Integrated stratigraphic analysis as a guide to oil exploration: An example from Miocene rocks of northern Colombia

Category Petroleum Geology
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Pulido Taborda, Mauricio Alejandro۱; Torres Torres, Vladimir۱; Martinez Rodriguez, Jose Ignacio۲
Holding Date 07 October 2008

Improving the stratigraphic resolution in an exploratory area requires the integration of different geological proxies. As an example a biostratigraphy and sequence stratigraphy analysis of an A-3 Wildcat Well (Lower Magdalena Valley Basin, Colombia) rendered definition of six sequences based on changes in: foraminiferal assemblages, microfaunistic abundance and diversity, identification of electrofacies and condensed sections. Comparison of the biostratigraphic scheme with a seismic profile intersecting the Well indicates correspondence between key depth-converted seismic reflectors and changes in foraminifera associations.
From base to top, the sedimentary succession may be divided into three discrete intervals. (1) Lower Miocene sediments deposited in an outer shelf – upper slope environment with a regressive tendency; this interval presented the main gas shows (2) Middle Miocene outer shelf - upper slope deposits with a transgressive tendency. (3) Middle - Late Miocene? shelf deposits with a transgressive tendency. Six benthonic foraminiferal assemblages were determined using cluster analysis, corresponding to: 1) Cibicidoides floridana - C. crebbsi - Textularia - Uvigerina - Gyroidina (CiTeUvGy), 2) Agglutinated - Planktonic (ArPl), 3) Uvigerina isidroensis - C. floridana - Bolivina floridana (UvCiBo), 4) Bolivina pisciformis (BoCi), 5) Agglutinated - Miliolids (ArMi) y 6) Planktonics (Pl).
Age model bases on Last Occurrences of planktonic foraminifera Globigerinoides diminuta, Praeorbulina glomerosa circularis, Globorotalia fohsi fohsi, Hastigerina praesiphonifera and Globorotalia continuosa – Globorotalia mayeri, which bound the N8, N9, N10, N13 and N14 scheme biozones (Blow, 1969) respectively, spanning from the Early Miocene to Late Miocene.
One of the exploratory targets in Northern Colombia is a conspicuous sandstone-mudstone interval characterized by a microfauna related to poor oxygen conditions and/or high organic matter content, where the UvCiBo assemblage and gas shows occur. This interval has been drilled by the A-3 wildcat well used in this study, and it is interpreted as a sea level fall deposits during the early Middle Miocene.
This study has contributed to: (1) refining the sequence stratigraphy and chronostratigraphic scheme of this area; (2) provide a robust framework for the biostratigraphic control of upcoming exploratory wells by means of BWD (Biostratigraphy while drilling); (3) determine sedimentary environments; (4) link seismic sequences to meaningful biostratigraphic units and; (5) identify potential source and reservoir rocks. The previous results proved the importance of integrating different exploratory tools.