Summary
In highly heterogeneous carbonate reservoirs, several acid systems have been
used to enhance acid diversion during matrix acidizing such as surfactant-based
acids and in-situ-gelled acids. In-situ-gelled acids are also used to reduce
leakoff rate in acid fracturing. The main acid used in this system is
hydrochloric acid (HCl). However, high reaction rates and severity of corrosion
problems, especially for wells completed with Cr-based tubulars, limit the use
of HCl at high temperatures. On the other hand, mixing organic acids with HCl
either increases the acid penetration or reduces the necessary strength of HCl
and the necessary load of the corrosion inhibitors. A few studies addressed the
systems that use both advantages.
The objective of this work is to investigate the behavior and the
performance of different in-situ-gelled HCl/formic acid blends as diverting
agents by conducting viscosity measurements and reaction-rate measurements
using the rotating-disk apparatus, and through coreflood study.
Formic acid was blended with HCl, and four in-situ-gelled acids were
examined. Formic acid concentration varied from 0 to 6.31 wt%, and HCl
concentration ranged from 0 to 5 wt%. Pink Desert limestone was used for
reaction-rate and coreflood experiments. The rotating-disk apparatus was used
to measure the reaction rate at 250degF at disk rotational speeds of 100 and
1,000 rev/min. The effect of formic acid concentration and zirconium
crosslinking on the reaction rate was examined. Coreflood experiments were
conducted at 250°F using two different rates of injection (2 and 10
cm3/min), and the core samples were imaged using a
computed-tomography (CT) scan technique after each coreflood experiment.
Increasing formic acid concentration decreased the reaction rate of
in-situ-gelled HCl/formic acid with calcite at both low and high disk
rotational speeds. This was confirmed by viscosity measurements, which showed
that increasing formic acid concentration increased the viscosity of the live
acids and decreased the viscosity of the spent acids. Coreflood results showed
that increasing formic acid concentration in HCl/formic acid blends reduced
acid ability for diversion. In the selected range of acid concentration and for
the type of polymer and crosslinking agent used, the in-situ HCl/formic acid
behaved more like gelled acid and reached a breakthrough in all coreflood
experiments. The higher the formic acid concentration, the higher the pore
volume of the acid required to break through.
The objective of this work is to investigate the behavior and the
performance of different in-situ gelled HCl-formic acid blends as diverting
agents by conducting viscosity measurements, reaction rate measurements using
the rotating disk apparatus, and through core flood study.
Formic acid was blended with HCl and four in-situ gelled acids were
examined. Formic acid concentration varied from 0 to 6.31 wt% and HCl
concentration ranged from 0 to 5 wt%. Pink Desert limestone was utilized for
reaction rate and core flood experiments. The rotating disk apparatus was used
to measure the reaction rate at 250°F at disk rotational speeds of 100 and 1000
rpm. The effect of formic acid concentration and zirconium crosslinking on the
reaction rate was examined. Core flood experiments were conducted at 250°F
using two different rates of injection (2 and 10 cm3/min) and the
core samples were imaged using a CT scan technique after each core flood
experiment.
© 2012. Society of Petroleum Engineers
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History
- Original manuscript received:
4 April 2011
- Meeting paper published:
28 March 2011
- Revised manuscript received:
4 October 2011
- Manuscript approved:
11 October 2011
- Published online:
29 March 2012
- Version of record:
1 May 2012
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