How hot is a 16,000-foot well? For years this has been a much debated question. All men are agreed that the answer depends on many variables. Among these are well location, drilling rate, type of drilling fluid, type of formation, and time since the hole was circulated or produced.
Probably the most elusive temperature in a well is the circulating temperature. A number of good theoretical papers on determining circulating temperatures have been written.1-5Very little recent data have been gathered to verify any of these theoretical treatments.
Since one of the most important factors affecting the choice of oilwell cement is the maximum circulating temperature, the API Committee on Standardization of Oil-well Cements setup a task group to gather such temperatures. This is a report of their work. Temperature is also useful in other phases of drilling, completing, and producing wells. Your help' and that of the whole industry is needed to get this information faster.
HOW IMPORTANT IS TEMPERATURE?
Just how important is temperature? Most of you know how much engineering and testing goes in to designing a cement for a super-deep well like the Lone Star No. 1, E.A. Baden Unit. You know that one of the big problems is to get enough retarder to overcome the high temperatures, yet not so much retarder that the cement will not set. Did you know that the same thickening time response problem exists at 12,000 feet as in the super-deep problem wells? An actual cement was tested at simulated bottom-hole temperatures of 125 F and 144 F. At 125 F it had a thickening time of 4 hours and 54 minutes. At 144 F the thickening time was only 2 hours and 57 minutes. In other words, increasing the temperature 19 degrees decreased the thickening time 117 minutes. This is nearly two hours.
Another cement, designed for greater depths, was tested at schedules which go to 206 F and 248 F. At the first temperature it pumped for 3 hours and 2 minutes. The 42 degree increase to 248 F reduced the pumping time 88 minutes to one hour and 34 minutes.
These two examples were taken at random from files of the API Committee on Standardization of Oil-well Cements. They are typical of thousands of tests that have been run all showing the importance of temperature on thickening time. These files also show the importance of temperature on compressive strength. One neat cement, for example, had an eight-hour compressive strength of 1575 psi at 230 F while it did not set in that time at 200 F. Curing temperatures represent static rather than circulating conditions.
These relationships between temperature thickening time and strength are always very important but they become even more so when cementing a long liner. Is it any wonder that we have so many failures in liner jobs when 30 degrees makes the difference of whether a cement will set in eight hours?