Wellbore flow rules in marine natural gas hydrate reservoir drilling

Wellbore flow rules in marine natural gas hydrate reservoir drilling

Natural gas

Gas hydrates

Methane

Finite difference method

Computer simulation

Crystal structure

Boreholes

Oil field equipment

Hydration

Petroleum prospecting

Two phase flow

Numerical methods

Petroleum reservoirs

Gases

Numerical models

Phase interfaces

Infill drilling

Rate constants

Drilling fluids

Natural gas wells

Mud logging

Drilling

Surface structure

As a new unconventional clean energy, natural gas hydrate has attracted attention in recent years. In marine natural gas hydrate reservoir drilling, hydrate cuttings will return upward in annulus. In this process, hydrate cuttings will decompose under higher temperature and lower pressure in upper wellbore. Because of the decomposition gas, liquidsolid two-phase flow in annulus turns into gasliquidsolid complex multiphase flow. This is different from that in conventional hydrocarbon reservoir drilling. Based on this, temperature and pressure models in wellbore are established. Hydrate decomposition process is divided into destruction of hydrate particles crystal surface structure and desorption of methane gas molecules at decomposition interface. And a hydrate kinetics decomposition model is derived considering fugacity of methane, decomposition rate constant, and superficial area. Then, complex multiphase flow coupling models are established considering the coupling relationships among varying temperatures, pressures, pipe flow, and hydrate decomposition in annulus. Finally, influences on temperature and pressure in annulus are analyzed through numerical simulation method. Moreover, multiphase flow coupled with hydrate decomposition in annulus has been calculated through finite-difference method under different operation parameters. The result shows that with higher delivery rate, temperature of cyclical drilling mud will be higher at bottom hole and lower at wellhead, leading to hydrate decomposition critical point moving down. And gas holdup and solid concentration will both decrease. Also, with increscent density of drilling mud, the critical point and end position of hydrate decomposition will both move up for higher pressure in annulus. And gas holdup and solid concentration will decrease. Besides, with increscent rate of penetration, hydrate decomposition critical point will move down to descendent pressure in annulus. And gas holdup and solid concentration will increase, and flow patterns will transform more acutely in annulus of upper wellbore. This research shows that rate of penetration should not be excessively high when drilling in marine natural gas reservoirs, and enhancing delivery rate and density of drilling mud can ensure safety control. This research provides important theories for wellbore flow rules in marine natural gas hydrate reservoir drilling. In addition, it can be used for analysis of wellbore flow safety. Springer Nature Singapore Pte Ltd. 2019.

1658-1672

0

7th International Field Exploration and Development Conference, IFEDC 2017, September 21, 2017 - September 22, 2017

2019

Wei, Na

Sun, Wantong

Meng, Yingfeng

Liu, Anqi

Chen, Guangling

Xu, Hanming

Xi, Yongzhao

Zhang, Xinyue

conferencePaper

18668755

10.1007/978-981-10-7560-5_151