{
  "version": 1,
  "topic": "PV12",
  "title": "PVT symbols units and calculation practice pack",
  "createdAt": "2026-10-24",
  "case": {
    "title": "Bg from two explicit absolute states",
    "premise": "Reservoir T = 600 °R and Z = 0.85; standard T = 520 °R, P = 14.7 psia, Z = 1. Reservoir pressure varies.",
    "formula": "Bg = Zr Tr Ps/(Pr Zs Ts); expansion = 1/Bg",
    "variables": "Bg in reservoir ft³/scf when both volumes use cubic feet. This explicit state ratio differs slightly from rounded field coefficients.",
    "steps": [
      {
        "label": "Define the baseline",
        "calculation": "Reservoir pressure (psia) = 3000",
        "explanation": "Reservoir T = 600 °R and Z = 0.85; standard T = 520 °R, P = 14.7 psia, Z = 1. Reservoir pressure varies."
      },
      {
        "label": "Select the relation",
        "calculation": "Bg = Zr Tr Ps/(Pr Zs Ts); expansion = 1/Bg",
        "explanation": "Bg in reservoir ft³/scf when both volumes use cubic feet. This explicit state ratio differs slightly from rounded field coefficients."
      },
      {
        "label": "Substitute the values",
        "calculation": "Bg = 0.85 × 600 × 14.7/(3,000 × 520) = 0.00480576923 ft³/scf; reciprocal = 208.083233 scf/ft³",
        "explanation": "Retain intermediate precision. The displayed values are rounded only after evaluation."
      },
      {
        "label": "Read the result",
        "calculation": "Bg (reservoir ft³/scf) = 0.00480576923; Expansion (scf/reservoir ft³) = 208.083233",
        "explanation": "Both state definitions are part of the factor; changing standards changes the explicit ratio."
      }
    ],
    "result": "Bg (reservoir ft³/scf) = 0.00480576923; Expansion (scf/reservoir ft³) = 208.083233",
    "interpretation": "Both state definitions are part of the factor; changing standards changes the explicit ratio.",
    "control": "Reservoir pressure (psia)",
    "columns": [
      "Reservoir pressure (psia)",
      "Bg (reservoir ft³/scf)",
      "Expansion (scf/reservoir ft³)"
    ],
    "rows": [
      [
        500,
        0.028834615384615386,
        34.68053888221955
      ],
      [
        1000,
        0.014417307692307693,
        69.3610777644391
      ],
      [
        2000,
        0.007208653846153846,
        138.7221555288782
      ],
      [
        3000,
        0.004805769230769231,
        208.08323329331733
      ],
      [
        5000,
        0.0028834615384615383,
        346.80538882219554
      ]
    ],
    "baseline": 3,
    "rowNotes": [
      "Reservoir pressure (psia) = 500. Bg (reservoir ft³/scf): 0.0288346154; Expansion (scf/reservoir ft³): 34.6805389.",
      "Reservoir pressure (psia) = 1000. Bg (reservoir ft³/scf): 0.0144173077; Expansion (scf/reservoir ft³): 69.3610778.",
      "Reservoir pressure (psia) = 2000. Bg (reservoir ft³/scf): 0.00720865385; Expansion (scf/reservoir ft³): 138.722156.",
      "Reservoir pressure (psia) = 3000. Bg (reservoir ft³/scf): 0.00480576923; Expansion (scf/reservoir ft³): 208.083233.",
      "Reservoir pressure (psia) = 5000. Bg (reservoir ft³/scf): 0.00288346154; Expansion (scf/reservoir ft³): 346.805389."
    ],
    "provenance": "Original synthetic teaching calculation. Equations and fixed controls are stated here; these are not field measurements.",
    "questions": [
      {
        "question": "Reproduce the baseline Bg (reservoir ft³/scf) without rounding intermediate values.",
        "answer": "Bg = 0.85 × 600 × 14.7/(3,000 × 520) = 0.00480576923 ft³/scf; reciprocal = 208.083233 scf/ft³. Bg (reservoir ft³/scf) = 0.00480576923. Both state definitions are part of the factor; changing standards changes the explicit ratio."
      },
      {
        "question": "Compare the first and last recorded scenarios. Which input changes?",
        "answer": "Reservoir pressure (psia) changes from 500 to 5000. Other controls remain as stated in the premise. Bg (reservoir ft³/scf) changes from 0.0288346154 to 0.00288346154."
      },
      {
        "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. Bg in reservoir ft³/scf when both volumes use cubic feet. This explicit state ratio differs slightly from rounded field coefficients. Both state definitions are part of the factor; changing standards changes the explicit ratio."
      }
    ]
  },
  "recorded": null
}