Design and construction of the Ningbo underground LPG storage project in China

Abstract

NCC International, Sweden and Chiyoda, Japan were awarded the EPC (Engineering, Procurement, and Construction) contract to design and construct the LPG gas storage project of Ningbo, China. Chiyoda was responsible for the process and pipe-work and NCC the civil construction. The basic design of the civil works was provided at the bidding stage by Geostock of France. The client was BP Amoco with 93% and Ningbo Huadong LPG Company Limited of China with the remaining 7%. The well known and proven design concept is to trap the gas in unlined caverns where the structural rock is fully saturated. That means that all joints and pores of the rock are filled with water under a pressure that exceeds the pressure of the stored gas. To ensure a safe and steady ground water table of the required height, infiltration of fresh ground water is a must as there is a continuous flow of water into the caverns. This recharging of ground water is provided by a number of mainly horizontal infiltration holes that are being drilled from purpose constructed infiltration galleries. In all there are five storage rooms giving a total storage volume of 0.5 million m3. The largest caverns are 20 m wide, 22 m high and 290 m long and hold 125.000 m3. For construction purposes the original design of the storage rooms were altered in order to favor a fast and economic excavation of them. It was judged that the quality of the rock was good enough to go for a larger a more square shaped cross-section which certainly favored a fast excavation. It is obvious that the as built one from production point of view has great advantages. The caverns were excavated in three and four steps by starting with an 8 m high top heading which was split in two equal halves. One of the halves was advancing a few rounds ahead of the other mainly to allow for a faster excavation as this concept offers another face to work at. Beside that the face is so wide that it cannot be covered by one set up of a drill rig. The three Atlas Copco drill rigs Boomer 353 E were provided by NCC and utilized by subcontractor, The Sixth Engineering Bureau of Hydropower & Water Conservancy was employed for the drilling and blast operations. The drilled length of the rounds were generally 4.5 m. The benching that was made in two steps each 7 m high. Thanks to the new design the benching could be performed with vertical drilling which here has meant savings on both time and cost. For the drilling drill rigs AC ROC 542 were provided by NCC and used by subcontractor. The explosive for both the top heading and the benches was cartridged emulsion provided by a local manufacturer. This project had a slow start with re-bidding and alteration of scoop of work. The client having very limited experience from these kind storage facilities had an opened mind and took the advantage of the knowledge provided by both the designer Geostock and the contracting JV of Chiyoda and NCC. The contract form EPC (Engineering Procurement & Construction) gave an easy access to the skill of the parties involved. There was a good understanding and acceptance of alterations in the design and construction process. A strong ambition to fulfill the time schedule at the requested quality standard together with no major geological deviations from the geological settings brought this construction project to completion two months ahead of schedule. (A) Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.