Khazzan Dubai 1: Design, Construction and Installation

Abstract

ABSTRACT In early August, 1969, a 15,000-ton, bottomless offshore oil storage tank was completed on the shore of the Trucial Coast of the sheikdom of Dubai. The successful launching, towing and submerging of the tank were spectacular operations receiving world-wide attention. These operations, however, were preceded by extensive research and development programs to answer the many questions surrounding a new or different structure. These include tests of crude and salt water, handling of sludge, model test work and development of construction and installation techniques. INTRODUCTION Khazzan Dubai #1, a 500,000barrel oil storage tank, placed in service December, 1969, is located sixty miles offshore in154 feet of water. The structure, the first of its kind, stores oil produced from the Fateh Field. Dubai Petroleum, a wholly owned subsidiary of Continental Oil Company, operates the field for its partners, Dubai Marine Area Ltd. (Compagnie Francaise des Petroles and British Petroleum), Deutsch Erdol-Aktiengesellschaft, Dubai Sun Oil Company and Continental Oil Company. Hispanoil has now replaced British Petroleum as a partner of the DUMA group. The 15,000-ton structure (Figure 1) is 270 feet in diameter and over 200 feet in height. It has no bottom and operates on the water displacement principle. It is always full with either water or oil or a combination of the two. Filling is accomplished by placing oil in the tank above water. The additional weight of the oil on the water creates an imbalance in pressure which forces the water out of the tank through openings in the wall. The unusual structure requires special construction techniques which enable it to be built onshore, launched and towed some sixty miles to its offshore location. The launching, towing and submerging were spectacular operations that created worldwide interest throughout the industry. Behind the success of the structure, however, were many years of meticulous study and research. A new structure such as this brings up unique and special operating conditions which must be considered. These include salt pickup by the oil and sludge buildup at the oil/water interface. Gaging techniques must be used to remotely monitor the oil/water interface, divert the incoming stream once the tank is filled or shut down the pumps once the tank is empty. Certain operating advantages are expected: free water will automatically precipitate to the water below the oil/ water interface, decreasing the salt content of the crude, and large buildup of wax or heavy ends at the interface can be removed by pumping when the tank is stripped out. The open sea location where the tank is installed gives ample opportunities for wind to generate large waves (over 39 feet in height with 10-second periods). Coupled with storm-driven currents, these waves create tremendous forces on the oil storage tank. These large forces are resisted by an anchorage system consisting of 36" ? steel piles cemented into the sea floor.