Using Flowback and Temperature for Closure Stress Diagnosis

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Издатель Oct 6, 2020

New technologies are required to access heat from conduction-dominated geothermal reservoirs. Dr. John McLennan discusses using flowback and temperature as diagnostics for closure stress in enhanced geothermal systems.

The concept of an engineered or Enhanced Geothermal System (EGS) in these sparsely fractured reservoirs, was first tested by the Los Alamos Scientific Laboratory in the 1970's, under the U.S. Department of Energy’s (U.S. DOE) Hot Dry Rock program. In its simplest form, an EGS consists of an injection well and a production well interconnected by a network of hydraulic fractures.

Developing an EGS reservoir has proven to be challenging. Despite numerous attempts worldwide over the last four decades, no commercial-scale EGS has been created. In 2014, the U.S. DOE initiated a multi-year initiative, known as the Frontier Observatory for Research in Geothermal Energy (FORGE) to develop technologies for characterizing, creating, and sustaining an EGS. Funds support the drilling, stimulation, and testing of two deep wells that will be drilled at the FORGE field laboratory in south-central Utah.

As can be imagined, the propagation of fractures interconnecting these EGS wellbores is essential. The magnitudes of the in situ principal stresses are the most basic element for understanding propagation. In 2017 and 2019, injection-based stress assessments were carried out in the openhole toe and in a cased/perforated section of a pilot vertical well. This seminar describes the basic measurement program and discusses the familiar complexities of interpretation.

Additional discussion is directed to flowback and temperature as diagnostics. In particular, preliminary measurements are described that used flowback rather than shut-in to rapidly identify closure. Flowback is not a new method. The technique remains very promising and lessons learned are described. Also, in one measurement campaign, bottomhole temperature during shut-in stands out to be a useful corroborative closure stress diagnostic.

The FORGE project is continuing and a brief update will be provided. The FORGE project is being led by the University of Utah.

What is FORGE? | The Department of Energy
https://www.energy.gov/eere/geothermal/what-forge

Dr. John McLennan | University of Utah
https://www.che.utah.edu/department/people/faculty/john_david_mclennan

Research that Matters: the Bureau of Economic Geology
https://www.beg.utexas.edu/