A Solution to Ground Subsidence Problems In Casing Strings and Wellheads
- J.D. Burley (Humble Oil & Refining Co.) | Andre H. Drouin (Rockwell Manufacturing Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- June 1971
- Document Type
- Journal Paper
- 654 - 660
- 1971. Society of Petroleum Engineers
- 4.3.4 Scale, 3 Production and Well Operations, 4.1.5 Processing Equipment, 1.6 Drilling Operations, 5.8.5 Oil Sand, Oil Shale, Bitumen, 1.10 Drilling Equipment, 1.14 Casing and Cementing, 4.1.2 Separation and Treating, 5.4.6 Thermal Methods
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A new wellhead assembly and method for restoring casing string tension provides a fast, economical solution to well problems created by ground subsidence. The new design permits one man, using simple and easily transportable equipment, to make casing string tension corrections rapidly and with minimum interruption of well production.
Subsidence has produced buckling of casing strings and wellhead failures due to force reversals in the production casing strings of oil and gas wells. Detection of active or potential subsidence in oil and gas producing areas has prompted development of remedial operations and techniques to control and relieve the resultant well problems.
We shall introduce here a new approach developed for combating subsidence problems in producing wells in the Houston-Galveston area of the Texas Gulf Coast. The advantages of this new solution have been substantiated by field tests.
Subsidence in the Houston-Galveston Area
Land subsidence has been recognized in the Houston-Galveston area for quite some time.1,2 Beginning in 1905-1906 the U. S. Coast and Geodetic Survey established nets of first- and second-order level lines covering the area. Major releveling surveys conducted in 1942-1943, 1953-1954 and 1964 have been used to develop maps of generalized surface subsidence (Fig. 1).4,5 Ground settlement has been continuous since it was originally identified. By 1964 maximum total subsidence had reached 5 to 6 ft. The area within which subsidence was 1 ft or more had increased from an 8-×18-mile oval shape of the 1906-1943 surveys to more than 40 miles in diameter with an additional extension to the southeast that included the Texas City vicinity.
Subsidence Problems in Oil Producing Operations
Humble has experienced subsidence problems in Houston-Galveston area fields involving approximately 500 total oil and gas wells. Other operators have also recognized these problems and have been active in repairing them. To understand the problem and forces involved, consider a line diagram of a typical well (Fig. 2). Many of the wells in this area were drilled 25 to 30 years ago. The surface pipe, consisting of 1,000 to 1,500 it of 9 5/8-in. casing, was cemented throughout the entire length while the pipe was in tension. The production string, consisting of 6,000 ft of 5 1/2-in. casing, was landed in tension with the bottom 1,000 ft cemented. When the production string was landed in the casinghead, the upper portion of the surface casing was placed in compressive loading. Under normal conditions there should be no appreciable change with time in the forces involved. However, when the wells have been re-entered it has been found that the forces originally in the casing strings have been reversed. The surface casing at the top of the ground is in tension, whereas the oil string is in compression. There has been no detectable movement of the casinghead relative to the ground surface.
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