1 It was Spring 2017 when our team started working on a proposal for NASEM-GRP, motivated to develop solutions that will plug wells for 1,000 yrs.! We all believed it needs to be done, we all believed we can make the difference and 3 yrs. later we can see that it is possible. The goal was to demonstrate that plugging and abandonment is a worthwhile endeavor and that it was time to examine the technology that needs to be revolutionized not only for the GoM, but worldwide. To be honest this was my dream project, something I have been thinking for a decade, but I needed a Team to be able to get it to work, and as you will see, this Project is VERY MUCH A TEAM effort. We are a Team of diverse thinkers, with expertise and dreams about the possibility of science and engineering. The best part is that we have a New Generation of experts who are proving every day we are in good hands when it comes to technological challenges in energy extraction at no cost to environment and life. The graphic above shows wellbores keep getting more complex and geologic conditions more challenging. However, we offer some possibilities on how new materials, like graphene, and minerals that are millions of years old, together with good old Portland Cement, can join forces and provide impermeable barriers. All this is still ongoing, we use experiments and models to predict the future of these materials. All of this would not be possible without the trust and support of the NASEM-GRP Team and tons of people that support us daily in our institutions, from Oklahoma, Texas, Louisiana, Pennsylvania and Norway. Finally, our team dedicates this Newsletter to Hope Asala, who tragically lost his life in 2019, with the intention to send a copy to his family and inspire his young daughter to follow her fathers passion for education and research. With thanks and gratitude, Mileva Radonjic, July, 2020, OSU. Summary of Plugging & Abandonment, M. Achang The depletion of an oil and gas well requires plugging and abandonment (P&A) by pumping cement into the wellbore in an attempt to restore the seal to the original subsurface condition. Inadequate P&A results in leakage of oil and gas contaminating underground sources of drinking water, fragile marine ecosystems, soils, and causing air pollution from methane. The Environmental Protection Agency (EPA) has estimated a total of 3.11 million abandoned wells onshore, among which 69% (2.15 million) were unplugged and 31% (0.96 million) plugged in a 2018 report. Thus, the need to advance our understanding of the subsurface, develop barrier materials compatible with acidic, high pressure, high- temperature subsurface environments, and novel placement technologies. Drilling and completion technologies have changed drastically over the years to accommodate multistage wells. Still, old traditional methods continue to be used for P&A. Cement degradation is the leading cause of leakage in plugged and abandoned wells as well as geologic seals for CO 2 sequestration. A review by Achang et al. (2020) on current P&A technologies and future options, inspired by the need to protect the environment concludes that: 1. Traditional P&A solutions and methods used for decades without transformational advancements have to change, as climate change and a large number of wells need permanent P&A. It would be cost-effective to design new drilling technologies that incorporate P&A, so-called Drilling with the P&A in mind. 2. The next-generation of P&A should use new materials. Solutions such as bismuth and termite technology are early indicators of the upcoming change. Also, activating shale as a barrier seems like July 2020 P&A Materials NEWS
Transcript
1
It was Spring 2017 when our team started working on a
proposal for NASEM-GRP, motivated to develop solutions that
will plug wells for 1,000 yrs.! We all believed it needs to be
done, we all believed we can make the difference and 3 yrs.
later we can see that it is possible.
The goal was to demonstrate that plugging and abandonment is
a worthwhile endeavor and that it was time to examine the
technology that needs to be revolutionized not only for the
GoM, but worldwide. To be honest this was my dream project,
something I have been thinking for a decade, but I needed a
Team to be able to get it to work, and as you will see, this
Project is VERY MUCH A TEAM effort. We are a Team of
diverse thinkers, with expertise and dreams about the
possibility of science and engineering.
The best part is that we have a New Generation of experts who
are proving every day we are in good hands when it comes to
technological challenges in energy extraction at no cost to
environment and life. The graphic above shows wellbores keep
getting more complex and geologic conditions more
challenging. However, we offer some possibilities on how new
materials, like graphene, and minerals that are millions of
years old, together with good old Portland Cement, can join
forces and provide impermeable barriers. All this is still
ongoing, we use experiments and models to predict the future of
these materials.
All of this would not be possible without the trust and support
of the NASEM-GRP Team and tons of people that support us
daily in our institutions, from Oklahoma, Texas, Louisiana,
Pennsylvania and Norway.
Finally, our team dedicates this Newsletter to Hope Asala, who
tragically lost his life in 2019, with the intention to send a copy
to his family and inspire his young daughter to follow her
fathers passion for education and research.
