Behzad hosseinzadeh

SharifWellStimulation,2017
StimPt Course

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Course Content
 Advantage and Disadvantage of StimPro Software
 Matrix Acidizing Experiment and Analysis of the Data
 Upscaling from Experiment to Field
 Matrix Acidizing Design
 SharifStim

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Advantage and Disadvantage of
StimPro Software

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What Can You Do with StimPro
select the proper fluids associated with
the type of damage in the well, and then
the proper pump schedule to achieve
the required penetration depth
evaluate skin reduction using bottom-
hole pressure matching from previous
job-design data
production response from the 2-D
FraPS reservoir simulators
determine the economically optimal size
for the reservoir

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StimPro’s Advantages
 Complete matrix acid design, simulation and scheduling for:
 Single Layer /Multi-layer reservoir
 Vertical /deviated /horizontal wells
 Matching of real-time pressure data
 Transient pressure and skin calculation even the job is being executed
 Treatment monitoring using Paccaloni plots
 Online graphics and reports
 Preloaded libraries of stimulation fluids, lithologies and formations
 Complex clays/HF reactions modeling in sandstone formations
 Filter cake modeling, foam modeling and scheduling

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StimPro’s Disadvantages
 Specific acid/additive library
 Consider simple carbonate acidizing and wormhole modeling
 Simple candidate selection capabilities
 2-D reservoir simulation
 Modeling VES, gelled and in-situ gelled acids same as foam by considering
all as non-Newtonian fluids
 Inability to predict exploration/appraisal wells when there might not be
acidized job exist
 Inability to show how wormholes propagate around wellbore
 Consideration a few damage types

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Matrix Acidizing Experiment and
Analysis of the Data

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Case study
Acidizing in Canada from the 1960’s to the present day
Very little science or
applied technology
Almost no acid
testing.
Pumped “bare-bones”
acid packages.
Bare-bones: acidic groups that can form salts with metals or other cations
1970’s

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Case study
Technology applied to acidizing - found that many of the acid
packages pumped could cause formation damage such as
sludge and viscous emulsions.  Study took about two years
to produce conclusive results.
1980’s
Determined that damage
was caused by a
combination of Asphaltic
Sludge and Spent Acid
Emulsion

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Case study
Swan Hills 1983 - 1987
Newly developed non-damaging acid stimulations ramp up
production. New life to 30 year old oil field.

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Case study
They concluded…
QC acid testing to verify acid package for each job
Non-emulsifying Thermally Stable
Water Wetting Devoid Of All
Sludges And
Precipitates

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Case study
Many of the acid package design features are listed below:
Acid and ferric iron-
induced asphaltic
sludges.
Emulsion blocks.
Fines liberation and
precipitates.
Formation oil wetting.
Acid additive
separation.
Load fluid and drilling
mud additive
compatibility.
Particulates from
tubing.
Aqueous phase
trapping.

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StimPro

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Coreflood Studies
1. Prepare the core samples
2. Scan the cores before exp.
3. Conduct the acidizing exp
4. Collect effluent samples
5. Measure the Δp, k, 𝜙, 𝜌
6. Scan the cores after exp.
7. Analyze the sample for Ca++,
pH, HCl concentration
8. Image processing
9. Generate plots (Analyze the
date …)

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Coreflood Studies - HCL
Face Dissolution
wormhole
Uniform Dissolution
Help us to determine
exact optimum injection
rate that causes to
design better acidizing
job

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Coreflood Studies - HCL
Maybe Causes
frac in formation

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StimPro

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Coreflood Studies - VES
No Additives 6% VES With Additives 8% VES
Rheology test help us to determine flow behavior index (n) and consistency index
(K) in any simulation special in StimPro

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StimPro

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Coreflood Studies - Single VES Flood
Maybe Causes
frac in formation

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Coreflood Studies - Dual VES Flood
Test#6 Ratio=2.4 Test#7 Ratio=4.6

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HCl vs. Alternate Systems
 Different type of acids have different reaction rate
 Additives change reaction rate of acid

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 Concentration of calcium measured in the reacted acid sample.
 At higher rotational speeds, the rate of dissolution becomes independent of
RPM indicating surface reaction limited regime.
Use for determining diffusion coefficient Constant reaction rate

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The calcium concentration in mg/L is plotted versus time and the dissolution rate
is determined from the slope of a given set of experimental data. The dissolution
rate is plotted versus the disk angular velocity to determine the limiting step of
the reaction.

