Boring or penetrating the earth – With signaling – indicating – testing or measuring – Indicating – testing or measuring a condition of the formation
Reexamination Certificate
1999-12-15
2001-08-14
Dang, Hoang (Department: 3672)
Boring or penetrating the earth
With signaling, indicating, testing or measuring
Indicating, testing or measuring a condition of the formation
C073S152420, C073S152460, C166S250160
Reexamination Certificate
active
06273202
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of wellbore drilling and more particularly to the field of downhole operations for the purposes of establishing performance or productivity of a zone of interest in a formation.
BACKGROUND OF THE INVENTION
Having reference to
FIG. 1
, a wellbore is been drilled to or through a formation or zone of interest. The zone of interest is sometimes identified roughly by a localized increase in the drill bit's rate of penetration (“ROP”) or by a the detection of hydrocarbon gas with at a total gas (“TG”) detector, which draws a sample of gas carried by the drilling mud when it returns to the surface.
Once the zone of interest is identified it is necessary to establish an understanding of the zone's ability to produce fluids. Production testing is accomplished by performing a prior art drill stem test or DST to establish the performance or productivity of a zone of interest in a formation.
For the DST, the wellbore is sealed above and below the zone of interest using packers. In order to set the packers, the rig must first trip out the drilling string and bit to allow a test tool to be attached to the bottom of the drill string. The drill string and tool is then reinserted into the wellbore. String weight is applied to expand the packers. Ports are opened in the tool exposing recorders to the pressure in the formation. Pressure and time are recorded for a variety of conditions, for example: initial hydrostatic (mud column) pressure, closed in pressure, flowing pressure when the tool is opened, final flowing pressure before closing the tool, closed in pressure and final hydrostatic pressure. After the test, the drill string must be tripped out of the well again to remove the tool and then run in again for reinserting the drill bit should the operator wish to continue drilling.
This DST is a time consuming and expensive process resulting in loss of valuable drilling time. Typically each trip out of the wellbore and back in can take a day meaning a loss of two days each time a DST is ordered. Further, the testing may take another day and DST specialists can cost upwards of $10,000 for each test.
SUMMARY OF THE INVENTION
A method is now provided for determining the productivity of a formation without a requirement to remove the drill string and bit. Compared to the drill stem test, the present invention save two trips, much expense and hours in conducting a productivity test.
In simple terms, the present invention applies a suction technique to the formation to stimulate production using the drilling apparatus—thereby avoiding removal of the drill string and bit. The drill bit is stroked up and down (swabbing), creating a suction in the wellbore and inducing a flow hydrocarbons into the wellbore. In contradistinction to the pressure measurement technique of the DST, the inventive method uses measurement of total hydrocarbon produced during the swab.
In a broad aspect then, a method is provided for testing the productivity from a zone of interest in a formation comprising the steps of positioning the drill bit at the bottom of the zone of interest, circulating drilling fluid through the zone until substantially no hydrocarbon gas is detected therein, rapidly stroking the drill bit, so as to create suction and cause hydrocarbon production from the zone, circulating drilling fluid through the zone and measuring the quantity of produced hydrocarbon gas therein for establishing measures of the formation's productivity, preferably by comparing it against predetermined relationship of TG gas produced and actual production.
Preferably, the detection of hydrocarbon is performed with a total gas sensor applied to gas liberated from the drilling fluid. More preferably, the bit is swabbed up and down a plurality of times for inducing production despite a certain wellbore resistance, such as that due to filter cake or mud invasion.
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Dang Hoang
Goodwin Sean W.
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