A NEW REAL-TIME CONTAMINATION METHOD THAT COMBINES MULTIPLE SENSOR TECHNOLOGIES

摘要

The accurate determination of fluid properties andcontamination while sampling with a wireline pump-outformation tester is essential to achieve the primaryobjective of obtaining representative reservoir fluidsamples with minimum rig time. Despite advancementin fluid identification sensors, sampling in mixedphases, especially immiscible fluids, still poses greatchallenges. In many cases, apparent erratic sensorresponses are attributed to sensor noise and consideredto be uninterpretable. However, careful study revealsthat the sensors are actually showing the true nature ofthe multi-phase fluid flow. If this multi-phase behavioris not taken into consideration, it is difficult todetermine fluid type and the level of contamination.This work addresses the development of new numericaland analytical models that make it possible to not onlyunderstand the cleaning behavior of formation fluids,but also quantitatively determine fluid-samplecontamination in real time. The techniques shown inthis paper highlight the variables that play importantroles in guiding the cleanup process. The methodspredict the contamination level in both the time andfluid volume pumped. Furthermore, the requiredpumping time, or volume needed to achieve the desiredlevel of contamination, is also calculated with thismethod. The statistical uncertainties of these estimatesare also considered based on how well the sensor datamatches the analytical contamination model. Examplesare provided to illustrate the efficiency of this techniquein oil-based-mud (OBM) and water-based-mud (WBM)contaminated examples for both hydrocarbon fluid andformation water samples.The new analysis technique is applied to a highresolutionfluid-density sensor that monitors the changein the resonance frequency of a vibrating tube-carryingfluid sample. The same interpretation method is alsoapplied to a capacitance sensor and a resistivity sensorto further confirm the results derived from the densitysensor.Once samples chambers are recovered at the surface,non-invasive measurements are performed on thesamples to verify the fluid type and sample quality.This is achieved through precise measurements ofsample density and compressibility without opening thechamber. When these measurements are compared withdowhole measurements, including mud-filtrate density,the contamination can be predicted. This technologyenables verification of downhole measurements andensures that sample integrity is maintained when theyare retrieved at the surface. This, in turn, enableswellsite decisions to be made regarding which samplesare the most representative before shipment to PVT lab.