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

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.