## 4 Discussion
Thus, based on the five schemes, three new schemes (added Schemes 1, 2, and 3) were added to repair the fracture through different chemical precipitates in different stages. Each scheme was divided into two stages. Stage I is similar to what has already been described, using different proportions of mixed precipitate or single Fe(OH)\({}_{3}\) precipitate for fracture repair, while Stage II continues the experiment with a single CaCO\({}_{3}\) precipitate by replacing the aqueous solution in pump B. Figure 4 shows that when mixed precipitates are used for fracture repair, an inflection point generally appears in the PR curve when the experiment continues for about 2 h (the PR rate begins to slow down significantly). Accordingly, the duration of Stage I in the new schemes is also 2 h. Other procedures and methods are the same as those described above. The PR curves of the three new schemes are shown in Figure 7. By comparing the PR curves of the two stages with curves corresponding to the similar schemes mentioned above, some rules can be observed. In Stage I, although the precipitate composition adopted in the added scheme is the same as that of the corresponding schemes (the three added schemes correspond to Schemes 2, 4, and 5, respectively), only the PR curve presented by added Scheme 1 is consistent with that of Scheme 2. By contrast, the corresponding curves of the other two added schemes display obvious deviations, directly leading to the low PR efficiency achieved by these two added schemes in Stage I compared with the first schemes. Therefore, it can be inferred that when the Fe(OH)\({}_{3}\) precipitate participates in fracture repair, its repair effect may be random. As for Stage II, Figure 8 shows that the PR curves of the three added schemes, especially added Schemes 2 and 3--accounting for a small proportion of CaCO\({}_{3}\) precipitate in Stage I--are all very similar to that of Scheme 1, with their curves basically overlapping. This shows that the effect of channel size and morphology on fracture repair caused by the Fe(OH)\({}_{3}\) precipitate in Stage I does not affect the PR trend caused by the CaCO\({}_{3}\) precipitate in Stage II. Moreover, the higher the proportion of CaCO\({}_{3}\) precipitate participating in the repair in Stage I, the greater its impact on the PR trend in Stage II. From this perspective, the effect of the CaCO\({}_{3}\) precipitate on fracture repair is more certain than that of the Fe(OH)\({}_{3}\) precipitate. By comparing the PR curves in the three added schemes, it can be seen that added Schemes 2 and 3 were prolonged mainly because the \"flat permeability\" trend at the end of Stage I and early Stage II lasted for a long time. This is similar to the situation in Scheme 3, indicating that the Fe(OH)\({}_{3}\) precipitate adsorbed on the fracture surface in Stage I restricts the implantation and growth of CaCO\({}_{3}\) crystals in Stage II. Comparing added Schemes 2 and 3, it can be further inferred that when the proportion of the Fe(OH)\({}_{3}\) precipitate in Stage I increases, this restriction may be weakened, similar to the difference between Schemes 3 and 4. Therefore, the closer the proportion of Fe(OH)\({}_{3}\) in the mixed precipitate is to zero or one, the better its repair effect on the fracture. The PR curve in added Scheme 1 transitions smoothly at the junction of the two stages. Therefore, it can be inferred that if the duration of Stage I in this scheme is prolonged, the time required to finally achieve fracture repair may be shorter. Accordingly, a mixed Fe(OH)\({}_{3}\) and CaCO\({}_{3}\) precipitate with a molar ratio of about 1:4 in the early stage and a single CaCO\({}_{3}\) precipitate in the later stage should be able to repair fractures with relatively good PR efficiency. However, further study is required to determine a reasonable transition time for the two stages.