Swelling behavior of shale/clay: Discrete element modeling, based on Monte-Carlo technique

Swelling of Shale-rocks create several problems [1] during underground drilling operations, such as stuck-pipe/drill-bit. However, swelling of shale-rocks can close the gaps between rock (wellbore) and casing –therefore no cementing is needed – which can save a lot of time and money and such a “natural” closing ensures “no-leakage” during further drilling and production phases (i.e., gas producing wells). The field experience reveals that some shale-rocks are good candidate for swelling and some are not. Understanding clay swelling and clay consolidation are important for clay deposit management works –especially in Port areas. There are several parameters influence the swelling and consolidation of clay/shale, such as- porosity, clay-quartz contents, stress difference between field and drilling zone etc. Therefore, to plan a safe and efficient drilling operation through shale-rocks and to manage clay deposits, we should understand the swelling mechanism of shale and the consolidation mechanism of clay. In this work, we have introduced a discrete element model, based on Monte-Carlo technique. We define a probability of swelling for all the clay grains in the clay/shale sample that includes the effect of stress-difference, porosity, temperature etc. The time evolution of grain swelling results in bulk swelling behavior of the sample and the simulation result qualitatively matches with the observations of shale/clay swelling experiments [2,3]. References 1. E. Fjær, R. M. Holt, P. Horsrud, A. M. Raaen and R. Risnes, Petrolum Related Rock Mechanics (Elsevier, 2008). 2. M. Deriszadeh and R.C.K. Wong, Transp Porous Med (2014) 101:35–52 DOI 10.1007/s11242-013-0229-8. 3. E. Rybacki, J. Herrmann, R. Wirth and G. Dresen, Rock Mech Rock Eng (2017) 50:3121–3140.