AUTOMATED LOG QUALITATIVE INTERPRETATION (KO KO RULES) BY USING CATGEOKU SOFTWARE

Using our software, you only need to drag and drop the triple combo from the LAS data and specify the depth analysis interval (e.g. every 5 metres) to read the well log data in 3 seconds by 6 rules from Ko Ko Rules.

Here are the 6 rules from Ko Ko Rules:

1. Tight non-reservoir: Right-Right-Right-Right.

• GR: High → shale/clay-rich, non-reservoir (radioactive minerals: U, Th, K).

• Resistivity: High → tight/impermeable formation with little conductive fluid.

• Density & Neutron: Both indicate low porosity → compact, poor-quality rock.

👉 Overall: High GR + low porosity (Density–Neutron) + high resistivity = non-reservoir, shale-dominated zone.

2. Shale: Right-Right-Right-Left.

• GR: High → shale/clay-rich zone with elevated natural radioactivity (U, Th, K).

• Resistivity: Generally high due to tightness, but may deflect left in conductive shales.

• Density: Indicates low porosity (tight formation).

• Neutron: Deflects left, showing artificially high porosity from clay-bound water.

• Key Feature: Reversed Density–Neutron crossover (Neutron > Density).

👉 Overall: This log response is characteristic of shale zones, where clay effects distort neutron readings.
📌 Note: Similar crossover can occur in dolomitic zones, but GR is typically lower there.

3. Low porosity (tight) reservoir: Left-Right-Right-Right.

• GR: Low readings reflect dolomite’s low natural radioactivity (low Th, K, U).

• Resistivity: Indicates rock compactness/tightness rather than fluid type—higher in impermeable zones.

• Density & Neutron: Track porosity but are strongly influenced by matrix effects; in dolomite, this often causes a reversed crossover.

👉 Overall: In dolomitic or tight carbonate reservoirs, log responses are driven mainly by matrix composition and rock tightness, not by fluid content.

4. Water bearing reservoir: Left-Left-Left-Left.

• GR: Low readings indicate clean sand/carbonate with minimal natural radioactivity (low Th, K, U).

• Resistivity: Differentiates fluids—low when water-filled, high when hydrocarbons are present.

• Density & Neutron: Indicate higher porosity, confirming good reservoir quality.

👉 Overall: A zone with low GR, porous Density–Neutron response, and resistivity controlled by fluid type represents a clean reservoir interval.

5. Oil bearing reservoir: Left-Right-Left-Left.

GR reads lower because of reduced radioactivity (Th, K, U). Resistivity increases in the presence of non-conductive hydrocarbons. Density-Neutron logs indicate higher porosity in the reservoir.

6. Gas reservoir: Left-Right-Left-Right.

GR is lower due to reduced radioactivity (Th, K, U). Resistivity is higher from non-conductive hydrocarbons. Density log shows lower bulk density because of low gas density. Neutron log indicates apparent low porosity in gas zones due to weaker neutron–hydrogen interactions in gas compared to water.

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YOUR WORKSPACE

LAS Well Log "Ko Ko Rules" Analyzer

Drag and Drop Your LAS File Here

Comparison Trend Interval:

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REFERENCE:
https://www.linkedin.com/pulse/six-ko-rules-easily-detect-oil-gas-water-from-well-log-dosh-nazlan/