Methods for determining a position of a droppable object in a wellbore
The position of a droppable object (e.g., a cementing plug or drillpipe dart) in a cased wellbore may be determined in real time during a cementing operation. A pressure data acquisition system is installed at a wellsite and a pressure transducer is installed at the wellhead. As the droppable object travels through casing it encounters regions with a positive or a negative change of inner cross-sectional dimension. The droppable object generates a pressure pulse as it passes through the regions. The pressure pulse and associated reflections are detected by the pressure transducer, and the signals are processed mathematically to determine the position of the droppable object. Special casing joints may be installed that comprise positive dimensional upsets that have a size of at least 3 mm. Such upsets may ensure the generation of pressure pulses of sufficient magnitude for detection by the pressure transducer.
1 . An apparatus, comprising:
a droppable object;
a casing string; and
a casing joint comprising at least three positive upsets, the casing joint being at a pre-known depth in the casing string, the at least three positive upsets all having a same length, and distances between at least two adjacent pairs of the at least three positive upsets being non-equidistant,
wherein the casing joint is configured such that, during travel through the casing joint, the droppable object encounters at least three of the at least three positive upsets that generate pressure pulses that travel to a surface level.
2 . The apparatus of claim 1 , wherein each of the at least three positive upsets have a size of at least 3 mm, but smaller than that which would prevent passage of the droppable object through an interior of the casing string.
3 . The apparatus of claim 1 , wherein the casing joint has a length between 3 m and 12 m.
4 . The apparatus of claim 1 , wherein the casing joint has an inside diameter between 3 in and 36 in.
5 . A method for determining a position of a droppable object inside a casing string, comprising:
installing the casing string into a liquid-filled borehole, the casing string comprising at least one casing joint installed at a pre-known depth, the at least one casing joint comprising at least three positive upsets, the at least three positive upsets all having a same length, and distances between at least two adjacent pairs of the at least three positive upsets being non-equidistant,
wherein a minimum magnitude of the at least three positive upsets is at least about 3 mm but smaller than that which would prevent passage of the droppable object through an interior of the casing string;
installing a pressure data acquisition system at a wellsite;
installing a pressure transducer at a wellhead at the wellsite;
placing the droppable object inside the casing string;
pumping a fluid behind the droppable object, causing the droppable object to travel through the interior of the casing string and pass through the at least one casing joint that comprises the at least three positive upsets, the droppable object encountering and passing by at least three of the at least three positive upsets during its journey through the at least one casing joint, thereby generating pressure pulses that travel to a surface level;
recording pressure data with the pressure transducer;
transmitting the pressure data to the pressure data acquisition system; and
mathematically processing the pressure data, the mathematically processing comprising:
obtaining at least one of: the pressure pulse or a pressure pulse reflection; and
determining the position of the droppable object based on the obtained at least one of: the pressure pulses or the pressure pulse reflection.
6 . The method of claim 5 , wherein the droppable object comprises one or more of: a top cementing plug, a bottom cementing plug, or a drill pipe dart.
7 . The method of claim 5 , wherein the mathematically processing at least one of: the pressure pulses or the pressure pulse reflection further comprises:
cepstral analysis, the cepstral analysis comprising producing a pressure cepstrogram in coordinates of quefrency and time; and
calculating a pressure pulse reflection time from the droppable object traveling through the casing string.
8 . The method of claim 5 , wherein the mathematically processing further comprises determining a tube wave velocity, based on a pressure pulse reflection time from a stationary object with a known position in the borehole.
9 . The method of claim 5 , wherein a pressure pulse reflection time from the droppable object is converted to the position of the droppable object by multiplication by tube wave velocity.
10 . The method of claim 5 , wherein:
the mathematically processing further comprises at least one of:
analyzing a pressure spectrogram and determining pressure pulses; or
analyzing a normalized energy spectral density of the pressure data; and
the normalized energy spectral density is computed by integrating the pressure spectrogram along a frequency axis followed by normalization or a correlation between anticipated pressure pulses based on casing tally information and the pressure pulses from the pressure spectrogram or normalized energy spectral density.
