While traditional mudlogging techniques provide largely qualitative data, the prime objective of Advanced Mud Logging (AML) is to provide quantitative real time measurements in aid of a complete formation evaluation. To achieve this, wellsite mudlogging technologies have been enhanced, and various techniques which historically were limited to laboratories, have been adapted for well site usage. AML well site techniques thus include: (1) high frequency, improved accuracy monitoring of drilling parameters; (2) enhanced cuttings image acquisition and processing; (3) direct measurements on cuttings, including graindensity, spectral GR, NMR, XRD, XRF; and (4) sophisticated mud gas analysis capabilities.We describe the main system components developed and present some results of the first pilot tests done in Saudi Arabia with AML techniques and a dedicated AML unit. Examples in the four areas mentioned above illustrate and confirm the potential of AML. On one special technology test well, different systems, from two different companies, were run in parallel to establish the merits and possible limitations of especially the hydrocarbon analysis systems.One of the most striking examples of the quality of AML is a perfect match between the hydrocarbon fluid composition determined from mud gas returns, and those subsequently obtained from PVT measurements on wireline fluid samples. To achieve this, AML technology developers in the industry advanced across the whole process chain affecting such quantification. First and foremost, improving sample extraction and handling, combined with enhanced calibration procedures, to convert from in situ to surface conditions. Second, in addition to sampling both the return mud flow and the inflow, a more precise tracking of flowrates and system volumes was made possible with modern operating systems. Third, adding a mass spectrometer to the gas chromatograph, improved the final measurement potential. Introduction.Several years ago, in Saudi Aramco, a clear business need emerged for additional petrophysical techniques in cases where traditional formation evaluation technologies were unable to provide all the necessary answers with sufficient certainty. Interpretation of tight gas formations in particular was challenging, because the formation properties typically were right at the edges of the operating envelopes of normal logging tool measurements and interpretation technology. With a perceived potential for AML technologies to aid in several of those challenges, an AML research area was set up. The mission was to expand and improve existing mudlogging technologies, and introduce and develop new ones. The vision had two related, but distinct elements. Firstly, also labeled as "ARCHIE'S DREAM" 1 , a complete, albeit preliminary, as a "first aid", formation evaluation, based solely on AML data, including mineralogy, fluid contacts and fluid characterization, porosity and even saturation, permeability and other parameters normally derived from conventional electric logging and cori...
In the framework of a long-term research on Advanced Mud Logging (AML) we have further developed innovative AML methods and techniques to be deployed while drilling, for real time formation characterization on cuttings. AML can deliver integrated, comprehensive Petrophysical Information Logs (PILs) for well evaluation, facilitates improved monitoring and thus optimization of drilling operations, as well as supports formation evaluation. In the following paragraphs we describe an innovative Spectral Gamma Ray (GR) instrument developed with a NaI(Tl) scintillation crystal, geared especially towards well site cuttings measurements. Gamma ray on cuttings complements the well-established AML well site techniques, including direct measurements on cuttings such as grain density, porosity by Nuclear Magnetic Resonance (NMR), X-ray diffraction (XRD), X-ray Fluorescence (XRF), etc. The spectral gamma ray measurements on cuttings allow resolving the ambiguity on cuttings depth shift, by comparison with conventional gamma ray logging tool, reducing the uncertainty and giving significance on the subsequent AML characterization on cuttings. As part of the development process, extensive laboratory tests were performed to validate and compare results of different types of instruments. A typical spectral gamma ray measurement on cuttings takes about 15 minutes and gives total gamma ray activity in API units, and the normal Uranium (U), Thorium (Th), and Potassium (K) spectral components. Laboratory tests proved a good signal to noise ratio (SNR) and a match with measurements done on large rock pieces with conventional lab tools, in terms of relative value of the GR readings. Next, results from laboratory test done with real cuttings collected from a well in Saudi Arabia and a conventional (non-spectral) GR showed a good correlation. Finally, actual field tests with the spectral gamma ray instrument on cuttings in the AML unit have shown a good match with wireline log results.
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.
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