CIDAI standard 4 : Well log loading

Purpose

To allow efficient loading of quality well log curve data.
To establish a process that will allow the digital data to be regarded as the master set of data.

Specific requirements

Digital log data is an important information resource. The acquisition of downhole data such as logs and core measurements may cost up to several millions of pound per well, and the results obtained from the data can affect business decisions on assets worth hundreds or thousands of millions. Ensuring the accuracy and completeness of this data is therefore an important responsibility.

Historically the digital record and the graphical quality control plots were made from different data files, subsequently modified separately, resulting in non-conformance. CIDAI are seeking to move to a situation where the digital record is regarded as the master and any sepia or paper plots are produced from the master set of digits.

Standard

In general

The data owner, ie the operating company and its designated representative, will undertake checks to ensure that :

data delivered for storage in CIDAI conforms to stated standards of accuracy and completeness,
that all relevant header data is present and correct,
that measured data appears to be complete and correct, having passed normal quality control procedures.

In any matters relating to the quality of company owned data the operating company representative will make the final decision.

While every effort should be made to quality control data as quickly as possible, for reasons of speed or efficiency the operating company may wish to store data in CIDAI which has not yet fully passed quality control procedures. This will be at the discretion of the operating company, but all such data will be clearly distinguished from data that has been quality checked and approved by the operator.

In particular

for New Raw Data

Unless there are particular operational reasons all new log data sets will normally contain all raw data channels and parameters necessary for the 'measured' data values to be re-processed or corrected. This requirement is particularly important for spectral, image, waveform, dipmeter, or other modern measurements where substantial value can be added to raw data channels by the application of re-processing. It is also a requirement where data is originally recorded versus time or another index, and subsequently converted into along-hole-depth indexed data. For older measurement types with only a simple constant transform applied between 'raw' and 'measured' values this requirement is optional.

Because of the specialist technical aspects of data acquisition it will be the responsibility of the service provider to supply the designated operating company representative with sufficient quality control information to ensure the accuracy and completeness of all data. The guiding principle will be that all useful information can be retrieved from the digital record, except in cases where it is clearly uneconomic or impractical to do so. In particular the operating company representative will quality control the accuracy and completeness of the data by means of plots, listings, or other playbacks, (provided by the service provider) which must be identical in value to the digital record.

Upon satisfactory completion of the operating company quality control procedures, CIDAI will be informed that a specific digital data set has been quality checked and is ready for loading into the system. CIDAI will then attempt to load all data entities and make reasonable and brief checks as to their validity. Simple media or transmission problems may be rectified by communication direct between CIDAI and the data supplier, but any non-conformance of data should be logged and reported immediately to the operating company representative, who has the knowledge and authority to rectify the situation with the supplier.

for Historic Raw Data

For a variety of reasons, mainly the evolution of log data recording and storage methods, older data will be substantially less complete and accurate than new data. For this reason historical (pre-1995) data will always require the storage of a graphical image of the 'log film' or equivalent, by either hardcopy or digital methods, as a primary data archive.

Data Completeness:

The standards of digital log data completeness are described below:

Overall:

All relevant data is stored in the digital record, including header, calibration, presentation and quality control files. Any playback or re-computation is possible.

Curve and Header Complete:

Calibration or parameter data may be absent from the digital record, but by reading the graphical record to extract required parameters a playback or re-computation from raw data is possible.

Raw Data InComplete:

Measured curve data and header data is present, but a re-computation is not possible as spectral, waveform, image or dipmeter raw data has not been stored.

Curve and Header InComplete:

Due to non-conformance of hardware, software or procedures basic data can only be recovered by reading the graphical record. Correction of such data sets is a skilled, time-consuming, and expensive process.

Analog Curve data:

Analog or graphical recording systems were used which required manual adjustment of gain and offset between digital values and the primary graphical reference. These data sets may have been recorded in this manner or digitised subsequently.

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