Chunxiao Li

Pore characterization of 3D-printed gypsum rocks: a comprehensive approach

AbstractWith advancements in additive manufacturing, now 3D-printed core plugs can be duplicated in order to replace natural rock samples. This can help us to control their parameters to be used in different types of experiments for model verifications. However, prior to such substitutions, we should ensure they can represent natural rock samples through characterizing their physical properties. In this paper, synthetic samples made up of gypsum powder are 3D-printed and then characterized for essential pores properties. The analysis included structures of the pores, quantitative porosity evaluation, pore size distribution, pore surface area, pore shape distribution, and corresponding anisotropy. Mercury injection porosimetry (MIP) and helium porosimetry (HP) combined with X-ray micro-computed tomography were performed to provide us with detailed information about the pores. Porosity was measured 32.66% from micro-CT based on watershed thresholding, which was found comparable with MIP and HP results, 27.90 and 28.86%, respectively. Most of the pores lay in the range from 4 to 10xa0μm in diameter with relative frequency of 92.04%. The pore shape distribution indicates that 3D-printed gypsum rocks host more spherical pores and fewer blade-shaped pores. In addition, pore anisotropy of the sample that was analyzed by collecting pore orientation in orthogonal axes represented the vertical transverse isotropy.n

Can 3-D Printed Gypsum Samples Replicate Natural Rocks? An Experimental Study

Abstract3D printing is an emerging technology which can offer valuable insight into rock characterization and theoretical model verification due to the sample reproducibility. Also, it will allow for the samples to be built at various scales with controlled geometries and specification to facilitate different types of analysis. In this study, gypsum powder was used for printing blindly to evaluate if mechanical and pore network characteristics of the specimens would resemble a natural rock. For this purpose, cylindrical specimens with different sizes were manufactured without inputting any pore network CT digital image of a natural rock. The objective was to study mechanical properties and deformation behavior of such samples by conducting a series of uniaxial compressive strength tests. Scanning electron microscope was utilized to characterize the microstructures of rock matrix prior to and after the experiments were performed. By determining the representative element area and image processing techniques, the surface porosity of 3-D printed samples was measured to be 5.8%. The analysis of pore size and shape distribution demonstrated the dominance of intermediate pore size as the main feature. This study enabled us to propose a new classification criterion for the pore shape based on printing procedures. Additional microstructural elements, micro-fractures, in particular, were identified, analyzed and classified into three separate categories, including intrapore micro-fracture, interpore micro-fracture and micro-fracture perforating pores. Finally, this study compared the mechanical properties and microstructurexa0of 3D printed gypsum samples with typical natural rocks, alsoxa0revealed the limitations in 3-D printing and suggested printing materials should be chosen, specific to the goal of the research study.

Multifractal Characteristics of MIP-Based Pore Size Distribution of 3D-Printed Powder-Based Rocks: A Study of Post-Processing Effect

Abstract3D printing technology offers an innovative approach to manufacture rock samples with controlled properties. However, in this process, pore structure is one of the major concerns when printing similar specimens to natural rocks. The purpose of this study was to lay out an optimal post-processing of 3D-printed samples that can facilitate replicating natural rocks with similar microstructure characteristics. In this study, four cylindrical rocks were manufactured without designed porosity by 3D printing using gypsum powder as the main component. Various types of infiltrants (Colorbond® and Surehold®) and coating conditions (SmoothOn® and WBAE®) were used after completing the printing process of binder jetting. Mercury injection porosimetry was then used to investigate their petrophysical properties including porosity and pore throat size distribution. Multifractal theory was applied to understand the heterogeneity of pore throat distribution within the 3D-printed samples on different pore size intervals. The results showed that 3D-printed rocks have a clustered and negative skewness of pore throat size distributions. The majority of pore sizes are micropores, while a small portion can be categorized under nanopore size category. Multifractal analysis results found a homogeneous distribution of micropores but a heterogeneous distribution of nanopores. Comparing four different samples, it was found that infiltrants could mainly affect the heterogeneous distribution of nanopores more than the micropores, whereas coating does not impact pore structure significantly. In comparison with pore multifractal characteristics of common types of natural rocks, 3D-printed rocks exhibited a higher heterogeneity of pore size distribution.

Nano-mechanical Properties

With the development of production from shale oil and shale gas in North America during the last decade, more studies are being conducted in order to improve our knowledge of the shale characteristics. In this chapter, we talk about mechanical properties of shale samples in micro- and nano-scale. Nanoindentation and Atomic Force Microscopy were newly used advanced techniques in petroleum engineering to investigate the mechanical properties of shales. X-ray diffraction and energy diffusive spectroscopy were used to study the mineral compositions. Based on nanoindentation experiments, elastic modulus and hardness can be extracted from the force-displacement curve. AFM Peakforce quantitively nanomechanical mode is a relatively new mode which can produce maps of surface height and DMT modulus at the same time. In this chapter, we report the application of these two techniques on shale samples taken from Bakken Formation in Williston Basin, North Dakota.

Multi-scale evaluation of mechanical properties of the Bakken shale

Understanding mechanical properties of shale has been the topic of research in the past decade due to its importance in hydraulic fracturing and rock physics modeling. Since shales are highly heterogeneous in constituent components, detailed understanding of mechanical properties in a multi-scale (nano, micro, macro and field) is vital and can present various results. In this study, we used a combination of analytical methods including high-resolution mineral mapping (MAPS), programmed pyrolysis and nanoindentation to identify mineralogy, geochemistry and nanomechanical characteristics of the Bakken shales in Williston Basin, North Dakota. Nanoindentation measurements were done both parallel and perpendicular to the bedding plane to examine mechanical anisotropy. Data were analyzed via multivariate statistical deconvolution technique (maximum likelihood approach and expectation–maximization algorithms) to reveal different mechanical phases, considering their Young’s modulus and hardness. Based on recognized components in the samples and measured values, Young’s modulus was upscaled through effective medium theory. Results showed that total organic carbon (TOC) content has a decreasing effect on Young’s modulus values. It was found that mechanical anisotropy increases with an increasing TOC content. Finally, upscaled Young’s modulus results were compared with reported measurements on core plugs which was found in a reasonable agreement.