With thanks and gratitude, Mileva Radonjic, July, 2020, OSU.
Summary of Plugging & Abandonment, M. Achang
The depletion of an oil and gas well requires plugging
and abandonment (P&A) by pumping cement into the
wellbore in an attempt to restore the seal to the original
subsurface condition. Inadequate P&A results in leakage
of oil and gas contaminating underground sources of
drinking water, fragile marine ecosystems, soils, and
causing air pollution from methane. The Environmental
Protection Agency (EPA) has estimated a total of 3.11
million abandoned wells onshore, among which 69%
(2.15 million) were unplugged and 31% (0.96 million)
plugged in a 2018 report. Thus, the need to advance our
understanding of the subsurface, develop barrier
materials compatible with acidic, high pressure, high-
temperature subsurface environments, and novel
placement technologies. Drilling and completion
technologies have changed drastically over the years to
accommodate multistage wells. Still, old traditional
methods continue to be used for P&A. Cement
degradation is the leading cause of leakage in plugged
and abandoned wells as well as geologic seals for CO2
sequestration. A review by Achang et al. (2020) on
current P&A technologies and future options, inspired by
the need to protect the environment concludes that:
1. Traditional P&A solutions and methods used for
decades without transformational advancements have
to change, as climate change and a large number of
wells need permanent P&A. It would be
cost-effective to design new drilling technologies
that incorporate P&A, so-called Drilling with the
P&A in mind.
2. The next-generation of P&A should use new
materials. Solutions such as bismuth and termite
technology are early indicators of the upcoming
change. Also, activating shale as a barrier seems like
July 2020
P&A Materials NEWS
2
a promising and sustainable alternative, but
requires in-depth field testing and verification.
Portland cement-based slurries are still the most
cost-effective materials used as wellbore hydraulic
barriers due to decades of usage and the amount of
research available, but, the stability and integrity of
the cement plugs are questionable due to chemical
incompatibility with the subsurface. A combination
of engineering materials and Portland cement will
be a great start and emerging technologies like
nanomaterials have been shown to improve the
properties of engineering seals over a short period.
Also, there is a need for better designs that mimic
or transition to geological seals over time.
3. Improving the placement of barrier materials, such
as better cleaning of the wellbore and reduction of
drilling fluid contamination/intermixing with
barrier materials is also needed. An ideal solution
that would eliminate the negative impact of drilling
fluid contamination is the development of universal
drilling to cementing fluid, as attempted for
water-based drilling mud by intermixing with blast
furnace slag slurries.
4. Lastly, the timely intervention of leaky wellbores to
restore sealing capacity can reduce contamination
even though it is not a method of choice. It would
be better and more environmentally responsible
than ignoring the slow-rate long-term leakage
scenarios with impactful consequences on the
environment.
Oklahoma State University
C. Massion, V. Vissa., M. Achang, M. Radonjic,
Plugging and abandonment of a well is sealing of the
petroleum reservoir after production is finished.
Cement is pumped downhole to create plugs that should
behave as close to the original cap rock as possible, for
an indefinite amount of time. Wellbore cement endures
harsh subsurface conditions such as high temperature
changes, high pressure, and chemically aggressive
fluids that cause leakage of the plug in which
subsurface fluids can migrate and contaminate aquifers
and surface soil.
Figure 1: Graphene enhanced cement at 0.65%wt of cement to see exaggerated effects and behavior of adding graphene in cement. Graphene nanoplatelets are seen to aggregate in open space such as pores and cervices.
The 21st Century super material, graphene, is made of
carbon atoms arranged in a single layer honeycomb
structure, making it the strongest and thinnest material
currently known.
It provides strength and ductility while yet being
lightweight. Graphene is being investigated to improve
wellbore cement properties, and with the addition of
less than 0.1%, improves the strength by 30%, and
provides an effective and cost-efficient slurry design to
accumulating in pore spaces of the cement. Triaxial
stress results for neat and 0.1% graphene cement are
shown in Figure 2.
3
Figure 2: Neat and 0.01%wt graphene cement samples tested under undrained triaxial loading at the same temperature but with different confining pressures. Under both 2,000 and 6,000 psi confining pressures, the graphene cement exhibits improvements in strength when compared with the neat cement. Triaxial tests of OSU designed cement samples were done at University of Pittsburgh.
