How Real-Time Sonic LWD Semblance Images can be Beneficial – A Case Study from Latin America

5/27/2018 How Real-Time Sonic LWD Semblance Images can be Beneficial A Case Study from Latin America

1/7

Mohamed Diab, Rebecca Nye, Jose A Becerra, Weatherford, Victor G V Arrieta, Jose D C Damas, Guillermo G SanchPemex.

Copyright 2001, Acipet.

This paper was prepared for presentation at the ACIPET XV Congreso Colombiano del Petrleo held in Bogot D.C., Colombia, 20 -22 November 2013.

This paper was selected for presentation by an ACIPET Technical Committee following review of information contained in an abstract submitted by the author(s).

AbstractThe majority of operating companies use logging-while-

drilling (LWD) sonic data principally for the compressional

slowness measurement. Virtually all LWD sonic data requires

post-drilling processing, from the recorded waveforms or

semblance, in order to verify the accuracy of the

compressional slowness transmitted in real-time while drilling.

A new generation of LWD sonic tool is now capable of

providing acoustic semblance images in real time (RT). Thispaper will discuss the benefits of using sonic semblance image

in RT.

The technological advances in LWD services have directly

impacted reservoir evaluation and helped in providing useful

data for production planning on an RT basis. One of the

biggest challenges for LWD technology has been the limit in

RT data transmission rates, as opposed to wireline

transmission rates. A new data compression technique has

been developed to meet the challenges of transmitting

relatively large amount of data to surface while drilling,

specifically sonic data. This paper will discuss the data

compression techniques and demonstrate the reliability with a

case study from Latin America.The case study, from Mexico, demonstrates that high-

resolution, RT semblance images are achievable and that we

can have confidence in the results from RT applications of

sonic data, over traditional delta-t data acquisition.

Some operating companies have an outdated prospective

that RT LWD sonic data is unreliable and always requires

post-processing. However, through the new advances in RT

transmission, high-quality semblance images can be provided

in RT, and this advancement has created a step change in the

way operating companies use the data for analysis

planning.

IntroductionTwo main challenges have prevented LWD sonic tools f

being able to produce a reliable acoustic measurement in

or from waveforms stored in the memory. The first challe

was overcoming the drilling environment, which inclu

shocks, vibrations, and drilling noise. The second challewas the slow data transmission rates inherent with L

telemetry systems. LWD tools overcame the dril

environment challenge with strong robust tool desi

however, only recent progress has been made in a LWD s

tool that is capable compressing downhole sonic data

transmitting it to surface while drilling.

A new data compression technique has been develope

meet the challenges of transmitting relatively large amoun

data to surface while drilling, specifically sonic data.

Tool Design and ConfigurationEnhancing the mechanical design of the sonic LWD

helped in enhancing the acoustic measurement. The tool h

single, focused transmitter, and an array of six sensireceivers located on the same side of the tool as shown

Fig. 1. The transmitter overcomes the conventional probl

with sonic tools, which are ruggedness, directionality,

frequency. The wireline monopole transmitters typically h

a shape of a large ring that is tuned to a frequency between

and 20 KHz. This design is not very efficient in the L

world, and thus the new, focused unipole transmitter pro

helpful. With an output 50% higher than the wire

counterparts, the 6000 Pascal of pressure measured at

ASOCIACIN COLOMBIANA DE INGENIEROS DE PETRLEOS (ACIPET)

How Real-Time Sonic LWD Semblance Images can be Beneficial A Case Study froLatin America


2/7

from the new LWD transmitter overcomes the noise sources

and allows clean slowness arrivals.

