Numerical modelling of the influence of in-situ stress, rock strength and hole-profile geometry on the stability of Radial Water Jet Drill (RJD) boreholes

J. P. Latham, A. Farsi, J. Xiang, E. Clark, R. R. Bakker

Research output: Chapter in Book/Conference proceedings/Edited volumeConference contributionScientificpeer-review

Abstract

Radial water jet drilling (RJD) is a method of enhancing heat recovery by accessing and connecting to high permeable zones within geothermal reservoirs. The wall rock geometry behind an advancing water jet borehole under in-situ conditions is largely unknown. Water jet drilling tests were performed on 300 mm cubical blocks of weak porous sandstone under true-triaxial boundary stress conditions at the Delft Technical University (DTU) rock mechanics laboratory. Some of these tests showed distinct breakout features depending on the applied stress field. Geometries of resulting boreholes are recovered using X-Ray CT scans, and are analysed using segmentation software (Avizo). The code Solidity, using a combined finite-discrete element method with a cohesive zone fracture model, simulates stress take-up and wall shearing giving breakouts comparable to the experiments. The results lead to the suggestion that criteria based on Kirsch solutions would be suitable to provide general guidance on in-situ stress and rock strength conditions free of breakouts. FEMDEM models appear well-suited to examine geometries and dimensions that can be sustained by given strengths under deeper in-situ conditions. Wall-rock failure and a process of jet-hole enlargement together with the potential benefits of greater heat recovery arising from larger holes is also briefly discussed.

Original languageEnglish
Title of host publication53rd U.S. Rock Mechanics/Geomechanics Symposium
Subtitle of host publication23-26 June, New York City, New York
PublisherAmerican Rock Mechanics Association (ARMA)
Number of pages8
Publication statusPublished - 2019
Event53rd U.S. Rock Mechanics/Geomechanics Symposium - New York Marriott, Brooklyn, United States
Duration: 23 Jun 201926 Jun 2019
https://www.armasymposium.org/

Conference

Conference53rd U.S. Rock Mechanics/Geomechanics Symposium
Abbreviated titleARMA 2019
CountryUnited States
CityBrooklyn
Period23/06/1926/06/19
Internet address

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