**3. Results**

#### *3.1. Development of Unconventional Petroleum*

Section 3 focuses on describing the technological development and convergence of the unconventional petroleum technologies. First, we can easily identify differences in the extent of technological development of unconventional petroleum by validating the annual patent counts of each technological domain. Figure 2 presents information concerning the granted patent counts of three technological domains and their converged technologies, and the weight of converged technology of DD, IP, and SS.

In Figure 2A, the orange, gray, and yellow lines represent the annual counts of granted patent, including the TIs of DD, IP, and SS with their converged technologies. Broadly, the granted patent counts of the three technological domains increased from 1997 to 2014. In particular, from 2009 to 2014, patents related with IP (gray line) rapidly expanded from 170 to 464 patents per annum. From 2011 to 2014, patents related to DD (orange line) rapidly expanded from 99 to 186 patents per annum, and patents related with SS (yellow line) rapidly expanded from 62 to 186 patents per annum.

Figure 2B shows the weight of converged technology of the three technological domains (DD, IP, and SS). Interestingly, the weight of converged technology of IP (gray line) shows a very low level of weight in converged technology. While the weight of converged technologies of DD and SS (orange and gray lines, respectively) have fluctuated around 0.2 from 1990s to 2000s, they have increased from 0.2 to 0.4 since 2011.

Figure 2C shows the annual counts of granted patents in converged technologies. The convergence of DD and SS (orange line) always shows higher annual counts than others and have expanded from 2011 to 2014. The convergence of IP and SS (gray line) showed a zero count before 2009, and then showed 11 patents per annum at its peak point in 2014. The convergence of DD and IP (yellow line) also showed a zero count before 2004; it expanded from 2 patents per annum in 2011 to 14 patents per annum in 2016.

Figure 2D shows the trend in the annual count of granted patents for DD, IP, and SS, which is very similar to the orange, gray, and yellow lines of Figure 2A. This is because the weights of the converged technologies are quite stable for the research period, as shown in Figure 2B.

**Figure 2.** Annual patent counts by technological domains–1997 to 2016 [27]. 163

In summary, the intensity of technological development has increased in the last 20 years. Moreover, in the past 10 years, converged technologies such as CDS, CIS, and CDI have been developed. Technologies related to DD and SS show a lower extent of technological development with a relatively higher weight of converged technology than IP. Technology related to IP shows a higher intensity of technological development with a lower weight of converged technology. Only two patent technological domains, those of CDS and CDI, rebounded in their annual count of granted patents in 2016. In the next subsections, this study presents technological development from the network aspect of technological relatedness.

#### *3.2. Network of Shale Petroleum Technologies*

This subsection attempts to describe the technological development of shale petroleum by presenting network properties and visualizing the networks of technological relatedness. The network properties show the development of the patent set from the aspect of a network of technological relatedness. Table 2 presents the network properties of patent technological relatedness in 5-year periods.


**Table 2.** Network properties of shale petroleum technologies' patents.

Table 2 describes the network development for di fferent research periods. The patent counts grew by 94% on average in each period, while the number of nodes grew by 83%, the number of edges by 123%, and the ratio between edges and nodes by 21%. As described in the previous subsection, the values of Table 2 also show that the intensity of development in shale gas technology has increased. In addition, the number of nodes, which means the number of TIs, has also increased. Meanwhile, the connection between nodes has increased more rapidly. The increased edges and nodes in these networks could mean that these patents contain more combinations of TIs than before. The increased combination of TIs means an increased combination of new technological components, and thus, the emergence of a new technology is expected.

Figure 3 shows networks of technological relatedness to help understand the growth of the networks. The visualized networks show only the network of technological relatedness in the first and last periods. The intermediate process is omitted because the networks show a steadily increasing trend during the research period. Figure 3A,B show the visualized networks of technological relatedness from 1997 to 2001 and from 2012 to 2016, respectively. Figure 3 was drawn using Gephi, a visualization network software [33].