In between the transmitter and the receiver array lays the

attenuator section, and its function is to stop or reduce the

unwanted noise signal from reaching the receivers. Fig. 2

shows the different noise sources that the tool fights while

drilling in order to achieve a clean acoustic arrival at the

receivers. Bit noise or drilling noise is a major factor that

affects the acoustic signal, shown as blue bi-directional

arrows. The red arrows indicate the signal generated by the

transmitter that travels directly to the receivers through the

body of the sonic collar, it is named Tool Mode. The Tool

Mode noise is maximized due to the use of a drill collar in the

LWD world, compared to being minimized in the wireline

sonde housings. The good acoustic waves that travel from the

transmitter out to the formation and refract back to the

receivers are the green arrows in the diagram.

By design the receivers are more sensitive to these arrivals

that come perpendicular to the tool and not very sensitive to

the waves moving in the axial tool direction. Moreover, the

receivers are mounted in special pockets to isolate their bodies

from contacting the drill collar. The piezoelectric receiver

material has a high degree of directional sensitivity, which

facilitates filtering out the noise and enhancing the signal-to-noise ratio.

Data ProcessingThe chart shown in Fig. 3 summarizes how the sonic tool

processes the six waves coming from the tool receivers, and

turns them into a semblance image plotted versus depth while

the tool is logging in RT. The first step is filtering the received

acoustic waves by applying pre-programmed filters, then

calculating the coherence across the six waves. From this

chart, the downhole tool process can determine the slowness

of the arrivals, their time, and their coherence percent. These

three findings are then plotted in the coherence map, which is

considered a 3-axis chart, as the color intensity reflects the

coherence percent. The next step is projecting this chart on its

vertical axis, plotting the slowness against the coherence

percent, and therefore identifying easily the first and second

peak arrivals, the P-wave and the S-wave. The downhole tool

again turns these values to a semblance color intensity log, but

this time versus depth and this is the RT sonic semblance

image that is needed to be sent to the surface in order to have a

RT semblance image log.

The tool firmware algorithm compresses the downhole

semblance image to allow it to be transported via the mud

pulses up the drillstring to the surface while drilling. The

surface system computer then decompresses the sonic data and

plots the semblance image log as the bit is drilling. Fig. 4

shows the sonic semblance image in different stages startingfrom being processed and acquired by the LWD downhole

tool on the left track, and ending by the right-most track

showing the decompressed semblance image on surface.

Case Study Abkatun Pol Chuc Field, MexicoThe Abkatun Pol Chuc field is located on the continental shelf

in the Gulf of Mexico, within the territorial waters of Mexico.

The structure that houses the reservoir is located on the flank

of a salt diapir, which is related to both the mid-Cretaceous

and the Jurassic, more specifically the upper Kimmeridg

The mid-Cretaceous is predominantly made up of fractu

carbonates, overlain with micro-breccia. The Jura

Kimmeridgian facies is an oolitic carbonate, which

primarily on the banks and bank edges of the structure.

The Abkatun Pol Chuc field reserve estimate accu

bares a significant importance for the client, Pemex, as

field produces a third of Mexicos crude oil. Any errone

estimates can have detrimental economic effects on

country. Consequently, accuracy of the formation evalua

has a substantial importance. In the evaluation of the Abk

Pol Chuc field, the client required the most precise,

economical, way of acquiring the data needed to evaluate

reserves and design the development phase. The client

required highly accurate RT formation evaluation data

making critical decisions during the drilling phases.

Weatherford LWD Sonic Tool i n Abkatun Pol Chuc K

field. The vertical exploratory well sonic data proved v

promising. The RT sonic semblance image showed h

resolution sonic slowness arrivals.Fig. 5 shows a part of

RT log including the gamma ray, the resistivity curves,

the slowness track, together with the semblance track

shows the RT sonic data. Pemex geologists compared the

semblance image to the memory image, and the results prothat the sonic application in RT was very important. Fig. 6

comparison plot between the RT and the memory s

semblance image. The semblance image tracks labels sh

that the memory is on track 3 and the RT is on track 2.

sonic slowness arrivals were plotted on the same scale to fo

on the differences on track 1; however, there was

noticeable difference.

