The Productivity Index

Abstract

Much has been said and written on the shortcomings of the open-flow andrestricted potentials of oil wells to determine their relative ability toproduce. The oil industry in general is agreed that the open-flow potential inparticular is grossly inequitable, wasteful and expensive, but that potentialis still used in many pools. This is partly because no thoroughly satisfactorysubstitute has been found and partly because operators are reluctant to adoptother methods that have been suggested; or, as Hamlet would say, we wouldrather "bear those ills we have than fly to others we know not of. In a great many pools the use of tubing potentials has been substituted foropen-flow potentials, but open-flow potentials through casing are still beingused in many pools, particularly in Oklahoma, although the expense of suchpotentials has been pointed out many times. In one of the most recent pools inOklahoma it is the practice to take open-flow potentials through the casingwith the tubing out of the hole. The well is usually tubed after it is drilledin for the purpose of washing it in and cleaning the hole. After preliminarytests are run the tubing is pulled under pressure preparatory to taking thepotential. After the potential is taken the tubing is rerun, under pressure. Inorder to accommodate the large capacity of the wells, it is customary to setthree separators, six vent lines and large oil-storage tanks. It isconservatively estimated that the equipment not needed for producing the wellcurrently but which is installed solely for the purpose of establishing largepotentials costs the operator at least $5000 per well-approximately 35 per centof the cost of equipping a well for production. Such needless expenditureconstitutes an economic waste in addition to the gas that is wasted in takingpotentials. Meaning of Productivity Index A method of measuring the relative ability of wells to produce without openflow that shows considerable promise is the Productivity Index.