Self-Healing of Wellbore Cement with Zeolites
A robust plug is ensured by having the plug material
with properties similar to the formation rock. The plug
material currently used is cement and the properties are
enhanced by introducing additives in the slurries. One
of the additive materials used that is of high interest is
Zeolites. FlexCem® is the low-density cement with
added zeolites, which has found application in
geothermal well cementing. In this research, we study
the functioning mechanism of zeolite in this cement and
seek to design zeolite cement suitable for plugging and
abandonment application. The highly porous nature of
zeolite makes it an interesting candidate for addition in
cement and it acts as ionic channels (Vaughan, P., The
crystal structure of the zeolite ferrierite. Acta Crystallo-
graphica, 1966. 21(6): p. 983-990). The SEM
micrographs show the morphology of Ferrierite, a
zeolite within the cement matrix, and indicates that the
Ferrierite can provide bridging of fractures (Figure 3).
Ongoing studies will examine the strength and petro-
physical properties of zeolite enhanced cement.
Figure 3: Morphologies of unreacted Ferrierite act as substrate for hydration, (b) Preliminary Images show self-healing properties in cement.
Olivine as sacrificial material in CO2 attack on
Wellbore Cement
The integrity of plugs in subsurface low pH (2-5), high
pressure, high temperature harsh formation fluids is
questionable because of the chemical attack on Portland
Cement-based wellbore materials leading to their
ultimate physical failure in strength. Nanomaterials
have been shown to improve the properties of
engineering seals over a short period except they are
designed on principles that mimic the geology. Olivine
is a material that is being added to cement as a filler
that will react in low pH (2-5) acidic environments and
carbon dioxide-rich brines to produce carbonates and
bicarbonates maintaining the strength of the cement
when chemically attacked and self-healing fractured
cement sheets reducing porosity and subsequently
permeability. Preliminary results of EDS of 5% olivine
enhanced cement indicate the olivine grains are stable
in a Portland-based cement high alkaline environment,
which is a pre-requisite for their carbonation if in
contact with CO2-rich brines that could potentially in-
vade cement (Figure 4). Detailed research is being pur-
sued to establish the complete story.
4
Figure 4: (a) is the EDS image of 5% woc olivine cement and the insert to the top right is the low mag image from
which the EDS was taken. The profile lines 1,2,3, and 4 are obtained at an interval on 2 µm and plotted to below the EDS
depicting the mineralogy along each line.
University of Texas at Austin (UT-Austin)
R. Ferron & F. Rahman
Introduction:
The research team
at UT-Austin is led
by Dr. Ferron, an
Associate Professor
in the Department
of Civil, Architectural and Environmental Engineering.
The team focus is on the materials side, specifically on
the design of barrier materials with enhanced zonal
isolation performance. To increase the likelihood that
the binder systems will be readily adopted in the field,
the team decided to focus on materials based on
Portland cement (PC) binders due to the wide
availability of PC, its low cost, large body of research
on these binders, and the huge familiarity of the oil and
gas field with these binder systems. Two approaches
are being explored: (1) ternary blends consisting of
Portland cement, limestone, and calcined clay (LC3)
and (2) silica modified PC slurries.
Moreover, the research team explored small-scale
manual printing of cementitious mixtures to provide
insight about application of 3D printed materials as
barriers. This proof-of-concept research was conducted
to determine potential mixture proportions and
extrusion methods for large –scale 3D printing, which
allows for formless, rapid automated and customized
construction and fabrication of barrier materials.
Summary of Findings:
The initial focus has been on designing the LC3
binders. For the calcined clay component of the LC3
systems, metakaolin (MK) is being used. MK has been
observed to possess pozzolanic properties, such that it
reacts with the calcium hydroxide to form calcium-
silicate-hydrate (C-S-H) and calcium-alumina-silicate
hydrates (C-A-S-H). C-S-H and C-A-S-H contribute to
increasing the strength and durability, whereas the
inclusion of fine limestone accelerates the rate of the
reactions (i.e., hydration kinetics). Compared to
conventional binder systems, the LC3 system is
expected to provide better zonal isolation at the
subsurface depths owing to these synergistic hydration
dynamics. Our research shows a moderate strength
improvement for LC3 systems (8%-13%) compared to
the control binder however, with respect to resistivity,
both the LC3 binders (see LS10MK15A and
Figure 5: Resistivity test
Dr. Raissa Ferron Associate Professor
Farzana Rahman PhD Student
5
LS10MK25A in Figure 5 perform significantly better
than the control and binary binder systems (see LS15A
and MK15A in Figure 5). This indicates that the blend-
ing of limestone and MK has filled up void spaces
inside the hardened cement matrix. This increased pore
refinement will likely result in a reduction in gas and
liquid penetration which makes these ternary binders
particularly attractive for wellbore applications. The
moderate increase in strength suggests that the
reduction in porosity is not associated with an increase
in brittleness which is encouraging from a fracture
mechanics perspective.
