Old And Modern Well Log Data And Its Reliability Through A Novel Certification

Old And Modern Well Log Data And Its Reliability Through A Novel Certification

Process.

Rodolfo Camacho V., Gerardo Lobato B., Sergio Berumen Campos / Pemex, Antonio Daal, Bernardo Martell, Dirk Adams,

Efrain Cruz, Vicente Hernandez / Neuralog, Inc.

Abstract

The main objective of this paper is to present a

certification process to achieve the reliability of well log data

for any user, independently where or when the log was run.

For example, the analog log data (old data) is digitally

recaptured and processed through quality control criteria,

edited and spliced curve by curve, where all technical steps are

documented in the corresponding digital file in order to

provide the user the details of how the technical process was

used and made. Finally, a digital signature certifies all files. At

that moment anyone can use the certified products for

interpretations, correlations or petrophysical evaluations.

As is the case in most oil producing companies, two

log data generations are present in Mexico: analog and digital.

The analogical process began in 1904, when the first well was

drilled, and the digital process began in 1979 through the

“Cyber System Unit” used by Schlumberger. Those two

generations, analog and digital log data, demand new

technologies and processes to equalize the quality of old and

modern data in order to use and manage this information in

applications and databases.

The certification process includes an online log

inventory using the log and services codification published by

The American Petroleum Institute (API), log quality control

routine for “Digital Log Interchange Standard” (DLIS), “Log

Information Standard” (LIS) and “Log ASII Standard” (LAS),

including: originals, edited and spliced logs. The authenticity

and reliability of each file is warranted by a digital signature.

It specifies who completed each step of the process and who

accepted the final product.

The certification process was designed to equalize the

quality of analog and digital log data sets, to establish the log

reliability for any user and, finally to improve the data

management. All these factors positively impact the quality of

log database for timely project execution in the future.

Past, present and future of well log data

On September 5th, 19271, when the Schlumberger

brothers ran the first electric log in a well in France’s

Pechelbronn field, the well logging era began and has lasted to

nowadays. Many kinds of logs and logging technologies have

been developed in order to obtain more information and

details from the subsurface. Now, two well differentiated log

data generations are present: analog and digital. Many efforts

have been made in order to equalize the analog generation of

data into the digital generation in terms of formats and quality

controls.

To support this goal, the main scope of this initiative

is to provide all logs: open and cased hole, to any user in

quality standards of integrity and reliability, allowing the users

to use those data directly, including the master log inventory,

original, edited and spliced well log data. All products in this

process have to be validated by the processor and certified for

the data owner.

As this process is applied to preexisting log data, it

also has to be applied to new log data (new acquisition) in

order to guarantee similar standards for both log data

generations. Finally all logs from existing or future wells are

conceived as an integrated product where the analyst can use

the master inventory and download the certified data that

he/she requires for his/her technical activities. Figure 1 shows

the general certification process and its products.

Well Log Data Certification Process

The general certification process includes open and

cased well logs; however, for this paper only open hole logs

will be considered.

The General Certification Process (Figure 1),

includes the following sub process:

1. Certification Process for analog log data. (Figure 2)

2. Certification Process for digitally captured log data:

LAS format (Figure 3)

3. Certification Process for digital-origin data: LIS /

DLIS format (Figure 4)

1. Certification Process for Analog Log Data.

The certification process includes the processing of

printed log information such as film, paper or other physical

item. The process begins with the physical item selection and

evaluation (Figure 2), including its restoration in order to

obtain the best image during the next phase, scanning. The

image scanned has to be validated and certified to officially

represent the physical item, in the database. After scanning,

the physical item has a substitute (the scanned image) and

physical preservation will be of secondary importance. This is

important because a physical logs disintegrate with time.

The image quality control begins running the skew or

stretch effects corrector in order to guarantee the accurate

relationship between depth and scale axes. In addition, this

warp correction will be used for future comparisons between

image and LAS files, using a virtual light table. Also, it is

useful for image printouts.

The following step is to digitize each curve over the

image. In this case the quality control is made using a virtual

light table and algorithms between curves and curves /

formation response. At that time both the LAS original file

and image are overlain and both of them are validated and

certified.

