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, a pressure transducer is installed at the wellhead and a flowmeter is placed to measure fluid displacement rate. The fluid displacement causes the droppable object to travel through the casing towards a target position. During displacement the pressure data and flow-rate data are transmitted to a pressure data acquisition system and a flowmeter, respectively. The pressure and flow-rate data are processed mathematically to obtain pressure pulses, pulse reflections or both. The fluid flow rate data and pressure data are processed by generating a pressure spectrogram converted to pulses. The pulses are then matched with casing tally pulses, thus allowing correction of the droppable object depth.
1 . A method for determining a position of a droppable object inside a casing string, comprising:
(i) placing the droppable object inside an interior of the casing string;
(ii) pumping a fluid behind the droppable object, causing the droppable object to travel through the interior of the casing string to a target position;
(iii) recording pressure data and fluid flow rate data, and transmitting the pressure data and the fluid flow rate data to a data acquisition system; and
(iv) processing the fluid flow rate data and processing the pressure data by:
obtaining a window-wise pressure spectrogram converted to pulses,
matching the pulses with casing tally pulses, wherein each match indicates a correction coefficient in a corresponding window, and
correcting a depth of the droppable object using the correction coefficient.
2 . The method of claim 1 , wherein the pressure data and the fluid flow rate data processing is performed at a time later than a pressure transient process that occurs responsive to movement of the droppable object.
3 . The method of claim 1 , further comprising:
converting the window-wise pressure spectrogram into the pulses by frequency pressure monitoring.
4 . The method of claim 3 , wherein a set of digital vectors is constructed, wherein each digital vector in the set of digital vectors corresponds to a correction coefficient.
5 . The method of claim 4 , wherein the set of digital vectors represent observed pressure peaks and expected pressure peaks.
6 . The method of claim 3 , wherein the pressure data is selected only from a set of pressure data having a time delay that is possible according to the casing tally pulses and the fluid flow rate data.
7 . The method of claim 1 , wherein the droppable object is a top cementing plug, a bottom cementing plug, or a drill pipe dart.
8 . The method of claim 1 , wherein a source of the pulses comprises casing collars or noise from a pressure pump.
9 . The method of claim 1 , wherein the data acquisition system installed at a wellsite comprises:
a pressure transducer configured to record pressure data;
a flowmeter configured to record fluid flow rate data; and
a data processing unit installed at a wellhead.
10 . The method of claim 1 , further comprising:
determining the position of the droppable object in real time.
11 . The method of claim 1 , wherein matching the pulses with casing tally pulses includes:
computing a moment of time t i for each pulse such that t i ΔL i/cv(t), where ΔL; is a distance between i and i+1 casing joints, v(t) is a volumetrically calculated speed of the droppable object at time t i , and c is a corresponding correction coefficient.
12 . The method of claim 1 , further comprising:
searching the window-wise pressure spectrogram such that a time delay between peaks of the pulses is at least a predicted distance between casing joints divided by a predicted speed of the droppable object.