GB2401177A

GB2401177A - Acquiring seismic data while tripping out a drill string from a wellbore

Info

Publication number: GB2401177A
Application number: GB0310248A
Authority: GB
Inventors: James C Jackson
Original assignee: Baker Hughes Inc
Current assignee: Baker Hughes Holdings LLC
Priority date: 2003-05-02
Filing date: 2003-05-02
Publication date: 2004-11-03
Also published as: GB0310248D0

Abstract

An autonomous seismic receiver 158 is inserted down the fluid passage in the drillstring 120 until it reaches a landing sub 150 near the drill bit 155. As the drillstring is tripped out, it is stopped at various predetermined locations of interest 105b, 105n and the receiver 158 receives seismic signals 160 from a seismic source 170 near the surface. The detected signals are stored in the receiver. At the end of the tripping procedure, the receiver 158 is retrieved from the sub 150 and stored data is transmitted to a processor 118. The data is used to provide an improved seismic map of the downhole formation and obviates the need for a wireline checkshot measurement for depth calibration purposes.

Description

2401 177 METHOD FOR ACQUIRING SEISMIC DATA WHILE T1lIPPING INVENTOR: James

C. Jacl;son s

BACKGROUND OF T} INVENTION

lo Field of the Invention

Tile present invention is related to the field of geophysical exploration and more specifically to a method of using a seismic receiver in a dull string in a wellbore to acquire seismic data while tripping the drill snaring from the wellbore.

Description of the Related Art

In drilling a borehole to recover oil from the earn, it is often helpful to turn or steer the downhole drill bit toward or away from subterranean targets. To facilitate this geophysical steering, drillers need to know drill bit location on the seismic section. The location of targets ahead of the bit is also required, as well as some warning or indication of drilling hazards such as over-pressured formations or thin, shallow gas intervals.

Surface seismic surveys generally include this information, but resolution and depth location is poor because surface seismic surveys are time based (rather than depth based).

For example, to determine the depth of a reflection, a speed of sound for the formation must be Move. Consequently, these systems require depth calibration to accurately determine locations of target horizons or drilling hazards. Traditionally, this calibration has been provided by either offset well sonic data or wireline checlcshor data in He current well. Offset data is often inadequate hoverer due to horizontal variations in stratigraply between wells.

During surface seismic surveys, a plurality of seismic sources and seismic receivers are placed on Me surface of the earth. Ike seismic sources are triggered in a predetermined sequence, resulting in the generation of seismic waves. These seismic waves travel downward through the earth until reflected ok some underground object or change in rock formation. The reflected seismic waves dlen travel upward and are detected at the seismic receivers on the surface. One or more clocks at the surface measure the time from generation of the seismic waves at each source to Reception of the seismic waves at each receiver. This gives an indication of the depth of the detected object underground. However, the exact speed of sound for these seismic waves is lo ur known, and thus, the exact depth of the detected object is also unknown. To more closely measure the exact speed of sound, a "wireline checkshot" may be used to calibrate depth measurements. During a "wireline checkshot," a receiver on a "wireline" is lowered a known distance into an already-drilled borehole. surface seismic source is then triggered and the time is measured for tile seismic wave to travel to the wireline receiver.

5 Because the depth of the wireline receiver is known, an average interval velocity indicating the average speed of the seismic wave can be detennined with some degree of accuracy. Wireline checkshots, however, require removing the bit out of the hole, commonly known as tripping, and are often prohibitively expensive.

The methods of the present invention overcome the foregoing disadvantages of so the prior art by providing a technique for deploying an autonomous wellbore seismic receiver in a drill string without the use of a wireline and acquiring seismic data as the drill string is removed from tile wellbore.

SUITABLY OF THE INVENTION

The present invention contemplates a method for acquiring seismic data while nipping a drill smog from a wellbore.

In one preferred embodiment, a method is described for acquiring seismic data while removing a drill string from a wellbore, comprising; conveying an autonomous seismic receiver down a fluid passage in the drill stony to a predetermined location proxLmate a lower end of He drill 0 string; - generating signals by a seismic source near a surface location; - detecting He seismic signals with at least one sensor in the seismic receiver at al: least one predetermined location of ingress in the wellbore as He drill smog is removed from He wellbore; and s - storing He detected seismic signals in the seismic receiver.