The last step of this process is to run a quality control

review over the LAS original file. It includes header integrity,

logging speed, repeat section, calibrations, and other

parameters in order to document the editing phase. The editing

phase is performed on that and a new LAS file is generated

which is called: LAS edited. All editing changes or

adjustments are documented in the new LAS edited.

Finally, the splicing process considers the edited files

by curve type. All merging is documented into the new LAS

spliced file. After this step, every file has to be certified by

the owner using a digital signature to complete the process.

2. Certification Process for Digitally Captured Log Data:

LAS format.

This process (Figure 3) is run on the digital LAS files

that comes from real digital or digitally captured log data. In

this case it is mandatory to check the image and LAS file

against each other, accomplishing the cross check for all

quality control described on the certification process for

analog log data.

The log quality certification for the LAS original file,

editing, and splicing procedures, are equal to that described in

the certification process for analog log data.

3. Certification Process for Digital Origin Data: LIS /

DLIS format.

This process (figure 4) is completed for LIS / DLIS

files. First of all, the LIS or DLIS file used in this process has

to be certified by a digital signature in order to assure the first

certified product in this certification process. After that, the

log quality certification for LIS or DLIS files, editing, and

splicing procedures, are equal to that described for analog log

data.

Certification Process Products.

The main objective of all certification processes is to

provide the user with well log data readily available for use.

The analyst does not have to waste time anymore trying to

find out what logs were run in a specific well. All logs and

curves are coded according to the American Petroleum

Institute (API) log coding scheme, and finally all logs are

validated and certified by a digital signature.

Considering the general certification process (Figure

1), includes the following sub process /products:

1. Master Logs Inventory (Figures 5 and 6)

2. American Petroleum Institute (API) log codification2.

Edited and spliced logs (Table 1)

3. Digital signature for well logs.

A description of these sub process /products is given below.

1. Master Log Inventory.

The Master Log Inventory (MLI) allows users to find

out what logs were run or were tried to run in a specific well.

The MLI contains operational information about what

happened in the well in case the run failed.

Figures 5 and 6 show how the basic information is

presented to the user. In this case of figure 5, it shows the

basic information by run, and figure 6 by log type. It is

important to mention that the MLI is also validated and

certified, and it represents the first product of any certification

process.

2. American Petroleum Institute (API) Log Codification.

Everyone who works with well logs has to deal with

logs mnemonics. Basically mnemonics are a function of

logging companies and not by its functionality. Considering

that and what API has published about this issue, the authors

highly recommend using the format suggested by API instead

of mnemonics. In other words, the mnemonics will be present

in the database but logs have to be identified by codes: log

type (service) and which curves are contained in that service.

Figure 7 presents an example of this codification for

an Induction service, which code is 06. The curves that are

present in this service are: Induction Conductivity, Induction

Conductivity Amplified, Induction Resistivity, Induction

Resistivity Amplified, Focused Resistivity, Caliper, Gamma

Ray, and Acoustic Interval Transit Time. The final

codification for this service and curves will be: 06-110, 06-

111, 06-120, 06-121, 06-220, 06-280, 06-310, and 06-520,

respectively. It will be useful for the users to see what type of

log they have available, and if it is in open hole or cased hole.

Besides these advantages, it is also useful for data

administration.

4. Digital Signature for Well Logs.

Digital signatures are created and verified by

cryptography, and its use in the oil industry for well log files is

currently under development. Well log files intrinsically

represents an asset; in addition it needs to be digitally

identified for any user. The digital signature presents the

evidence of authenticity and integrity, assuring the analyst

should be confident about its use.

The efficiency and logistics of well log data analysis

through the use of a digital signature is significantly improved

because each well log data file is self protected.

Conclusions

Many efforts have been made in order to improve the

quality of well log data, and the process presented in this paper

is the best for the technical user and DB manager. The

certification process creates a reliable digital product where

the users can make use of well log data directly for geological

geophysical interpretation, as well as petrophysical

evaluations, productions projects, etc.

The certification process emphases the need to

equalize the quality of analog and digital log generations, to

establish the log reliability for any user and, finally to improve

the data management of existing logs and future logs

References

1.- Hill Pike and Exploration Technology: “Logging history rich

with innovation”, Hart’s E&P (2002) 52-53.

2.- Recommended Standard Format for Recording Digital

Well Log Data on Magnetic Tape ( API Bulletin D9 ).