In this work we develop, validate, and apply the "reciprocal rate method" to estimate oil reserves using only rate-time production data. This approach requires the development of boundary-dominated flow, and can be used to validate reserve extrapolations from numerical/analytical reservoir models. The methodology does presume that flowing well bottomhole pressures are approximately constant — but we will demonstrate that the method is tolerant of substantial changes in the flowing bottomhole pressure.

This approach requires a plot of the reciprocal of flowrate (1/q) and the so-called "material balance time" (cumulative production/flowrate or Np/q). The "secret" to this approach is the use of material balance time — this function accounts for most variation in rate/pressure, and permits the extrapolation of the 1/q function.

This methodology has been applied for oil wells (including oil wells with high water production) — and in all cases, the reciprocal rate method has proven to be robust and consistent.

The primary technical contributions of this work are:

  • Direct method to estimate reserves using only rate-time data (time, rate, and cumulative production).

  • The reciprocal rate method is based on variable-rate theory, and is more rigorous than Arps approach (exponential or hyperbolic rate relations).

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