Search

In this work, we probed the physical and chemical alteration of the carbonate-rich Utica Shale following CO2 exposure when thin films of water were present at the shale surface. All reaction conditions were examined at 40 °C and CO2 pressures up to 10.3 MPa for 14 days. CO2 dissolution in the water layer at 2342 cm−1 and carbonate dissolution and precipitation at 1424, 874, and 712 cm−1 were discerned with in-situ Fourier Transform infrared spectroscopy (FT-IR). Significant etching and pitting from exposure to CO2 and water were observed with feature relocation scanning electron microscopy (SEM). Application of the density function theory (DFT) for pore size analysis showed that micropores between approximately 0.9 and 2 nm disappeared while the mesopore volume increased after dissolution of carbonate. These results may provide new insights that carbonate rich shales such as the Utica may have a greater potential for alterations of pore space due to the reactivity of CO2 which may affect 1) how CO2 storage in shale formations plays a role in Carbon Capture and Storage (CCS) activities, 2) if CO2 can be utilized as a potential fracturing agent, and 3) whether CO2 is an effective fluid for enhanced hydrocarbon extraction.

Traditionally, shale formations have been studied as sealing layers that prevent vertical migration of hydrocarbons and CO2 due to their low permeability and fracture porosity. Recent research has focused on storing CO2 in hydrocarbon-bearing shale formations that have already undergone depletion through primary production and using CO2 as a potential fracturing agent for unconventional reservoirs. The injected CO2 will interact with shale components (i.e. clays, organic matter) and affect rock properties through chemical alteration, matrix swelling/shrinkage, and related geomechanical effects. As changes in rock properties will impact both anthropogenic CO2 storage and hydraulic fracturing, it is imperative to increase our understanding of the CO2-shale interactions. In-situ Fourier Transform infrared (FT-IR) spectroscopy coupled with high temperature and pressure capability was used to examine the interaction of dry CO2 on Utica Shale, clay, and kerogen samples at the molecular scale and characterize vibrational changes of sorption bands sensitive to the gas-solid environment. The Utica Shale was also analyzed for micro and macro-scale chemical and physical changes before and after exposure to dry CO2 at subsurface storage conditions using surface relocation techniques via high-resolution field-emission scanning electron microscopy (FE-SEM). Brunauer-Emmett-Teller (BET) surface area/pore size analysis and quantitative adsorption isotherms were applied to understand changes in surface area, pore volumes, and understand the storage potential of CO2 in the Utica Shale sample. FT-IR and feature relocation via FE-SEM indicate carbonate formation and dissolution occurs in shale exposed to dry CO2. Results indicate that etching and pitting occur, with minor calcite precipitation along the surface of the shale sample. Quantitative isotherm results indicate that shales with a higher content of kerogen and illite-smectite clays would be expected to have the highest CO2 storage capacity provided these constituents were accessible for interaction.

The objective of this paper is to evaluate the physical and dynamic mechanical properties of foamed cement generated at a field site and compare them to similar cements fabricated within the laboratory. Physical and mechanical properties such as porosity, permeability, Young's modulus, Poisson's ratio, bulk modulus, shear modulus, etc. will be discussed. Mechanical properties were obtained under cyclic confining pressures ranging from 12 – 52 MPa. This paper will document the final results of a long-term project that examined the differences between foamed cements generated with laboratory equipment and field foamed cementing equipment. The cement samples in this study were generated at pressure using field foamed cementing equipment as part of a joint effort between the API Sub-Committee 10 and the National Energy Technology Laboratory (NETL). The samples were characterized using helium porosimetry, ultrasonic velocity, and permeability measurements after they were depressurized. To test the variation in permeability and strength parameters of various foam cements, stepwise loading and unloading experiments were conducted. Effective pressures varied between ≈6.8 MPa to ≈46 MPa in ≈4 MPa increments. Permeability was measured at each effective pressure step to determine the change in flow pathways due to cyclic confining pressures. Dynamic moduli including Poisson's ratio and Young's modulus were calculated to determine the impact of effective pressures on the flexibility of the cement. The data shows that the cement's physical and mechanical behavior varied along the length of the sampling containers. During the initial loading of some of the samples, permeability decreased to a point lower than the initial permeability and stayed constant for the remainder of the pressure cycle, which was observed in previous experiments. However, some of the permeability values increased suggesting that the pressure cycles had permanently reconfigured the internal structure of the samples. Our approach to evaluating foamed cement is somewhat novel in that we have collaborated with the API, operators, and service companies, to obtain foamed cement generated at pressure using field equipment enabling a robust comparison to those generated in a laboratory per the API's RP 10-4B. Not only will the information provided by these comparisons help to facilitate the better design and implementation of foam cement generation processes but it will also help improve the understanding of the physical and mechanical behavior of foam cement.

