Unit Consistency Checker

Level 2

Chapter 2: Python Essentials

descriptionProblem

One of the most common (and most dangerous) sources of error in petroleum engineering is mixed units: feeding a value in metres into a formula that expects feet, or kg/m³ into one that expects ppg. Real incidents have been traced to a single line of code that quietly multiplied wrong-unit numbers together.

Write hydrostatic_psi(mud_weight, tvd, mw_unit, depth_unit) that returns the hydrostatic pressure in psi. It must accept:

mw_unit: either "ppg" or "kg/m3"
depth_unit: either "ft" or "m"

Use these conversions:

1 ppg = 119.826 kg/m³
1 ft = 0.3048 m
Hydrostatic in oilfield units: $P_{\text{psi}} = 0.052 \times MW_{\text{ppg}} \times TVD_{\text{ft}}$

Convert both inputs to oilfield units internally, then return psi.

Reject unknown unit strings with ValueError. It is much better to crash on bad metadata than to compute a confidently wrong number.

> Think about it: verify that computing (10.0, 10000, "ppg", "ft") > and the same well expressed in SI units ((1198.26, 3048, "kg/m3", "m")) > produce the same psi within rounding tolerance. If they don't, your > conversion has a bug.

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codeYour solution

main.py

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Try solving it yourself first — the hints walk you through it. The solution below is one valid approach; yours may differ and still be correct.

def hydrostatic_psi(mud_weight, tvd, mw_unit, depth_unit):
    if mw_unit == "ppg":
        mw_ppg = mud_weight
    elif mw_unit == "kg/m3":
        mw_ppg = mud_weight / 119.826
    else:
        raise ValueError(f"unknown mw_unit {mw_unit!r}; use 'ppg' or 'kg/m3'")

    if depth_unit == "ft":
        tvd_ft = tvd
    elif depth_unit == "m":
        tvd_ft = tvd / 0.3048
    else:
        raise ValueError(f"unknown depth_unit {depth_unit!r}; use 'ft' or 'm'")

    return 0.052 * mw_ppg * tvd_ft


a = hydrostatic_psi(10.0, 10000, "ppg", "ft")
b = hydrostatic_psi(1198.26, 3048, "kg/m3", "m")
print(f"oilfield: {a:.2f} psi")
print(f"SI:       {b:.2f} psi")
print(f"|Δ|     : {abs(a - b):.4f} psi  (should be < 1)")

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2.4 Production Alert System

2.6 Daily Production Report Cleaner

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