Abstract

The mobile production and storage platform with subsea mat oil tank is an important platform form for "BEE Mode" of marginal oilfield development. The calculation of temperature drop and maintenance for subsea oil storage tank is very important, especially for the crude oil with high condensation point, which affects the safety operation of platform directly. In this study, a numerical model of tank has been established based on the subsea mat oil storage tank of a mobile production and storage platform designed for the offshore oilfield in Beibu Gulf of the South China Sea. Through the study for heat transfer mechanism of subsea oil tank, the temperature drop characteristics of oil tank in different ballast plan have been analyzed. Besides, cyclic heating has been used to maintain the temperature of the oil, and the heating parameters and temperature field characteristics in this situation have been studied. The results show that, compared with the plan that the inner ballast tank is filled with seawater, the plan that inner ballast tank is void is more conducive to the maintenance of oil temperature. No matter what ballast plan is, the temperature drop at the outer bottom edge of tank is the most obvious; the temperature drop at the outer top edge of the tank is relatively obvious too; the temperature drops of other positions are relatively slow. For the mobile production and storage platform, the recommended cyclic heating temperature is 65°C; the positions far away from the inlet and outlet of cyclic heating are easy to form "Temperature Dead Zone", but the temperature will not be lower than the wax precipitation point as long as the cyclic heating is timely; the recommended cyclic velocity for heating is 1.0-1.5m/s, and higher velocity is not conducive to heat transfer.

Introduction

The jack-up mobile production and storage platform can be used in "BEE" offshore marginal oilfield development mode. The investment cost can be recovered and income can be improved by platform serving in multiple oilfields like a bee. However, the oil storage capacity of the oil storage tank placed on deck is very limited, and this problem can be effectively solved by using subsea mat oil storage tank (Tan et al.,2011). The temperature drop characteristics of subsea oil storage tank have a decisive impact on safe operation of platform. Therefore, the research on the temperature drop and temperature maintenance of subsea oil storage tank has great significance on the large-scale application of mobile oil storage platform. However, the relevant research results are very limited.

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