Mehdi Ostadhassan

Nano-dynamic mechanical analysis (nano-DMA) of creep behavior of shales: Bakken case study

Understanding the time-dependent mechanical behavior of rocks is important from various aspects and different scales such as predicting reservoir subsidence due to depletion or proppant embedment. Instead of using the conventional creep tests, nano-dynamic mechanical analysis (nano-DMA) was applied in this study to quantify the displacement and mechanical changes in shale samples over its creep time at a very fine scale. The results showed that the minerals with various mechanical properties exhibit different creep behavior. It was found that under the same constant load and time conditions, the creep displacement of hard minerals would be smaller than those that are softer. On the contrary, the changes in mechanical properties (storage modulus, loss modulus, complex modulus and hardness) of hard minerals are larger than soft minerals. The results from curve fitting showed that the changes in creep displacement, storage modulus, complex modulus and hardness over creep time follow a logarithmic function. We further analyzed the mechanical changes in every single phase during the creep time based on the deconvolution method to realize each phase’s response independently. Two distinct mechanical phases can be derived from the deconvolution histograms. As the creep time increases, the volume percentage of the hard mechanical phase decreases, while this shows an increase for soft phases. The results suggest that nano-DMA can be a strong advocate to study the creep behavior of rocks with complex mineralogy.

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.

Geomechanics and Elastic Anisotropy of Shale Formations

Deep shales are the most abundant yet least characterized sedimentary rocks in petroleum industry while they have become significant sources of hydrocarbon unconventional resources. This chapter aims to fulfill an investigation of anisotropy in this rock type in several different facets through integration of field and lab data. I seek to generate key information to better understand elastic anisotropy as well as in situ stresses to better perform drilling, well completion, perforating, and hydraulic fracturing for the purpose of geomechanical modeling.

A Multidisciplinary Study of Stimulation Designs in the Three Forks Formation, ND

The Three Forks Formation in the state of North Dakota is one of the main plays with the record of one million barrels a day of hydrocarbon production, recently, combined with the Bakken. Three Forks formation is highly heterogeneous due to the presence of interbedded shale layers. The reservoir properties vary significantly within the basin, which makes the stimulation designs challenging. It’s well understood that to maintain the production, well completion and stimulation designs should be applied in a given field in Williston Basin; in this paper we combined several data sources in a multidisciplinary manner and compared completion design parameters such as: amount of proppant injected and type, fracturing fluid type, using acid, etc. with the goal of improving well productivity. The main objective of this study is to investigate how different fracturing components can impact the production. The production history data was limited to the days after the stimulation. Our investigation is based on proprietary and public data of the Three Forks Formation. We also included the name of each operator active in a single field to make an assessment of how different companies are performing completion and fracturing design compared to production. Introduction In the last decade, the Bakken shale has emerged as a major oil play in North America. Lately, however, more effort has been spent on Three Forks Formation. From across the country, oil companies have been flocking to the Williston Basin to get their shares. These companies have brought along their unique knowledge and experiences. They are constantly testing and refining their methods in order to have the most production out of the Bakken and Three Forks formations. As a result, there is a variety in the way these companies stimulate their wells. Each different approach had produced different result. Some approaches will result in higher production comparing to others. In this study, the focus will be on the Three Forks since it is the “next” formation. The Three Forks Formation was deposited during the late Devonian, in a very shallow and extensive epeiric platform. It is a mud dominated system composed of dolomitic siltstone, claystone and mudstone (Gutierrez et al., 2013). Even though Three Forks is an unconventional play, there are many subsurface structures involved in it, such as dome and anticlines, which form conventional traps throughout the basin. As such, production from these structures should be higher since they benefit from the conventional trap. For a major part, this study devotes to answer two questions: • What are the correlations between different fracing parameters and its corresponding production result? • Does it require higher pressure to open fracture on top of an anticline vs. away from an anticline? URTeC 2015 Page 1941