Caracterización de las interfaces mecánicas en la Formación Agrio inferior y evaluación de su impacto en su desarrollo como reservorio no convencional.

Abstract

In recent decades, unconventional reservoirs have received special attention due to their high potential to meet energy supply demands. The production of these low-permeability reservoirs requires specialized techniques such as hydraulic fracturing. This process enhances reservoir conductivity and maximizes hydrocarbon production. In the Neuquén Basin, the Vaca Muerta Formation is considered the primary source rock of the basin and the most significant shale unconventional reservoir in South America. However, in recent years, the Agrio Formation (Late Valanginian–Late Hauterivian) has emerged as an unconventional play due to the potential of the organic-rich intervals of the lower Pilmatué Member. Despite extensive geochemical and sedimentological knowledge of this unit, its geomechanical aspects remain poorly understood, particularly regarding mechanical properties, rock heterogeneity,anisotropy, and local stress conditions. The successful development of this unconventional reservoir requires a detailed understanding of rock mechanical properties and stress states to optimize hydraulic fracture design. However, characterizing the reservoir, understanding its heterogeneity, and assessing its impact on productivity pose significant challenges, as they require integrated multi-scale studies, both in the field and laboratory. This study provides a comprehensive analysis of the vertical and lateral variability of the Pilmatué Member, offering an in-depth evaluation of discontinuities and lithologies across three locations in the Neuquén Basin. A multiproxy approach was applied to analyze rock heterogeneity, focusing on mineralogical, textural, and mechanical properties such as strength and hardness. Additionally, field observations were integrated with microscopic and mechanical assessments to identify weak and strong interfaces, their distribution within the unit, and to characterize the organic-rich intervals (OL1, OL2, OL3, and OL4) of current interest. The findings of this research establish a close relationship between lithological discontinuities, mechanical properties, and facies variations. Quantitative and qualitative descriptions of discontinuities reveal lateral variability between the southernmost sector, Pichaihue, and the northern sectors, El Portón and Arroyo Cieneguita. The Pichaihue sector, characterized by a more siliciclastic composition, exhibits lower rhythmicity, more abrupt contacts, and higher roughness indices. Northward, the sequences become more carbonate-rich, with more transitional contacts and smoother roughness in net contacts. Vertical variability was found to be similar in mixed carbonate-dominated environments, with the middle interval of the surveyed sections exhibiting the highest rhythmicity, as well as the greatest lithological and geomechanical heterogeneity. Mechanical property contrasts were attributed to textural and compositional changes detected from macroscopic to microscopic scales. Moreover, the evidence from this study suggests that the organic-rich intervals meet optimal conditions to be considered as future targets based on their geomechanical properties. They exhibit thicknesses greater than 20 m, low clay content, and are predominantly composed of non-expandable minerals such as illite. The presence of quartz and carbonates makes these rocks strong and hard, which is advantageous in terms of brittleness. The organic-rich intervals OL2 and OL3, located in the middle/upper interval, exhibited a higher number of discontinuities and weak interfaces compared to OL1 in the lower interval and OL4 in the upper interval. The rhythmic limestone-mudstone cycles, along with the presence of calcareous concretions, thin tuffaceous levels, and sandy layers, increase the complexity of OL2 and OL3 intervals, imparting significant vertical variability and heterogeneity to the Pilmatué Member that must be considered in the geological and geomechanical model. The results of this study are important as they can contribute to a more efficient exploitation of the Pilmatué Member. A thorough understanding of the vertical distribution of facies and microfacies will enable better estimations of rock mechanical properties and the selection of target levels for drilling navigation and hydraulic fracturing. Identifying rock fabric and mapping the distribution of interfaces and lithological boundaries is crucial, as they can significantly impact drilling and completion stages and affect the production potential of this reservoir unconventional reservoirs have received special attention due to their high potential to meet energy supply demands. The production of these low-permeability reservoirs requires specialized techniques such as hydraulic fracturing. This process enhances reservoir conductivity and maximizes hydrocarbon production. In the Neuquén Basin, the Vaca Muerta Formation is considered the main source rock of the basin and the most significant shale unconventional reservoir in South America. However, in recent years, the Agrio Formation (Late Valanginian–Late Hauterivian) has emerged as an unconventional play due to the potential of the organic-rich intervals within the lower Pilmatué Member. Despite the unit’s extensive geochemical and sedimentological knowledge, its geomechanical aspects are limited, particularly regarding the mechanical properties, rock heterogeneity, anisotropy, and local stress states. A successful development of this unconventional reservoir requires a detailed understanding of the mechanical properties of the rocks and stress conditions to optimize hydraulic fracture design. However, reservoir characterization, understanding its heterogeneity, and evaluating its impact on productivity pose significant challenges, as they require integrated studies at multiple scales, both in the field and in laboratory. This study provides a comprehensive analysis of the vertical and lateral variability of the Pilmatué Member, delivering an exhaustive assessment of the discontinuities and lithologies present at three locations within the Neuquén Basin. A multiproxy approach was applied for the heterogeneous rock analysis, focusing on mineralogical, textural, and mechanical properties, such as strength and hardness. Additionally, field visual observations were integrated with detailed microscopic and mechanical evaluations to identify weak and strong interfaces and their distribution within the unit. The findings of this research are significant as they can be utilized to develop the Pilmatué Member more efficiently. A thorough understanding of the vertical distribution of facies and microfacies will allow for better estimating the rock’s mechanical properties and selecting target intervals for landing and hydraulic fracturing. The identification of rock fabric and the mapping of interface and lithology boundary distribution are crucial, as they can significantly impact the drilling and completion stages and affect the production potential of this reservoir.