November 03, 2004
Last night a cold front came in, dumping almost an inch of rain at the drill site. Although the rain had stopped by the time everyone arrived at the drill site at AM, the temperature had fallen to a cold and damp 40 degrees.
Before the drilling resumed for the day, the rig operators cleared out the drilling area by blasting a mixture of air and water down deep into the hole, forcing out extra debris. Next, before inserting the drill, an inclinometer was carefully attached to a cable and slowly dropped down 116 feet to the bottom of the hole. The inclinometer measures the deviation in degrees from vertical in the drilled borehole. Because of the way the strainmeter instrument is manufactured, anything larger than a 5 degree deviation will result in inaccurate strainmeter measurements, possibly causing the drillers to start an entirely new hole. Thus, needing to be within the 5 degree range, everyone held their breath while four inclinometer tests were taken. Miraculously, all four tests came out between 89.4 to 89.8 degrees, plus or minus .3 for error! The inclinometer also reads the temperature at the bottom of the hole showing a chilling temperature of only 8 degrees (F).
Ready to begin drilling again, the rig operators equipped the rig with a new 8-inch drill bit, called a “hammer.” In contrast to the tri-cone bit, the hammer is used to drill through solid rock. Having reached basalt by the end of the day yesterday, drillers knew that it would now take the intense pounding of the hammer bit to break through the bedrock efficiently.
By 10:30 AM, the hole reached a depth of about 200 feet below ground surface. Unexpected amounts of water started showing up in the cuttings. A normal amount of water (about 1-2.5 gallons per minute) was expected so crews were surprised to see around five gallons of water per minute coming out of the hole. At this stage, the cuttings are compromised of dark-colored basalt rock and samples are taken at every 10 feet. Once the cup-size sample is collected from the spewing arm of the rig, it gets rinsed with water to wash the small debris away from the larger chips. PBO geologists noted colorization of some of the stones indicating chemical weathering, most likely through fractures in the rock.
It was almost noon when a second inclinometer measurement was taken. Having drilled 268 feet at this point, the very long drill pipe needed to be tripped, or taken out of the hole, to get the inclinometer in for testing. It took almost 45 minutes to get the 15 - 20 foot pieces (weighing about 360 pounds each!) of drill pipe out of the hole. Again, four tests resulted in wonderful news, ranging between 89.7 and 89.8 degrees.
Drillers use an additive called “foamer” which lowers the density of water and helps the rock chunks come up easier, effectively floating them out of the hole. Usually put in at a certain depth by the discretion of the drillers, the additive was added to the Clarke West borehole just after 1 PM.
The afternoon brought nicer weather, still in the 50`s but breaks of sun came through the clouds burning off the fog. As the rig continues to drill down further into the earth, what appears to be mineral deposits (chlorite, pyrite, and quartz) begin to show up in the cuttings at 385 feet.
By about 2:30 PM, at a depth of approximately 485 feet, the usual color of the cuttings changed from dark brown into a light brown/beige. This unexpected change created a bit of excitement at the drill site when it was discovered that the bit had hit a layer of clay. Most likely, the clay was created by a trapped layer of soil in between two layers of volcanic material. Fortunately the clay cuttings only lasted about 10 feet.
At about 500 feet the basalt cuttings returned, showing up in smaller and finer pieces than before possibly indicating that solid rock may be near. When drillers reached the “TD” (Target Depth) of 508 feet at 3 PM, another inclinometer measurement was taken, once again verifying the drillers are well within the five degree error range.
Now that the drilling is finished, logging of the hole will begin tomorrow. Results from logging will give us a “worms-eye” view of the hole, exposing more information about the characteristics of the rock from the bottom of the hole to the top.
Last modified: Sunday, 11-May-2014 18:02:04 UTC