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Backpressure - Why should I be concerned about that?
Because anything we can do to reduce backpressure on the formation can result in substantial increases in productivity! With high PI wells, small reductions in pressure drops can result in substantial increases in productivity.
Some of the most economically profitable acquisition candidates are those properties with the greatest production facility disabilities. High Productivity Index (PI) wells, even at low volumes, will result in significant increases in productivity when you can effectively lower flowing bottom hole pressure. Searching public databases for high PI wells will invariably result in substantially more profitable acquisition candidates every time you find one!
When a well is first drilled and completed, the surface equipment is installed and many times is never changed again until the end of the well's life. However, the well's performance characteristics have changed dramatically over this same time period.
I commonly see situations where a well, flowing initially and still productive later in life, is converted to artificial lift, and the choke is still in the system. That's like driving with your foot on the break! A choke, even in full, open position creates considerable pressure drop resulting in backpressure on the formation.
From our previous discussions of Darcy's Law and the Q/ΔP (PI equation), we know that if we had a well with a PI of 5 Bbl/day/psi, and if we are able to lower the well's backpressure (by removing a choke) by 100 psi, the resulting incremental improvement in production would be 500 bbls/day of total fluids.
PI = (Qoil + Qwtr) / (Pr - Pwf) ...where Pr is Reservoir Pressure and Pwf is Bottom Hole Flowing Pressure
Pwf = Psep + Pfl + Pfit + Pchk + Ptbg ...where Psep is separator pressure, Pfit is pressure drop across the fittings, Pchk is the drop across the choke, Ptbg is the drop in the tubing
As you can see from these equations, anything we can do to reduce backpressure on the formation by lowering separator pressure, taking out elbows and shortening flow lines, changing out tubing strings, and/or removing a choke (or at least at a minimum moving it closer to the separator), will substantially increase productivity. With high PI wells, small reductions in pressure drops can result in substantial increases in productivity.
It is an easy process to use industry mapping software to identify high PI wells in any basin in the world for acquisition and drilling prospects. If the wells you are evaluating have been producing for a considerable amount of time, the surface facilities may be an obstruction to the producing capability of the well. It may be time to review all of your company's operated surface facilities on older wells and see if there are areas productivity can be greatly improved, especially on high PI wells. Likewise, you can review all your non-operated high PI wells, for acquisition candidates to acquire the operator's interest of those properties, who may not be as perceptive as you, which would allow you to take advantage of his lack of awareness.
Back to December 2003 Newsletter
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