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OILWELL TESTING                                    223






                               AMERADA WITHIN
                               LUBRICATOR


                                                           GATE VALVE


                                                           MASTER VALVE




                                                              CASING           WIRELINE WINCH
                                                            TUBING



                     Fig. 7.34  Lowering the Amerada into the hole against the flowing well stream

                     Amerada records the increasing pressure which can be related to the closed-in time ∆t,
                     fig. 7.33 (b).

                     At the end of the pressure buildup survey the Amerada is pulled out, with the well still
                     closed-in, and a static pressure survey is measured as a function of depth in a manner
                     similar to the flowing survey made while running in. In this case, stops should be made
                     at fairly short intervals of say 100-200 ft, close to the survey depth, and at wider
                     spaced intervals of 500-1000 ft, higher up the hole. The information gained from such a
                     survey can be vital in referring actual measured pressures in the well to a datum level
                     in the reservoir, in cases where it is not possible to conduct the buildup survey adjacent
                     to the perforated interval to be tested (refer Chapter 4, sec.6).

                                                                                 DATUM LEVEL

                                                                                  AMERADA

                                                                  H
                                               DATUM                               MEASUREMENT DEPTH
                                                                                            (p )
                                                                                              m
                                         MEASUREMENT DEPTH            h
                                                                                   TOP PERFORATIONS

                                          OIL-WATER CONTACT
                                      (a)                                   (b)

                     Fig. 7.35  Correction of measured pressures to datum; (a) well position in the reservoir,
                                (b) well completion design

                     Consider, for instance, a survey conducted in the well shown in fig. 7.35 (a), (b). When
                     closed-in, the distribution of fluids in the well could vary between the two extremes
                     illustrated in fig. 7.36 (a), (b). In case (a), in which the well has been producing with a
                     watercut, the fluid distribution may be as indicated by the solid line, which is necessary
                     to obtain the correct pressure in the oil at the top of the perforations, the virtual oil
                     gradient being shown by the dashed line. Alternatively, there may be no water entering
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