Print this pageFluid Detection and Porosity Determination Using Acoustic Logs in the Wilmington Field, CA
MOOS, DANIEL
As part of a project co-funded by the Department of Energy (DOE PON#PS22-94BC14972), we have recorded monopole and dipole acoustic waveforms to detect bypassed oil in cased wells. The project has been carried out in the Wilmington Field, Los Angeles, CA, which is composed of relatively unconsolidated turbiditic sands waterflooded for more than 40 years.
Although acoustic detection of hydrocarbons had been demonstrated elsewhere, a number of questions were addressed by this work. Could sufficiently high-quality data be obtained in old, cased wells? Is the difference between low gravity (14-24 API) oil and brine sufficiently large to allow detection using acoustic methods? And, could rock-log models be developed to allow application of the technique to other fields without careful calibration for varying conditions?
Theoretical calculations based on expected fluid properties predicted that the acoustic technique would work at Wilmington in spite of the relatively low API gravity oils. In field tests, the acoustic detection method was capable of discriminating between fully water-flooded sands adjacent to an injection well and sands with high Archie's Law - determined saturations in a selectively completed production well. A modified Hashin-Shtrikman Lower Bound theoretical model accurately predicted both in situ and laboratory rock properties. Using the modified HSLB model, porosity could be determined from shear-wave velocity recorded through casing. The success of the model shows that the technique should be applicable to other fields in a relatively straightforward manner, provided it is possible to obtain the acoustic data.