Authors: Andrés Pastor-Chacón (presenter), Oscar Romero, Miled Niño, German Pardo, Alexandra Delgado, Cristian Benavides, Karen Rodriguez, John Ortiz, Fabricio Combita, Andrés Fuenzalida, Servicio Geológico Colombiano
The reports of the Agencia Nacional de Hidrocarburos (ANH) on the prospective resources of gas in source rock plays (SRP) for the Tablazo Formation in the Middle Magdalena Valley (MMV) show values of at least 6.0 Tcf of gas. However, the identification of sweet spots in these plays require the integration of thermal maturity, TOC (%), clays composition, porosity, thickness, depth and free hydrocarbon saturation data. One of the aims of the Dirección de Hidrocarburos (DTH) of the Servicio Geológico Colombiano (SGC) is to generate public knowledge about the geological parameters for the characterization of proven Cretaceous units with source rock potential. Therefore, in this contribution, we compiled data from the Banco de Informacion Petrolera (BIP), together with new data obtained from outcrops. We present seismic interpretation, well correlations, facies analysis, fracture patterns analysis, geochemical and mineralogical crossplots and geochemical maps for the Paja-Tablazo formations.
We propose three structural domains based in seismic interpretation of the northern part of the MMV basin: The Northern Domain (ND) includes SW-NE strike-slip faults related to the Central Cordillera (CC) and minor deformation of the Cretaceous units; The Central Domain (CD) includes NW-SE transpressive strike-slip faults related to tectonic inversion influenced by the Central and Eastern cordilleras uplift and the Southern Domain (SD) includes N-S thrust faults related to the Eastern Cordillera uplift, re-activation of pre-Eocene faults and fold of Cretaceous and Cenozoic units. The Cimitarra Fault System seems relevant in the history of the basin, separating blocks of Cretaceous units with different depths, thicknesses and facies.
We divided the Paja-Tablazo in two intervals (six facies associations) separated by a regressive surface: The lower interval includes the Aptian maximum flooding surface (MFS), which has good to very good TOC values (2%-5% TOC), type II kerogens, and ≤0.8 % Ro values; The upper interval is described as a retrograding succession with good TOC values (2%-3% TOC), type II kerogens, and ≤0.8 % Ro values. However, these values are affected by thermal maturity, evidenced by a transformation ratio (TR) of 0.95 for the Paja-Tablazo Formations. We mathematically restored original Hydrogen Index (HI) and TOC values for the Paja-Tablazo Formations, obtaining HIo values of 220-250 mg HC/g TOC and TOCo values of 6.5-12.1 %TOC. Based on the X-Ray Diffraction (XRD) analysis we identified several strata of the Paja-Tablazo formations with brittle behavior, produced by the proportional higher concentrations of carbonates and quartz. Through the fracture patterns analysis, we established that the lower interval has a higher natural fracture density compared with the upper interval.
We concluded that the Paja-Tablazo formations, particularly the lower interval, have a good to excellent generation potential, thermal maturity, facies, mechanical properties, depth and thickness. Thus, making the ND the most prospective area of the basin, followed by the CD and SD. Our results might prove useful to the identification of sweet spots and future exploration targets for the MMV source rock plays.
Andres Pastor-Chacón, Servicio Geológico Colombiano
Andres earned a MSc in Geology from the Universidad Nacional de Colombia. With 7 years of experience in the industry, he works as geologist at the Hydrocarbon Department of the Colombian Geological Survey (SGC) in Bogotá.
Before SGC he worked for four years as Junior Geologist in Interoil Colombia E&P, an E&P company with assets in the Middle Magdalena and Llanos Orientales basins.