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The Vaca Muerta (VM) formation, one of the largest unconventional reservoirs worldwide located in the Neuquén basin, has ceased to be a promise and is becoming a venturous reality. During recent years, the investments in its development have increased significantly. By the year 2040, it is believed that the VM formation may generate 560,000 bbl of liquid and 6,000 million cubic feet of gas per day.
One of the primary challenges of many operators has been to select the most productive landing zones; consequently, the performance of an accurate and complete petrophysical evaluation of the reservoir has become vitally important to increase production and to optimize well completion costs. The evaluation of shale formations using electrical logs is a major challenge for most petrophysicists because many of the measurements from the logging tool are affected by the organic matter concentrated in this type of rock.
This paper highlights the way in which these challenges were addressed. It describes the logging operation, as well as the integral petrophysical interpretation performed for a pilot well located in the oil window of the VM formation.
The key element for the success of this work was the implementation of the integrated workflow to evaluate the potential of the shale oil well. The integrated workflow enabled the identification of hydrocarbon-bearing formations, quantification of reservoir properties and hydrocarbons in place, determination of lithology variations within the objective section, and establishment of reliable correlations between electrical logs and the organic richness of the VM formation. In addition, the assessment of geomechanical properties has become vitally important to optimize well placement and to select the best hydraulic fracturing design.
The integrated analysis of the pilot well presented in this paper has proven to be a successful case in which an effective characterization of the VM formation, following the proposed formation evaluation workflow, and the integration of wireline data with the various data acquisition program components, enabled the delivery of recommendations about the prospective interval in which to land the programmed lateral well.
The initial high cost of exploitation of the sustained, increasingly growing development of unconventional resources in Argentina has resulted in concentrating all efforts to increase well productivity while reducing construction and completion costs. The optimization of hydraulic fracture (HF) treatments is vitally important. It is the primary strategy used to achieve an optimal reservoir drainage area, consequently characterizing the fracture geometry, including the height, for the continuous improvement of HF treatment and planning.
Several types of technologies and methodologies are used to estimate fracture height during and after a hydraulic stimulation treatment. These technologies can provide information about the fracture geometry and extension in the near-wellbore (NWB) and far-field areas. The determination of a reliable correlation between those methodologies represents a challenge as a result of formation complexity, heterogeneity, and limitations of evaluation technologies. It is well-known that some areas in the Vaca Muerta formation contain layers that can act as fracture barriers and are responsible for fracture containment.
This paper presents a fast and simple methodology that uses conventional well logs [gamma ray (GR), sonic, and density] from pilot wells to identify potential fracture barriers. This approach establishes a means to evaluate the degree to which the rock will have the ability to control fracture height growth. This methodology was determined useful for planning perforation intervals or clusters placement, particularly in those formations with stress profile showing reduced stress contrast and, when complemented with geological information, this method also provides useful information for horizontal well trajectory. Case studies are provided to illustrate examples of the proposed fracture barrier index (FBI) being calibrated or compared to other fracture height assessment. Additionally, the benefits of adding this new approach to current methodologies and technologies to aid completion design optimization and decision making is discussed.