RIASSUNTO
Abstract
The reuse of existing well bores is one cost saving technique employed by oil and gas producers in mature fields. This process usually requires the removal of tubing and packers to allow the well to be deepened or side-tracked. The tubing removal process is often made difficult due to its being stuck inside casing due to mechanical binding, or binding caused by dehydrated mud or sand in the annulus between the tubing and casing. Conventional direct and indirect methods of finding the stuck point(s) along an interval of tubing, such as Free Point Indicator Tools or Acoustic Attenuation measurements, have proven themselves useful in finding the point(s) where the tubing is stuck. However, when the sticking is due to uncompacted sand that has entered the annular space between the tubing and casing, these conventional stuck pipe indication methods are often inconclusive.
Technological advancements in the design and development of slim, 1-11/16 in. OD, radial cement bond tools allow the application of a new measurement to find sand-stuck tubing intervals. These tools provide up to six independent, short-spaced, acoustic attenuation measurements distributed radially around the tool body. When recorded inside tubing, their increased sensitivity to sound attenuation, as compared to conventional omni-directional amplitude signals, allows sand intervals along the outside of the tubing to be distinguished from intervals where little or no sand is present. This information is used to select the best depth to sever or back-off the free tubing in order to reduce the interval length and expense associated with the washover process required to remove the remaining tubing from the wellbore.
An overview of conventional stuck pipe recovery techniques is discussed along with a brief explanation of applied acoustic technology. A case example of a South Louisiana well is presented to demonstrate the application and illustrate the cost savings gained by use of this newest technology.
Introduction
Oil and gas producers operating in maturing fields such as the U.S. Gulf of Mexico basin continually strive to reduce the expense of drilling new wells. The presence of oyster leases and dredging restrictions in inland bay fields severely limit, and in some cases prohibit, the drilling of new wells. One method of overcoming these obstacles includes reentering existing wells to take advantage of the casing string already cemented in place. This process usually requires the removal of old tubing and packer assemblies that were once used to produce hydrocarbons from now depleted zones. Their removal clears the way for recompleting to shallower zones, deepening the well, or sidetracking to reach new reservoirs.
The recovery of stuck tubing has plagued the oil and gas industry since its inception and is a commonplace activity necessary in remedial well operations.[1] Conditions that can cause tubing to be stuck are often mechanical in nature that include collapsed or parted casing, dehydrated drilling mud, and/or formation sand filling the annular space between the tubing and casing.
The most common methods of recovering stuck tubing include impact tools (jars), washover operations, low-frequency vibrators, and milling tools.[2] These recovery techniques have been utilized in the industry for many years with varying degrees of success depending upon the amount of time spent on the process. Because jarring, washover, and milling techniques require a drilling or workover rig to be mobilized to the wellsite, the amount of time spent on the pipe recovery process is kept to minimum so as not to negatively impact project economics.