The Job Of A Wireline Gyro Survey Operator
A Wireline Gyro Truck.
What A Wireline Gyro Survey Operator or Gyro Hand Does
Among the many service companies that support the oil and gas drilling industry there are companies that provide wireline surveying services. A truck such as the one above is equipped with a cable spool (note cable leading from back of truck up into the air toward the drilling rig) and surveying equipment. Wireline trucks may be used for well logging and other more sophisticated services but the truck shown above is purposed mainly for taking gyro surveys.
The high strength cable which is held on a large drum and controlled by the wireline survey operator contains a center cable through which information from the logging or surveying tool is sent. A set of block and tackle placed at the Vee door of the rig and up on the draw works guides the wireline cable down into the well bore.
The wireline gyro surveying tool is a slim tubular device which can be seen in the foreground above just in front of the truck's tires, held up on jack stands and ready to be placed into the well bore. This particular well that we were working on in West Texas produced poisonous H2S gas. The yellow object a the the corner of the truck, next to a guy line leading to the derrick, is a SCBA or self contained breathing apparatus to be used in case of a H2S related accident to rescue a downed worker.
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Why Is Wireline Surveying Needed?
It is required by state agencies regulating oil and gas drilling, such as the Texas Railroad Commission or SONRIS in Louisiana, that a well being drilled be surveyed every so many feet. On land in the state of Texas a legal survey is required every two hundred feet of new open hole. If MWD or measure while drilling equipment is used these surveys can be taken without having to stop the drilling to place a conventional gyro survey device down the hole. When MWD equipment is not use the rig may drop a device called a "single shot" surveying tool down the open hole to obtain a legal survey. In many cases however a survey will need to be taken when there is magnetic interference from metal such as casing.
Such cases include when a whipstock, or deflecting device is placed into the hole in preparation for drilling the well horizontally. The directional driller needs to know the exact placement of the bottom hole location so that he can have a starting point and use that point for his calculations. Since the hole has most likely been lined with metal casing at this point a regular MWD tool, which contains magnetometers that seek true north, will not work.
What Is A North Seeking Gyro?
A gyro is a device that is set spinning and oriented toward true north. A north seeking gyro is contained in the slim tubular device seen above. It is initialized and sent down into the casing and well bore. The "gyro hand" or wireline survey operator stops at various depths from surface to the bottom of the well taking surveys. A gyro is able to indicate the direction in which it is oriented based on the principle of conservation of angular momentum. Because of this effect a north seeking gyro is immune to interference from magnetic fields.
The wireline survey tool is able to record the azimuth or compass direction that the well bore is pointing, as well as the inclination. Using this data a profile of the well can be created. The job of the wireline survey operator must be performed precisely and accurately or else there could be serious legal issues, such as crossing into another oil companies lease or colliding with another well. I have heard of cases where bad surveys cost oil companies millions of dollars when it was found a well had crossed a lease line.
Wireline survey equipment is also used to orient devices placed down the well bore, such as a whipstock.
The Life Of A Gyro Hand In The Oilfield
Nearly every worker that performs a physical task directly related to drilling the well is called a "hand" of some type. There are MWD hands, directional hands, floor hands, whipstock hands, etc. The term "hand" refers to a worker that has completed the break out training and is a fully stand alone worker. Gyro hands or wireline survey operators spend many hours waiting on the rig to be ready for them or traveling from one rig to another. Rarely do they remain onsite for very long unless there are problems.
Wireline survey operators make decent money but spend hours on the road driving and have to sleep when they can in a cramped logging truck in all kinds of weather. Since gyro surveys are needed at all hours of the day and night gyro hands are on call and must be ready at a moment's notice to leave for a distant jobsite. This can be hard on family life, as many oilfield jobs are. Gyro surveying takes place both on and offshore and wireline survey operators may go to a rig aboard a crew boat, helicopter or barge. Offshore the gyro equipment may be housed in a portable unit that is lifted up to the rig floor or is permanently attached to the drilling rig. In inland barge drilling operations I have seen wireline surveying trucks floated out on a barge and placed next to the rig.
Companies that provide wireline gyro surveying include Scientific Drilling Controls, Weatherford, Schlumberger, Analog, Baker Hughes and others.