Determining Barrier Distance from Transient Well Test Data

摘要

Wellbore storage, short producing times and variable rate effects usually make the identification and computation of the well-to-fault distance from well test data a difficult bask. The semilog method is, by far, the most popular method to estimate the fault distance. Several approximated formaulte applicable to seminlog methods are widely used in field practice. Sometimes, however, these equations have been used out of their range of applicability. Such practice introduces an error which can be eliminated by a correction factor derived in this work. The resulting new equations are rery accurate, yet simple enough for field applciations. New equations for determining fault distance for vriable rate tests are also provided. The new equations are based on the well known superposition time function, therefore the proposed expressions can be applied directly to field data without any extra computation. One of the major difficulties of the semilog methods is the proper selction of the straight lines. In this work, a plot of the presrithm of time is used to idnetify the semilog straight lines. This plot also allows an independent estimate for the fault distance and skin facotr. For the wellbore storage case, the pressure to pressure derivative ratio presents a distinct behavior when a sealing sault esists near a well. It is also shown that the existent wellbore storage and skin type curves for infinite reservoirs can be used to calculate the fault distance. Field examples are presented to illustrate the use and the reliability of the new analysis procedure.