Saturday, February 4, 2012

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.

Wednesday, February 1, 2012

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.

Sunday, January 1, 2012


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.