Session: 11-08-01 Multiphase Flow & Flow Assurance

Paper Number: 102218

102218 - Study on Influencing Factors of Deep-Water Shallow Gas Jet Height via Numerical Simulation 

The field and direction of global deep-water oil and gas exploration and development are constantly expanding. And the offshore oil and gas exploration and development is gradually moving from shallow sea to deep-water and ultra-deep water sea, and from offshore sea to open sea. As one of the shallow geological disasters in deep-water sea, shallow gas is generally buried shallow, and there is abnormal pressure in its formation process.

This paper studies a new countermeasure to deal with shallow gas in deep water, that is, the shallow gas is actively released from the ground in advance by drilling the pilot hole, and then the drilling operation is carried out. For a long time, most of the measures to deal with shallow gas are to avoid the risk of shallow gas by reselecting well location. Compared with the reselecting well location method, actively releasing shallow gas method can significantly save operation time and increase economic efficiency.

The main controversy of actively releasing shallow gas method is that the shallow gas floating up may accumulate on the sea surface around the platform, reducing buoyancy and causing the platform to sink. It is found that in certain deep-water areas, after the shallow gas spews into the sea from the underground area, it will be completely broken up when it reaches the height of 42-96 m, that is the shallow gas jet height is about 42-96 m. And then these small bubbles will diffuse and disperse, without affecting the operation platform on the surface. Therefore, the actively releasing shallow gas method is feasible to some extent. Generally, there are less than 7 cycles in the early stage of shallow gas release. As the shallow gas continues to spew into the seawater, the pressure of the shallow gas reservoir decreases gradually, and the periodic phenomenon will be weakened. The shallow gas jet height refers to the maximum collapsing and dispersing height of the last shaped shallow gas bubble, which occurs in the first cycle. The shallow gas jet height is the key factor to determine the safety of actively releasing shallow gas operation. The main influencing factors of shallow gas jet height include water depth, shallow gas reservoir pressure, shallow gas buried depth, pilot hole size and sea current. The increase of shallow gas reservoir pressure will stimulate higher jet height, while the increase of water depth, shallow gas buried depth and pilot hole size will reduce the jet height of shallow gas, and the existence of sea current will accelerate the collapse and diffusion of shallow gas bubbles. The study variation law of shallow gas jet height with each influencing factor is systematically carried out via numerical simulation, and the sensitivity of each factor is analyzed to form the influence coefficient model of shallow gas jet height, which provides theoretical support and guiding significance for the decision of actively releasing shallow gas by pilot hole in deep-water sea.

Presenting Author: Yang Long China University Of Petroleum (Beijing)

Presenting Author Biography: Ms. Yang Long is a Ph.D. candidate majored in oil and natural gas engineering in China University of Petroleum-Beijing. She holds a master’s degree of civil engineering from the University of Ottawa. Her research interests include deep-water drilling technology and shallow geological disasters.

Authors:

Yang Long China University Of Petroleum (Beijing)
Jin Yang China University Of Petroleum (Beijing)
Qishuai Yin China University Of Petroleum (Beijing)
Li Li China University Of Petroleum (Beijing)
Qianling Xue China University Of Petroleum (Beijing)