The equations presented in previous literature on well interference are adequate when there has been no pressure interference at the observation well prior to pressure interference at the observation well prior to shut-in. However, tests made during the later stages of the development of a reservoir frequently reveal that this interference has occurred. A modified equation is developed here to account for it. Pressure at a closed-in observation well, due to continued oil production at off set wells, is given by:



aj = distance from jth well to the observationwell ftPws = pressure at the observation well at t hoursof shut-in, psiapi = initial pressure of the reservoir, psiaq = production rate at the observation well priorto shut-in, RB/Dqj = production rate at the jth interfering well, RB/Dtj = total production time elapsed at jth wellprior to shut-in of the observation well, hourstj = producing time of the jth well at the time ofpressure observation after shut-in of theobservation well, hoursNw = total number of interfering wells. CC = ----------0.00105k162.6qm = -----------kh

When t is very small compared with tj,


or when tj + tj is very small,


Eq. 1 can be written as


A plot of pws vs on semilogarythmic paper for small t should yield a straight line of slope m =

162.6 and an intercept defined by


Substituting the value of pi from Eq. 5 into Eq. 1 yields.

P. 149

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