Laboratory trial testing was conducted to determine
extrudable mixtures for the purpose of 3D printing as a
novel processing method for barrier materials. The
work focuses on the rheology of the paste matrix of the
extrudable mixtures, which are to be scaled up later for
large-scale printing (via robotic arm, gantry systems
etc.). The trial tests were conducted using a handheld
setup, with the intent that the results will be used to
form the basis to optimize the mixture proportions.
Mixtures were prepared using cement, limestone
powder, a dispersant (i.e., high range water-reducer)
and a viscosity modifying agent to prepare extrudable
mixtures. Figure 6 summarizes the process used to
identify suitable mixtures from the small-scale trial
printing tests and optimization approach.
Figure 6: Flowchart for mixture design formulation for 3D printing
Next steps: In our ongoing work, we are examining
the effect of temperature on strength retrogression of
the LC3 binders. In addition, we will examine the
hydration products and kinetics of these samples.
Rheological tests at sub-surface pressure and
temperature conditions will be conducted to examine
the flow behavior of the systems and the effect of
chemical admixtures on the binders. Acidic conditions
at subsurface level threatens well integrity. Hence, tests
will be conducted to study the degradation process of
the proposed binders due to sulfuric acid attack. Also,
we will investigate the effect of nanosilica on oil well
cement strength retrogression, since silica is known to
favor phase transformation and pozzolanic reactions,
which leads to formation of a spatial cement matrix
which is more resistant to compression and fluid flow.
Specifically, we will look at leveraging nanosilica
dispersion to promote enhanced performance. With
respect to the novel processing work, further studies
need to be conducted to understand how cohesion of
the flocculated state correlates with the printability
aspect of those mixtures. Rheological tests and in-situ
particle size tests will be conducted to characterize the
fresh state flow behavior and microstructural state,
since this was a small-scale setup for laboratory testing
to determine 3D printing cementitious mixture
proportions, large-scale printing is required to
corroborate the test results from here.
University of Pittsburgh
A. Bunger & Y. Lu
The University of Pittsburgh (Pitt) team is investi-
gating perfor-
mance of plugging
materials under the
harsh high tempera-
ture high pressure
(HTHP) conditions
of Gulf of Mexico (GoM) wells and proposing ad-
vanced materials that can thrive in these challenging
conditions. As a baseline, the performance of Class H
cement, which is the most common barrier material, has
been studied in a series of mechanical and hydraulic
6
tests under HTHP.
The results were published in the Journal of Natural
Gas Science and Engineering. Furthermore, a new
material is being developed by Pitt called Geologically
Activated Cements (GAC). It turns the challenging
HTHP conditions into an advantage by providing the
necessary acceleration of the hydration and carbonation
reactions that turn granular ultramafic raw materials,
such as olivine sand, into the cemented rock. The
feasibility of generating GAC under simulated HTHP
reservoir conditions has been demonstrated by
experiments in a small-scale, wellbore-emulating batch
reactor (Figure 7.a).
Figure 7. (a) laboratory setup for GAC generation; (b) experimental setup for self-healing test; (c) Cemented rock after carbonation reaction; (d) micro-structure of GAC under SEM
The carbonated rock is shown in Figure 7.c and its
micro-structure (Figure 7.d) was observed under SEM.
Most importantly, the damaged GAC system (Figure
7.b) was observed to have reducing permeability over
time (Figure 8). In contrast, damaged Class H cement
exhibits increasing permeability over time (Figure 9).
This comparison shows that damaged Class H cement
continues to deteriorate while GAC is able to self-heal.
Hence, GAC can provide resilience to failure and
therefore provides the potential to be an important
advanced material for the next generation of resilient
wellbore cementing and plugging systems.
The laboratory reopened after the COVID shutdown on
10 June 2020. All safety protocols are now satisfied to
resume testing and equipment is prepared with new
tests commencing on 15 June 2020. These tests include
exploring behavior of cement containing graphene and/
or olivine in triaxial shear tests, triaxial creep tests, and
triaxial permeability (i.e. self-healing) tests at a
temperature and pressure ranges relevant to GoM wells.