Figure 3 shows networks of technological relatedness of shale petroleum technologies from 1997 to 2001 (Figure 3A) and from 2012 to 2016 (Figure 3B). In Figure 3, the letters in orange, red, and blue represent the TIs of IP, DD, and SS.

When Figure 3A is compared to Figure 3B, the latter has a more compact shape than the former. This di fference in the visualized results is due to the quantitative di fference in patent count, the number of nodes and edges between the two patent groups as shown in Table 2, and the di fference in ratio between the number of edges and nodes. In addition, the distance between the TIs of DD and SS have become closer. The TIs of IP are still separated from other TIs. This point seems to be influenced by the high number of patents of CDS, as shown in Figure 2C. These di fferences in the distance between TIs can be described by the association strength similarity of TI, which represents technological relatedness. The technological relatedness between technological domains is presented in Table 3.

**Figure 3.** The network of technological relatedness of shale petroleum technologies for 1997 to 2001 (**A**) and 2012 to 2016 (**B**).


**Table 3.** Technological relatedness between technological domains.

Table 3 presents the association strength between the center nodes of the technological domains, the number of edges between technological domains, and the sum of association strength similarity of edges between technological domains.

Lines 1–3 in Table 3 show association strength, which represents the weight of the edge between the center nodes of technological domains such as DD, IP, and SS. These association strength similarities show the relatedness between the technological domains. In addition, the higher the association strength, the closer the distance between the converged technologies in the network of TIs. In lines 4–6 of Table 3, the number of combinations of TIs between technological domains represents the number of ways technologies converge. Thus, the convergence of DD and SS represents CDS, the convergence of IP and SS represents CIS, and the convergence of DD and IP represents CDI. In the lines 7–9 of Table 3, the sum of association strength in each combination between the TIs shows the changes in the aggregate quantitative relatedness between technologies.

In the case of CDS, the association strength similarity between DD (DD04) and SS (SS00) has increased by 2.80% for approximately 20 years. The number of combinations also increased by approximately two times over the same period. Moreover, the sum of the association strength increased by 33.82% over the same period. These changes in values are in concordance with the results from Figure 3. These changes show that the convergence in technology is conducted in a more detailed way. Thus, it implies an improvement in the level of technological development.

In the case of CIS, the association strength similarity between IP (IP26) and SS (SS00) occurred for the last two periods. Compared to the initial state, the association strength from 2012 to 2016 increased by 35.61%. The sum of association strength increased by 175.33%. The number of combinations has more than doubled. However, the number of edges was the lowest compared to the other converged technologies. Furthermore, compared to other technologies, CIS occurred recently and has not grown yet. In Table 4, while the granted patent counts of CIS increased, the ratio between the edges and nodes of CIS decreased compared to the initial state in the period from 2012 to 2016. Information pertaining to granted patent counts and other network properties by technological domains are summarized in Table 4.

In the case of CDI, the association strength between DD (DD04) and IP (IP26) occurred for the last three periods. Compared to the initial state, the association strength increased by 121.53%, while the sum of association strength increased by 305.76%. Interestingly, the number of edges increased two times for each of these periods. These results show that CDI has developed in a manner that has increased the various ways in which technology converges. In particular, the newly emerged ways of technological convergence seem to increase the technological relatedness between DD and IP. In Table 4, the granted patent count for CDI is six to ten times bigger in the period 2012 to 2016 compared to the previous periods. Furthermore, the ratio between edges and nodes increased two times in the period 2012 to 2016 compared to the previous periods.


#### **Table 4.** Network properties by technological domains.

Furthermore, Table 4 shows that IP (15.93) is the highest for the ratio between edges and nodes by technology area, followed by CDS (12.96), DD (12.03), SS (10.84), CDI (9.95), and CIS (6.48). Interestingly, although the IP has converged less with DD and SS, the technological development of IP shows that the combination of technology elements has progressed in a more complex pattern (high connectivity).

