Effects of inhibitor KCl on hydration swelling and softening of a smectite-poor mudstone
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ORIGINAL PAPER-EXPLORATION ENGINEERING
Effects of inhibitor KCl on hydration swelling and softening of a smectite‑poor mudstone Xiuping Chen1,3 · Hao Yi1,3 · Leiyu Gao2 · Xiangchao Shi2 · Yuehao Liu2 Received: 2 May 2020 / Accepted: 29 June 2020 © The Author(s) 2020
Abstract The swelling and softening of mudstones caused by water often lead to serious geological disasters. In petroleum exploration and development, the hydration expansion of mudstone can also lead to serious wellbore instability hazards. The swelling of smectite clays is the main reason for this hydration expansion in mudstones. It is generally recognized that illite and illite–smectite mixed layer clays are both poor swellable and has a low effect on rock strength of smectite-poor mudstone. Furthermore, weakening law and degree of smectite-poor mudstone in water is not clear. This study conducted swelling tests and rock mechanics experiments on a smectite-poor mudstone from the Sichuan basin. The results show that both water content and swelling capacity tend to remain steady after soaking the samples for 24 h. The mudstone water content reached 5.36%, and the swelling rate was 2% after soaking in water for 72 h, and the rock had a lower unconfined compressive strength (UCS) value of 1.41 MPa. Adding KCl inhibited these processes, and elevated KCl concentrations drastically reduced the mudstone water content and swelling rate. Compared to water, the water content and swelling rate of mudstone soaked in a 6% KCl solution both decreased by 50%. The UCS and the elastic modulus also increased for a half-dry mudstone, although the inhibitor was important. At elevated KCl inhibitor concentrations, the UCS and elastic modulus of the hydrated mudstone were lower than those of the dry mudstone. The findings of this study can help for better understanding of the application of KCl inhibitor in water-based fluid for drilling engineering. Keywords Mudstone · KCl · Swelling · Unconfined compressive strength
Introduction The swelling and softening characteristics of mudstones are closely related to many engineering accidents (Al-Homoud et al. 1996; Jiang et al. 2014; Zhang et al. 2013). For example, in petroleum engineering, serious wellbore instability is often caused by the hydration, swelling, and softening of mudstones in the borehole. This slows the construction rate of many drilling projects (Gholami et al. 2018). Oil-based * Xiangchao Shi [email protected] 1
Petroleum Engineering Technology Research Institute of Sinopec Northwest Oilfield Company, Urumqi 830011, Xinjiang, China
2
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China
3
Key Laboratory for EOR of Fracture Vuggy Reservoir of Sinopec, Urumqi 830011, Xinjiang, China
drilling fluid may be the solution, but water-based drilling is increasingly being used for shale exploration and is considered to be more environmentally acceptable (Anderson et al. 2010). As a result, it is an urgent and challenging work
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