11 . The method of claim 5 , wherein the determining the position of the droppable object is performed in real time during pumping, allowing an operator to control movement of the droppable object.
12 . The method of claim 5 , wherein the fluid is a displacement fluid.
13 . The method of claim 5 , further comprising:
determining that a change of inner cross-section dimension at a casing collar joint is insufficient to generate an adequate pressure pulse as the droppable object passes through the casing string; and
installing the casing joint in response to the determining that the change of inner cross-section dimension at the casing collar joint is insufficient,
wherein the casing joint comprises the at least three positive upsets configured to generate pressure pulses detectable at the surface.
14 . A method for cementing a borehole penetrating a subterranean formation, comprising:
installing a casing string into the borehole, the borehole being liquid-filled, the casing string comprising at least one casing joint installed at a pre-known depth, the at least one casing joint comprising at least three positive upsets, the at least three positive upsets all having a same length, each of the at least three positive upsets comprising at least one of: a screw joint or a weld joint, distances between at least two adjacent pairs of the at least three positive upsets being non-equidistant,
wherein a minimum magnitude of the at least three positive upsets is at least about 3 mm but smaller than that which would prevent passage of a top cementing plug through an interior of the casing string;
installing a pressure data acquisition system at a wellsite;
installing at least one pressure transducer at a wellhead at the wellsite;
placing the top cementing plug inside the casing string;
pumping a displacement fluid behind the top cementing plug, causing the top cementing plug to travel through the interior of the casing string and pass through the at least three positive upsets, the top cementing plug encountering and passing by at least three of the at least three positive upsets during its journey through the at least one casing joint, thereby generating pressure pulses that travel to a surface level;
using the at least one pressure transducer to detect the pressure pulses and transmit pressure data to the pressure data acquisition system, the pressure data comprising:
pressure pulse propagation velocity; and
reflection time; and
processing the pressure data mathematically, the processing comprising determining a position of the top cementing plug based on the pressure data.
15 . The method of claim 14 , further comprising:
placing a bottom cementing plug inside the casing string;
pumping a cement slurry behind the bottom cementing plug, causing the bottom cementing plug to travel through the interior of the casing string and pass through the at least three positive upsets, thereby generating a pressure pulse;
using the at least one pressure transducer to detect the pressure pulse and transmit pressure data to the pressure data acquisition system, the pressure data comprising a pressure pulse propagation velocity and a reflection time; and
processing the pressure data mathematically and determining the position of the bottom cementing plug.
16 . The method of claim 15 , wherein the processing comprises:
cepstral analysis, the cepstral analysis comprising producing a pressure cepstrogram in coordinates of quefrency and time; and
calculating the pressure pulse reflection time from the top cementing plug or the bottom cementing plug.
17 . The method of claim 14 , wherein the processing further comprises determination of tube wave velocity, based on reflection time from a stationary object with a known position in the borehole.
18 . The method of claim 14 , wherein reflection time from the top cementing plug is converted to the position of the top cementing plug by multiplication by tube wave velocity.
19 . The method of claim 14 , wherein:
the processing comprises at least one of:
analyzing a pressure spectrogram and determining pressure pulses; or
analyzing a normalized energy spectral density of the pressure data; and
the normalized energy spectral density is computed by integrating the pressure spectrogram along a frequency axis followed by normalization or a correlation between anticipated pressure pulses based on casing tally information and pressure pulses from the pressure spectrogram or normalized energy spectral density.
20 . The method of claim 14 , wherein the determining the position of the top cementing plug is performed in real time during pumping, allowing an operator to make instant decisions concerning treatment progress.
21 . The method of claim 14 , wherein a velocity of tube wave propagation is determined from measurements recorded while cementing a previous section or a neighboring well with similar characteristics.