Study on the Mechanism of Gas Intrusion and Its Transportation in a Wellbore under Shut-in Conditions

Haifeng Zhu, Ming Xiang, Zhiqiang Lin, Jicheng Yang, Xuerui Wang (), Xueqi Liu and Zhiyuan Wang
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Haifeng Zhu: CNOOC International Limited, Beijing 100028, China
Ming Xiang: CNOOC International Limited, Beijing 100028, China
Zhiqiang Lin: CNOOC International Limited, Beijing 100028, China
Jicheng Yang: School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266555, China
Xuerui Wang: College of Computer Science and Technology, China University of Petroleum (East China), Qingdao 266555, China
Xueqi Liu: School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266555, China
Zhiyuan Wang: School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266555, China

Energies, 2024, vol. 17, issue 1, 1-17

Abstract: This paper presents a comprehensive study based on multiphase-seepage and wellbore multiphase-flow theories. It establishes a model for calculating the rate of gas intrusion that considers various factors, including formation pore permeability, bottomhole pressure difference, rheology of the drilling fluid, and surface tension. Experiments were conducted to investigate the mechanism of gas intrusion under shut-in conditions, and the experimental results were employed to validate the reliability of the proposed method for calculating the gas intrusion rate. Furthermore, this research explores the transportation rates of single bubbles and bubble clusters in drilling fluid under shut-in conditions. Additionally, empirical expressions were derived for the drag coefficient for single bubbles and bubble clusters in the wellbore. These expressions can be used to calculate gas transportation rates for various equivalent radii of single bubbles and bubble clusters. The initial bubble size of intrusive gas, the transportation speed of intrusive gas in the wellbore, the rate of gas intrusion, and variations in the wellbore pressure after gas intrusion were analyzed. Additionally, a method was developed to calculate the rising velocity of bubble clusters in water based on experimental results. The study reveals that the average bubble size in the bubble cluster is significantly smaller than the size of single bubbles generated from the orifice. When the viscosity of the drilling fluid is low, the transportation velocity of the bubble cluster exhibits a positive correlation with the average bubble diameter. When the average bubble diameter exceeds 1 mm, the bubble velocity no longer varies with changes in the bubble-cluster diameter. The research results provide theoretical support for wellbore pressure prediction and pressure control under shutdown conditions.

Keywords: offshore well drilling; gas intrusion rate; bubble initial size; bubble transport velocity (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2024
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