## 2 Materials and Methods
### Analysis of the Efficiency of Radial Jet Drilling Technology at the Perm Territory Oil Fields  
At the oil fields of the Perm Territory, the RJD technology has been used since 2006. By now, to date, 648 RJD operations have been completed (Figure 1) [9].  
The number of operations carried out on the carbonate reservoir (594) was much greater than that on the terrigenous one (54). The efficiency of the operations carried out on the carbonate reservoir was much higher than that on the terrigenous one. The average incremental oil production was 33,291 barrels per well at the carbonate sites, while at the terrigenous sites it was 25,880 barrels. For one-third of all the operations, the effect of RJD at the terrigenous sites lasts for less than one year, and in 15% of cases the oil  
Figure 1: General characteristics of RJD (radial jet drilling) use.  
production increment was less than 14.56 barrels. At the carbonate sites, the number of well interventions with the effect lasting for less than a year was 7%, while the number of failed interventions was only 1%.  
The main reason for the high efficiency of the RJD technology at carbonate reservoirs is the additional hydrochloric acid treatment (HAT) which is much more efficient for carbonate rocks than for terrigenous ones. There are several possible reasons for the low efficiency of RJD at terrigenous sites, such as clay swelling, canal colmation, the Jamin effect, and low residual oil reserves at the moment of RJD. The technological characteristics of RJD and the variability of its efficiency create the need for detailed special research of the conditions for using the RJD technology on carbonate and terrigenous sites [1]. Due to the rare use and low efficiency of RJD at terrigenous reservoirs, this study will only elaborate on its use on carbonate reservoirs.  
At carbonate sites, 590 RJD operations were carried out. Figure 2 shows the distribution of sites by the cumulative incremental oil production due to RJD.  
The greatest amount of the incremental production was registered at the T-Fm sites (42%--8386 thousand barrels); a comparable amount was collected from the Bsh sites (33%--6610 thousand barrels); they are followed by the V3V4 sites (25%--5059 thousand barrels) and an insignificant contribution was made by the KV1 sites (0.5%--87 thousand barrels).  
At the next stage, the results of well flow tests (WFTs) were analyzed. The WFTs were not carried out for all the wells, the study only covers the data for 417 wells before and after RJD. Figure 3 shows the success rate, i.e., the percentage of positive changes in the hydrodynamic properties of the reservoir.  
The success rate of the parameter change varies from 70 to 92% (on average 80%) for all the parameters except for skin factor (success rate 67 to 71%).  
In the last ten years, the RJD technology became one of the major technologies at the Perm Territory oil fields for wells with a decreasing productivity and a low production rate at the end of their service life. The technology efficiency varies depending on the geological and technological conditions, which requires a thorough approach to selecting candidate wells, in order to increase the general technological efficiency of the method.  
Figure 2: Distribution of sites by the cumulative incremental oil production due to RJD.