Role of nanocomposite additives in well bore stability during shale formation drilling with water based mud – A comprehensive review J. Sudharsan a , Sunil Kumar Khare b,⇑ a Doctoral Research Fellow, Department of Petroleum Engineering and Earth Sciences, University of Petroleum and Energy Studies, Dehradun – 248007, Uttarakhand, India b Department of Petroleum Engineering and Earth Sciences, University of Petroleum and Energy Studies, Dehradun – 248007, Uttarakhand, India article info Article history: Available online 18 April 2022 Keywords: Drilling fluid Wellbore Shale Nanoparticles Oil and gas abstract Drilling operations require suitable drilling fluids to maintain the wellbore stability by stabilizing the shale formations near well bore that are prone to swelling and collapse due to their interaction with water in drilling fluid. The conventional drilling fluids are not effective in maintaining the shale stability due to bigger size of mud additives compared to shale pore spaces. Water based mud, when added with suitable volume of nanoparticles shows improvement in well bore stability, besides improvement in mud rheology and its thermal characteristics. Addition of nanoparticles and shale inhibitors to drilling fluids significantly improves well bore stability in shale sections of well bore. Nanoparticles added with shale inhibitors produce synergic effect to achieve efficient shale inhibition. Therefore, nanocomposites com- bined with nanoparticle and shale inhibitor improve the shale section well bore stability compared to nanoparticles and the conventional shale inhibitors. This paper presents the effect of different nanocom- posites on shale inhibition, their inhibiting mechanism and their associated advantages and disadvantages. Copyright Ó 2022 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Confer- ence on Materials, Mechanics, Mechatronics and Manufacturing. 1. Introduction The global reserves of conventional oil and gas are declining, therefore there is a growing need to explore and develop uncon- ventional shale hydrocarbon reserves to meet the ever-growing energy demand [1]. Shale and clay minerals such as illite, smectite and montmorillonite have abundant pore spaces with very small radii (less than 2 nm) and poor interconnectivity (permeability) [2]. Well construction activity involves drilling of shale and clay, which accounts for approximately 75% of the total formations drilled during the oil and gas drilling phase and 90% of borehole instability challenges are encountered while drilling shale and clay formations.[3]. Water penetration into the shale formation from water based mud (WBM) increases pressure loss that leads to clay swelling, which results in drilling problems such as borehole col- lapse, weakening the wellbore, and stuck pipe etc. [4]. Since there is long depth interval interaction of drilling fluid with shale and clay during horizontal drilling in shale gas wells, the well bore sta- bility is major challenge in drilling such well sections with WBM [5]. Plugging the nanopores in shale is a way forward to solve well- bore instability during drilling of shale sections since the size of conventional shale inhibitors such as calcium walnut shell powder, asphalts and carbonates are too large to plug and seal the nano- pores of shale formations [6]. Although nanosilica seals nanopores, it has limited role in tackling the problem of shale instability due to the aggregation. Nanosilica has demerits such as high cost, more time required to synthesize it, and micro emulsion instability prob- lems when added in the drilling fluid etc. [7]. When silica nanoparticles added and formulated appropriately with drilling mud, fluid invasion from the mud into shale forma- tion can be reduced effectively [8]. Addition of graphene oxide to WBM also improves the shale inhibition [9]. But these inorganic nanoparticles are rigid in nature and the deforming capacity is low that results in weak interaction with shale matrix [10]. Further research on role of organic nanoparticles in shale inhi- bition [7] shows that addition of nano terpolymer exhibits high dispersion capability with the drilling mud and [10] hyper branched polyamine nanoparticles exhibit high interaction with shale pores, and show enhanced shale pore plugging capacity https://doi.org/10.1016/j.matpr.2022.04.009 2214-7853/Copyright Ó 2022 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Materials, Mechanics, Mechatronics and Manufacturing. ⇑ Corresponding author. E-mail address: skhare@ddn.upes.ac.in (S. Kumar Khare). Materials Today: Proceedings 62 (2022) 6412–6419 Contents lists available at ScienceDirect Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr