THE ISOCHRONAL TESTING OF OIL WELL

ABSTRACT

This paper presents the results and methods of analyzing isochronal and flow after flow multipoint back-pressure tests conducted on oil wells. Tests were conducted in reservoirs with permeabilities ranging from 6 MD to > 1000 MD. Reservoirs in which oil well multipoint back-pressure tests were obtained ranged from highly under saturated, to saturate at initial reservoir pressure, to a partially depleted field with a gas saturation existing above the critical. Each of these three reservoir fluid states can result in different interpretation methods. Back-pressure tests were run to pseudo-steady state in the field where the saturation was above the critical gas saturation. In all cases, oil well back-pressure curves were found to follow the same general form as that used to express the rate-pressure relationship of a gas well: qo = JO ‘(𝒑̅𝑹 𝟐 − 𝒑𝒘𝒇 𝟐 ) n From some 40 oil well back-pressure tests examined, the exponent n was found to lie between 0.568 and 1.000, very near the limits commonly accepted for as well back-pressure curves. Flow point alignment to establish an oil well back-pressure curve on the customary log q vs. log ∆(p2 ) plot is considered to be as good as that obtained on gas well back- pressure tests. This paper demonstrates that gas wells and oil wells behave very similarly and should be tested and analyzed using the same basic flow equations.