The block under analysis is located at the south of Neuquén basin (Argentina), where Vaca Muerta formation (VMF) produces gas from organic rich black shales. Quintuco Fm., the overlying unit, is composed by limestones and mudstones deposited in shallow waters and presents carbonate build-ups interpreted as oyster floatstone. During drilling, it was observed that if well paths cross these carbonates build-ups, important mud losses and/or gas kicks may occur. Therefore, the objective of this work is to establish the distribution of these bodies to avoid them when wells are drilled and reduce the associated risk. Additionally, these geobodies cause some issues in seismic data affecting the image below them and some procedures like PSDM.
Based on seismic analysis like RMS amplitude and diffraction imaging, electrical logs interpretation combined with outcrops analogs, a new geological view was proposed, allowing the adjustment of directional plans and reducing drilling risks.
The study area is in the shale gas sector of Vaca Muerta Fm. located in the Neuquén basin, Argentina, within the morphostructural zone of the Embayment (Figure 1), described by Cristallini et al. (2009) and Pángaro et al. (2011).
The Quintuco-Vaca Muerta system model consist of a mixed siliciclastic-carbonatic ramp, with a SE-NW orientation, where organic rich black shales (Vaca Muerta) are mostly located in the bottomset with an agradational setting, interpreted as distal platform and center basin deposits. While limestone facies (Quintuco) correspond to foreset and topset mainly with a progradational setting and represents the proximal platform deposits (Figure 2).
The present analysis includes two blocks in the gas window, where VMF is developed with horizontal wells of variable lateral length. The main objectives or landing zones correspond to bottomset facies, with the highest organic rich content (TOC), yielding the best productive benches in the area. However, in the overlying level called Berriasian, within an interval of 200m approximately, seismic amplitude anomalies were observed and interpreted as carbonate build-ups. A schematic diagram in Figure 2 shows the proposed paleoenvironmental model for the Berriasian, where the genesis of these bodies is associated with a low energy environment (Pángaro et al., 2005).
