Geological Survey Water-Supply Paper 1475-M Ground-Water Resources of the Bryce Canyon National Park, Utah

On the basis of information given in this report, the National Park Service decided to drill a well into bedrock to test the quantity and quality of water that could be produced from the Wahweap and Straight Cliffs sandstones. The test well was located approximately at the site shown on plate 24 and was to be drilled to the top of the Tropic shale or to 2,000 feet, whichever was shallower.

For the drilling of this test well, the cable-tool method was chosen. This method was preferable to the hydraulic rotary method for the following reasons:

1. It was anticipated that the final yield of the well would be the aggregate of the yield of many thin water-bearing zones. The cable-tool method would make detection of these small zones easier.

2. Because the final yield of the well would probably come from fracture porosity rather than "between-the-grain" porosity, it would be necessary to keep the diameter of the mud-invasion zone to a minimum. This should make development easier after completion of the hole. The bottom of a hole drilled by the cable-tool method is under less fluid pressure than is the bottom of a hole drilled by the rotary method, and therefore has a smaller mud-invasion zone.

3. Because there was a possibility of encountering water of unsuitable chemical quality, it was advisable to have an inexpensive method of obtaining relatively clean water samples. These could be obtained from the bailer.

4. Water-level measurements could be made easily at any time during the drilling of the well.

The rotary method of drilling had two advantages over the cable-tool method.

1. Drilling would be faster.

2. The probability of the sides of the hole caving in would be lessened. However, because this was a test hole, the information produced by the cable-tool method outweighed the mechanical advantages of the hydraulic rotary method. Rotary-air drilling was not considered separately from the hydraulic rotary method because the anticipated saturation of the material penetrated would have demanded conversion to hydraulic rotary when fracture zones were encountered.

The contract for drilling the test well was awarded to Perry Bros. Drilling Co., of Flagstaff, Ariz. Drilling began in August 1959. The first string of casing was 16 inches in diameter, and the hole was about 18 inches. Subsequently the casing size was decreased to 14, then to 12, and finally to 10 inches. Owing to many unexpected caving zones and the onset of winter, the hole was not finished until May 1960.

Many caving zones were encountered in the course of the drilling, ranging from severe cave-ins which buried the drilling bit and broke the cable, to mere sloughing of the side walls. It is difficult to determine the exact location of many of these zones because the material fell into the hole from an unknown height above the bottom. Although there were many caving zones, one seems worthy of particular mention because of its size and persistence. When the depth of the hole was 650 feet, a loose running sand filled it to a depth of 400 feet. It is not known exactly where this sand entered the hole; it may have been at 400 feet, or it may have been the entire zone between the depths of about 500 and 600 feet. The neutron log (pl. 26) shows that it was probably the latter. Other caving zones indicated that the bit could not advance far ahead of the bottom of the casing without trouble. Much of the lower part of the hole was underreamed to prevent these difficulties.

PLATE 26.—LOGS OF THE TEST WELL AT BRYCE CANYON NAITONAL PARK, UTAH. (click on image for an enlargement in a new window)

Owing to the problem of caving, four strings of casing of different diameters were used. A record of the depths of each casing size is shown on plate 26.

A composite driller's and sample log is shown under "lithology" on plate 26. The formations penetrated are identified from considerations of the driller's log, sample log, and the gamma ray and neutron logs. The top of the basal conglomerate of the Wasatch formation and the top of the Kaiparowits formation are easily identified. However, owing to the similar lithologies of the two formations, there is less certainty about the top of the Wahweap and Straight Cliffs sandstones. It is believed by the writer that the well did not penetrate the Tropic shale.

Most of the samples of the Wahweap and Straight Cliffs sandstones from the well are blue or gray sandy shale. This is different from the lithology of most of these formations in outcrops below the rim where they consist of tan sandstones alternating with blue shales. In the well the more neutral tan colors may have been obscured by the stronger blues. It is difficult to account for the absence of sandstone in the driller's and sample logs. However, the weakly cemented sandstones may have appeared as loose sand and become mixed with shale from other parts of the hole to give the appearance of sandy shale.

Gamma ray and neutron logs were made to check driller's and sample logs, and are shown on plate 26. They were very helpful in selecting the zones to be perforated (pl. 26); however, they did not show any thick sequences of sandstone. Other factors used in selecting the zones to be perforated were reports of caving zones, water levels measured while the hole was being drilled (pl. 26), and chemical analyses of water samples collected by the bailer while the hole was being drilled (table 8).

Water levels during drilling usually are depressed owing to the increased specific gravity of the muddy water in the hole. When a zone is perforated and cleaned the water level is higher. These two types of water-level information are distinguished on plate 26. The final composite water level of all zones that were perforated and cleaned was 647 feet below the surface. Above this level are several perched water bodies, and below this are several zones that have a much lower water level associated with them.

The well was perforated from the bottom upward, and as each zone or group of zones were perforated and cleaned, a water sample was obtained for chemical analysis. These analyses are given in table 8. While the well was pumping samples were collected also, and the analyses of these samples showed the water to be of similar chemical character to the perforated zone between depths of 860 and 890 feet. The reason for this was that the pumping water level was not below the static level of the better quality water zones. The entire 200 gpm that was finally produced, therefore, came exclusively from the 860 to 890 foot zone or above.

TABLE 8.—Chemical analyses of water from the lest well at Bryce Canyon National Park, Utah
[Chemical constituents are given in parts per million]

Two pumping tests were made, and a graph of the final one is presented in figure 60. However, it must be emphasized that this was not a test of the water-yielding ability of the lower three perforated zones. The lower two of these zones were bailed at a rate of 20 gpm. The pumping test indicated that the well had a specific capacity of 1.5 gpm per ft of drawdown and that it would yield 200 gpm without excessive drawdown.

FIGURE 60.—Graph of the water level during pumping of the test well at Bryce Canyon National Park, Utah.

Additional measurements have been made on several springs in the area. Because the measurements in table 6 are only indicative of the flows in 1957, the additional measurements are reported in table 9. The well was not pumped for a sufficient length of time to determine whether or not it affected the flow of Yellow Creek Spring.

TABLE 9.—Measurements of springs below the rim, 1958-60