Let's evaluate the **source rock types** (Type I, II, III, IV) using the **Van Krevelen diagram** based on the provided plot of HI (Hydrogen Index) vs. OI (Oxygen Index). --- ## **Step-by-Step Explanation** ### **1. Understanding the Van Krevelen Diagram** - **HI** (Hydrogen Index, y-axis): Indicates the hydrogen richness, usually in mg HC/g TOC. - **OI** (Oxygen Index, x-axis): Indicates the oxygen content, usually in mg CO₂/g TOC. **Source Rock Types:** - **Type I:** Oil-prone (algal, lacustrine); HI > 700, OI < 50 - **Type II:** Oil & gas-prone (marine planktonic); HI ~ 300–700, OI < 50 - **Type III:** Gas-prone (terrestrial, woody); HI ~ 50–250, OI > 50 - **Type IV:** Inert, non-source (highly oxidized, reworked material); HI < 50, OI variable --- ### **2. Interpreting the Plot** #### **Color Clusters (as per your plot):** - **Green cluster:** HI ~ 300–500, OI < 20 - **Red cluster:** HI ~ 400–500, OI ~ 20–50 - **Yellow cluster:** HI ~ 200–300, OI ~ 20–120 - **Blue cluster:** HI ~ 150–200, OI ~ 20–60 --- ### **3. Assigning Source Rock Types** #### **A. Type I (Oil-Prone)** - **Criteria:** HI > 700, OI < 50 - **Observation:** No samples with HI > 700, so **no clear Type I**. The highest HI is ~500. #### **B. Type II (Oil & Gas-Prone)** - **Criteria:** HI 300–700, OI < 50 - **Green and Red clusters** (HI: 300–500, OI: <50) fit here. - **Interpretation:** **Green and Red clusters** are **Type II** source rocks. #### **C. Type III (Gas-Prone)** - **Criteria:** HI 50–250, OI > 50 - **Some Yellow and Blue clusters** (HI: 150–250, OI: 50–120) fit here. - **Interpretation:** **Yellow and Blue clusters** are mostly **Type III** source rocks. #### **D. Type IV (Inert)** - **Criteria:** HI < 50, OI variable - **Observation:** No points with HI < 50, so **no clear Type IV**. --- ### **4. Detailed Assignments from Your Plot** | Color | HI Range | OI Range | Rock Type | Interpretation | |--------|----------|----------|-----------|-------------------------------| | Green | 300–500 | 0–20 | II | Good oil/gas-prone | | Red | 400–500 | 20–50 | II | Good oil/gas-prone | | Yellow | 200–300 | 20–120 | III | Mostly gas-prone | | Blue | 150–200 | 20–60 | III | Gas-prone | --- ## **Summary Table** | **Cluster** | **HI** | **OI** | **Type** | **Potential** | |-------------|-------------|-------------|-------------|----------------------------| | Green | 300–500 | <20 | Type II | Oil & gas-prone | | Red | 400–500 | 20–50 | Type II | Oil & gas-prone | | Yellow | 200–300 | 20–120 | Type III | Gas-prone | | Blue | 150–200 | 20–60 | Type III | Gas-prone | --- ## **Conclusion** - **Your shales and coals are mostly Type II and Type III source rocks.** - **Type II (Oil & gas-prone):** Green and Red clusters (HI 300–500, OI < 50) - **Type III (Gas-prone):** Yellow and Blue clusters (HI 150–300, OI 20–120) - **No evidence for Type I (very oil-prone) or Type IV (inert) in your data.** **This means the rocks have moderate to good oil and gas potential, with some being predominantly gas-prone.** --- **If you have questions about specific data points, let me know!**