Biomicrite, Marlstone, and Shale Properties. Exploration of Non–conventional Hydrocarbons from the Cretaceous Colombian Back–Arc Basin   

Javier GUERRERO, Alejandra MEJÍA–MOLINA, and José OSORNO

ISBN impreso obra completa: 978-958-52959-1-9

ISBN digital obra completa: 978-958-52959-6-4

ISBN impreso Vol. 2: 978-958-52959-3-3

ISBN digital Vol. 2: 978-958-52959-8-8​

The nonconventional hydrocarbon potential of the Cretaceous Colombian back–arc basin is explored taking into consideration the properties of fine–grained units, including biomicrite, marlstone, and shale, in terms of total organic carbon content, gas content, vitrinite reflectance, porosity, permeability, pyrolysis, and organic geochemistry of samples collected from outcrop sections and wells in several localities in the core of the Eastern Cordillera, Middle Magdalena Valley, and Catatumbo. The best properties are from the Turonian to Santonian limestones of La Luna Formation and time–equivalent units, but other limestones of Albian and Campanian ages, including the Hilo Formation and the Oliní Group, have potential. La Luna Formation was deposited during a transgressive and relatively high sea level interval; it is composed of biomicrites of planktonic foraminifera, with minor interbedding of marlstones. Diagenetic cherts resulting from replacement of calcite by quartz are also present. The average total organic carbon values of the formation are excellent, between 4.9 and 11.6% for sections in the area of Aguachica, 5.4 to 8.6% in the area of Barichara, and 6.1 to 7.2% in the area of Cúcuta. These high values of total organic carbon are systematically associated with moderate values of thermal maturity, between 0.8 and 1.3% Ro; the interval contains mainly type II kerogen, with minor mixtures of types II–III.

Keywords: Cretaceous, back–arc, nonconventional hydrocarbons, limestones.​

Resumen 

El potencial de hidrocarburos no convencionales de la Cuenca Cretácica Colombiana de back–arc se explora teniendo en cuenta las propiedades de unidades de grano fino, incluyendo biomicrita, marga y lodolita, en términos de contenido de carbono orgánico total, contenido de gas, reflectancia de vitrinita, porosidad, permeabilidad, pirólisis y geoquímica orgánica de muestras recolectadas de secciones de afloramiento y pozos en varias localidades del núcleo de la cordillera Oriental, Valle Medio del Magdalena y Catatumbo. Las mejores propiedades provienen de las calizas del Turoniano al Santoniano de la Formación La Luna y unidades equivalentes en tiempo, pero otras calizas de edades albianas y campanianas, incluyendo la Formación Hilo y el Grupo Oliní, tienen potencial. La Formación La Luna se depositó durante un intervalo transgresivo y relativamente alto del nivel del mar; está compuesta por biomicritas de foraminíferos planctónicos, con intercalaciones menores de margas. Cherts diagenéticos resultantes del reemplazo de calcita por cuarzo también están presentes. Los valores promedio de carbono orgánico total de la formación son excelentes, entre 4,9 y 11,6 % para secciones en el área de Aguachica, 5,4 a 8,6 % en el área de Barichara y 6,1 a 7,2 % en el área de Cúcuta. Estos altos valores de carbono orgánico total se asocian sistemáticamente con valores moderados de madurez térmica, entre 0,8 y 1,3 % Ro; el intervalo contiene principalmente kerógeno tipo II, con mezclas menores de los tipos II–III.

Palabras clave: Cretácico, back–arc, hidrocarburos no convencionales, calizas.​

Abbreviations 

ANH                             Agencia Nacional de Hidrocarburos

HC                                   Hydrocarbon

HI                                       Hydrogen index

HST                                Highstand systems tract

ICP–MS                  Inductively coupled plasma mass spectrometry

MMV                           Middle Magdalena Valley

MORB                        Mid–ocean ridge basalt

PI                                       Production index

Ro                                   Thermal maturity

RST                               Regressive systems tract

SEM                             Scanning Electron Microscope

Tmax                           Temperature of maximum hydrocarbon generation

TOC                              Total organic carbon

TST                               Transgressive systems tract

UMV                            Upper Magdalena Valley

XRD                              X–ray diffraction​

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