A specific type of mathematical model of Decline Curve Analysis, based on the following equation:
(1) | q(t)=q_0 \cdot \left( 1+b \cdot D_0 \cdot t \right)^{-1/b} |
where
q_0 = q(t=0) | Initial production rate of a well (or groups of wells) |
D_0 | model parameter characterizing the decline rate (the higher the D_0 the stronger is decline) |
0 \leq b \leq 1 | defines the type of decline (see below) |
It can be applied to any fluid production: water, oil or gas.
The cumulative production is then given by:
(2) | Q(t)=\int_0^t q(t) \, dt |
and the ultimate recovery is defined as:
(3) | Q_{\rm max}=Q(t=\infty)=\int_0^\infty q(t) \, dt =\frac{q_0}{D_0 \cdot (1-b)} |
Arp's model splits into three types based on the value of
b coefficient:
Exponential Production Decline | Hyperbolic Production Decline | Harmonic Production Decline | ||||||
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b=0 |
0<b<1 | b=1 | ||||||
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The Exponential and Hyperbolic decline are applicable for Boundary Dominated Flow with finite reserves Q_{\rm max} \leq \infty while Harmonic decline is associated with production from the reservoir with infinite reserves Q_{\rm max} = \infty. In other words the Harmonic decline is very slow.
Since all physical reserves are finite the true meaning of Harmonic decline is that up to date it did not reach the boundary of these reserves and at certain point in future it will transform into a finite-reserves decline (possibly Exponential or Hyperbolic).
Exponential Production Decline has a physical meaning of declining production from finite drainage volume V_e with constant BHP: p_{wf}(t) = \rm const (a specific type of Boundary Dominated Flow under Pseudo Steady State (PSS) conditions).
Harmonic and Hyperbolic declines are both empirical.
The DCA Arps do not cover all types of production decline, but their application is quite broad and mathematics is quite simple which gained popularity as quick estimation of production perspectives.
See Also
Petroleum Industry / Upstream / Production / Subsurface Production / Field Study & Modelling / Production Analysis / Decline Curve Analysis
[ Exponential Production Decline ][ Hyperbolic Production Decline ][ Harmonic Production Decline ]