Wells – Processes – With indicating – testing – measuring or locating
Reexamination Certificate
2000-05-30
2001-10-23
Tsay, Frank (Department: 3672)
Wells
Processes
With indicating, testing, measuring or locating
C175S092000
Reexamination Certificate
active
06305469
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of creating a wellbore in an earth formation, the wellbore including a first wellbore section and a second wellbore section penetrating a hydrocarbon fluid bearing zone of the earth formation.
In conventional methods of wellbore drilling a drill string including a drill bit at its lower end is rotated in the wellbore while drilling fluid is pumped through a longitudinal passage in the drill string, which drilling fluid returns to surface via the annular space between the drill string and the wellbore wall. When drilling through an earth layer not containing a fluid, the weight and the pumping rate of the drilling fluid are selected so that the pressure at the wellbore wall is kept between a lower level at which the wellbore becomes unstable and an upper level at which the wellbore wall is fractured. When the wellbore is drilled through a hydrocarbon fluid containing zone the drilling fluid pressure should moreover be above the pressure at which hydrocarbon fluid starts flowing into the wellbore, and below the pressure at which undesired invasion of drilling fluid into the formation occurs. These requirements impose certain restrictions to the drilling process, and particularly to the length of the wellbore intervals at which casing is to be installed in the wellbore. For example, if the drilling fluid pressure at the wellbore bottom is just below the upper limit at which undesired drilling fluid invasion into the formation occurs, the drilling fluid pressure at the top of the open-hole wellbore interval can be close to the lower limit at which undesired hydrocarbon fluid influx occurs. The maximum allowable length of the open-hole interval depends on the specific weight of the drilling fluid, the hydrocarbon fluid pressure in the formation, and the height of the drilling fluid column.
Furthermore, it has been practised to drill through a hydrocarbon fluid bearing zone at wellbore pressures below the formation fluid pressure, a methodology commonly referred to as under-balanced drilling. During under-balanced drilling hydrocarbon fluid flows into the wellbore, and consequently the drilling equipment at surface has to be designed to handle such inflow. Moreover, special measures must be taken to control the fluid pressure in the wellbore during the drilling process.
An advantage of the invention is to provide a method of drilling a wellbore through a hydrocarbon fluid bearing zone of the earth formation, which method alleviates the restrictions imposed to the drilling process in conventional wellbore drilling and which allows the wellbore pressure to be below the formation fluid pressure while any hydrocarbon fluid inflow into the wellbore can be adequately handled.
SUMMARY OF THE INVENTION
In accordance with the invention there is provided a method of creating a wellbore in an earth formation, the wellbore including a first wellbore section and a second wellbore section penetrating a hydrocarbon fluid bearing zone of the earth formation, the method comprising
drilling the first wellbore section;
arranging a remotely controlled drilling device at a selected location in the first wellbore section, from which selected location the second wellbore section is to be drilled;
arranging a hydrocarbon fluid production conduit in the first wellbore section in sealing relationship with the wellbore wall, the conduit being provided with fluid flow control means and a fluid inlet in fluid communication with said selected location;
operating the drilling device to drill the second wellbore section whereby during drilling of the drilling device through the hydrocarbon fluid bearing zone, flow of hydrocarbon fluid from the second wellbore section into the production conduit is controlled by the fluid flow control means.
By drilling through the hydrocarbon fluid bearing zone using the remotely controlled drilling device, and discharging any hydrocarbon fluid flowing into the wellbore through the production conduit, it is achieved that the wellbore pressure no longer needs to be above the formation fluid pressure. The wellbore pressure is controlled by controlling the fluid flow control means. Furthermore, no special measures are necessary for the drilling equipment to handle hydrocarbon fluid production during drilling.
In case the second wellbore is to be drilled through one or more layers from which no hydrocarbon fluid flows into the wellbore, it is preferred that the drilling device comprises a pump system having an inlet arranged to allow drill cuttings resulting from the drilling action of the drilling device to flow into the inlet, and an outlet arranged to discharge said drill cuttings into the wellbore behind the drilling device.
Suitably said outlet is arranged a selected distance behind the drilling device and at a location in the wellbore section where a fluid is circulated through the wellbore, which fluid entrains the drill cuttings and transports the drill cuttings to surface.
The second wellbore section can be a continuation of the first wellbore section, or can be a side-track (i.e. a branch) of the first wellbore section.
REFERENCES:
patent: 4051908 (1977-10-01), Driver
patent: 5868210 (1999-02-01), Johnson et al.
patent: 5944009 (1999-08-01), Longbottom
patent: 6237638 (2001-05-01), Pringle et al.
Coenen Josef Guillaume Christoffel
Maekiaho Leo Bernhard
Shell Oil Company
Tsay Frank
LandOfFree
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