The KAA-1 well location on the west end of the reser

allowed the geologists to complete their earth models for

Abkatun Pol Chuc KAA field using the LWD data in RT.

memory data was delivered on the well site, confirming

RT reliability. This is a step change in the sonic logging

reliable data can save the operating company days of rig tiand allow faster decision making.

More applications are evolving for using the sonic dat

RT. Geomechanical analysis is a good example that Pem

decided to use by processing the sonic slowness arrivals w

the LWD density and getting Youngs Modulus, Poiss

Ratio, and brittleness index.

Processing centers are turning to be Real-Time Opera

Centers (RTOC) with less interaction with sonic petrophy

because more of the processing is shifting to RT in the field

ConclusionsThis field in Mexico was the start of a continuously evolv

work with RT sonic tools and using the new technology

shift from memory-only applications into RT service. direct results are eliminating processing time, getting to kn

more about the reservoir while drilling, and verifying the s

slowness arrivals by simply getting the entire sembla

image to the surface.

Technology leaps in LWD tools prove useful every da

every country. Sharing this knowledge between opera

companies is a way of building more bridges to achieve

utmost reservoir knowledge in the shortest period of time.


3/7

AcknowledgmentsMany thanks to the Weatherford petrophysics and operations

department in Mexico and Latin America region for allowing

the use of this information, as well as the Weatherford global

team.

Thanks to Pemex for approval to publish the data, and the

continuous help in supporting new technology advance.

NomenclatureDTC delta time compressional slowness arrival

DTS delta time shear slowness arrivalLWD logging-while-drilling

RT real time

RM recorded memory

SEMP semblance projection image

References1. Talwani, Manik. 2011. The Future of Oil in Mexico Geol

Production Rates, and Reserves. Rice University, April.

2. Mickael, Medhat, Barnett, Craig, and Diab, Mohamed. 2Azimuthally Focused LWD Sonic Logging for Shear W

Anisotropy Measurement and Borehole Imaging. Paper

160133, SPE Annual Technical Conference and Exhibition,

Antonio, Texas, October 8-10.

3. Mejia, Miguel Camilo, Casanova, Mauricio. 2012. Integra

and Formation Evaluation and Geomechanical PropertieReal-Time for Horizontal Sections. Convocatoria Cong

Mexicano del Petroleo.

4. Nye, R. 2013. Benefits of Real-Time LWD Sonic SemblImagesCase Studies from the North Sea and Offshore Ch

Paper, Offshore Mediterranean Conference and Exhibi

Ravenna, Italy, 20-22 March.

5. PEMEX Exploration and Production. 1999. HydrocaReserves of Mexico. Volume 2.

6. Wyllie, M. R. J., Gregory, A. R., and Gardner, L. W. 1Elastic wave velocities in heterogeneous and porous me

Geophysics, 21, no. 1, 41-70.


4/7

Fig. 1Configuration of the LWD sonic tool

Fig. 2need caption

Green uni-directional

arrows correspond to

the signal transmitted

into the formation.Blue bi-directional arrows

correspond to drilling-induced

noise that is reduced whilepassing through theattenuatorsection andis minimized at the

receivers.

Red uni-directional arrowscorrespond to tool-mode

waves travelling through the

body of the collar that are

reduced while passing

through the attenuator section

and are minimized at the

receivers.


5/7

Fig. 3Downhole sonic processing technique

Fig. 4Far-left track shows the down-hole semblance image before compression, while the far-right track shows the decompressed

semblance image on surface


6/7

Fig. 5RT LWD log with sonic semblance image


7/7

Fig. 6A comparison between real-time LWD acoustic data and recorded LWD acoustic data from the KAA-1 well.

How Real-Time Sonic LWD Semblance Images can be Beneficial – A Case Study from Latin America

Documents

Transcript of How Real-Time Sonic LWD Semblance Images can be Beneficial – A Case Study from Latin America