En another preferred embodiment, a method is described for acquiring seismic data while removing a drill string from a wellbore, comprising; synchronizing, at the surface, a surface clock in a surface controller with a downhole clock in an autonomous seismic receiver; so prograrnming, a: the surface, a processor in the autonomous seismic receiver to activate during at leas: one predetermined dine window after a predetermined delay nme, - conveying an autonomous seismic receiver down a fluid passage in Me drill string to a predetermined location proximate a lower end of the dull swing; generating, under control of a surface processor, signals by a seismic source near a surface location; detecting the generated seismic source signals with a near-source sensor and storing said signals in We surface processor; - detecting Me seismic signals with at least one sensor in Me seismic receiver at at least one predetermined location of interest in the wellbore as to Me drill stnng is removed from the wellbore; - storing Me detected seismic signals in the seismic receiver; - transferring, a: Me surface, tile detected seismic signals from the seismic receiver to the surface processor; and processing Me near-source signals and tile seismic receiver detected signals according to programmed instructions to generate a seismic reap.

Examples of the more important features of the invention thus have been summarized rather broadly in order that Me detailed description thereof that follows may be better understood, and in order that the contributions to the arc may be appreciated.

There are, of course, additional features of the invention that will be described hereinafter and which will fonn the subject of me claims appended hereto. l

BEEF DESCRIPTION OF THE DRAVGS

For detailed understanding of die present invention, references should be made to He following derailed descnprion of the preferred embodiment, taken in conjunction win the accompanyulg drawings, in which like elements have been given like numerals, wherein: Figure 1 is a schematic diagram of a seismic acquisinon system for use in one ernlodiment of the present invention; Figure 2 is a block diagram of a seismic receiver for use in one embodiment of the present invention; and Figure 3 is a schematic of a seismic acquisition system for use in one eInbodimen t5 of He present invention.

DESCRIPTION OF PREFERRED:1BODIMENTS

Referring lo Figure 1, a system 100 according to the present invention includes a derrick 110 win an attached drillstring 120. A dull bit 155 creates a well bore 130 to through the surrounding formation 140, which Inay also include formation boundaries corresponding to, for example, an over-pressurized zone 145. A seismic receiver 158 with appropriate seismic sensors is inserted into the drillstri.ag 120 and falls by gravity to a landing sub 150 near the drill bit 155. Alternatively, He seismic receiver 158 may be deployed using die drilling fluid 135 to effectively pump the receiver 158 to He landing sub 150. flue seismic receiver 158 receives seismic signals 160 from a seismic source 170, such as a mechanical vibrator, located at the surface. The use of a mechanical vibrator is exemplary only, as the system may be either land or manna-based, and is not seismic source-type specific. For example, an offshore system may include an air gun s array, either hung from an offshore platform or located near a service boat OT anchored buoy. The seismic source 170 thus provides a suitable vertical seismic profiling quality source signal. Also located at the surface is a depth indicator 115 to measure the depth of the drillstring 120. The depth indicator signals are transmitted to a surface controller 118 where they are time stamped and stored in memory. The surface controller 118 is 0 connected to the seismic source 170 for controlling the generation of seismic signals. The actual connection between the controller 118 and the seismic source 170 can be a hardwire, radio telemetry or any over suitable communication system. Surface controller 118 contains circuitry, processing capability, and memory storage, and functions according to programmed instructions to control the generation of seismic signals. The surface controller circuitry contains a real-time clock for time coding the transmitted source signal. A near-field sensor 180 is located near the source 170 and is used to record the acoustic signature of thy source 170. The output of sensor 180 is transmitted to the surface controller 118 where it is time stamped and stored in memory. The memory used for storing data in the surface processor mater be internal random access memory, magnetic storage, optical storage, or any combination of these.

Referring lo Figure 2, the seismic receiver 158 may include a combination of sensors 201 such as hydrophores and geophones along with suitable sensor interface circuitry 202, a processor 203, and memory 204 for storage of programmed instructions arid storage of received seismic data. A real time clock circuit 205 is also included in the receiver 158 to provide time stamps for the received seismic signals. The surface located real-time clock and the receiver located real-time clock 205 are synchronized at the surface before deploying the seismic receiver 158 into We wellbore 130. A communications port 206 is included to download program instructions to memory 204 and to upload stored seismic data lo a surface system such as surface processor 118. The receiver 158 is powered by batteries (nor shown). A similar slick-line deployable receiver is described in US Patent 5,55S,220 to Minto, assigned to die assignee of this application and incorporated herein by reference. Sub 150 is adapted to physically latch to the landed receiver 158 to substantially prevent the receiver 158 from bouncing as:he drill string lO 120 is tripped from the wellbore 130.

