However, as service companies have developed new capabilities in data acquisition and have extended new services to clients, the need to offer flexibility not available under current log data recording formats is evident.

A number of enhanced data recording techniques have been designed in response to the requirements of new logging technologies and methods, as well as to requests from clients for more complete information on the recorded data. While some of the enhancements could have been implemented within current formats, others required the introduction of new concepts and mechanisms for the representation of information. The result is a more efficient and powerful standard for log information recording which is referred to as the Digital Log Interchange Standard (DLIS).

The following sections outline the nature of the most significant enhancements incorporated in the DLIS.

The DLIS provides a more powerful mechanism for recording Frame Data, Static Information, and Transient Information by means of a uniform syntax and an "object oriented" approach.

Frame Data consists of the values of Data Channels as stored in Frames. Static Information is information that establishes an environment in which Frame Data can be understood. Transient Information is information that occurs during the processing of Frame Data or that modifies Static Information.

New mechanisms for information representations offer greater compactness, uniformity and coherence. The standard supports the definition of Objects that are described in terms of Attributes and may be organized in Sets. This general technique for defining and representing new information allows the range of information items that can be represented under the DLIS to be extended indefinitely.

The DLIS provides a means for unambiguous identification of Data Channels by using Origin information. The Origin concept provides for uniquely tagging Data Channels from different borehole passes and descents in such a way that they subsequently can be merged and still remain distinguishable. Origin Objects also provide summary information about the circumstances surrounding the recording of Channels. For example, the well identification, the date and time, and the original file specification are recorded as Attributes of Origin Objects.

Perhaps the most significant new capability is the allowance for defining and recording of multiple Frame types in a single data file. This permits Frames to be organized by indexing (i.e., time-based Frames can co-exist with depth-based Frames), or by sampling rate (i.e., distinct Frames to collect data at 6" and 2" intervals). This capability facilitates making measurements with different tools at different depth intervals. The sampling frequency can be adjusted to the depth resolution of the measurements, permitting optimization of the amount of recorded data. Additionally, the possibility of interleaving Frames of different types within a log file permits embedding station measurements within a continuous depth log data file.

Under current formats, Parameters are set before the start of a log run and then recorded at the beginning of the data file. Even though the operator or the system may change certain Parameters during the log, these changes go unrecorded. This has led to difficulties in processing the data after the fact.

The DLIS permits changes to be recorded in the form of Update Objects, so that Parameters can be correctly updated when a log is processed.

The DLIS introduces two new types of information in the form of source references and Calibration Objects.

Source references are a mechanism for data Channels to specify their immediate source history to a Tool or Process Object, and for Process Objects to specify their input and output Channels. This allows a path to be traced from a computed or acquired Channel all the way back through its source history.

Calibration Objects provide a greatly improved way of recording calibration measurements. Associated with each calibrated Channel, the new Objects allow recording of extensive information about the calibration.

Though the actual methods for encryption lie outside the domain of the DLIS, the standard does allow for encryption at the level of the bodies of Logical Records.

The DLIS introduces a more efficient approach to mapping logical structures to the physical structure of the recording medium. Multiple Logical Records can be packed into the same physical record. Additional mechanisms for Logical Record continuation permit independence from physical record boundaries. Improved data recovery capability is provided by a checksum at the Logical Record Segment level and both header and trailer Logical Record Lengths.