Paul G. King, Baker Oil Tools Inc.
Packers are run in oil and gas wells primarily to confine fluids. Usually the objective is to confine high-pressure or corrosive fluids and/or, in the case of multiple completions, to confine the fluid to specific tubing strings. Many side benefits are obtained because of the confinement; such as, protection of the casing from high-pressure or corrosive fluids, separation of zones in the well bore, directing the flow of treating fluid, and also as a safety feature. Various questions always arise; e.g., how much weight to set on the packer, how much do you pull, how much psi will it hold, how much do you pull to release the packer? There are a number of computer programs that have been written to analyze and predict tubing and packer loading forces and tubing movement. The computer certainly has its place, especially in the deeper wells where the conditions become more extreme and critical and the calculations become more complex. However, most applications can be quickly and accurately analyzed by applying a few basic calculations to determine the net result of the various operating conditions. Quite often it is possible to rely on an experience factor to design a hookup; but for more extreme conditions, the present and future well conditions should be anticipated and a hookup designed that would be compatible with these operations. This discussion will concern itself with calculations involving the hydraulics and various other forces as they affect packers. An attempt will be made to focus the emphasis on calculations that can be readily made at the wellsite without sacrificing accuracy. It would be oversimplifying the subject to say that all packer application problems are pressure and area calculations; but many of the calculations simply involve pressure and area. A little further in this discussion we will touch on tubing movement calculations involving piston (axial), helical buckling (corkscrewing), ballooning (radial) and temperature (axial). In a total analysis, many complex theories are utilized but that is not the purpose of this paper.