Apparatus and method for determination of formation bubble point in downhole tool

摘要

An apparatus for estimating a bubble point of a fluid in an earth formation penetrated by a borehole includes: a pump configured to pump fluid from the earth formation through an extendable probe into a volume; and a processor. The processor is configured to perform a pressure-volume test on the fluid sample. The test includes: increasing the pressure of the fluid sample above formation pressure and logging the pressure and volume of the fluid sample; calculating a reference compressibility of the fluid sample; decreasing the pressure of the fluid sample and logging the pressure and volume; calculating a compressibility of the fluid sample using the logged pressure and volume obtained from during the decreasing; comparing the calculated compressibility to a threshold; and estimating the bubble point as the current fluid sample pressure when the calculated compressibility first meets or exceeds the threshold factor.

主权项

1. An apparatus for estimating a bubble point of a fluid in an earth formation penetrated by a borehole, the apparatus comprising:
a carrier configured to be conveyed through the borehole; a probe disposed at the carrier and configured to extend from the carrier and seal to a wall of the borehole; a pump in fluid communication with the probe, the pump having a variable volume configured to pump fluid from the earth formation into the volume within the pump; a volume sensor configured to sense the volume within the pump; a pressure sensor in pressure communication with the fluid in the volume of the pump and configured to sense the pressure of the fluid in the volume in the pump; an isolation valve coupled to the probe and configured to isolate a sample of the fluid pumped through the probe, wherein the sample is isolated in the pump; and a processor coupled to the volume sensor, the pressure sensor, and a prime mover configured to operate the pump to change the variable volume, the processor being configured to perform a pressure-volume test on the fluid sample, the test comprising:
increasing the pressure of the fluid sample above formation pressure by decreasing the volume within the pump and logging the pressure and volume of the fluid sample using the pressure sensor and the volume sensor during the decrease in volume of the pump;calculating a reference compressibility of the fluid sample;decreasing the pressure of the fluid sample and logging the pressure and volume using the pressure sensor and the volume sensor;calculating a compressibility of the fluid sample using the logged pressure and volume obtained from during the decreasing;comparing the calculated compressibility to a threshold; andestimating the bubble point as the current fluid sample pressure when the calculated compressibility first meets or exceeds the threshold factor.