W-1 Permit depths inaccurate?

Anyone know why RRC allows operators to inaccurately estimate well depth in their W-1 permit applications, e.g., 25% variance in the actual wellbore depth? RRC’s User Guide says nothing except to enter total vertical depth on the W-1. I thought 21st century drilling was technologically advanced such that E&P companies know more precisely their target depths, especially their own & competitor wells in the area?

Example, W-1 & permit papers estimated “total depth” 15,000 for two long laterals drilled from shared well pad, but the G-1 completion depths vary dramatically. One well is 10,782 total depth TVD and 20,663 total depth MD, while the sister well is 11,148 TVD and 21,118 MD. Presumably the first well is Wolfcamp A and the sister is Wolfcamp B. The disparity between W-1 permit depth and G-1 as drilled depths are 26%-28%.

I suppose you just can’t trust the W-1, wait and see the G-1 completion report?

Have you looked at the plat that is filed with the permit and shows the proposed path and length of the lateral? Most as-drilled surveys seem to match those pretty closely.

Permit lists maximum vertical depth of well and possible formations. Operator will set depth lower than intended in case targeted formation is deeper than anticipated. If you look at completion reports in the same area, you will see that the listed top of a particular formation varies, even within the same section. The permit does not list the total depth (I.e. vertical depth plus length of horizontal wellbore). The completion report lists the total vertical depth (TVD) and the total length of the wellbore from surface to toe of horizontal wellbore (total MD). It will also note the producing interval which is the distance from the first take point to the last takepoint within the horizontal wellbore. This information is needed for PSA wells which allocate production based on portion of producing wellbore within each tract.


Thx, helpful & informative. My take is as follows. Before drilling, novices e.g. royalty owners don’t know much about stacked laterals from the W-1 permit info. After drilling, detailed info becomes available in the G-1 completions report.

W-1 permit docs are not user-friendly for novices. The vertical depth is presented, but is inaccurate, according to TennisDaze the depth is maximum not actual (typically 50% off for Wolfcamp). Moreover, the W-1 does not require Measured Depth (MD) which reveals total wellbore length. Users can guess the lateral length by examining the surveyor’s plat.

G-1 provides both TVD and MD, but after completion.

RRC designed the system for themselves and operators, not royalty owners IMO.

RRC said permit fees are based on vertical depth. Apparently, maximum and not expected vertical depth. It would seem operators have a good idea of TVD due to numerous offset wells in the vicinity. RRC said Measured Depth (total length) is unknown at time of permit application (makes sense).

G-1 Completion Report discloses TVD 10,782 and MD 20,663 in the “Completion Information” section. The as-drilled plat adds horizontal distances from surface hole location, take points (first and last), bottom hole location etc.

G-1 “Formation Record” section shows two depths for a half dozen formations, e.g., Wolfcamp Depth TVD 10,503 and Wolfcamp Depth MD 10,571. No idea why two numbers are shown. I assume the top of Wolfcamp is 10,503, and operator drilled down vertically 279’ into Wolfcamp before angling into the horizontal stretch.

Compared Wolfcamp formation depths for six long lateral wells spanning 10 miles in north Reeves County Dixieland oilfield, G-1 Completions “Formation Record”, the so-called “Depth TVD” for Wolfcamp ranged from 10,315 to 10,512. I guess this means the top of Wolfcamp bench angles upward (anticline?) 200’ over this ten mile stretch.

Measured depth is length of wellbore from surface, including curve. So vertical depth is surface down in straight line. As wellbore curves into horizontal wellbore, the measured depth will keep increasing, although there will be relatively difference in vertical depth. Measured depth is not final until drilling has ceased.