Sunday, July 8, 2012

Shale Gas In Place Calculation

Original shale gas in place calculation consists of two volumes, desorbed gas and free gas volume. Desorbed gas volume can be estimated from the core measurement of total organic carbon (TOC) and gas content (Gc). Refer to my previous post for the determination of TOC with wireline logs.  The correlation of TOC and Gc from lab measurement gives the gas content as input for the desorbed gas volume calculation.

Desorbed gas volume = Gas Content * Shale Density * Thickness * Area
Free gas volume = Effective Shale Porosity * (1-Sw) * Thickness * Area
Total Shale Gas Volume = Desorbed gas volume + Free gas volume

* most cases, free gas volume refers to tight gas volume or gas volume from interbeded sand layers.

https://1drv.ms/u/s!AlPn9kC8z9NkauGqNuCQOvTuuTo

Thursday, July 5, 2012

Total Organic Carbon (TOC) calculation from well logs

This app allows you to estimate TOC content for source rock, using EXXON method, published by Passy et. al. (1990).  TOC is critical parameter for quantifying unconventional reseources, CBM or Shale gas. The adsorbed gas content is a correlation with TOC, derived from lab measured data.

The estimated TOC is best to calibrate with lab measurement by adjusting the Level of organic maturity,LOM.  Vitrinite Reflectance (Ro) from lab may be available to derive LOM with graph below.