important as this is essentially the energy that drives production to the surface. You will also get a measure of 'Skin'- which is pressure drop in the reservoir near the wellbore caused by damage to the reservoir resulting from drilling or production actions: damage cuased by mud for example, or by scale dropping out of the production stream in the reservoir or across the perforations.

The other bottom hole pressure is the Flowing Bottom Hole Pressure- this is the pressure downhole when the well is flowing and stable (remember to make a note of the stable flowrate that you measure the FBHP at!). You should get both of these numbers from a well designed Build Up/ Flowing WellTest. Get your petroleum engineering department (or the service company) to model the expected test before you start, to make sure that you shut the well in long enough to get meaningful results- I've recovered gauges to surface to find that I should have left them there for another 48hrs in the past!

If you know Reservoir presusre, FBHP at a particular flowrate and skin value, you can work out the production index of the well, which will allow you to forecast the rates for different Flowing Top Hole Pressures ie after opening the choke, reducing separator pressure, that kind of thing.

If you know the skin value, you may be able to suggest some stimualtion actions: acidising, reperforating, washing the well or something.

Finally, if you know the Reservoir pressure, the FTHP and FBHP for a given flowrate, you should be able to model the well's hydraulics and make recommendations about the well's lifting performance. So if it's a gas well, what the flowrates and FTHPs should be to bring any liquids to surface too, to stop the well killing itself; if it's an oil well there may be recommedations about artificial lift or something.