Determining an Apparent Molecular Weight for a Depth Interval for a Wellbore

A non-transitory, computer-readable medium storing computer-readable instructions executable by a computer and configured to:

• set an initial value for an apparent molecular weight for a depth interval for a wellbore;
• and
• iterate on calculations to determine a converged value for the apparent molecular weight, including:
• determining a specific gas gravity;
• determining pseudo-critical gas properties;
• determining a pseudo-reduced gas pressure and temperature;
• determining a gas deviation factor using the pseudo-reduced gas properties;
• determining an average pressure, an average temperate, and an pressure gradient for each depth interval;
• determining a new apparent molecular weight;
• determining the absolute value of a relative error between a current value of the apparent molecular weight and the new apparent molecular weight;
• determining if the absolute value of the relative error has converged to a constant;
• and
• terminating the iterating upon determination that the relative error has converged to the constant.

A computer-implemented system, comprising:

• at least one computer interoperably coupled with a memory storage and configured to:
• set an initial value for an apparent molecular weight for a depth interval for a wellbore;
• and
• iterate on calculations to determine a converged value for the apparent molecular weight, including:
• determining a specific gas gravity;
• determining pseudo-critical gas properties;
• determining a pseudo-reduced gas pressure and temperature;
• determining a gas deviation factor using the pseudo-reduced gas properties;
• determining an average pressure, an average temperate, and an pressure gradient for each depth interval;
• determining a new apparent molecular weight;
• determining the absolute value of a relative error between a current value of the apparent molecular weight and the new apparent molecular weight;
• determining if the absolute value of the relative error has converged to a constant;
• and
• terminating the iterating upon determination that the relative error has converged to the constant.