Formations containing gas hydrates are encountered both during ocean drilling for oil or gas, as
well as gas hydrate exploration and exploitation. Because the formations are usually permeable
porous media, inevitably there are energy and mass exchanges between the water-based drilling
fluids and gas hydrates-bearing formation during drilling, which will affect the borehole’s
stability and safety. The energy exchange is mainly heat transfer and gas hydrate dissociation as
result of it. The gas hydrates around the borehole will be heated to decomposition when the
drilling fluids’ temperature is higher than the gas hydrates-bearing formation in situ. while mass
exchange is mainly displacement invasion. In conditions of close-balanced or over-balanced
drilling, the interaction between drilling fluids and hydrate-bearing formation mainly embodies
the invasion of drilling fluids induced by pressure difference and hydrate dissociation induced by
heat conduction resulting from differential temperatures. Actually the invasion process is a
coupling process of hydrate dissociation, heat conduction and fluid displacement. They interact
with each other and influence the parameters of formation surrounding the borehole such as
intrinsic mechanics, pore pressure, capillary pressure, water and gas saturation, wave velocity and
resistivity. Therefore, the characteristics of the drilling fluids invading into the hydrate-bearing
formation and its influence rule should be thoroughly understood when analyzing on wellbore
stability, well logging response and formation damage evaluation of hydrate-bearing formation. It
can be realized by establishing numerical model of invasion coupled with hydrate dissociation.
On the assumption that hydrate is a portion of pore fluids and its dissociation is a continuous
water and gas source with no uniform strength, a basic mathematical model is built and can be
used to describe the dynamic process of drilling fluids invasion by coupling Kamath’s kinetic
equation of heated hydrate dissociation into mass conservation equations.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/1061 |
| Date | 07 1900 |
| Creators | Ning, Fulong, Jiang, Guosheng, Zhang, Ling, Bin, Dou, Xiang, Wu |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | text |
| Rights | Ning, Fulong |
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