This paper was prepared for the Deep Drilling Symposium of the Society of petroleum Engineers of AIME, to be held in Amarillo, Tex., Sept. 11–12, 1972. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers Office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.
Many major oil companies, gas companies, funded companies, independents and contractors are involved in the drilling of deep wells in the Anadarko basin. The casing designs figured by these companies can vary considerably even on nearly identical wells. The purpose of the first part of this paper is to report variances in how part of this paper is to report variances in how these designs are calculated. The second part of this paper will review casing programs with emphasis on the compatibility of the key. industry drilling bits and casing. The 11-3/4-in. intermediate string program will be discussed.
There is a general understanding in our industry that, if someone uses the term standard with regard to casing design safety factors, he means using 1.125 for collapse, 1.800 for tension and 1.000 for burst. A standard casing design would be one considering a pressure gradient of 0.5 psi/ft and applying the above safety factors to the three design conditions. Most casing designs are handled in this manner, particularly those for shallow wells. There are particularly those for shallow wells. There are companies that deviate from the standard. Some design higher and some lower. Each of the three design conditions will be reviewed to show the variances in how companies are designing in the Anadarko basin.
As previously mentioned, the standard safety factor used in collapse is 1.125. This safety factor is the minimum ratio of the tube collapse resistance over the collapse pressures. The collapse pressure on the outside of the casing is usually figured by calculating the hydrostatic pressure of the fluid the casing is set in. The inside is considered void. All companies correct for the tension effect on the collapse resistance of a tube.
Some companies deviate from the standard safety factor by lowering it to 1.050 or 1.000. A few companies take credit for cement behind the pipe and use a lower safety factor below the top of cement than that above. In this regard the lowest safety factors seen are 0.850 below the top of cement and 1.000 above the top of cement.
Another unique method one company uses is to apply a safety factor of 1.000 to the bottom section of casing and then switch to 1.125 at the first section change. This design method is supported by the theory that, when casing is set and cemented, the bottom portion of the string is in compression rather than tension because of the buoyant effect and slacking-off procedures. A tube in longitudinal compression procedures. A tube in longitudinal compression will have a higher collapse resistance than a tube under no load.