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Faster, lower-cost measures of multiphase permeability of conventional reservoirs are promised by a digital rock analysis method developed by BP and Exa, which is marketing software to measure relative permeability. This paper describes the development of “digital-rocks” technology, in which high-resolution 3D image data are used in conjunction with advanced modeling and simulation methods to measure petrophysical rock properties.
Wellbore instability has been experienced in areas of the Marcellus Shale and can become particularly troublesome in the superlaterals that are becoming more prevalent in that play. Often the instability while drilling these very long lateral wells is minimal; problems are more likely to occur while tripping out after reaching TD. The most common instability events when pulling out of the hole appear to be tight hole, pack-off and stuck pipe. These problems often worsen with time, indicating there is some time-dependence to the failure mechanism.
In order to develop effective mitigation strategies to combat the instability, it is imperative that the failure mechanism be correctly identified. Previous publications (Kowan and Ong, 2016; Addis et al. 2016; Riley et al. 2012) have suggested that bedding planes may play a role in some of the drilling problems experienced in the Marcellus Shale. In this paper, we will present a case study from the Marcellus that shows conclusive proof of weak bedding plane failure along a lateral well, where thousands of feet of anisotropic failure were captured with a LWD image log.
This image provided confirmation of the presence and failure of weak bedding planes in the Marcellus Shale. The image was also used to validate an existing geomechanical model for the area and gave the operator more confidence in the mitigation strategies developed from that geomechanical model, which had been based on the assumption that weak bedding was contributing to difficulty experienced on multiple lateral wells when tripping out of the hole.
This case study will begin with an overview of the geomechanical model, including the drilling history, stress/pore pressure model and rock properties. Next, some highlights from the image log, showing anisotropic bedding plane failure, will be featured as well as a comparison of the image to the geomechanical model. This case study will conclude with a review of proposed mitigation strategies that could be implemented by the operator to limit the risks posed by weak beds and minimize instability, when drilling laterals in this area, or similarly complex areas, of the Marcellus Shale.
Sugar, Antonia (King Abdullah University of Science & Technology) | Serag, Maged F. (King Abdullah University of Science & Technology) | Torrealba, Victor A. (King Abdullah University of Science & Technology, now at Chevron Corp.) | Buttner, Ulrich (Nanofabrication Core Lab, King Abdullah University of Science & Technology) | Habuchi, Satoshi (King Abdullah University of Science & Technology) | Hoteit, Hussein (King Abdullah University of Science & Technology)
Understanding polymer transport through porous media is key to successful field implementations, including well conformance control and EOR processes. Polymer retention is typically assessed indirectly through its effect on pressure drops and effluent concentrations. Microfluidic techniques represent convenient tools to observe and quantify polymer retention in porous media. In this paper, we demonstrate how a soft-lithography microfluidics protocol can be used to gain insights into polymer transport mechanisms through rocks.
The design of the microfluidic chips honors typical pore-size distributions of oil-bearing conventional reservoir rocks, with pore-throats ranging from 2 to 10 μm. The fabrication technology enables the design transfer on a silicon wafer substrate using photolithography. The etched wafer holding the negative pattern of the pore-network served as a mold for building the microfluidics chip body out of polydimethylsiloxane (PDMS). The oxygen plasma bonding of the PDMS to a thin glass slide resulted in a sealed microfluidic chip, conceptually referred to as "Reservoir-on-a-Chip". We conduct single-phase polymer flooding experiments on the designed chips to understand how polymer-rock interactions impact polymer transport behavior in rocks. These experiments allow for polymer transport visualization at the molecule-scale owing to the use of polymer tagging and single-molecule tracking techniques.
This study presents, for the first time, a direct visualization of polymer retention mechanisms in porous media. We identified three mechanisms leading to polymer retention: adsorption, mechanical entrapment, and hydrodynamic retention. Polymer adsorption on the chip surfaces resulted in flow conductivity reduction in specific pathways and complete blockage in others, inducing alterations in the flowpaths. This mechanism occurred almost instantaneously during the first minutes of flow then, dramatically diminished as adsorption was satisfied. In addition to static adsorption, flow-induced adsorption (entrapment) was also distinguished from the binding of flowing polymer molecules to the already adsorbed polymer layer. Evidence of polymer desorption was observed, which consents with the presumed reversibility character of polymer retention mechanisms. The narrowest channels along with the reduced area due to adsorption, created favorable conditions for polymer entrapment. Both mechanical and hydrodynamic trapped polymers were successfully imaged. These phenomena led to polymer clogging of the porous network, which is one of the major concerns for operational aspects of polymer flooding processes.
