## 1 Introduction
Also, there is a more pronounced problem related to possible reservoir damage, especially in the large open-hole section, which is often the case in extended-reach drilling. With all the above, extended-reach drilling requires excellent control of other extremely important factors, such as torque and drag, equivalent circulating density (ECD) and lost circulation [18; 22; 26; 27], to avoid non-productive time and the possible above-mentioned problems. As mentioned earlier, during drilling conventional and especially for a horizontal well, various technical problems can occur, and most of them are due to high values of torque and drag forces which are caused by high friction. High torque and drag values represent a big problem while drilling deviated wells, especially in the deviated and horizontal part of the well and, basically, they affect the possibility of drilling wells, that is, they affect the possibility of drilling wells with a designed path. The important thing for successfully drilling this type of well is using the drill string to put weight on the bit through the deviated and horizontal section of the well. This means placing the drill collars as well as  
Figure 1: Different well types [18]. heavy-weight drill pipe in the vertical section of the wellbore, while the rest of the drill string through the deviated and horizontal section is composed of drill pipe. Another thing that should be paid attention to is to not allow the bending of the drill string if it is under a lot of compression load, which is often the case during the drilling of the large horizontal section in extended-reach drilling. This significant increase in compressive load is directly a consequence of the position of the drilling string within the wellbore. Unlike the drilling of the vertical well, where the used drill string is positioned theoretically in the center of the wellbore with minimum contact with the wellbore wall, in directional, horizontal, and extended-reach drilling the used drill string lies on the lower wall of the wellbore. This situation entails increased contact between the used drill string and wellbore wall as well, significantly increasing torque and drag forces during drilling and casing installation operations. Except for drilling operations, all the above-mentioned problems make well completion and workover operations difficult to perform as well. Despite increased torque and drag forces, there are extensive problems related to the drill pipe joint wearing, since the joints are the most exposed part of the drill pipe and in direct contact with the wellbore wall (steel casing or rock in the open-hole section). This problem can be solved by adding pipe protectors/nonrotating rings on the pipe body or by the hardbanding of the pipe joint with wolfram carbide or some other materials (Figure 2). In the first case, adding the pipe protectors/nonrotating rings on the pipe body inevitably increases the contact point between the drill string and wellbore wall, and in the second case, the hardening of the pipe joint can cause excessive wear of the installed casing string. Decreasing the torque and drag values can be achieved using different methods because usually using only one method does not solve the issue related to increased values of torque and drag. Most research conducted by different groups of researchers is directed at reducing the friction factor by changing the mud fluid composition (using lubricants or oil-based muds, as well as protecting the drill string/casing from mechanical wear) [28; 29]. [PERSON] et al. (2023) have introduced a new lubricant derived from triolein. After the preparation of graphene and triolein, they were incorporated in the mud system. After aging for 16 h at a temperature of 240 \({}^{\circ}\)C, an examination of the rheological and filtration properties was conducted to test the impact of the lubricant on the mud system as well as the lubricating performance of the drilling fluid.