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Invasion of water-based drilling mud into marine gas-hydrate-bearing sediment; one-dimensional numerical simulations

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Authors:Ning Fulong; Zhang, Keni; Wu Nengyou; Jiang Guosheng; Zhang Ling; Liu Li; Yu Yibing
Author Affiliations:Primary:
China University of Geosciences, Faculty of Engineering, Wuhan, China
Other:
Lawrence Berkeley National Laboratory, China
Chinese Academy of Sciences, Guangzhou Centre of Gas Hydrate Research, China
Volume Title:Diqiu Wulixue Bao Acta Geophysica Sinica
Source:Diqiu Wulixue Bao = Acta Geophysica Sinica, 56(1), p.204-218. Publisher: Science Press, Beijing, China. ISSN: 0001-5733
Publication Date:2013
Note:In Chinese with English summary. 73 refs.
Summary:Integrating 3D seismic survey and well logging can achieve more accurate quantification of natural gas hydrates as a potential energy and environmental impact. However, some factors can influence the accurate interpretation and evaluation of well logging results. Except washouts, the invasions of drilling fluid probably also seriously distorts the results of well logging. In this work, we performed numerical simulations to study the dynamic behavior and general rules of mud invasion into oceanic gas hydrate bearing sediments (GHBS) by taking hydrate reservoirs in the Gulf of Mexico as a case. Compared with the conventional oil/gas-bearing sediments, hydrate dissociation and reformation are the main characteristics of mud invasion in GHBS when the invasion condition is in an unstable region of gas hydrates phase diagram. The simulation results show that the density (i.e., corresponding pressure), temperature, and salt content of drilling fluids have great effects on the process of drilling fluid invasion. When the temperature and salt content of drilling fluids are constants, the higher the density of the drilling fluid is, the greater degree of invasion and hydrate dissociation are. The increased pore pressure caused by the mud invasion, endothermic cooling with hydrate dissociation compounded by the Joule-Thompson effect and lagged effect of heat transfer in sediments, together make water and gas forming secondary hydrates. The secondary hydrate together with existing hydrate probably makes the hydrate saturation higher than original hydrate saturation. This high saturation hydrate ring could be attributed to the displacement effect of mud invasion and the permeability reduction because of secondary hydrates forming. Under the same temperature and pressure of drilling fluids, the higher the salt concentration of the drilling fluid, the faster rate and greater degree of hydrate dissociation due to the stronger thermodynamic inhibition effect and heat transfer efficiency. The occurrence of high-saturation hydrate girdle band seems to mainly depend on the temperature and salinity of drilling fluids. The dissociated free gas, the dilution of water salinity associated with hydrate dissociation and the occurrence of high saturation hydrate ring probably cause the calculated hydrate saturation based on well logging is higher than that of actual hydrate-bearing sediments. Our simulations suggest that in order to keep wellbore stability and well logging accuracy during drilling through the hydrate-bearing sediment, it is better to adopt the managed pressure drilling and low-temperature mud circulation, and add kinetic inhibitors or anti-agglomerants instead of salts into drilling fluids for preventing hydrate re-formation in the well.
Subjects:Drilling muds; Fluid injection; Formation damage; Gas hydrates; Marine sediments; Numerical models; Petroleum; Petroleum engineering; Production; Sediments; Simulation; Atlantic Ocean; Gulf of Mexico; North Atlantic
Coordinates:N180000 N300400 W0803000 W0980000
Record ID:759112-17
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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