The Formation MicroScanner sonde (FMS) consists of four orthogonal imaging pads each containing 16 microelectrodes which are in direct contact with the borehole wall during the recording. The button current intensity is sampled every 0.1 in (2.5 mm). The tool works by emitting a focused current from the 4 pads into the formation. The current intensity variations are measured by the array of buttons on each of the pads.

Processing transforms the current intensity measurements, which reflect the microresistivity variations of the formation; into high resolution grey or color images of variable intensity. Black and white (darkest or lightest color) indicate low and high microresistivity respectively. The tool also includes a General Purpose Inclinometry Cartridge (GPIT) which provides accelerometer and magnetometer data in order to allow one to define the tool position and spatial orientation of the data.

Applications

• Mapping of bedding planes, fractures, faults, foliations, and other formation structures and dip determination.
• Detailed correlation of coring and logging depths.
• Precise positioning of core sections where core recovery is less than 100%.
• Analysis of depositional environments.

Limitations

Environmental Effects:

To produce high-quality FMS images, the pads must be pressed firmly against the borehole wall. The maximum extension of the caliper arms is 15.0 inches. In holes with a diameter larger than 15 inches, the pad contact will be inconsistent (not all 4 pads touching the wall) and the FMS images can be blurred. The maximum borehole deviation where good data can be recorded with this tool is 10°. Irregular borehole walls will also adversely affect the images because the pads can not make sufficient contact with the borehole wall.

Depth of Investigation and Vertical Resolution:

In smooth boreholes with very homogeneous bedding the depth of investigation is about 10 in (25 cm). The vertical resolution is 0.2 in (5 mm).

Log Presentation

FMS images can be plotted with identical vertical and horizontal scales to see features without exaggeration. However, due to physical constraints, different vertical and horizontal scales are commonly used. To display the images, we use an oriented plot, also called an azimuthal plot, because the images are positioned according to their orientation in the borehole with N in the center and S on both edges. Images from two passes of the tool can be merged and plotted together. The calipers or other curves can be plotted alongside the images as well.

With an additional processing step on the VAXstation, dipmeter calculations can be made. Standard dipmeter plots consist of borehole drift, calipers, dip angle and direction (tadpoles), azimuth frequency plots, and pad traces.

Turbidite sequences are imaged here by the FMS data. Red sine waves on the images trace bedding planes. The corresponding "tadpole" plot shows the average dip is roughly 40 degrees to the west. Interpretive work of the FMS data can be performed either on the ship or onshore with the GeoFrame software.

Tool Specifications

Temperature Rating	350°F (176° C)
Pressure Rating	20 kpsi ( 13.8 kPa)
Tool Diameter	3 5/8 in (9.2 cm)
Tool Length	25.3 ft (7.72 m)
Sampling Interval	0.1 in (2.5 mm)
Max. Logging Speed	1,800 ft/hr
Vertical Resolution	0.2 in (5 mm)
Depth of Investigation	10 in (25 cm)