Three-dimensional Hydrogeological Modelling Around the Large Rock Cavern For the LPG Storage Project

Maejima, T. (Japan Oil, Gas and Metals National Corporation) | Uno, H. (Tokyo Electric Power Services Co., Ltd.) | Mito, Y. (Kyoto University) | Chang, C.S. (Kyoto University) | Aoki, K. (Kyoto University)

OnePetro 

ABSTRACT:

A three-dimensional hydrogeological modelling method for the large LPG storage project is developed in order to predict the hydraulic behaviors around the caverns precisely for the observational design and construction from a hydrogeological point of view. The Namikata LPG storage cavern under construction, one of the world’s largest LPG storage caverns is the subject of this study. More than a thousand of hydraulic conductivity data have already been obtained from the site investigation.The geostatistical technique is employed to deal with a large amount of the spatial data that can be obtained at each stage of the project. The ordinary kriging (OK) is implemented to obtain a spatial distribution of hydraulic conductivity and that of its estimation error at each stage. The sequential indicator simulation (SIS), one of the widely used geostatistical simulation methods, is also implemented to assess the uncertainty of hydraulic conductivity. A set of realizations, which are generated using different series of random numbers, gives a map of the upper tail probability above a specific threshold value. This map is convenient for the risk assessment related to the uncertainty of hydraulic conductivity. Furthermore a new hybrid modelling methodology considering geostatistical and hydrogeological correlations between a pair of spatial data at different locations is proposed to obtain a geostatistically and hydrogeologically relevant model that can enable to predict the hydraulic behaviors in the subsequent stage of the project precisely.The models based on the realizations of SIS are used to simulate the observed hydraulic behaviors of the site by FiniteVolume Method. The most relevant model is identified and validated by comparing the measured and the computed values of pore pressure at the specific positions. The validated SIS model shows lower hydrogeological connectivity than theOKmodel that has an unfavorable smoothing effect and is apt to overestimate the hydrogeological connectivity due to that effect. In fact the computed pore pressure from the validated SIS model shows better agreement with the measured value than that from the OK model. Thus the higher performance of the modelling method is clarified.



1 INTRODUCTION

The constructions of the Namikata and the Kurashiki LPG storage caverns are two of the world’s largest underground LPG storage projects being operated by JOGMEC in Japan. To maintain the air tightness of the storage caverns at normal temperature and high storage pressure, JOGMEC designed the water containment system. The system of water curtains is established above the LPG storage caverns and provides higher surrounding water pressure than storage pressure to maintain the air tightness, instead of using concrete and steel of lining works. The LPG storage pressure is designed as 0.95MPa for keeping the propane (boiling point is 15◦ at 0.75MPa) in liquid phase at normal temperature. To ensure the air tightness of LPG tank and the water containment ability of water curtains, it is important to grasp the hydrogeological structure in site-scale.