Boring or penetrating the earth – With signaling – indicating – testing or measuring
Reexamination Certificate
1999-04-12
2001-03-06
Batson, Victor (Department: 3671)
Boring or penetrating the earth
With signaling, indicating, testing or measuring
C173S152000
Reexamination Certificate
active
06196335
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to collection of data from the earth using seismic measurements and more particularly collection, at or near a drill bit, of data relating to vibrations of the drill bit.
BACKGROUND OF THE INVENTION
Conventional seismic technology uses surface sources of seismic energy and surface receivers to detect reflections from underground geologic formations such as layers and faults. The collected seismic data can be used to locate the underground formations and guide drilling operations to sources of hydrocarbons.
In Vertical Seismic Profiling (“VSP”), drilling operations are interrupted to place a series of seismic sensors at discrete depths in a borehole being drilled. A surface source releases energy that is reflected off underground geologic formations. The seismic sensors in the borehole sense the reflected energy and provide signals representing the reflections to the surface for analysis. The seismic data is used in analysis of the geology of the earth near the borehole.
In a subsequent development, known as “drill bit seismics”, seismic sensors were positioned at the surface near the borehole to sense seismic energy imparted to the earth by the drill bit during drilling. The sensed energy was used in the traditional seismic way to detect reflections from underground geologic formations. Further, this technique was used to detect “shadows”, or reduced seismic energy magnitude, caused by underground formations, such as gas reservoirs, between the drill bit and the surface sensors.
Analysis of drill bit seismic data entails determining the amount of time between the generation of the seismic energy by the drill bit and the detection of the seismic energy. This can be accomplished by using a “pilot sensor” near the top of the drillstring to which the drill bit is attached. The pilot sensor detects the vibrations transmitted through the drillstring by the drill bit. Those vibrations, corrected and filtered to account for the delay and distortion caused by the drillstring, can be correlated with the seismic energy received at the surface sensors to determine the distance traveled by the seismic energy received at the surface sensors. With this information, the location of the underground formations can be determined.
Drill bit vibrations can be resolved into “axial” accelerations, which are accelerations in the direction that the drill is drilling, and “lateral” accelerations, which are accelerations perpendicular to axial accelerations.
There is evidence that lateral waves, which are caused by lateral acceleration, generated below the neutral point (the point at which tension is zero) of the drillstring do not propagate to the surface along the drillstring. Accordingly, the pilot sensor will not detect lateral waves generated by the drill bit.
If, however, lateral waves (generated by the drill bit are of sufficient magnitude, it is likely that the bottom hole assembly (“BHA”) will contact the borehole wall at random times and at random locations, in an event called a “wall slap”. These contacts will generate strong seismic events that will be detected by the surface sensors and the pilot sensor.
The pilot sensor and surface sensor measurements would not indicate that excessive lateral motion (and hence a possible wall slap) is associated with the event. Such an event would be difficult (and probably impossible) to analyze.
SUMMARY OF THE INVENTION
The invention provides an improved reference for drill bit seismics with a downhole tool for use at or near the bit that measures vibrations at or near the bit. The tool has a downhole microcontroller and a very accurate downhole clock (which drifts no more than about 1 ms during the downhole mission). The downhole controller continuously samples the vertical vibration level and compile statistics on the signal being generated by the bit. When a strong event occurs, the time of the onset of the event is recorded and telemetered, for example via mud pulse telemetry, to the surface. The criterion used for picking an event may be very simple. For example, an event might be selected if its amplitude was more than three times the mean amplitude. For random noise, three standard deviations would be chosen. In addition, a minimum time interval can be specified for reporting pulses. Alternatively, the strongest impulse in a pre-set time interval can be selected, and the amplitude and time of the pulse can be telemetered to the surface.
In general, in one aspect, the invention features an apparatus for enhancement of drill bit seismics through selection of events monitored at the drill bit. The apparatus comprises an axial transducer sensitive to axial acceleration of a drill bit. The axial transducer is configured to produce an axial transducer signal representative of the axial acceleration of the drill bit. The apparatus includes an axial sampler coupled to the axial transducer signal which is configured to take samples of the axial transducer signal to produce axial samples. The apparatus includes a lateral transducer sensitive to lateral acceleration of the drill bit and configured to produce a lateral transducer signal representative of the lateral acceleration of the drill bit. The apparatus includes a lateral sampler coupled to the lateral transducer signal. The lateral sampler is configured to take samples of the lateral transducer signal to produce lateral samples. The apparatus includes a pulse selector configured to select axial samples for analysis and to transmit to the surface the axial samples and a time related to the time that the axial samples were sampled.
Implementations of the invention may include one or more of the following. The pulse selector may comprise a clock configured to provide the time when the axial samples and the lateral samples were sampled and a signal processor configured to select the axial samples for analysis by scanning the axial samples to find events comprising contiguous groups of axial samples which meet a criterion. The criterion may comprise the amount of time between the sampling of the first pulse in the event and the sampling of the last pulse in the event being between a lower limit and an upper limit. The criterion may comprise the amplitude of the axial samples in the event not deviating a predetermined multiple of the standard deviation of the magnitudes of the axial samples in the event from the mean of the magnitude of the axial samples in the event for more than a predetermined time. The criterion may comprise the magnitude of the lateral samples taken during the event and for a predetermined time before the event and a predetermined time after the even not exceeding a predetermined amount. The criterion may comprise the amount of time between the sampling of the first sample in the event and the sampling of the last sample in the event being between a lower limit and an upper limit. The criterion may comprise the amplitude of the axial samples in the event not deviating a predetermined number of standard deviations of the magnitude of the axial samples in the event from the mean of the magnitude of the axial samples in the event for more than a predetermined number of milliseconds and the magnitude of the lateral samples taken during the event and for a predetermined time on either side of the event not exceeding a predetermined amount.
The signal processor may be configured to compute the mean and the standard deviation of the magnitudes of the axial samples. The signal processor may be configured to compute a moving average estimate of one or both of the mean and the standard deviation of the magnitude of the axial samples in the event. The signal processor may compute the moving average estimate using the following equation:
⟨
y
i
⟩
=
1
1
+
γ
·
∑
j
=
0
i
-
1
(
γ
1
+
γ
)
j
·
y
j
-
1
+
(
γ
1
+
γ
)
i
·
y
0
where
y
i
is the ith standard deviation or mean to be averaged; and
<y
i
> is the ith averaged value;
<y
i−1
> is t
Batson Victor
Dresser Industries Inc.
Speight Howard L.
LandOfFree
Enhancement of drill bit seismics through selection of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Enhancement of drill bit seismics through selection of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Enhancement of drill bit seismics through selection of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2533242