<?xml version="1.0" encoding="ISO-8859-1"?><article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<front>
<journal-meta>
<journal-id>0016-7169</journal-id>
<journal-title><![CDATA[Geofísica internacional]]></journal-title>
<abbrev-journal-title><![CDATA[Geofís. Intl]]></abbrev-journal-title>
<issn>0016-7169</issn>
<publisher>
<publisher-name><![CDATA[Universidad Nacional Autónoma de México, Instituto de Geofísica]]></publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id>S0016-71692024000200817</article-id>
<article-id pub-id-type="doi">10.22201/igeof.2954436xe.2024.63.2.1710</article-id>
<title-group>
<article-title xml:lang="en"><![CDATA[Forward modeling of spectral gamma-ray (SGR) logging in sedimentary formations]]></article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Lechuga-Lagos]]></surname>
<given-names><![CDATA[F.M.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Aquino-López]]></surname>
<given-names><![CDATA[A.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Valdez-Grijalva]]></surname>
<given-names><![CDATA[M.A.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Campos-Enriquez]]></surname>
<given-names><![CDATA[J.O.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
</contrib-group>
<aff id="Af1">
<institution><![CDATA[,Instituto Mexicano del Petróleo Posgrado del Instituto Mexicano del Petróleo ]]></institution>
<addr-line><![CDATA[Ciudad de México (CDMX) ]]></addr-line>
<country>Mexico</country>
</aff>
<aff id="Af2">
<institution><![CDATA[,Instituto Mexicano del Petróleo Geofísica Cuantitativa ]]></institution>
<addr-line><![CDATA[Ciudad de México (CDMX) ]]></addr-line>
<country>Mexico</country>
</aff>
<aff id="Af3">
<institution><![CDATA[,Universidad Nacional Autónoma de México Instituto de Geofísica ]]></institution>
<addr-line><![CDATA[Ciudad de México (CDMX) ]]></addr-line>
<country>Mexico</country>
</aff>
<pub-date pub-type="pub">
<day>00</day>
<month>06</month>
<year>2024</year>
</pub-date>
<pub-date pub-type="epub">
<day>00</day>
<month>06</month>
<year>2024</year>
</pub-date>
<volume>63</volume>
<numero>2</numero>
<fpage>817</fpage>
<lpage>834</lpage>
<copyright-statement/>
<copyright-year/>
<self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_arttext&amp;pid=S0016-71692024000200817&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_abstract&amp;pid=S0016-71692024000200817&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_pdf&amp;pid=S0016-71692024000200817&amp;lng=en&amp;nrm=iso"></self-uri><abstract abstract-type="short" xml:lang="en"><p><![CDATA[Abstract We propose a new approach to improve spectral gamma-ray (SGR) logging forward modeling by considering the radioactive minerals present in the rock as gamma-ray sources. This is based on the radioactive attenuation theory. The assumptions are: 1) minerals with K40, U238, and Th232 content are considered radioactive sources uniformly distributed in the rock; 2) the measured radioactivity is proportional to the concentration of radioactive minerals and inversely proportional to the rock bulk density; 3) the radioactivity is only attenuated by absorption of gamma-rays. The forward modeling was tested using a synthetic case of sandstone with clay minerals and brine-saturated pores to analyze the sensitivity of SGR to changes in illite/smectite-illite/mica ratios and sandstone porosities. Finally, it was further validated with 44 core samples, of which 22 are from two shale gas and 22 from two clastic formations. The Pearson correlation coefficient applied to measure the misfit between the simulated and observed K, U, Th, and SGR data attained values of 0.82, 0.83, 0.61, and 0.57, respectively. A further improvement to 0.87, 0.85, 0.65, and 0.69 was achieved when applying joint inversion for data where illite/smectite and illite/mica ratios were not specified. The correlation between the simulated and observed data supports the viability of the proposed SGR forward modeling approach method.]]></p></abstract>
<abstract abstract-type="short" xml:lang="es"><p><![CDATA[Resumen Proponemos un nuevo enfoque para mejorar el modelado directo del registro de rayos gamma espectral (SGR) al considerar los minerales radioactivos presentes en la roca como fuentes de rayos gamma. Este se basa en la teoría de la atenuación radiactiva. Los supuestos son: 1) los minerales con contenido de K40, U238, y Th232 son considerados fuentes radiactivas que están uniformemente distribuidas en la roca; 2) la radiactividad medida es proporcional a la concentración de minerales radiactivos e inversamente proporcional a la densidad aparente de la roca; 3) la radiactividad solo se atenúa por absorción de rayos gamma. El modelado directo fue probado usando un caso sintético de arenisca con minerales arcillosos y poros saturados con salmuera para analizar la sensibilidad de SGR a cambios en las relaciones de ilita/ esmectita e ilita/mica y porosidades de la arenisca. Finalmente, el enfoque fue validado con 44 muestras de núcleo, siendo 22 de dos formaciones de gas en lutita y 22 de dos formaciones clásticas. El coeficiente de correlación de Pearson se aplicó para medir el desajuste entre los datos simulados y medidos de K, U, Th y SGR, obteniéndose valores de 0.82, 0.83, 0.61 y 0.57 respectivamente, y una mejora adicional de 0.87, 0.85, 0.65 y 0.69, respectivamente. Estos resultados fueron alcanzados aplicando inversión conjunta para los datos donde las relaciones ilita/esmectita e ilita/mica no fueron especificadas. La correlación lograda entre los datos simulados y observados sustenta la viabilidad del nuevo enfoque para el modelado directo propuesto de SGR.]]></p></abstract>
<kwd-group>
<kwd lng="en"><![CDATA[Spectral gamma-ray logging]]></kwd>
<kwd lng="en"><![CDATA[Forward modeling]]></kwd>
<kwd lng="en"><![CDATA[Radioactive minerals]]></kwd>
<kwd lng="en"><![CDATA[Sedimentary formations]]></kwd>
<kwd lng="en"><![CDATA[K40]]></kwd>
<kwd lng="en"><![CDATA[U238]]></kwd>
<kwd lng="en"><![CDATA[Th232 radioisotopes]]></kwd>
<kwd lng="es"><![CDATA[Registro de rayos gamma espectral]]></kwd>
<kwd lng="es"><![CDATA[Modelado directo]]></kwd>
<kwd lng="es"><![CDATA[Minerales radioactivos]]></kwd>
<kwd lng="es"><![CDATA[Formaciones sedimentarias]]></kwd>
<kwd lng="es"><![CDATA[Radioisótopos K40]]></kwd>
<kwd lng="es"><![CDATA[U238]]></kwd>
<kwd lng="es"><![CDATA[Th232]]></kwd>
</kwd-group>
</article-meta>
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