Better understanding and quantification of polymer retention in porous media can help to make better decisions related to field-scale implementations of polymer-based processes in the subsurface. In this study, we used a soft-lithography fabrication technique and single-molecule imaging, to show, for the first time, polymer transport insights at the molecule- and pore-scales. This approach opens a new avenue to improve our understanding of the first principals of polymer retention while flowing through porous media.
Alyafei, Nayef (Texas A&M University at Qatar) | Bautista, Jerahmeel (Texas A&M University at Qatar) | Mari, Sahar (Texas A&M University at Qatar) | Khan, Talha (Texas A&M University at Qatar) | Seers, Thomas (Texas A&M University at Qatar)
We present a project-based learning prototype for visual analysis of petrophysical properties using 2D cross-sections and micro-models of porous media. Micro-computed Tomography (CT) scans are used to create the quasi-2D micro-models that are printed using Stereolithography (SLA) 3D printers to study petrophysical properties in porous media. The methodology involves obtaining 8 different cross-sections of rocks either from micro-CT scans or online libraries. 2D cross-sections are segmented into black and white binary images and then skeletonized to create quasi-2D models. The flow of oil and water in initially water saturated pores in the printed 2D models mimics the drainage and imbibition processes, respectively. High definition photography is used to capture still and dynamic photographs of flow processes. The binary images are used to analyze porosity and grain size distribution while the still and dynamic photographs are used to analyze fluid saturation and displacement efficiency. The images are analyzed using open source software where a systematic tutorial is provided. The primary outcome of this project is to improve the understanding of petrophysical concepts and 3D printing by the utilization of imagery to create porous media. This project has been tested in teaching and showed major improvements in students’ understanding of petrophysical concepts when compared to pre-project. The data and tutorials used in this project are made available for the community to use through a link in the paper.
Ebadi, Mohammad (Skolkovo Institute of Science and Technology) | Makhotin, Ivan (Skolkovo Institute of Science and Technology) | Orlov, Denis (Skolkovo Institute of Science and Technology) | Koroteev, Dmitri (Skolkovo Institute of Science and Technology)
The approach to handle the unresolved pores at 3D X-ray Micro Computed Tomography (μCT) images of core samples is developed. It enables a sufficient widening of digital rock studies for tight rocks. The μCT images of a low-permeable sandstone with a resolution of 1.2 μm/voxel have been generated. Pore Size Distribution shows the presence of a significant amount of sub-resolution pores. Downsampling has been applied to estimate the actual porosity with extrapolation.
Visual noise, artifacts, and roundoff errors are the major factors affecting the quality of μCT images. We apply transform and spatial domain filtering to minimize all the artifacts. Regarding the overall concept of porosity and through running a geometrical histogram analysis, the Random Walker segmentation as a robust mathematical algorithm has been applied to turn the greyscale μCT images into binary ones resembling pores and grains. Next, the porosity of the binary images with a resolution of 1.2 μm/voxel has been calculated. The procedure continues with downsampling to artificially reduce the resolution and calculate the corresponding porosity.
It has been observed that the calculated porosity for the highest resolution of 1.2 micrometer is still lower than the experimental value which is due to the existence of pores which their sizes are less than 1.2 micrometer, and cannot be seen in the CT images. In order to take the effects of sub-resolution pores into account, an extrapolation relying on the downsampling technique has successfully been applied. The implemented technique is based on the fact that the porosity of the reservoir rock sample is not a function of resolution. However, plotting of the calculated porosities versus their relevant resolutions indicates that the value of porosity has an inverse relationship with the voxel size. In other words, it could be interpreted that the closest values of the calculated porosity to the laboratory reports will be the output of the image processing when the size of voxel moves towards zeros as much as possible, which is technically impossible. Instead, a trendline can be fitted into the scatter plot of porosity versus resolution and find its extrapolation value for the voxel size of zero, which provides the porosity as close as possible to the experimental value.
