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Eldorado Oil and Gas Field

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Chelsea Dome: Promising Oil Territory Inadequately Tested

The Chelsea dome, which lies in the immediate vicinity of the Eldorado field, has not, in the judgment of the writer, been adequately tested for oil and gas. The inadequacy of the testing was pointed out in a preliminary statement issued to, the public press on November 4, 1918, at a time when there was a crying need for increased production during the prosecution of the World War. Although the statement of November 4, 1918, was preliminary in nature and not based upon a thorough study of all the available evidence, the later more detailed studies have strengthened rather than diminished the writer's confidence in the original conclusions as expressed in the press notice.

At the time the preliminary statement was issued two dry holes had been drilled on the Chelsea anticline—one on its west side, about 20 to 25 feet below the crest as indicated by the surface rocks, in the southwest corner of the NW NW, sec. 1, T. 25 S., R. 5 E.; and the other on the north slope, about 15 to 20 feet below the crest, in the SE SE, sec. 36, T. 24 S., R. 5 E. Since then, according to trade journal reports, another dry hole has been drilled in the southwest corner of the SE, sec. 1, T. 25 S., R. 5 E., which is about 60 feet below the crest. None of these wells were located in the most favorable position for testing the structure, as will be pointed out, and for this reason it seems probable that some very promising oil territory still lies (April, 1920) undeveloped on the Chelsea anticline.

A study of the distribution of the Stapleton zone oil in relation to the structure shows that the oil lies much farther down on the east flanks of the anticlines and domes than on any other portion, and further, that in these positions it is present in relatively larger quantities. This is particularly true of the Wilson, Robinson, Chesney and Oil Hill domes, and this relation is not only in reference to the structure as developed in the surface rocks, but is even more marked in reference to the folds in the Stapleton pay. The proof of this relation is to be found on plate XIV, in the distribution of the Stapleton sand wells with reference to the contours, showing the structure of the top of the Stapleton zone. This relation, although pointed out in the structural discussions of the Stapleton sand, will again be summarized briefly.

On the Oil Hill dome production extends to the southeast as far down as the -1,440-foot contour and to the south as far down as the -1,520-foot contour, whereas to the west and northwest dry holes have been drilled at places as high as the -1,140- and -1,120-foot contours. Producing wells in section 27 have been brought in on the southeast flank of the Chesney dome as low as the -1,410-foot contour, whereas a well in the southeast corner of section 16 on the north flank, and as high as the -1,080-foot contour, was dry.

Similarly, on the Wilson dome oil has been found on the east side as far down as the -1,240-foot contour, whereas dry holes have been drilled on the southwest and northwest sides which were located as high as the -1,060- and -1,080-foot contours. On the Robinson dome dry holes were drilled on the west side as high as the -1,030-foot contour, and oil wells brought in on the east side as low as the -1,160-foot contour.

If these relations hold in the Stapleton pay zone for the Robinson, Wilson, Chesney and Oil Hill domes, it would seem that they should also hold for the Chelsea dome.

It is not only, however, on the relation of the oil to the structure in the Stapleton zone that the inadequacy of the testing of the Chelsea dome must be judged, but also by the location of the dry holes with respect to the structure of the surf ace rocks, which is the only evidence available pointing to the structure of the possible oil-bearing Stapleton zone, 2,500 feet or more below. The dry hoie located on the southwest flank lies structurally about 60 feet below the crest of the dome. (See plate 1.) On the Wilson dome, similarly located, dry holes lie but 30 to 50 feet below the crest, yet these had no value in determining whether that structural feature was productive. The dry hole located on the west slope of the Chelsea dome is 20 to 25 feet below its crest, which is considerably lower than a similarly located dry hole on the Robinson dome, which is only about 10 feet below the crest of that fold. In like manner, the dry hole on the northeast flank of the Chelsea dome is more than 15 feet below the crest, and because of the uncertainty in the exact location of contours here may be in excess of 20 feet. On the Robinson dome a similarly located dry hole lies about the same vertical distance structurally below the crest, and one to the north lies but 25 feet below the crest. The northeast flank of the Wilson dome has also been proven dry at a point but 30 feet below the crest. On the basis of such evidence it would seem that additional drilling must be done on the Chelsea dome before it can reasonably be concluded to be barren of oil.

In view of these inadequate tests, it is suggested that additional drilling be undertaken to test the structure more thoroughly. Since the prevailing tendency of oil in this region is to congregate on the southeast and east flanks in preference to other parts, it is suggested that the southeast flank presents the most favorable location for further testing, and the recommended locations as given in the press notice issued on November 4, 1918, are still considered good. The first location suggested was the center of sec. 6, T. 25 S., R. 6 E., which is on the southeast slope of the dome and about 5 to 15 feet below its crest. Should a test here prove unsuccessful it is suggested that two more test wells be drilled before the anticline is condemned as valueless. One about a quarter of a mile north of the southeast corner of section 6, farther down the southeast slope, and the other about a quarter of a mile south of the northwest corner of section 6, on the crest of the anticline.

