Petrophysical characterization as a potential reservoir of the siliciclastic paleogenes sucesions of the ANH-TIERRALTA-2-X-P well in the Sinú-San Jacinto Basin, colombian Caribbean

Abstract

A petrophysical evaluation was carried out for the siliciclastic levels of the ANH-TIERRALTA-2-X-P well in the Sinú-San Jacinto Basin, Northwest of Colombia. The well was divided into five informal units that contain ten stratigraphic cycles based on the lithology and response of the gamma ray log. The fist from surface to 1100 ft (El Carmen Formation, Oligocene), the second (1100 ft - 3100 ft) composed of biomicrites (Tolúviejo Formation, Eocene). Unit 3 corresponds to quartzitic and lithic sandstones interbedded with shales (2000 ft thick); Unit 4 corresponds to conglomerate sandstones (5530 ft - 6620 ft); Unit 5 (6620 ft to 6770 ft) contains gray limestones; these last three, correlate with the San Cayetano Formation, from Paleocene. The basal unit (6770 ft to 8711 ft) contains dark gray shales, and correlates with the Cansona Formation of the Upper cretaceous. Petrographically, 26 thin sections of Cycle 8 (Unit 3) were analyzed. Early diagenesis is represented by compaction, alkali feldspar kaolinitization and plagioclase sericitization, and the burial diagenesis by neoformation of calcite cement. The basal siliciclastic cycles (4, 5 and 6 in Unit 4) are the most prospective for the accumulation of hydrocarbons, while Cycle 7 (in Unit 3) will correspond to the cap rock of the possible oil system. The shale volume was calculated from the gamma ray and density-neutron logs. The porosity calculations made from the density log (between 8 and 15%) are the closest to the values calculated in the laboratory from the recovered plugs (5%). The water saturation was estimated using the calculated porosity and the deep resistivity log, reporting an average value of 95% in potential reservoirs analyzed.