Fundamental Forces Involved in the Use of Oil Well Packers

The successful use of oil well packers requires, in part, an understanding ofthe pressures which exist at the packer in various applications and anunderstanding of the characteristics of the various types of packers. It iswith these pressures, the resultant forces, and the characteristics of packers, that this paper is primarilyconcerned. An oil well packer may be defined as a mechanical device for blocking thepassage of fluids in an annular space. In the more usual case, the annularspace is that between the tubing or drill pipe in a well and the casing, andpackers which block such an annular space are broadly referred to as casingpackers. In the other case, the annular space is that between the tubing ordrill pipe and the walls of an open hole, and packers for blocking this spaceare generally called formation packers. While the hydraulics involved areessentially the same for casing and formation packers, a greater variety of conditions areencountered in the use of casing packers and only casing packers will bediscussed. After a packer has been set and a pressure seal effected between tubing andcasing, the packer is comparable to a piston in a cylinder. Pressures actingupon a piston result in forces which will move the piston unless some means isprovided to prevent such movement. In the same manner, pressures acting upon a packer will move the packer unlessthere is present a sufficiently great restraining force. Packer Classifications Packers may be classified according to the pressure conditions under which theyare capable of blocking the annular space between tubing and casing. Fig. 1shows schematically two types of packers in common use. These packers arecapable of blocking the annular space against the passage of fluids under adifferential pressure of significant magnitude only when the pressure in theannular space above the packing element is greater than the pressure below. Itmay be seen that in Fig. 1-a, slips with teeth which bite into the casing andprevent downward movement are provided. In Fig. 1-b, an anchor preventsdownward movement. In each case, there is only the tubing to prevent upwardmovement when differential pressures act to move the packers upwardly. Packerswhich hold only a significant differential pressure acting downwardly have beenin use since the early days of the oil industry and will hereafter be referredto as conventional type packers. T.P. 2710