Tasks of the Project
Task
4.0. Theoretical Analysis of Field Applications and Database Building
The
objective of Task 4 is to identify where particle gels can be effective
and how
to best use them. Results from this field data analysis will provide
instructive information on the design work in Task 5 of the project.
Published
documents show that several of the novel particle gels mentioned above
were
economically applied to reduce water production in mature oilfields.
Preformed
particle gels were applied in about 2,000 wells to reduce fluid
channels in
waterfloods and polymer floods in China (Liu 2006). Swelling
micron-sized polymers were applied in around 10 injection wells for
in-depth
profile modification in different areas by BP and Chevron (Cheung
2007).
Microgels were used to shutoff water in a gas storage well (Zaitoun
2007). We
will collect as much related field data as we can to build a database
and use
the database and our analysis methods (Wang 2006, Seright 2005) to
identify if
fractures or fracture-like features are present. Because the principle
investigator
Dr. Baojun Bai developed and participated in field testing of preformed
particle gels, we have extensive access to field data for this
application. We
already collected valuable data from China, including injection
volume,
real-time injection rate and pressure, particle sizes and related
production
performance before, during and after each treatment. Soft-computing
methodologies, such as neural network (Saeedi 2006) and fuzzy logic
(Liu 2000),
will be used to identify the best model for candidate selection and
well
performance prediction.
Task 5.
Particle Gel Transport through Fractures
and Fracture-like Channels
The
objective of Task 5
is to quantify particle gel propagation and dehydration during
extrusion
through fractures and fracture-like channels and identify the best
particle
gels for different formation. Selecting the right size of gel particle
for a
fracture and a fracture-like channel is of major importance to the
success of
gel treatments. However, gel particles are different from conventional
particles because they are elastic and deformable during extrusion. We
will
study how the deformable particles transport through open fractures and
fracture-like channels and determine if the particles can effectively
plug
these channels. This task has three subtasks.
Subtask 5.1:
Experiments will be performed in screens and fractured and channeled
cores to
screen gel particles for different formations. These tests will
determine what
pressure gradients are needed to propagate the gel particles through
fractures
and fracture-like channels and how big a role gel dehydration and
screen-outs
play in plugging fractures and channels. In addition, gel damage in/on
matrix
rock will be evaluated to minimize gel damage to the matrix. Detailed
core
flooding methodologies can be found (Seright 2003). Use of screens with
a wide
range of mesh size will aid in targeting the proper fracture width and
channel
permeability.
Subtask 5.2:
We will study the effects of gel particle concentration, gel strength,
and flow
rate on injection pressure. Gel placement will be studied to optimize
gel
treatment design using core floods.
Subtask 5.3:
Theoretical models used in Task 4 will be updated in light of the new
experimental results/models for particle gel transport through
fractures. This
updating will help to optimize models for performance prediction.
Task 6.
Improved Particle Gel Treatments
Some
novel processes will be tested to determine if they can improve gel
particle
treatment efficiency. One method involves addition of a secondary
crosslinker.
Delayed crosslinking after gel-particle placement may make the
dispersed gel
form a bulk gel―thus increasing the resistance to wash out. A second
method
incorporates gel particles with surfactant, so that the filtrate that
is
squeezed into the matrix during gel injection alters the wettability of
rock
near the fracture faces. By reducing interfacial tension between
hydrocarbon
and water, we hope to lower the capillary pressure and reduce the
capillary end
effect, which is a dominant factor that is responsible for low
hydrocarbon
recovery from tight-gas reservoirs (Penny 2005, 2006). A third method
involves
exploitation of gravity segregation to control gel placement. Usually
particle
gels have a higher density than the carrier fluid. We will test if the
density
difference can be exploited to optimize gel placement in vertical
fractures
where we wish to plug the bottom part (i.e., the water-source zone)
while
leaving the upper part open (i.e., the oil source zone).
Task 7.
Customized PPG Products
PPG is not
just a
simple, single product, but has several chemical components, such as
monomer,
cross-linker agent, and polymerization initiator before synthesized.
The key
properties and subsequent behavior of the PPG will vary depending upon
the
details of its composition and it synthesis. Another important
parameter is the
average size and size distribution of the final PPG ground particle
product. ChemEOR
will provide a series of customized, well-characterized laboratory
scale PPG
products that cover a wide range of size and chemical characteristics
for
laboratory performance testing. The variety of results may be
interpreted to
aid in the field design of PPG treatments for a large range of well
conditions.
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