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StimPro
The Mineral Reaction tab is the second tab on the Mineral Properties - Shift + F8
screen in StimPro dialog.

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StimPro
Fluid Diffusivity: Each fluid must have an Acid Diffusivity, which is the key
parameter in Carbonate Acidizing mode.

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Upscaling from Experiment to
Field

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Most Common Causes For A Failure Of Acidizing Treatment
Daccord et al. found
where rwh is the radius of wormhole penetration, b is a constant, and df is
the fractal dimension, found to be equal to about 1.6. Again substituting qt
for V and differentiating with respect to time yield
• Diffusion limited model (Does not consider fluid loss)
• Is based on the water/plaster experiment
• Overestimate the distance of the wormhole penetration

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Matrix Acidizing Design

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1. Using the wrong type of acid;
2. Using improper acid volumes ;
3. Using improper acid concentrations for the formation
minerology;
4. Over/mis-using additives;
5. Inadequately perforated wells;
6. Too long acid treatment before reproduction;
7. Wrong identification of the cause of formation damage;
8. The rate of corrosion increase. Thus, the effect of elevated
temperatures on fluid properties and on various steps of
the acidizing treatment has to be determined.

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Matrix Stimulation Methodology by ExxonMobil
The technology of
carbonate matrix
stimulation has
advanced significantly
over the past 10 years
through innovative
laboratory testing,
new fluid
developments, and
advanced computer
models to simulate
the process.
However, the
existing approaches
are not sufficient to
meet the challenges
of optimized
stimulation of wells
in massive
carbonate
reservoirs.

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Reservoir Objectives - Completion Strategy
From a resource standpoint, the ultimate objective is
to economically extract the maximum amount of
hydrocarbon from the reservoir. In order to
accomplish this, the optimum production flow
profile for reservoir depletion is required.
Well completion strategy must be developed to
achieve an optimum flow profile. Geological
characterization is necessary to understand the
variability in rock type from layer to layer and well
to well. Distribution of rock types, magnitude and
distribution of permeability and porosity, and
expected reservoir pressures provide important
input into the completion and stimulation design.

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 Below picture shows thin section photomicrographs of limestone and dolostone
with similar permeability, but much different porosity structure.
 Formation and rock characteristics not only affect the acid rock interactions,
but can also affect the susceptibility of the rock to formation damage.
 Testing of individual zones with a single dominant mineralogy has provided a
range of pre-stimulation skin (damage) for different rock types.
 Higher fluid leakoff during drilling dolostone intervals.
stimulation design must
be sufficiently robust to
ensure both rock types
are stimulated to the
desired extent,
consistent with
reservoir objectives.

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The variability in kh
distribution and location
of high permeability
streaks have significant
impact on the
stimulation design. A
single stimulation design
or "cookie-cutter"
approach is not possible.
By following the
integrated carbonate
matrix stimulation
methodology,
stimulation designs
tailored to each well can
be developed,

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Stimulation Design - Productivity Modeling
In many cases, the capabilities of the equipment are
pushed to the limit (rates, volumes, horsepower,
etc.) during the stimulation of very thick reservoirs.
The use of mechanical isolation can provide added
assurance that certain zones are stimulated;
however, additional operational risks and costs can
prohibit its use.
Once the stimulation treatment is performed, it is
critical to evaluate the effectiveness of the
treatment and the ability of the well to meet the
reservoir objectives. Well testing has proven to be a
powerful. The effectiveness of the treatment cannot
be determined by well testing alone. Production
logging provides the flow distribution along the
completion and, when used in combination with
single-well and reservoir modeling, can provide
insight into the effectiveness of the stimulation.