CO2 miscible and immiscible displacements and hydrocarbon miscible floods are commonly plagued by low volumetric sweep efficiency, early gas breakthrough, high gas utilization ratios, and significant gas re-compression and recycle. Rather than addressing these problems via the water-alternating-gas (WAG) injection sequence that reduces gas relative permeability or the generation of gas-in-brine foams for reduced mobility, we propose increasing the viscosity of high pressure CO2 or NGL via the dissolution of dilute concentrations of thickening agents. There are two strategies for increasing the viscosity of high pressure fluids; the dissolution of ultrahigh molecular weight polymers or associating polymers, or the dissolution of small molecules that self-assemble in solution to form viscosity-enhancing linear or helical supramolecular structures. Ideally a very small amount of the thickener will be required (roughly 0.1wt%) to elevate the CO2 or NGL viscosity to the same value as the oil being displaced (typically a 10-100 fold increase). Further, the thickened CO2 or thickened NGL should be a stable, transparent solution that does not require a heating/cooling cycle for viscosity enhancement to occur. Thickener solubility and viscosity were determined over a 25-100oC range. Each of the three major NGL constituents (ethane, propane and butane) was thickened with an ultrahigh molecular polymer (commercial drag reducing agent), resulting in a 2-30 fold increase in viscosity at polymer concentrations of 0.5wt% or less. The polymer dissolved at the lowest pressure in butane and was most effective as a thickener in butane. Three small molecule thickeners were identified for the NGL constituents; tri-alkyl-tin fluoride, hydroxyaluminum disoap, and a phosphate ester-crosslinker mixture. Remarkable viscosity enhancements were attained for propane and butane with the tri-alkyl-tin fluoride and aluminum soap; the crosslinked phosphate ester solutions exhibited modest viscosity increases. Only tri-alkyl-tin fluoride thickened ethane. CO2 thickeners were assessed with a falling ball viscometer and pressure drop associated with flow through Berea sandstone. 4-5 fold increases in viscosity were attained with 1wt% of a high molecular weight polyfluoroacrylate. 3-4 fold increases in viscosity were attained with 1wt% high molecular weight polydimethyl siloxane, but a very large amount of toluene co-solvent was required. Although a remarkably effective small molecule thickener was designed for CO2 (100-fold increase at 1.3wt%), it required a heating/cooling cycle and a very large amount of hexane co-solvent. We have identified the first polymeric and small molecule thickeners ever reported for ethane. Further, this study presents the largest viscosity increases ever reported for propane and butane with polymers and small molecule thickeners. We have presented the most effective polymeric thickeners for CO2 reported to date. This paper also summarizes numerous molecular architectures that are not viable for CO2 and highlights the most promising compounds that continue to be refined.

A detailed description of the United States Department of Energy (US-DOE) methodology for estimating CO 2 storage potential for oil and gas reservoirs, saline formations, and unmineable coal seams is provided. The oil and gas reservoirs are assessed at the field level, while saline formations and unmineable coal seams are assessed at the basin level. The US-DOE methodology is intended for external users such as the Regional Carbon Sequestration Partnerships (RCSPs), future project developers, and governmental entities to produce high-level CO 2 resource assessments of potential CO 2 storage reservoirs in the United States and Canada at the regional and national scale; however, this methodology is general enough that it could be applied globally. The purpose of the US-DOE CO 2 storage methodology, definitions of storage terms, and a CO 2 storage classification are provided. Methodology for CO 2 storage resource estimate calculation is outlined. The Log Odds Method when applied with Monte Carlo Sampling is presented in detail for estimation of CO 2 storage efficiency needed for CO 2 storage resource estimates at the regional and national scale. CO 2 storage potential reported in the US-DOE's assessment are intended to be distributed online by a geographic information system in NatCarb and made available as hard-copy in the Carbon Sequestration Atlas of the United States and Canada . US-DOE's methodology will be continuously refined, incorporating results of the Development Phase projects conducted by the RCSPs from 2008 to 2018. Estimates will be formally updated every two years in subsequent versions of the Carbon Sequestration Atlas of the United States and Canada .

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).