| Lots of countries have started and expanded the capacity of the petroleum strategic storage to deal with tight international petroleum market. To meet the IEA's (International Energy Agency) proposed minimum 90d's petroleum reserve, state petroleum strategic reserves with capacity of 10?15% annual consumption (20?30 billion cubic metres) is required.Water-sealed underground storage is considered due to safety and economics. The storage facility must be located at sufficient depth below the groundwater table and in the vicinity of a permanent source of groundwater recharge so that the natural hydrostatic head cannot be depleted by drainage into the cavern. In other words, the groundwater pressure around the caverns should be strong enough to prevent any petroleum leakage. The water curtain system plays an important role in petroleum storage in the underground rock caverns. It provides an artificial water recharge in the rock mass in order to enhance flow patterns and to maintain a high hydraulic potential in the storage cavern vicinity. Therefore, effective water sealing performance is key to underground petroleum storage.With the help of technology survey, theoretical analysis, numerical simulation, laboratory and field tests, computer programing and inductive method, a series of studies are carried out to analyse water sealing effectiveness, based on Jinzhou and Huizhou state reserve projects. It covers water sealing performance analysis in different states and designs of water curtain system, quality detection technology of water curtain, grouting performance study in petroleum storage caverns and research on evaluation criteria of water sealing effectiveness.This paper studies construction technology of water curtain system firstly. Then, theoretical analysis and experimental research are conducted to systematic study water sealing effectiveness of water curtain system. Next, balanced grouting theory is developed for particular underground petroleum storage. Based on the above research results, assessment system of water sealing effectiveness is built in the end. The main achievements in this dissertation are listed as follows:Key construction technology of water curtain system and sealing principle are systematically elucidated in this study. Furthermore, correspondences between important input rock mechanics parameters and Q values for Q-system rock classification are investigated and L- equations are acquired, thereby bringing convenient to rapidly obtain available parameters when it's hard to collect measured field data in underground storage projects. Compares between Q-system and other rock quality classification methods are also drawn to improve accuracy of Q values. Research results of Q values in the rock provides convenience for the following water sealing studies.With the improved transient UPNM, numerical simulations are carried out to analyze the seepage field of the underground petroleum storage project in Jinzhou, China. The 3D discrete fracture pipe network model is adopted to systematically analyse the effects of the water curtain system (different water curtain states and water curtain pressure) on the water sealing effectiveness of the rock caverns in the fractured rock mass in both construction phase and storage phase. It is found that water curtain is an essential part of underground petroleum storage facility and the effect of the horizontal water curtain is more important than the vertical water curtain. Moreover, 0.4MPa water curtain pressure can achieve an optimum water flow balance, which is enough for water-sealing, without water seepage problem in the excavated tunnels during construction phase.Water-sealing performances of different water curtain system schemes with different length and spacing of the water curtain boreholes, the angles between horizontal plane(xz-plane) and horizontal water curtain system and various fracture networks are also discussed. Although the interconnectivity in the fracture network is very intricate, the result clearly illustrates the flow path. The 3D transient UPNM is capable of simulating DFNs with any complex geometry. Both construction phase and storage phase have been considered in the study. Results indicate that the reducing of the pressure of the water curtain, the length of the water curtain boreholes and the increase of the spacing of the water curtain borehole can deteriorate the seal effect of the water curtain, but increase of angles of horizontal water curtain can't improve water-sealing. In addition, it is worth mentioning that the failure of the water seal effect can occur locally. The locally connected unsaturated flow paths have been observed in the study, which cannot be found by using the continuous simulation model. This is because of the discontinuity and irregularity of the discrete fracture network. The water flow in the fracture network can be very complex. Conventional continuous model may cause inaccurate results. In view of the discontinuity of the fracture network, the continuous horizontal water curtain boreholes and relatively more closely spaced water curtain boreholes are recommended.Moreover, spacing and the number of boreholes influence the water-sealing efficiency,sufficiently close spacing of the drainage holes is needed in fractured rock because minor joints can affect water flow. What's the most important, it is only effective connectivity of fractures make sure water-sealing performance work well. Taking full advantage of water curtain boreholes to form connected fractures network for water flow is key to effectiveness of water curtain system. Finally, considering flow control in construction optimal water curtain system design is suggested - 0° horizontal water curtain borehole with 62.25m and vertical water curtain borehole with 58m, 20m-space in Q<10, 10m-space in Q?10.Quality detection technology of water curtain system is developed in this study to guarantee water sealing performance,as shown in the following steps: each water curtain borehole completed (water pressure test) ? all the water curtain boreholes finished(efficiency test)? petroleum storage caverns finished (integrity test). And hydrologic monitoring, especially groundwater level and seepage measurement should be carried out in every above step. Taking advantage of water sensitivity of transient electromagnetic method(TEM), this study makes assessment on the effectiveness of water curtain system for underground petroleum storage caverns during excavation period and also detects fracture water flow during the excavation process, in the light of the practice of two pilot large underground petroleum storage caverns in China. And comparative maps of apparent resistivity derived from TEM measurements before and after water-filling during excavation process have been made to improve quality of water curtain system. This is the first case to apply TEM to detect quality of water curtain system during construction in underground petroleum storage caverns projects, and it turns out to be practical, more visualized and worth popularizing.Computational algorithm of penetration length of grout in fracture network with 2D pipe network model is developed in this dissertation. Here, grout is regarded as Bingham fluid.Then, GIN (Grouting Intensity Number) method for underground petroleum storage is proposed to achieve a balanced water-grout state. GIN numbers are selected for four storage caverns in Jinzhou with GIN curve computing method proposed in this study.Four stages (S1-S4) assessment system is built to evaluate water sealing effectiveness throughout the whole project construction phase. Also, combined with results of Lugeon test,effectiveness test and TEM test in the field, connectivity evaluation criteria is developed to determine the effectiveness of water-sealing system in the field. In addition, a method for multivariate parameter (dip, dip angle, trace length, joint opening, joint space, surface morphology of discontinuities,infilling materials, effect of the groundwater and time)dominant partitioning of discontinuities rock mass is developed to determine optimal cluster number and grouping with fuzzy C-means clustering. On this basis, average validity index VIm is proposed combined with five cluster validity indexes to help grouping validity check.Reasonable achievements obtained from above a series of researches have been adopted in practical construction of water curtain system as a reference. This dissertation provide a case study for the safe and efficient construction of underground crude petroleum storage caverns,and may promote technological development of energy storage. |
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