Image log data come in a variety of formats depending on logging tool type and acquisition company. Raw data comprises numerous curve data that are used for a variety of purposes. The most important ones are orientation data (magnetometers) and tool speed data (accelerometers) that are needed to properly orient the images in 3D space. The raw image further consists of data sensor output data and data that control the functioning of the tool. For each tool and acquisition company the various data types are represented by a host of mnemonics. It is up to the interpreter to filter through and translate these data mnemonics into the correct curve and image data for import into the processing software. After the data loading a number of QC steps have to be performed to ascertain that the logging tool functioned properly. In some cases the collected data can be corrected by the processing software, in other cases data may be irreparable. Intervals with poor date will be flagged in this process.
The data processing is aimed at producing images that properly reflect the lithological variation encountered in the logged section and to properly depth reference the data. Wireline resistivity tools are very sensitive to tool speed variations. Cable speed and tension are only an approximate indication of tool speed. Due to the friction of the tool pads that are pressed against the borehole wall the tool may experience an irregular, jerky motion that is not properly recorded in the cable parameters. Accelerometer data from the orientation tool in the logging string are needed to get images where borehole features are properly aligned between the different tool pads.
Montsec Geoscience uses Terrastation II software from Terrasciences Inc. for image data processing, integration of various types of well data, image log interpretation and presentation of results in cross plots, rose diagrams, log plots, correlation panels, etc.
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