Part III - Well stimulation methods

Dissolution Kinetics

Measuring kinetics of dissolution

Experimental set up for studying reaction rate as a function of revolutions per minute

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Wormholes

Due to the acid attack pores increase their diameter in such a way that wider channels grow faster

The faster growth of larger channels can have an unstable character and can lead to a “catastrophic” behavior.

An example of such behavior is reaction between limestone and hydrochloric acid HCl that produce long and empty channels in limestone called wormholes

In matrix acidizing such a phenomenon results in much larger stimulated zone than can be predicted assuming a uniform advancement of the reaction front

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Fractals in porous media

Results of stochastic reservoir simulation

Distribution of phases at the	Final distribution of phases (water
water breakthrough time	cut = 95%)

Mathematically homogeneous and isotropic media

М=100

Fractals in porous media

Lab modeling of matrix acidizing:	Top view
a fractal structure (wormholes)
development in carbonate
reservoirs

Ref.: JPT, October, 2010

Side view

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Fractals in porous media

Lab modeling of matrix acidizing: a fractal structure (wormholes) development in carbonate reservoirs

High resolution CT images of acidized core plugs at low, optimum, and high acid flux

Ref.: SPE 134379

35

Fractals in porous media

Numerical simulation of flow behavior in the vicinity of wormholes developed by carbonate acidizing

Stream lines towards the system of channels with fractal structure developed by carbonate acidizing

Ref.: SPE 134379

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Matrix acidizing

Wormholes

Wormholes as a result of dissolution of the limestone by hydrochloric acid (after Daccord and Lenormand, 1987)

Lab experiments	Stochastic simulation
(Daccord and Lenormand,	(Zirngast, 1993)
1987)

12 October 2012

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Wormholes

Theoretical and experimental studies have proved that (Daccord and Lenormand, 1987):

The pattern formed by the etched channels is a fractal, characterized by its fractal dimentions, df

When considering the hydraulic properties of this ensemble of wormholes, an equivalent wellbore radius r’w can be defined:

rw rw e S

where S is a skin-factor

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Wormholes

Results of experiments show that the following relationship is valid for both types of reaction kinetics:

	1			bV
S		ln 1 Ac Pe	1/ 3
	d			h rw	d

where Pe=q/(Dh), b=1.7x104 md-2

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Wormholes

Growth regime in carbonate acidizing:

Compact	Wormholes	Uniform
dissolution	growth	dissolution

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