The "Conroe Crater" looks like a lake you would see anywhere in the USA today, but its orgins, stemming from a catastrophic oil well blowout in 1933, is truly extraordinary! This Earthcache is on private property, but is visible from the road. Accordingly, do not go onto the private property! You can park on the side of the road near the listed coordinates and easily see the data needed to answer the questions in order to log this cache as a find.
INTRODUCTION
I work in the finance side of the oil and gas industry, but the operational side has always fascinated me. When I heard about the “Conroe Crater”, I did some research on the internet about how it came to be, where it is now, and how blowouts occur. Then, through the help of Google Earth, I found out where the Conroe Crater is, took my caching jeep out to the physical location and decided that this would be great thing for an Earthcache. This Earthcache includes some fascinating technical information about the oil and gas industry, as well as an interesting story behind how the Conroe Crater was inadvertantly "man-made".
WHAT IS THE “CONROE CRATER”?
In 1931, George Strake drilled the South Texas Development Company #1 well, which was the initial discovery well of the Conroe Oil Field. The South Texas Development Company #1 came in at a depth of about 5,000 feet with a gas rate of several million cubic feet of natural gas and several hundred barrels of oil. George Strake followed that up with a second well that came in at 10,000 barrels of oil per day. After 60+ more wells were drilled, the Conroe Oil Field quickly became one of the largest oil fields in the USA with a production peak as high as 65,000 bbls/day of crude oil.
The Conroe Oil Field produces at an average depth of 5,050 feet from the Upper Cockfield and Main Conroe Sands. The geology of the Conroe Oil field includes shallow unstable gas-charged sands that proved to be disastrous. In January 1933, Standard Oil drilled the Madely#1 and the well came in as a gusher. The gas gushing out of the well ignited and there were several failed attempts to kill the well using dynamite. A huge crater developed, swallowing the Madely #1 well and a nearby drilling rig that was drilling the Alexander #1 well. The crater quickly spread into an uncontrolled lake of burning oil. Dubbed the “Conroe Crater, the crater was thought to be about 600 feet deep, although some thought it was bottomless.
In order to control the flow of oil and gas into the crater, a nearby drilling rig owned by George Everett Failing was brought in to drill a dozen or so relief wells to relieve the enormous sub-surface pressure in the formation that was spewing forth the natural gas that was fueling the blowout. By reducing the reservoir pressure and thus reducing the flow of gas to the surface, the relief wells would kill the blowout. It the company three months, but they did finally extinguish the fire in the crater.
Even though the fire was out, the crater still spewed forth about 6,000 bbls/day of crude oil from the destroyed oil wells. Humble Oil Company purchased the Conroe Crater and made a fortune off of skimming the oil out of the Conroe Crater, because it did not technically fall under the “allowable production” regulations of the Texas Railroad Commission because the oil was not technically being "produced". In late 1933 yet another relief well (the first directionally drilled relief well ever) was drilled and the uncontrolled oil flow into the Conroe Crater was permanently stopped. Here is the actual diagram covering the planning of drilling the relief well to stop the oil flow from the Conroe Crater:
WHAT IS A BLOWOUT?
In laymen terms, blowout occurs when fluids (oil and/or water) and natural gas are released from a high-pressure formation in an uncontrolled manner. In the past, this was referred to as a “gusher”. Now, with the use modern technology, blowout preventers and specialized drilling mud to equalize down hole pressures, “gushers” are extremely rare. When they do occur, they are referred to as “blowouts”. Perhaps the most famous recent blowout is the deep water “Macondo” blowout that occurred in 2010 offshore Louisiana.
PREVENTING A BLOWOUT – FIRST LINE OF DEFENSE
The first line if defense of a blowout is drilling fluid, which is also referred to as mud. As a well is drilled, mud is pumped down the drill string to the drill bit at the bottom and returns up the well-bore in the space between the outside of the drill pipe and the casing that line and protect the well. The column of drilling fluid being pumped into the well has considerable weight and exerts a tremendous downward hydrostatic pressure in the well. At the bottom, where there is an “open hole” with no casing, the circular tubing through which the well drilled, the hydrostatic pressure provides an “overbalance” of pressure that exceeds the natural pressure of the reservoir into which the well is drilled. The overbalance of pressure prevents oil and gas fluids from entering and coming up the well bore to the surface, which could result in a blowout.
PREVENTING A BLOWOUT – LAST LINE OF DEFENSE
Oilfield technology has come a long ways since the 1930’s. Now the primary last line of defense against a blowout is a blowout preventer, referred to a BOP, which is required to be on every well that is drilled. The BOP is positioned at the top of a well and just under the drilling floor of the rig while the well is being drilled. It contains mechanical “rams,” which are to be closed if there is an uncontrolled flow of fluids and/or gas up the well. Shutting the rams will seal off the well, preventing the oil and gas from reaching the rig floor, which would likely cause a deadly fire or explosion.
LAST RESORT FOR STOPPING A BLOWOUT – THE RELIEF WELL
If all efforts at the surface fail to contain a blowout, the last resort is usually to drill a “relief well” which is drilled very near the blowout well to relieve down hole pressure or provide a way to pump water into the formation to effectively “kill” the well. In the case of the Conroe Crater, that was the first time a relief well was drilled directionally to stop a blowout. With today’s directional drilling technology, a relief well can actually intersect the bore hole of the blown out well, That is exactly what happened with the Macondo well blowout in 2010:
To get credit for this Earthcache email the cache owner the answers to the following questions:
1. Permeability is ”the measure of the ease for which fluid can move through a porous rock”. Oil and gas is typically produced from sandstone, because sandstone has the permeability characteristics that allow oil and/or gas to move through the rocks under pressure in a subsurface environment. On the other hand, granites and clay typically do not easily flow oil or gas because they have low permeability characteristics. Look at the ground around the listed coordinates. Soil at the surface is not necessarily what is also at the subsurface section that produces oil and gas. Take a sample of the surface soil and examine whether it is sandstone, granite or clay. Is the surface soil sandstone, which would be conducive to oil and gas production or is it mainly clay or granite, which would not?
2. Visually estimate the length and width of the Conroe Crater. Assuming the Conroe Crater is 600 feet deep, estimate the volume of water in gallons within the crater assuming it is cube shaped and has a depth of 600 feet (use the formula of (length x width x depth) and 1 foot equals 7.48 gallons).
3. If this was oil, what would it be worth today (divide the gallons in question 1 by 42 and multiply it by $100 per bbl).
4. What is located on the other side of the road and what is the name of the company that operates it?
Optional: take your picture with the Conroe Crater in the background and post it with your log.
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