Bottom-hole Pressures in Oil Wells

Abstract

There is nothing more important in petroleum engineering than a definiteknowledge of the pressure at the bottom of an oil well at any existingoperating condition, and the relation of this pressure to the pressure withinthe producing formation. A knowledge of bottom-hole pressures is fundamental indetermining the most efficient methods of recovery and the most efficientlifting procedure, yet there is less information about these pressures thanabout any other part of the general problem of producing oil. Determination Of Bottom-Hole Pressures Bottom-hole pressure may be calculated or determined by several methods. On aninactive well it may be calculated from the fluid head or, if the well is shutin, by adding the casinghead pressure, the static head of the gas and the fluidhead. In wells flowing naturally through tubing the pressure at the bottom ofthe tubing may be calculated by adding the pressure at the casinghead betweenthe tubing and the casing and the pressure due to the weight of the column ofgas, but there is always possibility of error caused by fluid being in theannular space above the bottom of the tubing. If a well with tubing is flowingthrough either the annular space or the tubing, sufficient gas may be injectedthrough the static space to insure that it is free of fluid but not sufficientto establish an appreciable friction loss. The pressure at the bottom of thetubing can then be calculated by adding to the pressure at the tubing head thepressure due to the weight of the column of gas. This is probably the mostaccurate method of calculating bottom-hole pressures. In wells flowing bygas-lift, the pressure at the point the gas enters the flow may be calculatedby a gas-flow formula. Several types of pressure bombs have been used to measure the pressure at thebottom of wells. One is a piece of steel tubing with a check valve in thebottom and a connection for a pressure gage at the top.