Figure 8. self-healing evidence of GAC under HTHP
(decreasing permeability over time)
Figure 9. increasing permeability of class H cement under HTHP
(a) (b)
(c)
(d)
7
Louisiana State University
H. Asala & T. Ajayi, I. Gupta,
The Geofluids Modeling Group (GMG) at the Craft and
Hawkins Department of Petroleum Engineering at the
Louisiana State University (LSU) participates in the
NAS GRP research for long-term assessment of
cement/barrier material integrity using numerical
modeling. Our participants are Hope Asala (PhD
student, deceased), Temitope Ajayi (PhD student) and
Ipsita Gupta (co-principal investigator).
Figure 10: Wellbore cement and plugs against GoM like reservoir stacking patterns (Ajayi and Gupta, 2019).
Coupled fluid and heat flow and reactive transport
models have been created to simulate geochemical
degradation of cement, rock and cement-rock interfaces
under subsurface conditions subject to long time scales
(includes after plugging and abandonment times).
The advantage of RTM over geochemical modeling is
its ability to model the transport of species through the
cement including micro annuli or fractures along with
the chemical reactions that can expand these features
(Ajayi and Gupta, 2019). Results from coupled heat and
fluid flow, and reactive transport suggest that
geochemical integrity of cement, and cement-rock
interfaces may last in the order of 100s of years under
ideal conditions but can undergo faster degradation if
interfaces are particularly vulnerable due to increased
reactions that affect integrity. Temperature, pH and
reactive surface areas impact geochemical integrity
assessment (Ajayi and Gupta, 2020).
Figure 11: 2D representations of models used in study (A) – cement only (B) – Cement and rock with interface at 0.25m (Ajayi and Gupta, 2020).
Both geochemical and geomechanical modeling results
indicate that the design of crack resilient barrier
materials must account for constitutive and interfacial
failure modes or loss of integrity. Current ongoing
work will next assess impact of supplemental
cementitious material on chemical integrity under long
term subsurface conditions.
8
Figure 12: Equilibrium constants for cement minerals used in our study (Ajayi and Gupta, 2020).
SINTEF, Norway
P. Cerasi
Initial work has focused on
investigating numerically the
potential benefits of designing P&A
plugs inside steel casings, where the end(s) of the plug
are composed of a softer material than the core of the
plug. This design criterion was inspired by collision
worthiness developments in rail and road traffic, with
the allocation of a sacrificial zone in the front of the
vehicle; this zone is designed to deform plastically and
absorb a considerable amount of the collision energy. It
was assumed that designing cement plugs with
deformable ends would greatly enhance their frictional
bond to the steel casing when subjected to differential
pressure (as a result of sustained casing pressure).
Numerical simulations using the DIANA FEA code
were performed by MSc student Rémi Coquard and
demonstrated, for several bonding scenarios between
cement and steel and steel to rock, that indeed, the
presence of soft zones could lead to internal
deformation of the plug and delay its complete loss of
friction with the casing wall (popping up like a
Champagne cork). This is illustrated in Figure 13,
where the deformation of the plug's edges is plotted as a
function of presence and importance of soft cement in
the plug.
Figure 13: Shear stress plotted as a function of deformation, sampled on the end surfaces of the modeled cement plug. Increasing Young's modulus (E) is plotted, 4 GPa to 20 GPa. The black, blue and green curves correspond to ¼, ½ and ¾ of the plug made of lower stiffness cement, respectively. Solid curves: cement plug surface exposed to higher well pressure; dashed lines: plug surface at lower pressure.
Figure 14 : CT-transparent pressure cell. Left: photograph showing the carbon wrap surrounding the aluminium exterior wall and the end-cap with connections for fluid injection. Middle: schematic showing cell structure with steel casing, cement sheath and surrounding rock. Right: reconstructed cross section (top) and axial section with identified casing, cement, sandstone and confining sleeve.
Figure 15: Reconstructed cross sections after fracturing tests. Left: no confining stress and pore pressure, casing pressure up to 35 MPa. Right: fracturing after reducing confining pressure from 10 to 8.5 MPa at casing pressure 35 MPa and pore pressure in sandstone of 5 MPa.
9
Figure 16 shows good agreement between the model and observed fractures in Figure 17.
Ensuing work is focused on developing a pressure cell
with X-ray CT-transparent walls to study fracture
patterns and remediation fluid placement. The cell is
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