BET, SEM-EDS and XRD Results Conclusions

Background

Introduction Wellbore Cement studies have been ongoing for decades. The studies vary from efforts to reduce permeability and

resistance to corrosive environment to issues with gas migration also known as Sustained Casing Pressure (SCP).

These practical issues often lead to health, safety and environmental (HSE) problems as well as economic loss in oil

and gas industry.

Expandable liner is a tube that after application of a certain tool can increase its diameter. The increase in diameter

creates extra force on hydrated cement that results in reducing width of interface fractures and cement-tube de-

bonding. Moreover, this also causes cement to change its microstructure and other porous medium properties,

primarily hydraulic conductivity.

In order to examine changes before and after expansion of casing and consequent mechanical manipulation of

cement matrix, cement pore structure must be well characterized and correlated to cement slurry design, hydration

level and any visual changes such as shrinkage fractures. As modern oil well pipes and tubes contain iron. Therefore,

it is impossible to perform x-ray imaging on samples composed of metal tube wall-cement-metal tube wall. Neutron

imaging is capable of imaging such samples and is a complementary technique to x-ray imaging and is well suited for

detection of light elements imbedded in metallic containers. Thus, Neutron Imaging (NI) is investigated as a tool for

the detection of fractures, imperfections and channels within hydrated wellbore cement.

Application of Neutron imaging in pore structure of hydrated wellbore cement:

comparison of hydration of H2O with D2O based Portland cements

Sample Preparation and Experiments

X-Ray CT and Neutron Imaging Results Discussion

Neutron Imaging is highly sensitive to light elements such as Hydrogen (H). Oil well cements that have undergone a

full hydration contain on average about 20% of bound water and about 6% of movable water in its pore structure.

The unreacted water is the main storage of the hydrogen atom. In such case, neutron tomography does not give

information of the pore structure as neutrons will strongly scatter of H and the data have low count and low statistics

or low neutron transmission. Hence, as the comparison neutron tomography measurements are performed on a

Deuterium Oxide (D2O) or heavy water samples of the same dimensions, cement composition, cement/liquid content

and hydration time as the H2O samples. The advantage of using heavy water is that the total neutron cross-section

for Deuterium is approximately four times smaller than Hydrogen’s and, thus, permits better neutron transmission,

i.e. better statistics. D2O does not alter cement properties or its chemical composition; therefore, the samples are

almost identical in chemical analysis. However, D2O based sample has almost by 50% lower hydration rate than the

water based sample.

Dinara Dussenova1, Hassina Bilheux2, Mileva Radonjic1

1. Louisiana State University(ddusse1@lsu.edu, mileva@lsu.edu); 2. Oak Ridge National Laboratory (bilheuxhn@ornl.gov)

Water and deuterium oxide based cement cores were prepared according to

American Petroleum Institute (API) standard 10B and let hydrated for over two

months. The API cement slurry mixing procedure is following:

• An API standard 10B based mixer with two preset speeds: MIX1 (4000

RPM), MIX2 (12000 RPM).

• First cement slurry is mixed at MIX1 for 15 seconds

• Following, cement slurry is mixed at MIX2 for 45 seconds

Liquid cement ratio of the cement cores was 0.38. Both water and deuterium

oxide based cement samples were prepared and kept at ambient temperature and

pressure and cured in water and deuterium oxide respectively. Various

experiments and tests were performed on fully hydrated cement samples in

order to identify difference in hydration, porosity and Computer Tomography

(CT) image quality between water and deuterium oxide cement samples. The

following tests were performed: X-ray Tomography, Neutron Imaging,

Brunauer-Emmett-Teller Surface Area Measurement (BET), Scanning Electron

Microscopy-Energy Dispersive Spectroscopy (SEM-EDS), X-Ray Diffraction

(XRD).

SEM-EDS, XRD and BET test samples were grinded and dried at room

temperature, 60oC and 300oC in vacuum oven respectively as it is required by

the test conditions. 3x5mm cores were drilled from 5x2.5cm cement cores for

imaging. The sample schematics are shown on Figure 1.

5x2.5cm samples along with 3x5mm samples were scanned using both X-ray

tomography and Neutron Imaging.

Acknowledgements The authors would like to acknowledge Shell Exploration and Production for provided funding; Oak Ridge National Laboratory for

provided beam time and conducting Neutron imaging; Dr. Ham and Louisiana State University Center for Advanced Microstructures

and Devices for X-ray beam time and scan run; Ms. Wanda LeBlanc for XRD scan, Dr. Dongmei Cao for SEM test, and Dr. Kerry M.

Dooley for BET equipment and provided test time, Dr. Clinton Willson for guidance; Darko Kupresan for preparing large cement

cores.

Figure 7 SEM-EDS for solid grain and void space for H2O based

hydrated portland cement sample. Blue - solid grains and red -

void space.

Figure 8 SEM-EDS for solid grain and void space for D2O

based hydrated portland cement sample. Blue - solid

grains and red - void space.

H2O

Total Pore Volume 0.0155 cc/g

Average Pore Diameter 18.66 Å

Density 1.92 g/cc

Weight 1.17 g

Specific Surface Area 33.22 m²/g

D2O

Total Pore Volume 0.0115 cc/g

Average Pore Diameter 17.51 Å

Density 1.92 g/cc

Weight 0.87 g

Specific Surface Area 26.33 m²/gFigure 9 XRD graphs showing compositional difference of

hydration products of portland cement mixed with D2O and H2O.

