Method for detecting changes in rate of discharge of fluid from a wellbore

A method for detecting changes in the rate of discharge of fluid from a well bore. Firstly, providing a flow nipple having a first end, a second end, and a flow line connection extending substantially radially from the flow nipple intermediate the first end and the second end. Secondly, providing a drilling fluid treatment tank. Thirdly, providing a flow line having a first end and a second end. The first end is connected to the flow line connection of the flow nipple and the second end to the drilling fluid treatment tank. This creates a flow path for drilling fluids from the flow nipple along the flow line to the drilling fluid treatment tank. Fourthly, providing an elongate antechamber adjoining one of the flow nipple, the flow line or the drilling fluid treatment tank. The elongate antechamber has a first end and a second end. The first end is positioned in fluid communication with the flow path. The second end extends above the flow path, such that the second end of the elongate antechamber is free of drilling fluid unless a sudden increase in flow rate results in an influx of drilling fluid into the elongate antechamber. Fifthly, positioning a fluid sensing probe in the elongate antechamber. The fluid sensing probe is spaced from and extends toward the first end of the elongate antechamber, such that the fluid sensing probe provides a reading of the level of drilling fluid in the elongate antechamber.

FIELD OF THE INVENTION 
The present invention relates to a method for detecting changes in the rate 
of discharge of fluid from a wellbore; with particular application to 
shallow rig drilling operations. 
BACKGROUND OF THE INVENTION 
When drilling for oil, drilling fluid is pumped from mud tanks by surface 
pumps down into the well through a tubular drill string. The drilling 
fluid then passes back up the well bore along an annular passage formed 
between an outside of the tubular drill string and the sidewalls of the 
well bore, referred to as the "annulus". When the drilling fluid reaches 
the surface, it is diverted through a flow nipple positioned on top of a 
blowout preventer into a flow line which, after some treatment, returns 
the drilling fluid to the mud tanks for recirculation. 
During drilling operations, the rate of fluid return is monitored. A 
increase in the rate of return of fluid could be indicative of an increase 
in flow due to gas, oil or formation water entering the well bore. Early 
detection of an increase in the rate of return allows the rig operator or 
driller to secure the well before the influx of fluid causes excessive 
pressure to build. 
A common method of detection is to place a flow sensing device in the flow 
line leading from the flow nipple. The flow sensing device, usually in the 
form of a paddle sensor, is positioned midway in the flow line. This 
method and associated apparatus tends to work well as long as the flow 
line is oriented with a downward slope. In shallow rig drilling 
operations, however, there is less clearance and, as a consequence, the 
flow line is horizontal. When the flow line is horizontal, it fills with 
fluid. In this environment the paddle sensor no longer provides advance 
warning of a change in flow rate. 
SUMMARY OF THE INVENTION 
What is required is a method for detecting changes in the rate of discharge 
of fluid from a wellbore that is better suited for shallow rig drilling. 
According to the present invention there is provided a method for detecting 
changes in the rate of discharge of fluid from a wellbore. Firstly, 
providing a flow nipple having a first end, a second end, and a flow line 
connection extending substantially radially from the flow nipple 
intermediate the first end and the second end. Secondly, providing a 
drilling fluid treatment tank, whereby drilling fluid is treated prior to 
being returned to mud tanks from which it originated for recirculation. 
Thirdly, providing a flow line having a first end and a second end. The 
first end is connected to the flow line connection of the flow nipple. The 
second end is connected to the drilling fluid treatment tank. This creates 
a flow path for drilling fluids from the flow nipple along the flow line 
to the drilling fluid treatment tank. Fourthly, providing an elongate 
antechamber adjoining one of the flow nipple, the flow line or the 
drilling fluid treatment tank. The elongate antechamber has a first end 
and a second end. The first end is positioned in fluid communication with 
the flow path. The second end extends above the flow path, such that the 
second end of the elongate antechamber is free of drilling fluid unless a 
sudden increase in flow rate results in an influx of drilling fluid into 
the elongate antechamber. Fifthly, positioning a fluid sensing probe in 
the elongate antechamber. The fluid sensing probe is spaced from and 
extends toward the first end of the elongate antechamber, such that the 
fluid sensing probe provides a reading of the level of drilling fluid in 
the elongate antechamber. 
With the method, as described above, an increase in fluid flow along the 
fluid path enters the antechamber where it encounters the probe. By 
monitoring the readings provided by the probe the rig operator or driller 
is provided with warning of an increase in flow rate. The probe can be 
connected to a visual or auditory alarm to draw the rig operator or 
drillers attention to such increase in flow rate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The preferred method for detecting changes in the rate of discharge of 
fluid from a wellbore will now be described with reference to FIGS. 1 
through 3. 
Firstly, providing a flow nipple 12 having a first end 14, a second end 16, 
and a flow line connection 18 extending substantially radially from flow 
nipple 12 intermediate first end 14 and second end 16. Secondly, providing 
a drilling fluid treatment tank 20, whereby drilling fluid is treated 
prior to being returned to mud tanks 22. In the illustrated embodiments, 
drilling fluid entering drilling fluid treatment tank 20 passes through a 
shaker 24. Thirdly, providing a flow line 26 having a first end 28 and a 
second end 30. First end 28 is connected to flow line connection 18 of 
flow nipple 12. Second end 30 is connected to drilling fluid treatment 
tank 20. This creates a flow path for drilling fluids, generally indicated 
by arrows 32, from flow nipple 12 along flow line 26 to drilling fluid 
treatment tank 20. Fourthly, providing an elongate antechamber 34 along 
flow path 32. As is demonstrated in FIGS. 1, 2, and 3, elongate 
antechamber 34 can be placed at various locations along flow path 32. In 
FIG. 1, elongate antechamber 34 is shown adjoining flow nipple 12. In FIG. 
2, elongate antechamber 34 is shown adjoining flow line 26. In FIG. 3, 
elongate antechamber 34 is shown adjoining drilling fluid treatment tank 
20. Elongate antechamber 34 has a first end 36 and a second end 38. First 
end 36 is positioned in fluid communication with flow path 32. Second end 
38 extends above flow path 32. Fifthly, positioning a fluid sensing probe 
40 in elongate antechamber 34. Fluid sensing probe 40 is spaced from and 
extends toward first end 36 of elongate antechamber 34. 
As drilling fluid circulates along flow path 32, second end 38 of elongate 
antechamber 34 is above the flow and, as such, is free of drilling fluid. 
However, should there be a sudden increase in flow rate, an influx of 
drilling fluid enters into elongate antechamber 34 and rises from first 
end 36 of elongate antechamber 34 toward second end 38. Fluid sensing 
probe 40 provides a reading of the level of drilling fluid in elongate 
antechamber 34. The readings provided by fluid sensing probe 40 is 
connected to instruments monitored by the rig operator or driller. A 
change is fluid levels within elongate antechamber 34, as indicated by 
fluid sensing probe 40, provides a warning of an increase in flow rate. 
Fluid sensing probe 40 can also be connected to a visual or auditory alarm 
to draw the rig operator or drillers attention to such increase in flow 
rate. 
It will be apparent to one skilled in the art that modifications may be 
made to the illustrated embodiment without departing from the spirit and 
scope of the invention as hereinafter defined in the claims.