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Completions and Perforation Strategy
 To improve acid distribution and ensure
optimum stimulation of low permeability
layers, selective perforating is utilized.
 By selective perforating, treatment is
reduced to levels that allow more effective
stimulation.
 Selective perforating involves initial
perforation and stimulation of the lower
permeability intervals followed by
perforation and stimulation of the higher
permeability intervals.
 Significant volumes of stimulation fluids
were predicted to be lost into the high
permeability layers. Additionally, the
anticipated flux rates designed to generate
optimum wormholes in the low
permeability rock were greatly reduced

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Mineralogy Analysis
A workflow chart for laboratory petrographic analysis
To improve the
success of acidizing,
the detail mineral
composition of the
target formations
must be known.
Otherwise, problems
with clay swelling,
fines migration, gel
formation, and
precipitation can be
encountered.

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Samples Preparation
To prevent a laboratory-induced damage, the core handling, cleaning and
preparation procedures should be specified with a complete understanding of the
mineralogy of the tested samples.
(1) Plug drilling that need to be performed with a compatible plug drilling fluid to
avoid fluid/rock and/or fluid/fluid reactions;
(2) Sample cleaning that need to be adjusted to the rock characteristics, i.e. low flow
rate cleaning for formations having delicate mineral morphology;
(3) Sample drying procedures to remove the fluids and prepare samples for the
flooding tests.

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Carbonate Formation

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Flowchart For Recommending Remedies
All of these
damage types
are treated in
the pre-flush
stage. This figure
illustrates the
types of damage
accounted for,
and the
corresponding
treatment
methods

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Pre-flush Stage

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Main Acid Stage

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Diversion Stage

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Post-flush Stage

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Additives

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Case Study

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Main Acid Stage

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Case Study
The relatively clean limestone formation at a
relatively high temperature of 250 ˚F requires the
use of a mixture of HCl and a retarded acid
(10% Acetic). The large vertical permeability
heterogeneity (10–1400 md) in the absence of any
significant iron content necessitates the use of
VDA as a diverting agent. Diesel and mutual
solvents are included in the post-flush because
VDA is used as a diverting agent. The existence of
relatively low amount of CO2 in these crudes does
not affect the main acid selection. In fact, CO2 acts
to assist in the back-flow process at the end of the
stimulation job. Nevertheless, a corrosion
inhibitor is added as a precaution since CO2 is
corrosive.

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Sandstone Formation

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Solubility of Sandstone Minerals in HCl And HCl-HF
The target formations are rarely
homogeneous porous mediums,
being a blend of i.e. silicate,
carbonate, and clay minerals.
Based on the mineralogy, its
minerals solubility formation
related factors and the
composition of the acid
injected varies

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Sharif Stim

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Wormhole Simulation

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CT-Scan

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Effect of Injection Rate

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Acidizing Curve

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Effect of Injection Rate - Radial

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Comparison of the acid efficiency curves

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Comparison of model output with experimental results

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Comparison of model output with experimental results

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Identify
Potential
Stimulation
Candidate
Evaluate
Stimulation
Economics
Evaluate
Treatment
Success
Return
Well to
Production
Modify
Stimulation
Guidelines
Matrix
Stimulation
Suitable
Identify
Formation
Damage (type
+ location)
Select
Treatment
Fluid
Compositions,
Additives +
Volumes
Select Treatment
Type, Diversion
Techniques and
Specify Injection
Rates and
Pressure
Treatment
Execution
Site and Job
Preparation
Operational
Stimulation
Program
(including well
clean-up
strategy)
The Stimulation Cycle

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 Which well?
 Damage type?
 Damage location?
 Fluid type?
 Is Acid needed?
 Fluid composition?
 Fluid additives?
 Fluid volume?
 Is Diversion needed?
 Pre-flush, post-flush?.
 ...
Screening and Data Gathering

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Other phenomena that
affect reactions of the
acid with the rock
other
phenomena
Temperature
Fluids
Lithology
The success percentage
can be increased through
a better evaluation and
control both in the study
and application stages
(Gidley, 1985)
Pumping
rate
Successful Well Acidizing

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Treatment Schedule Production Forecast
Acidizing Design Production Analysis
Estimated Skin Reduction
Acidizing Analysis
Wellbore/log/layer Info. Production DataTreatment Data
Save and Optimization
Stimulation Software

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Thanks

Behzad hosseinzadeh

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Behzad hosseinzadeh