The increasing complexity of today's reservoirs demands an accurate understanding of formation composition and mineralogy. This is particularly true for unconventional reservoirs, in which quantification of both mineralogy and organic carbon is critical for resource evaluation. The new geochemical spectroscopy tool described here combines the advantages of inelastic and capture gamma ray spectroscopy, opening new avenues for detailed description of complex reservoirs. Capitalizing on advances in technology, the new service provides higher precision and improved accuracy for the analysis of key elements in rock formations and simultaneously offers a standalone quantitative determination of total organic carbon (TOC). The measurements are offered at faster logging speeds. Eliminating the americiumberyllium (241AmBe) radioisotopic source makes combination with traditional measurements a much more attractive and viable logging option for both conventional and unconventional markets.
Geochemical logging was introduced over 30 years ago, starting with a wireline tool based on a pulsed-neutron generator (PNG) and a thallium-doped sodium iodide (NaI(Tl)) scintillation detector (Hertzog, 1980). The emergence of new scintillation detectors led to tools based on gadolinium oxyorthosilicate (GSO) (Scott et al., 1991) and bismuth germanate (BGO) (Herron and Herron, 1996a), both of which are still in active use. Ruggedization of PNG technology enabled the introduction of nuclear spectroscopy to logging-whiledrilling (LWD) environments (Weller et al., 2005). Recent developments include combining capture and inelastic spectroscopy (Pemper et al., 2006; Herron et al., 2011), introducing new scintillation detectors (Odom et al., 2008), and innovating on a traditional design (Galford et al., 2009). Existing spectroscopy tools suffer from several technical shortcomings. The precision of measured elements is a function of count rate, and currently the maximum count rate is limited by the available scintillator, photomultiplier tube (PMT), and electronics technologies. Existing spectroscopy tools suffer from several technical shortcomings.
