Homework SourseThe purpose of this exercise is to develop an understanding
The purpose of this exercise is to develop an understanding of down hole, measured depth that is the standard reporting format from the rig floor back to the office and when reading depths directly from well logs. In most cases the measurements begin from the drill floor (DF) or from the Kelly bushing (KB) mounted on the drill floor. DF and KB values are essentially unique to each well given that they are referenced to the ground elevation at the drill site. In order to correlate from well-to-well and generate cross sections between multiple wells, it is essential to establish a normalized depth reference or \"datum\". In most cases this is datum ties to sea level. Part of the cross-section exercise is based on a measured section from an outcrop in southwestern Montana. This will be tied to data from four wells from the Williston Basin of central Montana. The elevation of the Top Mississippian Unconformity is at an elevation of +2000ft relative to sea level. The cross section extends from the measured section to Well D. *It is important to know that the evaporitic Potlatch Formation is the eastern equivalent of the Wabamum Dolomite. The wells are already positioned as vertical lines on the attached templates. You do not have to construct a column for each well, just use lines connecting each formation top positioned along the well bores. Fill in the blanks on the attached data table. The formation tops are reported as measured depths. You will need to calculate the subsea depth for each formation top as well as an interval thickness for each stratigraphic unit. A.
Solution
SOLUTION
Calculating the subsea elevation:
Subsea elevation = (KB elevation or DF Elevation) - Measured depth
| WELL (A) DRY and Abandoned (D&A) | |||
| Elevation (DF) | 4291 | ||
| Total depth - D | 6642 | ||
| Formations | Measured Depth | Subsea Depth | Interval thickness |
| A | SS=DF -A | I = D/A | |
| Mississippian Unconformity | 4622 | -331 | 1.44 |
| Sun River Fm | 4622 | -331 | 1.44 |
| Lodgepole / Mission Canyon | 4780 | -489 | 1.39 |
| Three Forks | 5850 | -1559 | 1.14 |
| Potlatch | Not seen | ||
| Nisku | 5850 | -1559 | 1.14 |
| Superow | 6070 | -1779 | 1.09 |
| 6090 | -1799 | 1.09 | |
| WELL (B) DRY and Abandoned (D&A) | |||
| Elevation (DF) | 4347 | ||
| Total depth - D | 4692 | ||
| Formations | Measured Depth | Subsea Depth | Interval thickness |
| A | SS=DF -A | I = D/A | |
| Mississippian Unconformity | 2872 | 1475 | 1.63 |
| Sun River Fm | 2872 | 1475 | 1.63 |
| Lodgepole / Mission Canyon | 3023 | 1324 | 1.55 |
| Three Forks | 4050 | 297 | 1.16 |
| Potlatch | 4050 | 297 | 1.16 |
| Nisku | 4075 | 272 | 1.15 |
| Superow | 4295 | 52 | 1.09 |
| 4338 | 9 | 1.08 | |
| WELL (C) Completed BPOD | |||
| Elevation (DF) | 3750 | ||
| Total depth - D | 3450 | ||
| Formations | Measured Depth | Subsea Depth | Interval thickness |
| A | SS=DF -A | I = D/A | |
| Mississippian Unconformity | 1910 | 1840 | 1.96 |
| Sun River Fm | 1910 | 1840 | 1.96 |
| Lodgepole / Mission Canyon | 1980 | 1770 | 1.89 |
| Three Forks | 3050 | 700 | 1.23 |
| Potlatch | 3050 | 700 | 1.23 |
| Nisku | 3115 | 635 | 1.2 |
| Superow | 3290 | 460 | 1.14 |
| 3350 | 400 | 1.12 | |
| WELL (D) Dry and Abondoned (D&A) | |||
| Elevation (DF) | 3714 | ||
| Total depth - D | 3590 | ||
| Formations | Measured Depth | Subsea Depth | Interval thickness |
| A | SS=DF -A | I = D/A | |
| Mississippian Unconformity | 1950 | 1764 | 1.9 |
| Sun River Fm | Not seen | ||
| Lodgepole / Mission Canyon | 1950 | 1764 | 1.9 |
| Three Forks | 3070 | 644 | 1.21 |
| Potlatch | 3070 | 644 | 1.21 |
| Nisku | 3158 | 556 | 1.18 |
| Superow | 3298 | 416 | 1.13 |
| 3350 | 364 | 1.11 |
