New Mexico Geological Society Annual Spring Meeting
April 13, 2018

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A Field-Scale Examination of Fault Controls on Subsurface Flow

Tyler Sproule1, Johnny Ray Hinojosa1, Glenn Spinelli1, Peter Mozley1, John Wilson1 and Michael Fort2

1New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM, NM, 87801, United States,
2HydroResolutions LLC

Geologic faults can substantially alter fluid flow fields in the subsurface. Depending on structural properties, a fault may act as either an impediment or conduit to groundwater flow; a clay-smeared or cemented fault slip surface hinders the movement of water, while an unconsolidated damage zone introduces efficient new pathways for flow. In geologic settings with numerous, extensive faults (e.g. rift zones), accounting for fault-fluid interactions quickly becomes essential in evaluating groundwater resources at a regional scale. However, conventional analytical methods and commercial aquifer modeling software often assume that a fault occupies a perfectly vertical plane of minute thickness. In reality, fault structures can have complex geometries with variable thickness in space. As a result, clear relationships are not established between fault geometry or composition and impacts to subsurface flow. Implications of this phenomena are not limited to hydrogeology applications: petroleum extraction, carbon sequestration, and geothermal energy each stand to benefit from a better understanding of this topic.

We postulate that the Loma Blanca Fault, located in central New Mexico, is an ideal candidate for gaining further insights into fault-fluid flow interactions. Our study will utilize an interdisciplinary geological, geophysical, and hydrologic approach. The Loma Blanca is a north-south oriented normal fault with sections of extensive outcrop. The fault is variably cemented with carbonate, dipping approximately 70ºE. Field analyses of the cemented outcrop reveals permeabilities low enough to substantially decrease fluid flow. A preliminary model of the local geology was created using samples from exploratory wells, directional cores, and near-surface geophysical data. The interim geologic model suggests that the fault extends into the subsurface with varying degrees of cementation. Multiple wells will be installed along each side of the Loma Blanca, allowing us to conduct groundwater pumping tests and gauge the aquifer response. If the fault is indeed cemented in the subsurface, we expect contrasting groundwater drawdown behavior on opposing sides of the fault following sufficient pumping. Additional field data will be obtained through innovative pneumatic oscillatory aquifer tests. Our future objectives are to analyze aquifer test data in conjunction with multiple modeling approaches to diagnose fault attributes and further explore the topic of fault-fluid flow interactions. Funding for this project is provided by the National Science Foundation.

pp. 74

2018 New Mexico Geological Society Annual Spring Meeting
April 13, 2018, Macey Center, New Mexico Tech campus, Socorro, NM