Measuring and testing – Borehole or drilling – Fluid flow measuring or fluid analysis
Patent
1999-02-01
2000-05-09
Williams, Hezron
Measuring and testing
Borehole or drilling
Fluid flow measuring or fluid analysis
7315222, 7315229, F21B 2108, F21B 4710
Patent
active
060587717
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the determination of fluid influx or efflux to or from a borehole during a drilling operation.
When drilling a borehole for a well, such as an oil or gas well, it is desirable to be informed when fluid is passing through the walls of the borehole between the borehole itself and the formation through which the borehole is passing. Whether a formation fluid, such as water, oil or gas is leaking/flowing out of the formation into the borehole, or drilling fluid (mud) within the borehole is being lost into the formation, it is necessary to know this in order to continue the drilling process properly and efficiently.
It has now been discovered that in certain circumstances useful information about the influx or efflux of fluid can be gained by observing the pressure within the borehole in the region of the drilling bit, this observation being carried out not when the drill is actually operating but when it is still (and the pipe string to which it is mounted is also still) and the drilling fluid is not being pumped; the basis for this is that the drilling fluid is thixotropic (like a non-drip paint), and when allowed to--when not disturbed--will form a gel, as is now explained.
Rather surprisingly it has been found that a gelled drilling fluid is capable of quite accurately transmitting the force created by moving fluids at the interface between the borehole and the earth formation being drilled through--that is, inflowing or outflowing fluids--displacing the drilling fluid along the borehole, and with an efficiency far greater than previously recognised. If the drilling fluid is effectively gelled, it acts like a solid in transmitting pressure, and can therefore respond to and transmit pressure changes due to volume changes occurring near the drill bit with great sensitivity, even if the relevant pressure sensors are themselves located some distance away. During the transition period from the non-gelled to the fully-gelled state pressure changes will increase to those achieved in the fully-gelled state. To use this capability the drilling fluid must actually be allowed to gel and that means that the drill must not be operating, the drill string must not be moving, and the drilling fluid must not be being pumped along the borehole. It is this which is the invention--it is primarily a method of determining fluid inflow or outflow during drilling, by using a gelling drilling fluid whose characteristics yield stress .tau..sub.y and gelation period t.sub.g --are known, and then, while all drilling and pumping is ceased, measuring downhole differential pressure .DELTA.P and using the observed changes therein to allow a determination of the fluid flow.
In one aspect, therefore, the invention provides a method of determining fluid flow into or out of a borehole during drilling of the borehole using a gelling drilling fluid, the method being characterised by including the steps of: drilling fluid; string stationary for a period of time t.sub.g, measuring the downhole differential pressure AP between two points spaced along the longitudinal axial orientation of the borehole; and changes in differential pressure .DELTA.P during the gelation period t.sub.g, determining the fluid flow.
In a second aspect the invention provides apparatus for use in the method of the invention, which apparatus, comprises: operative to measure the differential pressure of fluid in the borehole along the longitudinal axial orientation of the borehole; and the surface.
The preferred forms of both the method and the apparatus of the invention will be seen from the following comments.
The apparatus employs a differential pressure monitor; this is conveniently two individual pressure sensors located on the exterior of the bottom hole assembly and suitably spaced apart from each other along the axial orientation of the borehole (preferably by a distance greater than one foot [about 30 cm]). The pressure monitor (its individual sensors) is desirably positioned near the bottom end of the bottom hole assembly.
Where individual
REFERENCES:
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patent: 4299123 (1981-11-01), Dowdy
patent: 5042296 (1991-08-01), Burgess
patent: 5184508 (1993-02-01), Desbrandes
patent: 5247830 (1993-09-01), Goode
patent: 5465609 (1995-11-01), Romieu et al.
Johnson Ashley Bernard
Rezmer-Cooper Iain
Christian Steven L.
Kanak Wayne
Schlumberger Technology Corporation
Soliz Chad
Williams Hezron
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