Summary
Different chelating agents were used as alternatives for hydrochloric acid
(HCl) in matrix acidizing to create wormholes in carbonate formations. Previous
studies demonstrated the use of ethylenediaminetetraacetic acid (EDTA), hydroxy
ethylenediaminetriacetic (HEDTA), and glutamic acid-N,N-diacetic acid (GLDA) as
standalone stimulation fluids to stimulate carbonate reservoirs. The main
problem of using EDTA and HEDTA is their low biodegradability.
GLDA was introduced as a standalone stimulation fluid for deep carbonate
reservoirs where HCl can cause corrosion and face dissolution problems. In this
study, calcite cores 1.5 in. in diameter and 6 or 20 in. in length were used to
determine the optimum conditions where the GLDA can break through the core and
form wormholes. GLDA solutions with pH values of 1.7, 3, and 3.8 were used. The
optimum conditions of injection rate and pH were determined using coreflood
experiments. Damköhler number was determined using the wormhole length and
diameter from the CT scan 3D and 2D images. GLDA was compared with chelates
that are used in the oil industry such as EDTA and HEDTA. GLDA also was used to
stimulate parallel cores with different permeability ratios (up to 6.25).
GLDA was found to be very effective in creating wormholes at pH = 1.7, 3,
and 3.8; at different injection rates; and at temperatures up to 300°F.
Increasing the temperature increased the reaction rate and less volume of GLDA
was required to break through the core and form wormholes. Unlike HCl, in GLDA
there was no face dissolution or washout in the cores even at low injection
rates (0.5 cm3/min). An optimum injection rate and Damköhler number
were found at which the pore volume (PV) required to create wormholes was the
minimum. GLDA at pH 1.7 and 3 created wormholes with a small number of PV (at 1
cm3/min, GLDA at pH 1.7 required 1.5 PV at 300°F, and at pH 3 it
required 1.8 PV). Compared with acetic acid, the volume of GLDA at pH 3
required to create wormholes was less than that required with acetic acid at
the same conditions. GLDA was found to be effective in stimulating parallel
cores up to 6.25 permeability contrast (final permeability/initial
permeability).
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
8 October 2010
- Meeting paper published:
21 September 2010
- Revised manuscript received:
17 February 2011
- Manuscript approved:
19 February 2011
- Published online:
27 June 2011
- Version of record:
23 December 2011
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