While traditional mudlogging techniques provide largely qualitative data, the objective of Advanced Mud Logging (AML) is to provide quantitative real time measurements and information in aid of drilling and a complete formation evaluation. Hence, during the past few years, various techniques which before were limited to laboratories, have been adapted for well site usage. Also, the whole surface logging system, from sensors to computer operating systems, have been enhanced.
A systematic comparison of results between laboratory instrument and field version instruments proved that the quality of results does not need to be given up when applying these techniques at the wellsite. At present AML well site techniques thus include (i) enhanced monitoring of drilling parameters, (ii) sophisticated mud gas analysis capabilities, (iii) enhanced cuttings image acquisition and processing, and (iv) several direct petrophysical measurements on cuttings.
We present some results of several field tests done in Saudi Arabia with a dedicated AML unit, where all these new techniques have been integrated. In this unit, next to conventional techniques, such as calcimetry, measurements on cuttings include X-ray diffraction (XRD), X-ray fluorescence (XRF), Nuclear Magnetic Resonance (NMR), spectral GR, grain density and porosity.
Examples in each of the four areas mentioned above confirm the potential of AML. AML mud gas analysis gives quantitative compositional HC analysis which perfectly matches results from PVT tests done on subsequent wireline fluid sampling. Also: while the depth resolution of mudlogging measurements, typically several feet, is less than of especially wireline logging, normally sampled at half foot increments, the latest AML NMR measurements have the potential for very high resolution measurements, making it possible to establish the petrophysical properties of very thinly laminated sequences, where normally neither conventional wireline logs nor core plug measurements can resolve those.