Formation Evaluation By The Reservoir Limit Test
Authors: Jones Park J. 
Published: December 2007

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Abstract
Applications or the reservoir limit test are made in this paper to the following; one producing well, the possible productive and proved acreage, the Y functions for transient and steady flow, the drawdown for a shut-in well, the permeability and radius of a skin and of a stimulated well, two producing wells, the distance from a producing well to a sealing fault, the pore volume and geometric shape or a fault block, the radius or an equivalent fictitious reservoir, the two principal equations for testing gas wells, and to the evaluation or the back-pressure equation [for gas wells completed in low-permeability reservoirs] from transient-flow field data.

Introduction
Consider a producing well completed in a homogeneous isotropic reservoir. A constant producing rate of BQ reservoir 3/D causes the pressure drawdown j= P - P at r ft from the well after t days of production. Darcy's law gives the resistivity to fluid flow in psi per unit flow rate as
M 0.1412 u D = = ..........(1) 1.127 (2 pi) hk hk
where h is the net pay thickness in feet and K, the effective Permeability in Darcy units. The resistivity D is one formation constant. Another is the diffusivity. In square feet per day, is
N = 6.328 K U E 0............................[2]
where h is the porosity. The effective coefficient of expansion E is the reservoir barrels of fluid available per psi drop on one barrel of pore space, cv E = EOSO + EgSg + EWSW + ..............[3] 0 in which + Sg + Sw - l
and Cv denotes the vertical component of rock compressibility. The coefficient of expansion for a reservoir oil EO may be estimated by Trube's method. For a reservoir gas, Eg is defined by
which can be evaluated with the aid of the paper by Rice. The formation constants D, E and can be evaluated from field data by methods considered below.
Kelvins line sink solution gives the drawdown j in terms of the dimensionless parameter u r2/4nt as*
BDQ j = W (u) ....................(4) 2
*For a variable producing rate, BQ = F [theta], the drawdown is given by
where theta is the time variable with limits zero and t.