Abstract

Drawdown Exploration is the name of a technique that enables the operator to determine from a single drawdown well test the following:

  1. ability of the rock to transmit a fluid,

  2. darcy-feet of pay connected with the well,

  3. well completion efficiency,

  4. drainage radius,

  5. distance to the productive limit, and

  6. barrels of oil or Mcf of gas connected with the well.

The technique will detect in place hydrocarbons at the rate of 100,000 to about 1,000,000 BOPD or 1,000,000 to about 10,000,000 Mcf of gas per day. If the well will flow for six hours or more and the hazard of sticking the drill pipe is negligible, the test may be run in an open hole before casing is set. A flowing water well may be tested in order to determine whether oil or gas is present at some distance away from the well.

A 1-mile radius explores about 2,000 acres. A 2-mile radius explores about 8,000 acres. The instrumental limitation on the radius of exploration needs further study in the field with a differential pressure bomb. The need for study on the electric analyzer of nonsteady-state flow is also emphasized.

The use of Drawdown Exploration for determining in place oil or gas, water contact, impermeable boundary and well completion efficiency is illustrated by six field examples.

By virtue of discovery, the phrase "Drawdown Exploration" is claimed for exclusive use by Park Jones.

Field Examples

Fig. 1 is for a Texas gas well that averaged 16 bbl of condensate per MMcf of reservoir gas. The curve labelled [P,t] shows the bottom-hole flowing pressure plotted against the logarithm of time, t, in days. The vertical logarithmic scale, Y, on the left side represents the daily rate of P decrease divided by the producing rate in reservoir B/D. The ability of a reservoir rock to transmit a fluid is measured in psi/reservoir B/D and is called the Darcy constant.

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