Blue line corresponds to H2O and red line corresponds to D2O.

Table 1 BET test results for H2O and D2O based hydrated

portland cement samples

Figure 2 D2O 5x2.5cm sample neutron imaging Figure 3 H2O 5x2.5cm sample neutron imaging

Figure 4 Neutron CT rendered

volume for 3x5mm samples

Figure 5 X-ray CT orthoview of

3x5mm hydrated portland cement

H2O sample

Figure 6 X-ray CT orthoview of

3x5mm hydrated portland cement

D2O sample

Neutron Imaging (Figures 2, 3, and 4)

• Shows low to 0% neutron transmission through in a 5x2.5cm water based sample

• Shows 5%-14% transmission in neutron transmission through in a 5x2.5cm water based sample

• 5x2.5cm samples were concluded to be thick for detailed neutron imaging for a given resolution

• 3x5mm neutron imaging confirms difference in transmission between H2O and D2O samples as the heavy water sample is brighter

and depicted on Figure 6 to be more transparent than water based sample

• Higher neutron capturing is observed in H2O based sample due to hydrogen presence

X-ray CT (Figures 5 and 6)

• Voids/Solids/Dense Solids segmentation is performed on both samples (Solids-0, Dense Solids-1, Voids-2)

• Large water or air bubble is observed in a water based sample, which corresponds to air/water void that is formed during cement

settling and is not significant for the study

• Deuterium oxide sample shows more homogenous void spacing as it can be seen on a segmented image. The void space is spaced

evenly throughout the image as small pores

• Estimated porosity from voxel count is 5.48% for deuterium oxide sample and 2.88% for water based sample

SEM-EDS (Figures 7 and 8)

• No difference in chemistry between H2O and D2O samples

• Higher oxygen peak in void space EDS graphs than in solid grain

• Suggested bound gel water presence in void space due to high oxygen presence

• Some visible difference in grain shape and void space distribution

XRD (Figure 9)

• Four major zones with visible difference were identified.

• Both samples show sharp and well defined peaks that correspond to well crystallized minerals: Portlandite and Fe-rich Magnesite

• The same chemical and mineralogical composition and mineral and element quantity

BET (Table 1)

• H2O sample has specific surface area of 33.22m2/g that is higher than specific surface are of D2O based sample of 26.33 m2/g

• H2O sample has average pore throat size of 18.66x10-10m, which is larger than the average pore throat size of heavy water sample

of 17.51 x10-10m

• The difference in specific surface area and pore throat diameter corresponds to the difference in hydration rate between two

samples

Based on the performed work and a set of experiments it has been concluded that

• H2O based sample has undergone a higher level of hydration than deuterium oxide sample

• The difference in porosity vs. pore throat size compensates for possible flow path propagation. As water based sample has lower

porosity but larger pore throat size versus the heavy water sample with higher porosity but smaller pore throat size, fluid flow

propagation should not exhibit significant difference between two samples

• Deuterium oxide based sample is a better candidate for neutron imaging due to good neutron transmission if a thick sample is

scanned and it can be used as a reference point for future imaging of H2O specimens

• Water based sample is a better candidate for neutron imaging if neutron capturing method is used and water saturation estimate is

required in a highly saturated sample

• Water based sample needs to be as small as experiment conditions allow in order to get a better neutron transmission and at the

same time provide a representative volume of cement sample

• Sample pre-treatment such as heating up the cement sample at 50C in a vacuum oven might be required if a water based sample is

imaged using neutron CT.

• In future work it is suggested to use water based cement sample as the neutron capturing method was chosen to be the leading

technique for NI interpretation. Moreover, heavy water is an expensive product requiring certain precautions.

• Neutron capture cross-section technique and a dark/bright picture contrast are suggested as the main techniques for neutron image

interpretation and quantification as it is the most helpful technique in identifying water saturated zones versus fractured or drained

zones in expandable liners

References A.T. Bourgoyne Jr., S.L.Scott, W. Manowksi: “A Review of sustained casing pressure occurring on the OCS”, 1998

D.R.M. Brew, F.C.deBeer, M.J.Radebe, R.Nshimirimana, P.J.McGlinn , L.P.Aldridge, T.E.Payne: “Water transport through cement-based barriers - A preliminary study

using neutron radiography and tomography”, 2009

S. Popovics: “Concrete Materials - Properties, Specifications and Testing (2nd Edition)”, William Andrew Publishing/Noyes, 1992

M. Tellisi, Halliburton; P. Pattillo, BP; K. Ravi, Halliburton: “Characterizing Cement Sheath Properties for Zonal Isolation”, 2005

S.K. Pedam: “Determining Strength Parameters of Oil Well Cement”, Master Thesis, The University of Texas at Austin, 2007

J. Heathman, Halliburton; E. Arredondo and A. Olufowoshe, Eventure Global Technology: “Enhanced Cementing Practices Address Unique Issue Found With Solid

Expandable Tubular Applications”, SPE /IADC 105227, SPE /IADC Drilling Conference, 20-27 February, Netherland, 2007

2.5 cm

5 cm

3mm

5m

m

Figure 1 Sample schematics of large

and mini cement cores

3 mm

Large cores are shown on Figures 2

and 3 and mini cores are shown on

Figures 4, 5 and 6.