Experimental Investigation of the Effect of Salt Precipitation on the Physical and Mechanical Properties of a Tight Sand
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ORIGINAL PAPER
Experimental Investigation of the Effect of Salt Precipitation on the Physical and Mechanical Properties of a Tight Sandstone Dujie Zhang1,2 · Yili Kang1 · A. P. S. Selvadurai2 · Lijun You1 Received: 30 April 2019 / Accepted: 10 December 2019 © Springer-Verlag GmbH Austria, part of Springer Nature 2019
Abstract Salt precipitation in rocks is a strongly coupled physico-chemical process, which has implications on natural gas extraction efficiency. The paper examines the effect of salt precipitation on porosity, permeability, permeability-stress sensitivity and elastic wave velocities of the rock matrix in tight sandstone with high salinity. Results show that the porosity and permeability decrease significantly after salt precipitation, and the permeability-stress sensitivity was aggravated by the salt precipitation. Following salt precipitation, the elastic wave velocities decreased significantly, the dynamic Young’s modulus of the rock decreased, and the dynamic Poisson’s ratio increased. Microstructural analysis suggests that following salt precipitation, the smaller pores and pore throats become the main seepage channels. The crystalline salt was deposited in the pores, the micro-fractures and on the surface of clay minerals, which not only reduces porosity and permeability, but contributes to the development of secondary cracks that weaken the rock matrix. Keywords Tight sandstone · Salt precipitation · Permeability-stress sensitivity · Elastic wave velocities · Secondary cracks
1 Introduction Salt precipitation is a common phenomenon encountered in many engineering endeavours, including the control of water loss from land surfaces (Scanlon et al. 1997), protection of pavements, roads and historical monuments (Flatt 2002; Espinosa-Marzal and Scherer 2010), and various geochemical issues related to intact geological formations (Shahidzadeh-Bonn et al. 2010). The mechanism for salt precipitation in deep geological formations is more complex than those encountered on surficial soils. For example, CO2 sequestration (Rathnaweera et al. 2015; Zhou et al. 2016), enhanced geothermal systems (Borgia et al. 2012; Cui et al. 2018), and natural gas production (Cui et al. 2016) are all situations, where salt precipitation can influence injectivity and productivity if salt precipitation causes alterations to the porosity and permeability of the geologic medium. * Dujie Zhang [email protected]; [email protected] 1
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, Sichuan, People’s Republic of China
Department of Civil Engineering and Applied Mechanics, McGill University, Montréal, QC H3A OC3, Canada
2
Field observations of salt deposition in gas wells indicated that salt crystals can gather in the wellbore and perforation zone, which affects the reservoir yield during gas production (Kleinitz et al. 2001). With reference to natural gas extraction, the gas reservoir can be divided into three zones depending on the degr
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