Potential for Induced Seismicity Near Conductive Faults: Examples From Fashing (Edwards) Field and Newark East (Barnett) Field

Abstract

While the increase in pore pressure resulting from subsurface saltwater disposal dominates the discussion of induced seismicity, limited inquiry is given to other factors that may contribute to a reduction of friction along existing subsurface faults. Our study identifies fluid-conductive faults near Fashing, Texas and Venus, Texas where anomalously high water production associated with oil and gas extraction may lead to water weakening of the fault as a result of friction reduction along the fault contacts. These field case studies highlight a potential link between seismicity and active water movement associated with hydrocarbon extraction along critically stressed fault zones.

Premature water production near faults can be indicative of conductive faults that allow saline aquifer invasion up the fault zone from deeper nonproductive zones. Structurally high, near-fault wells in the Fashing field produced high volumes of water, while structurally low wells located farther from the fault continued to produce water free. The first reported quakes near Fashing coincide with increased water production and declining gas production from wells proximal to the trapping fault. The Venus epicenters are similarly focused near wells that either intersect or communicate with the fault and produce anomalous volumes of water. The source of anomalous water in Barnett Shale wells is typically from the underlying Ellenburger formation via faults and associated fractures. Seismicity in Parker County near Azle shows a similar pattern of epicenters clustered near anomalously high-water producers.

Continuous production of fault-plane water over time may lead to various water-weakening mechanisms through which a decrease in the frictional strength of the fault zone can lead to seismicity. Common geologic characteristics at Fashing and Venus are recognizable in advance of drilling and may be avoided to effectively reduce the potential for increased water flow through conductive fault zones. Early realization of these geologic and production characteristics during field development may promote improved well planning, cost-effective staging and selection of intervals for fracture stimulation, and mitigation of potential hazards pertaining to induced seismicity. Proper well-site selection of both producing wells and disposal wells should consider safe setback distances when geologic conditions indicate a potential for communication with conductive faults.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018