Author: Petar Mijić, mag.ing.petrol.
The first scientist who pointed out that devices and materials could one day be produced in a size corresponding to the size of an atom was Richard Feynman in 1959. The term "nanotechnology" was first used in 1974 by scientist Norio Taniguchi. Although nanotechnology penetrates all areas of human activity, from the automotive industry, computers and electronics, robotics, medicine to the textile industry, its application in the oil industry has begun a few years ago. Nanotechnology means the use of materials which have very small dimensions, between 1 and 100 nanometers.
Water-based muds have been used during wellbore drilling since the early 1900s, and the main reason for their application is that they are usually cheaper and more environmentally friendly than other types of drilling muds. Nevertheless, today their application has technical limitations for their usage in increasingly demanding drilling conditions such as horizontal well drilling, extended reach drilling, etc. Accordingly, the biggest problem of water-based mud application is the inherent reactivity of water with clay minerals that are an integral part of shales which, during drilling, can lead to problems related to wellbore instability (May et al., 2020). Wellbore instability is defined as any unwanted wellbore diameter change (narrowing or widening) relative to the diameter of the drill bit by which a particular section of the wellbore was drilled. Over 90% of all problems related to wellbore instability occur during drilling through shales, rocks that compose 75% of all rocks through which the wellbore is drilled (Pašić, 2007). Since the classic additives used in drilling muds are not always suitable for solving problems during the drilling through different rocks, in the last ten years, the oil industry started to test new materials that could be used as additives in muds - nanoparticles (Mijić et al., 2017; Gaurina-Međimurec and Mijić, 2019). Nanoparticles in the drilling mud fill the pores in the shale (and in the created mud cake) and prevent the further flow of water from the mud into the rocks. Tests have been conducted mainly in various laboratories around the world, with no commercial application of nanoparticle-based drilling mud in practice. The results of previous laboratory tests are often contradictory because some types of nanoparticles have a positive effect in some tested muds, while in other muds, they give even worse results. Therefore, there is a need for a detailed study of the influence of type and concentration of commonly used nanoparticles on the properties of selected muds and on the swelling properties of pellets, which represent laboratory-prepared samples of water sensitive rocks to determine their applicability in practice.
For conducting laboratory tests of the influence of nanoparticle addition on different mud properties, SiO2 nanoparticles (particle diameter was 8, 20, 60 and 80 nm), Al2O3 (20, 30 to 60 and 100 nm), TiO2 (30 to 50 nm) and Fe2O3 (20 to 30 nm and 50 nm) were used in various concentrations. The emphasis was placed primarily on filtration properties (API filtration and PPT filtration) because their values have a significant effect on wellbore stability, such as swelling of the pellets in the nanoparticle-based drilling mud. In the laboratory tests, pellets containing 50% of bentonite (water-sensitive, active component) and 50% of quartz sand (inactive component) were used. Figure 1 (a) shows a case where conventional lost circulation materials (LCM) have been added to the mud to fill cracks and pores in rocks to create a mud cake on the wellbore walls, but the water from mud still penetrates the rock. By adding nanoparticles, the spaces between larger particles in the mud cake become filled, which results in the creation of a high quality, thin and impermeable mud cake (Figure 1 b).
Figure 1 Effect of nanoparticles on reducing filtration and increasing wellbore stability (Contreras et al., 2014).
In addition to tests related to increasing wellbore stability, measurements of rheological properties of selected muds at room and elevated temperature were performed. Taking into account the change of rheological parameters for each mud, the pressure drop around the characteristic set of drilling pipes was calculated in order to determine the Equivalent Circulating Density (ECD) of the mud and the possibility of applying these muds in practice. Furthermore, zeta-potential values were measured to confirm that there was no agglomeration of nanoparticles in the drilling mud and that the created nanoparticle-based mud was stable. Using a scanning electron microscope (SEM), the mechanism of filling the pores with nanoparticles from the mud was determined, as well as the reason for the reduction of pellet swelling (see Figure 2).
Figure 2. SEM image of SiO2 nanoparticles in a mud cake.
SEM images at different magnifications confirm that nanoparticles are deposited in the mud cake, as well as in the pore space of the ceramic disks used in the PPT mud filtration test. Nanoparticle-based drilling muds have lower filtration values than muds without nanoparticles because nanoparticles fill nanopores and thus prevent the penetration of water from mud into clay rocks and increase their stability (see Figure 3).
Figure 3 Increasing the wellbore stability by applying nanoparticle-based mud.
Considering everything mentioned above, nanoparticles have a favorable effect on increasing wellbore stability, especially in unconventional oil and gas reservoirs through which horizontal sections of the wellbore are drilled in order to increase hydrocarbon recovery.
May, P., Deville, J., Miller, J., Burrows, K., 2020. Environmentally Acceptable Shale Inhibitors for High Performance Water-Based Muds, IPTC-19902-MS, International Petroleum Technology Conference, 13-15 January, Dhahran, Saudi Arabia, pp. 1- 10.
Mijić, P., Gaurina-Međimurec, N., Pašić, B., 2017. The Influence of SiO2 and TiO2 Nanoparticles on the Properties of Water-Based Mud, ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering, Trondheim, Norveška, pp. 1-10.
Gaurina-Međimurec, N. i Mijić, P., 2019. Nanočestice u isplaci - rješenje problema tijekom bušenja kroz nekonvencionalna ležišta ugljikovodika?, Godišnjak 2018 Akademije tehničkih znanosti Hrvatske, str. 275-278.
Pašić, B., 2012. Primjena peleta u laboratorijskim ispitivanjima međudjelovanja inhibirane isplake i šejla, Rudarsko-geološko-naftni zbornik, 25, str. 63-72.
Contreras, O., Hareland, G., Husein, M., Nygaard, R., Alsaba, M., 2014. Wellbore Strengthening in Sandstones by Means of Nanoparticle-Based Drilling Fluids, SPE-170263-MS, SPE Deepwater Drilling and Completions Conference, Galveston, Texas, USA, pp. 1-24.
Petar Mijić, mag. ing. petrol. is a teaching assistant at the Department of Petroleum and Gas Engineering and Energy at the Faculty of Mining, Geology and Petroleum Engineering, University of Zagreb. He is a member of the Croatian student chapter of the Society of Petroleum Engineers (SPE) and is currently completing his doctoral dissertation entitled Improving wellbore stability using nanoparticle-based drilling fluids.
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