{
  "version": 1,
  "topic": "MB08",
  "title": "Explore gas in place sensitivity to porosity and saturation",
  "createdAt": "2026-10-24",
  "case": {
    "title": "Gas occupancy sensitivity",
    "premise": "160 acres, 50 ft net pay, φ = 0.15 and Bg = 0.005 reservoir ft³/scf; only Sw varies.",
    "formula": "G = 43,560 × 160 × 50 × 0.15(1 − Sw)/0.005",
    "variables": "Sw is the water fraction of the same pore volume represented by φ.",
    "steps": [
      {
        "label": "Define the baseline",
        "calculation": "Water saturation (fraction) = 0.25",
        "explanation": "160 acres, 50 ft net pay, φ = 0.15 and Bg = 0.005 reservoir ft³/scf; only Sw varies."
      },
      {
        "label": "Select the relation",
        "calculation": "G = 43,560 × 160 × 50 × 0.15(1 − Sw)/0.005",
        "explanation": "Sw is the water fraction of the same pore volume represented by φ."
      },
      {
        "label": "Substitute the values",
        "calculation": "G = 348,480,000 × 0.15 × (1 − 0.25)/0.005 = 7,840,800,000 scf",
        "explanation": "Retain intermediate precision. The displayed values are rounded only after evaluation."
      },
      {
        "label": "Read the result",
        "calculation": "Gas in place (scf) = 7840800000; Gas-filled pore fraction = 0.75",
        "explanation": "An absolute saturation change must be compared with the remaining gas fraction to obtain its relative volume effect."
      }
    ],
    "result": "Gas in place (scf) = 7840800000; Gas-filled pore fraction = 0.75",
    "interpretation": "An absolute saturation change must be compared with the remaining gas fraction to obtain its relative volume effect.",
    "control": "Water saturation (fraction)",
    "columns": [
      "Water saturation (fraction)",
      "Gas in place (scf)",
      "Gas-filled pore fraction"
    ],
    "rows": [
      [
        0.1,
        9408960000,
        0.9
      ],
      [
        0.2,
        8363520000,
        0.8
      ],
      [
        0.25,
        7840800000,
        0.75
      ],
      [
        0.3,
        7318080000,
        0.7
      ],
      [
        0.5,
        5227200000,
        0.5
      ]
    ],
    "baseline": 2,
    "rowNotes": [
      "Water saturation (fraction) = 0.1. Gas in place (scf): 9408960000; Gas-filled pore fraction: 0.9.",
      "Water saturation (fraction) = 0.2. Gas in place (scf): 8363520000; Gas-filled pore fraction: 0.8.",
      "Water saturation (fraction) = 0.25. Gas in place (scf): 7840800000; Gas-filled pore fraction: 0.75.",
      "Water saturation (fraction) = 0.3. Gas in place (scf): 7318080000; Gas-filled pore fraction: 0.7.",
      "Water saturation (fraction) = 0.5. Gas in place (scf): 5227200000; Gas-filled pore fraction: 0.5."
    ],
    "provenance": "Original synthetic teaching calculation. Equations and fixed controls are stated here; these are not field measurements.",
    "questions": [
      {
        "question": "Reproduce the baseline Gas in place (scf) without rounding intermediate values.",
        "answer": "G = 348,480,000 × 0.15 × (1 − 0.25)/0.005 = 7,840,800,000 scf. Gas in place (scf) = 7840800000. An absolute saturation change must be compared with the remaining gas fraction to obtain its relative volume effect."
      },
      {
        "question": "Compare the first and last recorded scenarios. Which input changes?",
        "answer": "Water saturation (fraction) changes from 0.1 to 0.5. Other controls remain as stated in the premise. Gas in place (scf) changes from 9408960000 to 5227200000."
      },
      {
        "question": "What would be needed to apply this example to a different physical system?",
        "answer": "Replace the synthetic controls with compatible documented inputs and check the relation's assumptions. Sw is the water fraction of the same pore volume represented by φ. An absolute saturation change must be compared with the remaining gas fraction to obtain its relative volume effect."
      }
    ]
  },
  "recorded": null
}