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Introduction
The Acid Consortium was established in 1992 and has 18 members. The group
investigates carbonate and fracture acidizing in vertical and inclined
wellbores, as well as sandstone matrix acidizing.
Previous work
In fracture acidizing a method has been developed to measure diffusivity of
acids vs. lithology, acid strength and temperature. Mass transfer rates of
carbonates and dolomites have been measured vs. flow rate, acid viscosity and
cell size. This has been put into a series of correlations to predict mass
transfer in carbonates with and without leakoff and conductivity have been
evaluated in a 100 sq. in cell to show methods to develop conductive channels.
The effectiveness of carbonate matrix acidizing has been measured in linear and
radial cells with and without drilling mud vs. acid strength, temperature and
rate, with oil present and with biologically generated acids. Sandstone
acidizing effectiveness has been measured in large radial cores vs. typical
linear core flow tests to show the differences that can be expected.
The consortium has evaluated the effectiveness of various organic acids and HF
strengths on problem cores submitted by members to arrive at acid type and
strength recommendations vs. formation lithology. HF acid diversion has been
investigated using particulates of various types and sizes in dual hollow cores
of various permeabilities and in multiple linear and radial core flow systems
using foam vs. core permeability, foam quality, slug size and surfactant
concentration with and without oil present.
Recent Work
During the 99 Program, fracture acidizing studies are measuring leakoff using
various alternating gel and acid systems vs. permeability gel type and acid
strength in multiple long cores. Conductivity tests are underway in a specially
designed biaxial rock mechanics system to look at conductivity vs. closure for
various etched volume ratios vs. rock mechanical properties (soft chalk to hard
dolomite).
The observed results are being programmed into a finite element simulator to
predict conductivity downhole based on etched area volume and mechanical
properties at downhole conditions. The results will be placed into a program
called SLFracAcid to predict the resulting conductivity and well productivity.
Carbonate matrix acidizing studies are being extended to a specially designed
large scale wellbore model. Work will look at acid wash treatments in horizontal
wells to evaluate the effectiveness of various rates, acid concentrations, and
viscosity with and without damage and with permeability variations.
Diversion studies are concentrating on the evaluation of diversion techniques in
carbonates such as viscosified acids, foams, emulsions and combinations thereof
in multiple linear and radial cores. Tests will evaluate each technique vs.
permeability contrast, with and without damage present.
Evaluation techniques include pressure drop, CAT scan imaging of wormholes and
SEM analysis of fines at the wormhole tip. Matrix sandstone acidizing studies
are being conducted in a newly devised radial flow simulator that allows the
determination of HFacidizing effectiveness at realistic velocities up to 2 ft
from the wellbore. The acid is pumped into a series of cores and flowed back as
in an actual treatment.
Elemental analysis of the flowback samples and permeability vs. depth are
measured vs. lithology, acid strength, pumping schedule and shut-in time. The
data from these tests will be compared to field flowback sample results provided
by members and can be used to calibrate newly developed HF acidizing models.
Membership to the Acid Consortium
Stim-Lab encourages new members so that research continues adding value to
participating company's lines of business. First year membership includes copies
of past years research results. Membership grants access to the "members only"
web site which contains research updates, reports for download, plus any
programs or spreadsheets developed within the program. Contact
Us
for membership information |
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