Title:

Laser-Enhanced Drilling and Laser-Assisted Fracturing for Subsurface EGS Applications

Authors:

Souheil EZZEDINE, Sasha RUBENCHIK, Robert YAMAMOTO

Key Words:

Drilling, laser, geothermal, hard rock, EGS, laser-enhanced-drilling, laser-assisted-fracturing

Conference:

Stanford Geothermal Workshop

Year:

2015

Session:

Modeling

Language:

English

Paper Number:

Ezzedine2

File Size:

1354 KB

View File:

Abstract:

Enhanced Geothermal Systems (EGS) is a green renewable source of geothermal energy that is broadly distributed, virtually inexhaustible and capable of providing base-load carbon-free energy. Conduction-dominated EGS targets represent an abundant source of energy at depths of 6 km or greater, rather than localized thermal anomalies at shallow depths. However, to be economically competitive, the production temperature should be between 200 and 300°C and the rate of working fluids must be 50 to 80 kg/s (MIT, 2006). These conditions could be met at deeper reservoirs, say 6 to 10 km below ground surface. Unfortunately, drilling at those depths leads to exorbitant drilling costs of more than 10 million dollars a well. DOE (2008) and MIT (2006) call for improving drilling technology to accommodate for deeper wells while minimizing drilling costs. MIT 2006 concluded that “both evolutionary improvements building on conventional approaches to drilling such as more robust drill bits, …, improved sensors, and electronics capable of operating at higher temperature in downhole tools; and revolutionary improvements utilizing new methods of rock penetration will lower production costs. These improvements will enable access to deeper, hotter regions in high grade formations or to economically acceptable temperatures in lower grade formations”. We believe that by applying laser shock heating to hard rock such as granite, in EGS applications will induce thermal expansion of the rock and fracturing the rock which leads to rock softening and fissures and micro-fissures network creation. Laser-Enhanced and Laser-Fracturing drilling (LED & LAF) will minimize costs of drilling in hard rocks enabling deeper geothermal exploration; moreover it allows for the creation of dense fracture network in the vicinity of the well which promotes decreasing the fracking pressures for subsequent re-stimulation or sequential fracture propagation. We will demonstrate experimentally and numerically that LED/LAF could substantially increase the rate of penetration the drill bit even at lower rate temperature (200oC) the speed-up is of factor two. Operating at temperature of 700 oC can triple the rate of penetration. These values reflect thermal softening and not the combined effect of thermal softening and rock fracturing due to laser induced thermal load under no fluid drilling circulation. We extended our results of the simulation under cooling drilling-fluid condition. The numerical simulations using HPC allow for optimal design of cooling fluid circulation rate in order to maximize temperature load for rock softening while keeping the hardware at operational conditions. We show that the combined effects will sill increase the speed-up of penetration of the drilling bit at far lower operational temperatures. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.


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