International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Since 90% of all problems related to the wellbore instability occur during drilling through shales, which are mostly consisted of clay minerals, the filtrate from drilling mud penetrate into shale rocks and lead to their destabilization, so the industry is considering the possible application of new types of additives because conventional additives, due to their size, cannot enter in pores of shales, plug them and reduce further filtrate penetration. The oil industry in last few years turns to investigate possible application of nanoparticles because they can enter in small shale pores and plug them, thus increasing the wellbore stability. In this paper the influence of the size (50 nm and between 20 and 30 nm) and concentration (0.5, 1, 3 and 5 wt%) of Fe2O3 nanoparticles on density, rheology, API filtration, and swelling of laboratory prepared pellets in contact with mud without and with nanoparticles was determined. Due to the fact that the rheological properties are significantly increased at higher concentrations, and that smaller particles give better results with an emphasis on increasing the wellbore stability further tests should be carried out with nanoparticles Fe2O3 which size is between 20 and 30 nm in maximum concentration of 1 wt%.

During mud circulation pressure losses occur in all sections of the wellbore: surface pipeline, inside drill string, drill bit and around drill string. The sum of the pressure losses calculated for each section is equal to the total pressure loss in the system, i.e. the pressure that is read on the manometer of the mud pump. The mud flow through annulus (between drill pipes/collars and open hole/casing) causes an increased pressure loss for the certain flow rate which increases the pressure exerted on the wellbore wall, so it is important to manage it. In this paper, the influence of SiO2 nanoparticles on the rheological properties of bentonite mud was examined. After tha t, for a typical wellbore construction and selected mud flow was calculated their influence on pressure losses in the area around drilling pipes and collars. The pressure losses were determined using the Bingham model which provides an easy way to obtain data of acceptable accuracy for the case of application in conventional vertical wells. The results indicate that the addition of SiO2 nanoparticles can reduce the pressure loss during mud circulation, in some cases by more than 50%.

Drilling mud is a working fluid which consists of a water and different added additives and is used during drilling of wells. By circulating through the wellbore, it ensures continuous cuttings removal, required pressure to stop the influx of reservoir fluid in wellbore, lubrication of drilling tools and maintaining wellbore stability while drilling through various types of formations. Since the well is often drilled through water-soluble rocks, which are mostly consisted of clay minerals, the penetration of the filtrate (water) into such rocks can lead to their destabilization, so the industry is considering the application of new types of additives because conventional additives, due to their size, can not enter in pores of rocks which has very low permeability, plug them and thus reduce further penetration of the filtrate. In recent years, scientists have paid great attention to the testing of nanoparticles (most tests are carried out with SiO2 nanoparticles) for drilling through low permeability rocks. Nanoparticles are particles whose diameters range from 1 to 100 nanometers so they can enter into the pores and create a high-quality mud cake, thereby reducing the filtrate invasion and increasing the wellbore stability. This paper describes a laboratory test carried out with SiO2 nanoparticles which average particle size was 20 and 60 nm added in concentrations of 1 and 3 wt% to water-based muds. Special emphasis was put on rheological and filtration properties. By
optimizing the concentration and size of the used nanoparticles, the rheological and filtration properties of the used drilling muds were improved.