Formation evaluation of clastic formations in Cased Hole uses the principals and logic of Sand and Complex Reservoir Formation Analyses. Included In the Program are the analysis from open hole surveys, when available, along with the analysis of the Carbon Oxygen Ratios, Silicon Calcium Ratios, the Gamma Ray, Compensated Neutron, Neutron Lifetime Log, near and for detector curvesfrom the Lifetime Log measurements. The Cased Hole Clastic Evaluation allows analysis of possible hydrocarbon bearing zones regardless of water salinities through casing.

The Carbon Oxygen ratio theory and measurement techniques are discussed in detail.

Matrix constants, formation salinities, clay volumes, formation fluid parameters, i.e., water, gas, and oil, are determined from comparison of a series of checks and balances of the survey responses and their material balance equations. The analysis is presented in analog form along with a printed report and commentary. Examples and results are shown from a number of different areas.


Evaluation of clastic formations in cased holes uses pattern recognition in addition to the principals and logic of Dresser Atlas' evaluation programs for Sandstone and Complex Reservoir formations. The evaluation technique allows analysis through casing on possible hydrocarbon bearing zones regardless of water salinities. Data are utilized from Gamma Ray Logs, Silicon/Calicum (Si/Ca) ratios, Silicon/Calcium (Si/Ca) continuous curves, Carbon/Oxygen (C/O) ratios, Inelastic Neutron Logs, Compensated Neutron Logs, Dual Detector Neutron Lifetime Logs ®and open hole surveys.

Matrix constants and formation salinities are determined from crossplots. Shale volume parameters are calculated. Then the data is compared in a series of checks and balancesusing crossplots of porosities that are shale volume corrected.

Data output is in analog and tabulated form. The analog plot is the Cased Hole Exploration Service Epilog ® (Figure BC). Displayed on a four track grid, the curves are recorded as follows:

  • Track I Lithologic characteristics – Shale % of Bulk Volume, Permeability Index, and C/O Ratio measurements.

  • Track II Fluid Analysis – Water Saturation (NLL) ® and Water Saturation (C/O ratio)

  • Track III Porosity and Fluids % Bulk Volume – % Hydrocarban Filled Pare Volume and % Water Filled Pore Volume.

  • Track IV Formation % Bulk Volume −% Shale, % Quartz and % Porosity.


Cased Hole Exploration Service (CHES) Epilog ® are designed to give the maximum information thru casing on possible hydrocarbon bearing zones. The evaluation makes use of the influences in the formation that affect the response of the several logs used. An Acoustic Cement Bond Log is run (when needed) to assure cement integrity.

Generally, the major factors adversely affecting the logs are:

Neutron Lifetime Log (NLL)

  1. Fresh to brackish water in the formation

  2. Shale in the formation

  3. Low porosity

Carbon/Oxygen (C/O)

  1. To a lesser extent, shale in the formation.

  2. Gas in the Formation

  3. Low porosity

  4. Matrix carbon content

Silicon/Calcium (Si/Ca) Ratio (station)

  1. Shale content

  2. Increasing salinity

Compensated Neutron Log (CNLog)

  1. Shale content

  2. Gas in the formation

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