I have been involved in selecting E&P well locations for many years. I’ve had the privilege to sit many of those wells, get dirty, and enjoy the “humor” of a tool pusher (TP). I confess, I never really understood what he was saying with his mouth full of chew. When I went independent, I thought, “I will run the wellsite and drill program the way I think it should be.” Some things are just meant to be beyond the control of the company geologist. Why else would drillers and engineers constantly ignore us?
Cost, cost, and cost speak at the pre-budget meeting, while the geos say “rock, rock, rock.” Drillers say “well bore, casing, and more mud.” Reservoir folks ask, “Do you guys know what you are doing? The engineers answer, “Hurry up and set casing.”
Meanwhile, on a daily basis, only two categories change: footage and dollars. My point—Is the goal a hole in the ground, or a producing well?
As the famous, anonymous quote from the accounting department goes, “Do we really have to drill a dry hole first, then add completion costs?” Every geo wants a wellbore to examine and hopefully test. Every driller wants to circulate and pull off, yet they invented overbalancing with mud just in case. It may save a blowout, but it pretty much kills geo investigation.
Examine what a drill bit looks like, and you immediately understand two things will occur, once that thing descends below surface casing. Adding the weight of the drill pipe, turning to the right, and grinding rock to dust while vibrating will guarantee mud-filled fractures within inches-to-feet of the center of the hole. Bits are even available on eBay! (Fig. 1).
“No problem,” says TP, the mud will flow to the surface under induced pressure, and you can find your rock in the shale shaker. We cry (cuss). To assure us that all is not lost, a poor, underpaid fellow is sitting in a separate doghouse to watch for gases in the return mud.
“Look, a show!” “Where?” I ask. “There, on that paper (now screen). It came from about there, see the depth number, plus or minus about 40 feet per the last few hours.” Oh my! I note the depth in futility, since that zone will sit behind casing long before we reach TD. Later, the office will lament that it was a great shale feature that someone could frac and get rich.
Totally lost, however, is the fact that the very jewel you want to evaluate is being pulverized. Appear MWD (measurement while drilling) — now added to the AFE (authorization for expenditure). This is a concept tool often deployed. However, the method lacks precision in any rank area of exploration. Ok, maybe inside a field where the rock column is understood, likely a competent sand, but often failing otherwise. Taking measurements of the wellbore within inches of the bit should have been called measurement while destroying. Other fast drilling aids used with MWD include slick drilling or diesel. The diesel really helps the mud logger determine nature’s hydrocarbons.
May I remind us that cement under wet pressure in a wellbore does not set overnight (24 hrs). Where can that cement go? The same place as the drill mud. So, what do we shoot perf holes into behind casing? Do you recall the many pages of charts that Schlumberger (now SLB) once published on the correction of open-hole geophysical well logs? Corrections are all accounted for as estimates of mud invasion, first in E logs, and somewhat to acoustics, neutron, and density tools. A better approach is to cross-plot the various in-hole technologies and compare them to calibration data or derived factors from nearby similar rocks at depth. PVT analysis is also helpful. Most active logging today does not allow you, the buyer, to see calibration background or to observe internal corrections before the log truck drives off or the logger gets into a helicopter. You are given the challenge of recommending further drilling to be expended in millions, based on mere color interpretations presented on a screen.
High-quality logs calibrated to superior resolution seismic is the fundamental way to lower risk.
IN REVIEW
A recovered rock in your hand is your first choice in exploration.
The triple combo log is likely the second choice for open-hole evaluation, plus or minus mud invasion.
One should never rely only on the combo tool to compare with seismic without running an acoustic tool, including VSP.
Forget the extra dollars of rig time.
Balance “sunk” costs versus the reward you seek.
Run time is the devil's work in exploration.
And finally, realize that MWD in horizontals is about as poorly understood today as water on the moon. All logging tools were designed to react to vertical changes in rock parameters.
Why nuts? Please. We repeat like the movie Groundhog Day. Oil and gas today cannot agree on climate change or the end of the Cretaceous, let alone admit that wells with shows were abandoned too early. The shale play was seen by drillers over 90 years ago, but few believed it was commercial. WO
WHTEXAS@AOL.COM / WILLIAM (BILL) HEAD is a technologist with over 40 years of experience in U.S. and international exploration.