Determining Effective Fracture Networks in Unconventional Wells: A Comparison Between Geochemistry and Other Methods in the Vaca Muerta and Permian Plays

Abstract

Effective fracture heights are a key determinant of estimated ultimate recovery in unconventional wells. However, there is no direct way to measure the height of stimulated fractures, nor to assess which fractures actually deliver fluids to the wellbore. Several methods have been applied to constrain fracture geometries, including microseismic surveys, chemical tracers, and geochemical fingerprinting. Here, we compare these methods using wells in the Vaca Muerta play of Argentina and the Permian play of west Texas. In one example, we compare geochemically‐derived effective frac heights (EFH) to high‐confidence microseismic events from a Vaca Muerta well. Both data types confirmed upward fracture growth, which led to the identification of a flow barrier or baffle below the wellbore. Microseismic heights tend to be higher than geochemical EFH estimates because they model the maximum reach of a fracture, whereas geochemistry provides a more robust analysis of which zones are actually contributing production to the wellbore. The added advantage of geochemistry is the ability to perform relatively cost‐effective time‐lapse sampling, which can help to monitor the effectiveness of the flow units and potential baffles/barriers through time. Although there are pros and cons to each method, the resulting fracture trends confirmed by both data types can help to constrain geomechanical models and influences future field development decisions. In another example from Argentina, geochemical samples were taken in tandem with chemical tracer samples from a three‐well pad to test lateral well interference. Time‐lapse samples were taken as each well was subsequently shut in. Initial results from the chemical tracer study did not provide conclusive answers regarding well connectivity and completions effectiveness; however, geochemical analysis revealed labeling errors due to operational switches at the pad. The geochemistry results not only helped to determine the proper source of the tracer samples, but also confirmed that the three wells were producing distinct fluids, and thus likely had separate fracture networks. In the Permian basin, the geochemical interpretations are then used to constrain the scenarios from geomechanical fracture geometry modeling, influencing well‐spacing and completion design decisions. Finally, geochemical data can also provide information about well interference. These data can be compared with pressure and production information to see lateral connectivity in the subsurface. We will share several examples from the Vaca Muerta and Permian plays.

AAPG Datapages/Search and Discovery Article #90349 © 2019 AAPG Hedberg Conference, The Evolution of Petroleum Systems Analysis: Changing of the Guard from Late Mature Experts to Peak Generating Staff, Houston, Texas, March 4-6, 2019