As described before, not only have shale petroleum technologies developed, the relationships between technologies have also changed. Next, this study attempts to determine the priorities of technological components, which are assumed to have changed with the development of technology, by presenting the betweenness centrality of TI.

#### *3.3. Priority of Technological Components*

In this section, the betweenness centrality is presented to validate the priority of technological components by technological domains. Table 5 presents the betweenness centrality of 10 TIs from the top for the four periods between 1997 and 2016.


**Table 5.** Betweenness centrality of technological indices (TIs) by period.

In Table 5, SS00 (automatic control system for drilling) is always ranked at the top. This result implicates that the technological development of the shale petroleum industry has focused on the smart system, which also has a high weight of convergence with DD for Figure 1. IP267 (reinforcing fractures by using prop) has been ranked the second highest from 2007 to 2016. This result is in concordance with the results of Shah et al. [14] Furthermore, DD04 (directional drilling), DD046 (horizontal drilling), DD06 (deflecting direction of borehole), and DD061 (tools such as shaft rotating inside a non-rotating guiding traveling) have been ranked between second and fifth. Interestingly, DD046 was ranked eighth in the last period, while DD06 was still ranked fourth. This result may implicate that the optimization of the production process seems to be more dependent on the technologies related to deflecting the direction of borehole than horizontal drilling, which is a recent technological development. SS005 (underground automatic control system), SS06 (tool feeds' automatic control, which responds to the flow or pressure of the motive fluid of drive), SS02 (automatic control of the tool feed), and DD068 (drilling by using down-hole drilling motor) have been frequently ranked between sixth and tenth. These TIs have a common point, that is, they can be applied to underground drilling systems. Lastly, IP263 (fracturing by using explosive) has seen an increase in its betweenness centrality rank since 2007. These increases in rank may indicate that the diversification of fracturing method has gathered interest since the year the industry came into existence.

To describe the primary focus of technological domains in the recent period, this study presents the betweenness centrality of TI by six technological domains from 2012 to 2016 in Table 6. Results bearing values less than 0.001 are omitted. As shown, there is a big di fference in the betweenness centralities of DD06 and DD046. The betweenness centrality of DD06 is approximately seven times bigger than that of DD046. Thus, the unconverged DD technologies have focused recently on the deflecting direction technologies. The unconverged technology of IP mainly focuses on IP267, reinforcing fractures (refracturing), in the recent period. In the case of the unconverged technologies of SS, SS00 is approximately 11 times bigger than SS02, which is ranked the second highest. The detailed component of the technology is not important for the development of the unconverged technology of SS. In the case of CDS, the betweenness centralities of the top two TIs are relatively bigger than that of the others. The top two Tis do not relate to the detailed function of the technologies. This shows that although the technological development of CDS is undertaken with a higher intensity than that of other converged technologies, the form of technological development is less related to the details of the technological component. CIS has only one TI, which shows that CIS has not grown yet. In the case of CDI, the betweenness centrality of Tis is quite similar. Interestingly, a more general level of TI has the lowest ranking value. Thus, it can be presumed that although CDI has a low intensity of technological development, these developments have shown relatively specific functions. In addition, converged technologies, such as CIS and CDI, show lower levels in the variety of priory technological components that pose high betweenness centrality.


**Table 6.** Betweenness centrality by technological domains—2012 to 2016.

Interestingly, some technology components such as DD046, DD067, and SS005 were relatively high within the converged technological domain compared to the order of priority within the unconverged technological domain. DD046 shows a lower priority than DD04 and DD06 within DD in Table 6. Meanwhile, DD046 shows the highest priority within CDI in Table 6. DD067 is not shown within DD, but DD067 shows the fourth priority within CDS in Table 6. SS005 shows lower priority than SS00 and SS02 within SS, but SS005 shows a higher priority than SS02 within CDS in Table 6. Thus, DD046 is an important component in the form of CDI technology. Furthermore, when DD046 is developed in the form of CDI, it is considered more important as a technological component. Moreover, DD067 and SS005 are considered as important technological components in the form of CDS technology.