In operation, shown in Figure 3, tile seismic receiver has been conveyed so the bottom of the drill strirl; 120 and is latched into the landing sub 150 prior to tripping the drill suing 120 out of the wellbore 130 and is located at position 105a. The seismic receiver is programmed at the surface to turn on the seismic receiving sensors 201 after a predetermined time delay. I he time delay is operator selected to allow the receiver 158 to reach the landing sub 150 before activating the seismic sensors 201. After dle programmed time delay, the surface processor 118 is initiated to begin to cycle tile surface source 170 generating seismic signals 160 at predetermined intervals. The interval between signals is selected, depending on receiver depth, in order to prevent overlap of successive signals.

In one preferred embodiment, the receiver 158 is programmed to take samples during predetermined time windows selected by the Operator. The surface processor is programmed to transmit dunng these predetermined rime windows. The predetermined time windows are selected to approximately correlate with Me normal tripping speed so that the sampling time windows will occur at desired sample locations in the wellboTe.

The operator stops motion of the drill string during these windows to provide a relatively low noise environment for the seismic sensors 201. The receiver processor 203 samples, time stamps, and stores the detected signals during the predetermined window in memory 204. After the initial on-bottom detection, the drill string 120 tripping process begins. Ale tripping is stopped at the predetermined locations in the wellbore 130 such as location 105b7 loon and the drill string 120 is held s':anonary during the rime sample windows.

While three locations of interest are shovrn in Figure 3, any number of locations of n interest may be chosen. The surface processor lax cycles the source 170 during each sample window. The near-field sensor 180 detects each generated source signal and transmits the detected signal to the surface processor 118 where it is time stamped and stored in memory in the surface processor 118. At the end of the tripping process, the seismic receiver 158 is retrieved from We landing sub 150. The timstamped seismic signals are transmitted via the communications port 206 to the surface processor where they are processed with the near-feld signals and We depth data, according to techniques known in the art, to provide an improved seismic map of the downhole formation.

In another preferred embodiment, the receiver 158 has at least one accelerometer 207 mounted in the receiver 158 to sense movement of the drill string 120, see Figure 2.

Signals from accelerometer 207 are conditioned by interface circuits 208 and fed to processor 203. Accelerometer 207 is powered continuously from We rime Me seismic receiver 158 is inserted into the wellbore until the receiver is resumed to tile surface after the seismic data acquisition process. These accelerometer signals are used to switch the seismic receiving cycle on and off in receiver 158. When the drill string 120 is positioned at a location where it is desirable to take seismic data, such as 105a, 105b, and 105n in Figure 3, the drill string 120 is held stationary al: the surface. The accelerometer generated signals are used by the processor 203 to determine chat the drill-string 120 has stopped moving and initiates the taking of seismic data. The processor is preprogrammed s to receive and store data for a predetermined period of time sufficient to receive several source signals. The source 170 is activated as described above and data is taken and stored from the nearfield sensor 180 and Me depth sensor 11', as described previously.

As before, the downhole received and stored data is transferred to the surface processor 118 when the seismic receiver 158 is resumed to tile surface.

O In yet another preferred embodiment, an acoustic source (not shown) is coupled to the drill-stung al the surface when the drill-stnnú- 120 is stopped to take seismic data. The acoustic source tranr,mits a coded signal Through the drill-string 120 that is detected and decoded by the seismic receiver 158. The coded signal can be used to initiate We taking of data by Me receiver 1C,8. Such acoustic systems are Woven in the art and are not discussed here furler.

