TY - GEN

T1 - Numerical investigations of thermally induced fractures in rock salt

AU - Zapf, D.

AU - Staudtmeister, K.

AU - Leuger, B.

PY - 2017

Y1 - 2017

N2 - For the storage of natural gas, compressed air or hydrogen in rock salt caverns it is necessary to carry out numerical calculations for the dimensioning of the relevant operation parameters. These are on the one hand the allowable maximum and necessary minimum internal pressure to ensure a gastight and stable cavern over decades and on the other hand the limitation of the withdrawal and refill rates between these geomechanical limits. During the withdrawal phases of the gas the temperature decreases which can lead to stress states in tensile regions at the cavern wall. Because the tensile strength of rock salt is relatively low compared to its compressive strength it is likely that tensile stresses lead to discrete fractures orthogonal to the direction of the tensile stresses. If fractures of this kind are created-whether vertical or horizontal-the gas will penetrate into the fracture at the relevant pressure and further extend the length of the fractures under certain circumstances. There are currently research projects in work that can describe whether the fractures might propagate into the not by temperature changes influenced rock salt mass during repeated cyclic pressure changes. Salt caverns cannot be entered but only explored by sonar measurements, with which it is not possible to detect tensile fractures at the cavern wall. Within this paper examples from mining configurations will be shown where temperature changes lead to tensile fractures in the surrounding rock salt. These fractures have been well mapped while the temperature development is well documented. The paper deals with recalculations under consideration of different salt properties of the temperature distributions and the resulting stress state in the surrounding rock salt mass. The stress calculation results and the consequences for the dimensioning of natural gas caverns are going to be discussed and assessed. A special aspect within this topic is the cooling of the cavern surrounding rock salt mass after the leaching phase with relatively cool fresh water and the influence on the first operation period.

AB - For the storage of natural gas, compressed air or hydrogen in rock salt caverns it is necessary to carry out numerical calculations for the dimensioning of the relevant operation parameters. These are on the one hand the allowable maximum and necessary minimum internal pressure to ensure a gastight and stable cavern over decades and on the other hand the limitation of the withdrawal and refill rates between these geomechanical limits. During the withdrawal phases of the gas the temperature decreases which can lead to stress states in tensile regions at the cavern wall. Because the tensile strength of rock salt is relatively low compared to its compressive strength it is likely that tensile stresses lead to discrete fractures orthogonal to the direction of the tensile stresses. If fractures of this kind are created-whether vertical or horizontal-the gas will penetrate into the fracture at the relevant pressure and further extend the length of the fractures under certain circumstances. There are currently research projects in work that can describe whether the fractures might propagate into the not by temperature changes influenced rock salt mass during repeated cyclic pressure changes. Salt caverns cannot be entered but only explored by sonar measurements, with which it is not possible to detect tensile fractures at the cavern wall. Within this paper examples from mining configurations will be shown where temperature changes lead to tensile fractures in the surrounding rock salt. These fractures have been well mapped while the temperature development is well documented. The paper deals with recalculations under consideration of different salt properties of the temperature distributions and the resulting stress state in the surrounding rock salt mass. The stress calculation results and the consequences for the dimensioning of natural gas caverns are going to be discussed and assessed. A special aspect within this topic is the cooling of the cavern surrounding rock salt mass after the leaching phase with relatively cool fresh water and the influence on the first operation period.

UR - http://www.scopus.com/inward/record.url?scp=85047854196&partnerID=8YFLogxK

M3 - Conference contribution

AN - SCOPUS:85047854196

T3 - 51st US Rock Mechanics / Geomechanics Symposium 2017

SP - 594

EP - 600

BT - 51st US Rock Mechanics / Geomechanics Symposium 2017

T2 - 51st US Rock Mechanics / Geomechanics Symposium 2017

Y2 - 25 June 2017 through 28 June 2017

ER -