This paper presents an approach by integrating advanced cutting analysis, such as x-ray fluorescence (XRF), and open-hole logs for enhanced formation evaluation of complex clastic formations in near real-time. To verify the methodology, results of surface cuttings analyses are compared to and validated with downhole elemental spectroscopy measurements. In general, when the formation contains clays, the minimum logging requirement to evaluate clastic formations is a triple combo (density, neutron and resistivity) with spectral gamma ray (SGR) logs. In addition to correcting the impact of the drilling fluid additives and properties such as the presence of k-formate in mud, SGR logs become very crucial to differentiate clay types present in the formation. In the absence of SGR, advanced cuttings measurements can be utilized to provide elemental data of major elements including SGR components from the cuttings in near real-time. A comparison was made to evaluate the cuttings analysis as a replacement for SGR. As a part of this work and to validate the petrophysical evaluation results, downhole wireline SGR and elemental spectroscopy data were acquired and compared to the analysis using advanced cutting measurements. This work was conducted in a siliciclastic formation containing abrasive sandstones of mixed clean quartz and clay minerals. The analysis of cuttings XRF was integrated with basic downhole logs to quantify the clay typing required for representative formation evaluation and well geosteering. Limitations of this approach are identified in drilling complex clastic formations including cutting sampling frequency and effects of drilling including drilling fluid contamination, mud additives, drilling parameters and drilling driving mechanism. Controlling these factors has led to good results from cuttings measurements. The advanced cuttings XRF analysis was benchmarked with wireline SGR and elemental spectroscopy logs. This approach of using cuttings XRF analysis and basic open-hole logs is a valid option for geosteering in a complex clastic mineralogy formation and providing a near real-time formation evaluation in the absence of spectral gamma ray or elemental spectroscopy. XRF has been proven to provide near real-time analysis with improved reliability across bad hole, wider spectrum of elements and eliminate critical operations risk. Recommendations to optimize the parameters for reliable measurements will be discussed in this paper.
Measurements from pulsed neutron devices have been available via wireline conveyance for more than three decades. Based on recent technology developments, their use has now been expanded to the logging while drilling (LWD) environments. Pulsed neutron generators (PNGs) are electronic devices that produce high energy neutrons without the use of traditional chemical sources. Measurements available for the first time from a commercial PNG-based LWD service include neutron-gamma density (NGD) for bulk density and density porosity. Extensive testing for neutron-gamma density was conducted in a diverse range of environments. Therefore, NGD was put under a benchmarking process against traditional gamma-gamma density (GGD). Consequently, comparing results from both density measurements will allow us to assess the quality of NGD measurement and its limitations; and ultimately qualifying it. Factors such as the invasion and presence of gas or light hydrocarbons may influence the GGD-NGD comparison. Results from various field testing of the NGD measurement while drilling that were recorded in a wide range of environmental conditions and formations indicate that in some cases, they require additional work to accurately characterize the measurement for quantitative analysis. Advantages and limitations of this measurement while drilling (NGD) technique will be highlighted and illustrated in the paper.
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