Therefore, one preferred method of acquiring seismic data while trippirg includes at least the stepsof; - programming the seismic receiver at the surface to turn on after a predetermined time interval, to stay on and acquire data for a JO predetermined time, and to activate the acquisition process at predetermined tunes where the predetermined times correlate to locations of interest for taking seismic data while tripping out of the wellbore; - synchronizing a surface clock in the surface processor with a downhole clock in the seismic receiver; conveying the autonomous seismic receiver to a landing sub located near Me drill bit; - generating seismic signals under control of the surface processor at the predetermined times correlating with the locations of interest of the s seismic receiver as it is tripped out of the wellbore; - detecting the generated seismic signals by a near-source sensor and storing the detected signals correlated with real tune and drill-siing depth in the surface processor; - receiving and storing the generated seismic signals correlated win real tinge in the downhole seismic receiver at the locations of interest as the receiver is tripped out of the hole; transferring the seismic receiver data to the surface processor when the receiver is removed from the wellbore; and generating updated seismic maps of the formations surrounding the wellbore.

The foregoing description is directed lo particular embodiments of We present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set form JO above are possible without departing from Me scope and the spirit of the invention. It is intended Mat Me following claims be interpreted lo embrace all such modifications and changes.

Claims

What is clammed is: 1. A method for acquiring seismic data while removing

a drill string from a 2 wellbore, comprising; 3 - conveying an autonomous seismic receiver down a fluid passage in the 4 drill string to a predetermined location proximate a louver end of the drill string; 6 generanag signals by a seismic source near a surface location; - detecting the seismic signals with at leas,: one sensor in the seismic B receiver at leas: one predetermined location of interest in the wellbore 9 as the drill string is removed from the wellbore; and lo - storing the detected seismic signals in the seismic receiver.
2. The method of claim 1 furler comprising landing said seismic receiver in a landing sub located in the drill Sating proximate a lower end of the drill string.

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3. The method of claim 2 further composing firmly latching the seismic receiver 2 in the landing sub to substantially minimize noise induced by movement of the drill 3 string.
4. The method of claim 1 farther comprising; 2 - detecting the seismic signal with at leas: one sensor located at the 3 surface; and - storing:he signal detected by the at least one surface sensor in a surface processor.

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5. The nleod of claim 1 further comprising downloading the signals stored in 2 the seismic receiver to the surface processor upon removal of the drill string from the 3 wellbore.

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6. Tile method of claim 1 furler comprising processing, according to 2 programmed instructions, Me surface detected signals and We seismic receiver 3 detected signals to generate a seismic map.
7. The method of claim 1 wherein conveying Me autonomous seismic receiver down the passage in the drill string comprises one of (i) allowing the autonomous seismic receiver to fall by gravity to the lower end of Me drill string, and (ii) pumping 4 the autonomous seismic receiver down the wellbore.

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8. A me:hod for acquiring seismic data while removing a drill string from a 2 wellbore, comprising; - synchronizing, at the surface, a surface clock ir1 a surface controller 4 with a downhole clock in an autonomous seismic receiver; - programming, at the surface, a processor in file autonomous seismic 6 receiver to activate during at leas,: one predetermined time window 7 after a predetermined delay tune, s conveying an autonomous seismic receiver down a fluid passage in the 9 drill string to a predetermined location proximate a 'ower end of the lo drill string; I 1 - generating, under control of a surface processor, signals by a seismic 12 source near a surface location; l 13 - detecting *ye generated seismic source signals with a near-sauree 14 sensor and stonug said signals in the surface processor; - detecting Me seismic signals with at least one sensor in We seismic 16 receiver at least one predetermined location of interest in Me wellbore 17 as Me drill string is removed from Me wellbore; le - storing the detected seismic signals in the seismic receiver; 9 - transferring, at the surface, tile detected seismic signals from the So seismic receiver lo Me surface processor; and 21 processing Me near-source signals and the seismic receiver detected 22 signals according to programmed instructions to generate a seismic 23 map.
9. The method of claim 8 wherein conveying the autonomous seismic receiver down Me passage in Me drill string comprises one of (i) allowing die autonomous seismic Teceicr to fall by gravity to the lower end of Me drill string, and (ii) pumping the autonomous seismic receiver down the wellbore.

1 O. The method of claim 8 furler comprising landing said seismic receiver in a 2 landing sub located in the drill string proximate a lower end of Me drill string.

I 11. The method of claim 10 further comprising finely latching Me seismic 2 receiver in Me landing sub to substantially minimize noise induced by movement of 3 the drill string.