kelly bushing elevation correction price

In the oil and gas industry, depth in a well is the measurement, for any point in that well, of the distance between a reference point or elevation, and that point. It is the most common method of reference for locations in the well, and therefore, in oil industry speech, “depth” also refers to the location itself.

Because wells are not always drilled vertically, there may be two “depths” for every given point in a wellbore: the measured depth (MD) measured along the path of the borehole, and the true vertical depth (TVD), the absolute vertical distance between the datum and the point in the wellbore. In perfectly vertical wells, the TVD equals the MD; otherwise, the TVD is less than the MD measured from the same datum. Common datums used are ground level (GL), drilling rig floor (DF), rotary table (RT), kelly bushing (KB) and mean sea level (MSL). [1]

Kelly Bushing Height (KB):The height of the drilling floor above the ground level. Many wellbore depth measurements are taken from the Kelly Bushing. The Kelly bushing elevation is calculated by adding the ground level to the Kelly bushing height.

In the oil and gas industry, depth in a well is the measurement, for any point in that well, of the distance between a reference point or elevation, and that point. It is the most common method of reference for locations in the well, and therefore, in oil industry speech, “depth” also refers to the location itself.

Because wells are not always drilled vertically, there may be two “depths” for every given point in a wellbore: the measured depth (MD) measured along the path of the borehole, and the true vertical depth (TVD), the absolute vertical distance between the datum and the point in the wellbore. In perfectly vertical wells, the TVD equals the MD; otherwise, the TVD is less than the MD measured from the same datum. Common datums used are ground level (GL), drilling rig floor (DF), rotary table (RT), kelly bushing (KB) and mean sea level (MSL). [1]

Kelly Bushing Height (KB):The height of the drilling floor above the ground level. Many wellbore depth measurements are taken from the Kelly Bushing. The Kelly bushing elevation is calculated by adding the ground level to the Kelly bushing height.

At a previous employer a coworker came to me and told me that a group within our company had asked for all the KB (kelly bushing) elevations for every well in Colorado. I replied that it made no sense and asked my coworker to see if the reference elevations were what they really wanted. The coworker returned the next day and indicated that they had insisted on the KB elevations. We supplied the KB elevations and sure enough, about a week later they came back and asked for the reference elevations.

It’s really important to understand the data you’re working with – what it is, where it came from, and what it can be used for. The problem is sometimes actually harder than it seems. If we use the example above, most logs are measured from the KB elevation, correct? So you want KB elevations when normalizing logs to the sea-level datum?

Yes, most logs are measured from the KB. No, never use just the KB. Some logs are measured from the DF (derrick floor), GR (ground), or CHF (casing head flange), and there are a few other strange places logs are measured from. In today’s world, where multiple rigs can drill multiple sections of a well, the KB can have different elevations depending on the run of the log. It’s really important to put things back together on a common reference point so the logs aren’t off and formations can be correlated and depth corrected. (Side note: the definition of MSL, mean sea-level, is also probably a good topic of future discussion. It’s probably not what or where you think it is).

I really like to use the CHF as the reference elevation because after surface casing is run and cemented in, it is a constant point that has a single elevation point throughout the drilling and completion cycle. No matter what the elevation of the rig or completion is, the CHF is always at the same elevation.

So the KB is a physical place on the rig and the reference elevation is the physical place where the log was measured from. They can be the same thing but equating them everywhere will certainly create incorrect data.

Where the elevations come from is another question. Elevations are often supplied on the drilling permit, the completion report, the logs, and probably a couple of other reports.

The elevation starts when the surveyor goes out and measures precisely where the oil and gas company wants the well. Today everything is done by GPS, and the surveyor gets a latitude, longitude, and elevation. At the precise spot, the surveyor pounds a steak into the ground and ties an orange surveyor’s ribbon on it. It’s usually in some pasture and hopefully not on the side of a hill or in the middle of some pond. That does happen, however, despite the fact that the geologist spends months studying the subsurface. The thing is, they probably don’t spend more than 10 minutes looking at the surface.

Some companies will actually call back the surveyor to have him give a final elevation of the ground and of the KB and/or DF. If you’re really lucky, the company will have also asked the surveyor to respot the well location so there is an updated lat/long, but don’t count on it. One of the most shocking comments I’ve heard about well locations is, “I don’t worry about well locations anymore because everyone uses a GPS.” Yes, the surveyor used a GPS to place the stake in the ground … just before the bulldozer pushed it into the dirt pile.

If the ground elevation changed between the permit and the completion report, there’s an excellent chance the surveyor came back and resurveyed (and hopefully he also included an elevation to something permanent, like the CHF).

So the question is, now that we have established that we might have several different elevations, what is the best one to use? Oh how I wish that were the only question that needed answering. Elevations are reported to the state and elsewhere from lots of different sources. Permits, completions, activity reports, and logs are the main documents where this data can be found. Locations are a different story, and it is a rare event to see a correction.

The elevations off the log are probably the best to use. Though I have seen them wrong on the log, it’s a rare occurrence. The elevations are generally captured to support the geologist in making structure maps, so there’s a good chance they’ve been checked and verified.

The completion information is also another good place to grab the elevations. However, grabbing them from the permit would personally be my last choice, but it’s a lot better than nothing or an estimated elevation from a topo map or DLG file.

So the next time you are looking for an elevation, ask yourself, what was it referenced to, what document did it come from and, probably most importantly, is it a reasonable value?

A couple of other TDs come into play when you are drilling directional or horizontal wells. MTD is the measured total depth, which is the distance along the wellbore. The other piece of information is the true vertical depth (TVD), which is the distance of the well from the surface. There is actually one other measurement, called true vertical depth subsea (TVDSS), which is the TVD as referenced from the reference elevation. In many instances this ends up with data below the sea level and the values are negative. Think of this like a thermometer, where some values are below zero (below sea-level).

A device fitted to the rotary table through which the kelly passes. It is the means by which the torque of the rotary table is transmitted to the kelly and to the drill stem. Also called the drive bushing.†

A hole in the rig floor 30 to 35 feet deep, lined with casing that projects above the floor. The kelly is placed in the rathole when hoisting operations are in progress.†

The hose on a rotary drilling rig that conducts the drilling fluid from the mud pump and standpipe to the swivel and kelly; also called the mud hose or the kelly hose.†

The principal component of a rotary, or rotary machine, used to turn the drill stem and support the drilling assembly. It has a beveled gear arrangement to create the rotational motion and an opening into which bushings are fitted to drive and support the drilling assembly.

Wedge-shaped pieces of metal with teeth or other gripping elements that are used to prevent pipe from slipping down into the hole or to hold pipe in place. Rotary slips fit around the drill pipe and wedge against the master bushing to support the pipe. Power slips are pneumatically or hydraulically actuated devices that allow the crew to dispense with the manual handling of slips when making a connection. Packers and other down hole equipment are secured in position by slips that engage the pipe by action directed at the surface.†

The top drive rotates the drill string end bit without the use of a kelly and rotary table. The top drive is operated from a control console on the rig floor.†

Mean Sea Level means, for purposes of the National Flood Insurance Program, the National Geodetic Vertical Datum (NGVD) of 1929 or other datum, to which base flood elevations shown on a community"s Flood Insurance Rate Map are referenced.