Abstract

In the centre of the Neuquén Basin, the Vaca Muerta formation is a 400 m thick over-pressurized shale characterized by presenting a 100% marl lithology with Total Organic Carbon (TOC) contents that can exceed 10 wt.%. This condition causes important logs distortion since it reduces their dependence on the rock matrix, being even almost impossible to determine facial changes by conventional mudloging visual techniques.

This work is focused in La Calera block, an unconventional asset operated by Pluspetrol S.A (in partnership with YPF S.A.) where a theoretical and operational crosschecked methodology was established as to reduce the Vaca Muerta pore pressure uncertainty.

Data from LCa.x-3001, the first unconventional exploration well in the block, was used to calibrate a Bowers’ pore pressure model, including lithology descriptions, operational and drilling events, and MPD tests. In addition, kerogen corrected synthetic sonic logs were incorporated in the pore pressure estimation workflow as a more accurate input, avoiding logs distortion.

The pore pressure model built for the Vaca Muerta formation show highly precise results, being implemented to date on 40 unconventional wells, with optimal performance, neither well loss nor Geological/Geomechanical NPTs.

Finally, X-Ray Fluorescence (XRF) from a Vaca Muerta horizontal well was used as a crosschecking input since it acts as an accurate indicator of facial changes and paleoenvironmental variations, existing high correlation between some elemental concentrations and the pore pressure variations.

Introduction

On the west part of Argentina, the Neuquén basin has been producing oil and gas from several proved conventional plays for more than 100 years (Carbone et al., 2020). In the last decade, Vaca Muerta has become a world-class example of an unconventional reservoir, being by its own the Argentina's most important energy source, with estimated resources around 20 to 40 Bbbl (Billion barrels) of oil (Gutiérrez Schmidt et al., 2014) and 150 to 250 TCF (Trillion Cubic Feet) of gas. Considering the country current consumption, it can supply its energy demands for the next 100 years.

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