Net pay determination in laminated sediments

The FMI tool is the preferred approach for determining net pay in the laminated sediments typical of fluvial and turbidite depositional environments.The method for obtaining an accurate sand count is to compute an averageresistivity curve from the FMI measurements and apply a cutoff that distinguishes sand from shale.
Laminations as thin as 0.2 in. can be resolved. Sections with laminations thinner than this intrinsic resolution
are analyzed by calibrating FMI lithofacies with the sand count from core. The resulting sand-shale curve can be analyzed for the bed-thickness distribution and used to derive mappable parameters.

In highly laminated sediments, the FMI log clearly shows the net pay zones that can contribute to production.

Characterization of rock structure From FMI Logs

FMI images provide critical information if the rock structure and sedimentary features are significant determinants of formation productivity. The figure below shows paired carbonates and sandstones with the same porosity but completely different permeabilities and hence production capabilities.

FRACTURE IDENTIFICATION FROM FMI LOGS

The electrical images are made by applying a gray scale to the resistivity wiggle-traces produced from the electrodes on the tool. In this way, low resistivity zones appear dark and high resistivity, low porosity intervals appear white. Since the array on each pad is two and a half inches wide, irregular features, such as vugs and fractures, show up as dark spots and lines on the images. Colour tones may be used instead of grey.

The image depth scale is usually 1:20 or 1:40, and the X axis is scaled from -180 to +180 degrees around the borehole, putting North in the middle of the track. Examples are provide  in the image. A dramatic near vertical fracture can be seen. Two vertical scales are used: one for reconnaissance and one for detail evaluation. Fracture orientation is roughly NNW - SSE dipping at more than 80 degrees. Other images on these two figures illustrate induced fractures, borehole breakout, inter-bedding laminations, slump brecchia, vugs with fractures, and stylolites.

 

A video on Neutron-Density interpretation tip

Ultrasonic Borehole Imager (UBI)

Other Common Names to this log:

1. CBIL (pronounced Cybill) stands for Continuous Borehole Image Log 

2. Borehole televiewer

COMPARISON WITH OTHER IMAGE LOGS:


Acoustic image logs, also called televiewer or CBIL logs, use a rotating transducer to measure acoustic impedance images over the entire borehole wall, as well as an acoustic caliper.
Resistivity imager logs, also called microscanner or FMS or FMI logs, carry an array of electrodes on pads used to produce an electrical image of the formations seen on the borehole wall.  Microscanners have better vertical resolution and dynamic range than televiewers, but televiewers see the entire wellbore while microscanners usually see less than 100%.

How to QC FMI data?

1. Check the calliper curves and see if the hole shape is
good and has no washouts.

2. Check the FMI images. 
Are they readable? 
Did all the pads work well?

3. Finally, it is good to check the deviation data of the well
and compare it with the deviation curve presented with the
FMI data.