## 4 Discussion  
To reduce the high values of torque and drag in extended-reach wells, usually one method does not solve the issue. One of the most common ways to reduce high values of friction and thus high values of torque and drag is to use lubricants in mud systems at certain concentrations. After conducting research, it has been shown that using only one method does not solve the problem by itself, so a combination of different methods should be used to reduce the high values of friction force. The method proposed in this paper to reduce the high values of friction is using lubricants in a polymer mud system in combination with protective sliding rings that would be put on the drill pipe joint. This idea is thought to reduce the friction that appears between two surfaces in contact and also reduce the wear of tool pipe joints.  
After conducting thorough research, thermoplastic polymers were found to be the most suitable choice to make the protective sliding rings, so three materials were chosen: PA6, Teflon and POM. The first step in testing these materials was to choose a polymer mud system with and without weighting additives in which lubricant was added at a concentration of 2% vol.  
The first part was to test the test blocks in polymer mud with and without weighting additives in which one of three lubricants, X, Y and Z, was added at a concentration of 2% vol. The results showed that, compared to the steel block, the blocks made from PA6, Teflon and POM showed significantly lower values of friction force in both polymer muds with and without weighting additives in which one of three lubricants, X, Y and Z, was added at a concentration of 2% vol.  
Comparing all three tested materials, PA6, Teflon and POM, the results presented in this paper show that the lowest value of friction force was registered for Teflon in all polymer muds with and without weighting additives in which one of three lubricants, X, Y and Z, was added at a concentration of 2% vol. After analyzing all the results obtained from these tests it was obvious that the next step in measuring the mechanical wear of one of these three materials (PA6, Teflon and POM) would be using the test block made from Teflon.  
The mechanical wear of the Teflon block was tested in both polymer muds with and without weighting additives in which one of three lubricants, X, Y and Z, was added at a concentration of 2% vol.  
From the presented figure above, small changes in the friction force value during testing time can be seen. It is very difficult to pick a special reason for this change, but it can be assumed that this change is due to a combination of factors such as the presence of the fine solid particles of weighting additives in a polymer mud system, chemical interaction between drilling fluid and material, and slightly increasing the temperature of the two surfaces in direct contact. Also, one of the reasons could be about the way the testing block was prepared (mechanically milling the curved contact surface) where it is noticeable that the rough surface has been smoothed with time. It would be beneficial to test the effect itself in future research.  
The protective sliding ring would be installed on the drill pipe joint, and it would have the role of reducing torque and at the same time protecting the drill pipe joint from excessive mechanical wear. In Figure 19, there is an example of installing the protective sliding ring on the drill pipe joint. The design shown in Figure 19 assumes that welding metal rings act as a border on both drill pipe joints (on the third of the length of each drill pipe joint from the end) and they will act as a barrier to hold the protective sliding ring in the same position, considering both drill pipe joints.