The depth to the Stapleton pay rock may be deeper on the Chelsea dome than in the developed field to the southwest-a very possible condition, since the position of the Stapleton zone is probably determined by the variable depth of the eroded Mississippian series from place to place. The well drilled in the SE, sec. 36, T. 24 S., R. 5 E., according to its log as given below, probably entered the Stapleton at a depth of 2,640 feet, but as was shown for the east flanks of other domes the Stapleton slopes off much more rapidly than the surface rocks, and hence the depth to the Stapleton at two of the suggested drilling locations will probably be considerably in excess of 2,640 feet, and may even reach as high as 3,000 or more feet.

For the guidance of drillers, the log of the hole drilled on the northeast flank is given below:

Log of Empire Gas and Fuel Company's Pippig Farm Well No. 1.
Location, SE, sec. 36, T. 24 S., R. 5 E. Elevation of well mouth, 1,415 feet, which is about 40 feet above the Fort Riley limestone. Log furnished by Empire Gas and Fuel Company.
Drillers' record Thickness
in feet
Depth in
Geological correlations
Clay, red, soft 15 15  
Shale, yellow, soft 20 35  
Lime, white, hard 25 60 Fort Riley limestone.
Shale, yellow, hard 10 70
Lime, gray, hard 30 100
Fresh-water sand 30 130 Florence flint.
Shale, blue, soft 25 155  
Shale, blue, shaly 15 170  
Red rock, soft 5 175  
Lime, gray, hard 40 215  
Red rock, hard 20 235  
Lime, broken, blue, hard 90 325  
Shale, blue, hard 65 390  
Lime, gray, hard 20 410  
Shale, blue, hard 40 450  
Lime, gray, hard 20 470  
Shale, gritty, white 30 500  
Lime, blue, hard 30 530  
Shale, blue, soft 25 555  
Shale, white, soft 20 575  
Shale, shelly, blue 30 605  
Lime, white, hard 10 615  
Shale, blue, soft 25 640  
l,ii-i-ie, broken, soft 40 680  
Shale, blue, soft 7 687  
Shale, shelly, white, soft 16 703  
Shale, light, hard 12 715  
Water sand, soft 8 723  
Shale, blue, soft 52 775  
Water sand, hard 25 800  
Shale, blue, soft 35 835  
Lime, broken, blue, hard 55 890  
Shale, blue, hard 18 908  
Lime, white, hard 20 928  
Shale, blue, shelly 112 1,040  
Lime, white, hard 20 1,060  
Shale, blue, soft 15 1,075  
Lime, blue, hard 31 1,106  
Shale, brown, soft 14 1,120  
Lime, white, hard 23 1,143  
Shale, blue, soft 10 1,153  
Lime, gray, hard 33 1,186  
Shale, blue, soft 13 1,199  
Shale, brown, hard 10 1,209  
Lime, gray, hard 7 1,216  
Shale, blue, soft 10 1,226  
Shale, brown, soft 14 1,240  
Lime, gray, hard 10 1,250  
Lime, white, hard 37 1,287  
Lime, gray, hard 9 1,296  
Sand, broken, soft 7 1,303  
Shale, blue, soft 7 1,310  
Lime, gray, hard 17 1,327  
Shale, blue, soft 26 1,353  
Lime, white, hard 18 1,371  
Shale, black, soft 7 1,378  
Lime, gray, hard 19 1,397  
Shale, blue, soft 15 1,412  
Lime, gray, hard 6 1,418  
Sand, yellow, hard, dry 10 1,428  
Shale, blue, soft 48 1,476  
Lime, gray, hard 45 1,521  
Shale, blue, soft 12 1,533  
Lime, white, hard 15 1,548  
Shale, blue, soft 65 1,613  
Sand, water, soft 37 1,650  
Shale, blue, soft 50 1,700  
Lime, gray, hard 12 1,712  
Shale, blue, soft 88 1,800  
Lime, gray, hard 100 1,900 Lansing formation.
Sand, water, soft 27 1,927
Lime, gray, hard 4 1,933
Shale, broken, hard 12 1,945
Shale, blue, soft 131 2,076
Lime, blue, dark 34 2,110 Kansas City formation.
Lime, shelly, blue, hard 115 2,225
Water sand, soft 35 2,260
Shale, shelly, blue, soft 65 2,325  
Shale, white, soft 65 2,390  
Lime, gray, hard 10 2,400  
Shale, blue, soft 35 2,435  
Lime, gray, hard 10 2,445  
Broken lime, blue, soft 55 2,500  
Shale, blue, soft 144 2,644  
Lime, broken, soft 56 2,700  
Sand, soft 100 2,800  
Shale, blue, soft 6 2,806  
Sand, white, hard 40 2,846  
Shale, blue, soft 6 2,852  
Lime, gray, hard 20 2,872  
Slate, black, soft 80 2,952  
Sand, white, soft 38 2,990  

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Kansas Geological Survey, Geology
Placed on web July 28, 2017; originally published 1921.
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