Production Log Analysis and Interpretation

After acquisition of production logging data, an interpretation of the measurements by an analyst will reveal the composition and distribution of the wellbore fluids.  One, two and three phase analyses are possible depending on the number and type of sensors run.  The main purpose of Production Log (PL) analysis is to determine how much of which fluid is coming from where.  In order to achieve this the fluid velocity along with the hold-up of each phase must be known.  From this information the flowrate of each phase in the wellbore can be established and the flow profile determined.

A wide choice of Production Logging sensors are employed to provide the raw data which the analyst requires to interpret the production log.  Typically, a centreline  flowmeter will provide the apparent velocity of the fluid mix - this must be corrected to give the average velocity.  A density sensor, along with the PVT data from the well, is used to allow calculation of phase hold up in a two phase system.  A set of all defined equations uses these results to provide the downhole rates for the fluids present.  In more complex situations where more than two phases exist in the wellbore, additional sensors can be deployed to provide direct measurement of water and gas hold-up.  These sensors allow enhanced analysis and more precise results.  Analysis may be further enhanced by production logging tools which directly measure the distribution of phases across the wellbore.  Such tools have many sensors deployed circumferentially across the wellbore.

Flow mechanisms are different in each well.  Factors such as flowrate, bubble point and well trajectory will determine the distribution of fluids in the wellbore.

In fast, well mixed flows, traditional centre measuring tools will yield good results of analysed data.  However, in wells where flows become stratified, confidence in results is increased when additional data from multi-sensor tools is available