Since its introduction to the Petroleum Industry in Canada in 1970, the Endless Tubing Unit is finding increasing application in oil, gas and injection well workovers. Gaseous nitrogen as well as various fluids including water, acid and cement have been pumped through the tubing string to depths over 12,000 ft. In most cases the use of the continuous string has proven faster and more economic than alternate methods of performing the work. Various applications and job details of the new service are discussed.
The equipment used for the service is complete on a tandem axle truck which carries 14,000 ft. of tubing coiled on a reel, the tubing injector and the blowout preventer and lubricator. Figure I diagrammatically illustrates the basic components of the system set up ready to run into a well. The lubricator allows the tubing string to be run into or withdrawn from a well under gas or fluid pressure. Table I gives the specifications of the Endless Tubing Unit and of the 3/4" Tubing String.
There are a wide variety of well services performed the continuous string, the most frequent of which are:
Clean out fill in tubing-packer Completions
Spot acid, cement, or chemicals on bottom or below packers
Jet back oil or gas wells after fracturing, using N2 to clean out and initiate flow
Clean out sanded -in tubing and Casing
Displace tubing to N2 for dry perforating
Circulate hot oil for dewaxing or hydrate plug removal
Continuously inject N2 to gas lift well fluids during Drill Stem Testing, or during unloading of a new gas well
Correlation of friction pressures experienced in the field with theoretically developed values has yielded a set of curves which can be used to predict pump pressures with a reasonable degree of accuracy.
Equations used in developing the friction pressure curves of 3/4 tubing, Figure 2 for fluids, and figure 3 for N2 Gas, are given in the Appendix.
Under most field conditions the injection rates and surface pressures experienced are approximately as shown in Table 2.
Some specific examples of 8 jobs performed by the ?" Endless Tubing Unit are cited to give pertinent details for typical applications.
Table 3 provides a more general summary of field experience with the new service.
Table (Available In Full Paper)
Field: Medicine Hat, Alberta
Formation: Milk River Sandstone, gas producing wells
Operation: 1,000 to 1,500 feet
Due to low reservoir pressure, these shallow gas wells often will not flow after fracture treatment, even with inclusion of c gaseous phase such as CO2 or N2 in the treating fluids. In order to assure flowback and cleanout of sand to PBD, some wells have been stimulated with straight KCl water, then subsequently cleaned out with nitrogen injected down the Endless Tubing to initiate gas flow.