In order to reduce greenhouse gas emissions while recovering hydrocarbons from unconventional shale formations, processes that make use of carbon dioxide to enhance oil recovery while storing carbon dioxide (CO2) should be considered. Here, we examine samples from three shale basins across the United States (Utica and Marcellus Shales in the Appalachian Basin, Barnett Shale in the Bend Arch-Ft. Worth Basin, and Eagle Ford in the Western Gulf Basin) to address the following questions: (1) do changes from reaction with CO2 and fluids at the micrometer and nanometer scale alter flow pathways and, in turn, impact hydrocarbon production, CO2 storage, and seal integrity and (2) can CO2 or fluid reactivity be predicted based on physical or chemical properties of shale formations? Experiments were conducted at 40 °C and 10.3 MPa to characterize the interaction between CO2 and shale using X-ray diffraction (XRD), carbon and sulfur analysis, in situ Fourier transform infrared spectroscopy (FT-IR), feature relocation scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), mercury (Hg) intrusion porosimetry, and Brunauer–Emmett–Teller (BET) surface area and pore size analysis coupled with density functional theory (DFT) methods. Changes in mechanical, physical, and flow properties of shale cores due to CO2 exposure were addressed using a New England Research Autolab 1500 and Xenon X-ray computed tomography (CT) scanning. Results showed that CO2 did not promote significant reactivity with the shale if water was not present; only shales with swelling clays or residual interstitial pore water reacted with dry CO2 to promote reactivity in shale. When water was added as a reactant, CO2 formed carbonic acid and reacted with the shale to dissolve carbonate pockets, etched and pitted the shale matrix surfaces, and increased the microporosity and decreased nanoporosity. Porosity and permeability increased appreciably in core shale samples after exposure to CO2 saturated fluid due to dissolution of carbonate. Shale mechanical properties were not altered. Trends were not observed that could tie CO2 or fluid reactivity to physical or chemical properties of the shale formations at the basin scale from the samples we examined. However, if the shale contained significant amounts of carbonate and water was available to react with the CO2, pore sizes were altered in the matrix and permeability and porosity increased.

The use of foamed cement systems for deepwater applications has been increasing and is often the system of choice for shallow hazard mitigation as in the Gulf of Mexico. However, there is little information regarding foamed cement behavior under wellbore conditions. Research is being conducted to develop a predictive relationship between the mesostructure and physical properties of foamed cements used in offshore applications. Samples of foamed cement have been generated using both atmospheric laboratory and high-pressure field preparation methods. Field-generated foamed cement samples were collected in constant pressure (CP) sample cylinders using the same full-scale field equipment used to generate foamed cements in a well. These samples were scanned while inside the CP cylinders using X-ray Computed Tomography with a scan resolution of approximately 35 m.Results of the laboratory testing indicate a correlation between foam quality, bubble size distribution and physical properties such as strength and permeability. Initial results also highlight key differences in laboratory and field-generated foamed cements. The variations in cement structure within the fieldgenerated foamed cement samples appear to indicate a strong relationship between the flow of the cement into the sample vessel and the final porosity and properties of the in-place hardened cement. This research will provide a better understanding of the effects that foam cement production, transport downhole, and delivery to the wellbore annulus has on the overall sealing process.

The objective of this paper is to evaluate the dynamic moduli of atmospheric generated foamed cements at varying foam qualities routinely used for zonal isolation during well construction. Mechanical properties of the hardened foamed cement samples, such as Young's modulus (YM) and Poisson's ratio (PR) will be discussed, as well as permeability. All of these properties were obtained as a function of cyclic confining pressure ranging from 12 -52 MPa (1,740 -7,540-psi). The dynamic parameters were derived from ultrasonic velocity measurements, while permeability was measured using the transient method. Stepwise loading and unloading schedules were conducted to test the permeability and mechanical properties of the foamed cement at simulated wellbore conditions. Applied pressures varied between 6.5 MPa (943 psi) to 46.5 Ma (6,744 psi) in 4 MPa (580 psi) increments in two full up/down cycles. At every increment during these cycles, ultrasonic compressional (P), fast shear (S1), and slow shear (S2) wave velocities were measured, as well as the samples' response to the upstream sine pressure wave of approximately 0.5 MPa amplitude. From the sonic velocity data the dynamic moduli including YM and PR were calculated, while the sample's response to the pressure wave was used for permeability calculations. Observations of both neat and foamed samples reveal variations in YM as well as changes in the other properties and characteristics. Differences were observed between the foam qualities, depending on the parameter being assessed. This information should enable design contingencies and allow for more resilient designs of foamed cements when used during well construction. In addition, industry can use these results as a baseline for comparison with previous, current, or future work including recently acquired field-generated foamed cement samples (Kutchko et al., 2014).

The National Energy Technology Laboratory (NETL) in conjunction with industry partners began a project to assess field-generated foamed cement at pressurized surface conditions. The collected samples were compared to previous field-generated samples as well as equivalent samples generated with current laboratory protocols following the recommended practices in American Petroleum Institute's Recommended Practice (API RP) 10B-4; atmospherically generated. In-situ samples of foamed cement were successfully captured in constant pressure (CP) cylinders under field conditions and analyzed while under pressure using multi-scale computed tomography (CT) scanning. The comparison of laboratory and field samples addresses changes to the cement under in situ conditions. Initial results highlight key differences in laboratory and field-generated foamed cements. Results of laboratory testing indicate a correlation between bubble size distribution, permeability, and strength. Field-generated samples show changes in pressure significantly influence the bubble size, while the flow of the slurry into the pressure cylinders created less homogeneous cured foamed cement. This paper discusses further research of in-situ field generated foamed cement behavior. These data provides insight to support the ongoing effort to help predict a method to correlate testing for foamed cement performance in the laboratory that would compare to more representative field behaviors.