The main logic behind the digital core analysis is to calculate the properties only according to the digital images. Although there are some studies in which modifications have been done to consider the effects of sub-resolution pores, they are severely suffering from mathematical complexities, and they are mainly based on the global thresholding. The proposed technique can provide an accurate value of porosity when there are no additional data about the pore structure of the sub-micron scale.
Vargas Grajales, Viviana (Pontifical Catholic University of Rio de Janeiro) | Pinto da Silva, Tamires Pereira (Pontifical Catholic University of Rio de Janeiro) | Barreto, Abelardo Borges (Pontifical Catholic University of Rio de Janeiro) | Pesco, Sinésio (Pontifical Catholic University of Rio de Janeiro)
An object-based algorithm that models turbidite channels using training images, called skeleton-based simulation or SKESIM, is proposed in this study. These images are interpreted as a graph and used to extract the statistical distribution of parameters selected from the graph. From this information, a 3D model of turbidite channel systems was built. These channels were generated within the turbidite lobe, creating a simulated depositional system. After the geometry of the channels were simulated by SKESIM, the petrophysical properties were mapped by Gaussian-like distributions. Numerical simulations were used to fit the simulated permeability field to a reference case through an objective function. A commercial finite difference simulator was used to compare the reference data to the simulated data, and comparable results were obtained.
We examined the feasibility of combining a superhydrophobic surface (SHS) and air layer drag reduction (ALDR) to achieve the frictional drag reduction (DR) shown achievable with traditional ALDR, but at a reduced gas flux to increase the achievable net energy savings. The effect of a commercial SHS coating on the gas flux required to maintain a stable air layer (AL) for DR was investigated and compared with that of a painted non-SHS at Reynolds numbers up to 5.1 X 106. Quantitative electrical impedance measurements and more qualitative image analysis were used to characterize surface coverage and to determine whether a stable AL was formed and maintained over the length of the model. Analysis of video and still images for both the SHS and painted surface gives clear indications that the SHS is able to maintain AL consistency at significantly lower gas flux than required on the non-SHS painted surface. Hydrophobicity of the surfaces was characterized through droplet contact angle measurements, and roughness of all the flow surfaces was measured. The results from these preliminary experiments seem to indicate that for conditions explored (up to Rex = 5.1 X 106), there is a significant decrease in the amount of gas required to establish a uniform AL (and hence presumably achieve ALDR) on the SHS when compared with a hydraulically smooth painted non-SHS.
Masnadi, Naeem (University of Maryland, College Park) | Erinin, Martin A. (University of Maryland, College Park) | Washuta, Nathan (University of Maryland, College Park) | Nasiri, Farshad (The George Washington University) | Balaras, Elias (The George Washington University) | Duncan, James H. (University of Maryland, College Park)
Air entrainment due to turbulence in a free-surface boundary layer shear flow created by a horizontally moving vertical surface-piercing wall is studied through experiments and direct numerical simulations (DNS). In the experiments, the moving wall is created by a laboratory-scale device composed of a surface-piercing stainless steel belt that travels in a loop around two vertical rollers; one length of the belt between the rollers simulates the moving wall. The belt accelerates suddenly from rest until reaching constant speed and creates a temporally evolving boundary layer analogous to the spatially evolving boundary layer that would exist along a surface-piercing towed flat plate. We report cinematic laser-induced fluorescence measurements of water surface profile histories, cinematic observations and measurements of air entrainment events, and air bubble size distributions and motions. To complement the experiments, DNS of the temporally evolving turbulent boundary layer were conducted, considering both the air and water phases. Because of cost considerations, only a portion of the belt was simulated at a lower Reynolds number, keeping the Froude number, however, at the same levels as in the experiments. The results of the experiments and DNS are found to be in qualitative agreement and are used synergistically to explore the physics of the air entrainment process; quantitative agreement is not to be expected given the differences in setup and Reynolds numbers. In the experiments and DNS, the free-surface motion is found to consist of a region near the belt with fast-moving uncorrelated large-amplitude ripples and an outer region of small-amplitude propagating waves. Entrainment events similar to plunging breaking waves are found in the experiments, and these and other entrainment mechanisms are examined in detail in the DNS. The spatial distributions of bubble numbers and velocities are reported along with their diameter distributions.