Dmitry Korost

Determining Physical Properties of Unconventional Reservoir Rocks: from Laboratory Methods to Pore-Scale Modeling

With the rapid progress of imaging methods it is now possible to obtain detailed rock structure information on different scales, ranging from nanometers to micrometers. Such knowledge facilitates use of pore-scale modeling approaches to predict numerous physical properties based on three dimensional structural data. Pore-scale modeling approaches can simulate different processes in the rock under natural conditions (pressure, temperature, etc.), which are more difficult to simulate in the laboratory. This is especially important for unconventional reservoir rocks such as the Bazhen formation siliceous rocks (black shales) used in this study. Based on X-ray microtomography and SEM imaging we develop a detailed categorization of different types of porosities (including micro, i.e. larger than µm size, and nano, i.e. sub-micron size, porosities) for samples of Bazhen siliceous rocks. Standard pore-scale modeling techniques do not account for different flow regimes within different pore sizes. Thus, we develop a pore-network model with different physics of gas flow for micro- and nanoporosity. High-resolution images are used for stochastic reconstructions of 3D structure and subsequently used for modeling of gas permeability. Resulting permeability values are in a good agreement with gas permeabilities measured for Bazhenov siliceous rocks. Finally, we present a framework to model gas permeability of unconventional reservoir rocks using multi-scale 3D structure information based on microCT scans and high resolution SEM/FIB-SEM imaging techniques. Nomenclature

Criterion for fracture transition to critical stage

AbstractWe have developed an analysis of data obtained in laboratory investigations of deformation of rocks by acoustic emission and X-ray microtomography. We found that defect accumulation occurs in fundamentally differing manners during loading. At first, defects are generated randomly and have a specific size determined by a typical structural element of a material (e.g., a grain in granite). Then the defects with sizes not dictated by the material structure are generated. The interaction between these defects gives rise to critical defects that are capable of self-development. In all probability, a sample breakdown results from the evolution of the ensemble of critical defects. We found that the fracture stages can be distinguished by the type of energy distribution function of the acoustic emission signals. At the first stage, the distribution is approximated by an exponential function, whereas the second stage is characterized by a power-law function that points to a self-organized criticality state...

Solution of the stokes equation in three-dimensional geometry by the finite-difference method

The recent progress in the methods for the study of the three-dimensional structure of porous and composite materials (microtomography, confocal microscopy, and FIB-SEM) and the significant improvement in the available computational resources make it possible to simulate various processes directly in the three dimensional geometry of samples of such materials (pore-scale modeling) in order to determine their effective properties or to get a more detailed understanding of the studied processes, such as filtration. In this work, we solve the Stokes equation by the finite-difference method using schemes of the second and fourth orders of accuracy in a three-dimensional domain whose geometry reproduces the microstructure of the investigated rock samples. The numerical values of permeability obtained for a sample of sandstone are consistent with the data of laboratory measurements.

Siliceous reservoirs of the Bazhenov formation, the Sredny Nazym Oil Field, and the structure of their pore space

The reservoirs of the oil-bearing Tutleym formation, Bazhenov horizon (analog of the Bazhenov Formation for Middle Nazym Oil Field), are studied. Their material composition, porosity and permeability, the geochemical characteristics of their organic matter, and pore space characteristics are examined, and the factors affecting the reservoir porosity and permeability are found. The changes in the structure of the porous medium, which provide primary oil migration from oil source rocks into the Tutleym formation reservoirs, are revealed.

The reservoir properties of the rocks of the bazhenovskaya formation

This work is dedicated to interpretation of the results of complex laboratory petrophysical studies of core samples of the rocks of the Bazhenovkaya Formation from several wells at Western Siberian deposits. The major aim of this study is the comparison and substantiation of analytical results that were obtained by various methods of determination of petrophysical rock properties, which is necessary to reveal the methods of complex petrophysical studies that are the most correct and applicable for the rocks of the Bazhenovskaya Formation.

Studying structure and determining permeability of materials based on X-Ray microtomography data (using porous ceramics as an example)

Modern noninvasive methods for probing the three-dimensional structure of materials, such as X-ray tomography, make it possible not only to obtain precise data on the structure of a sample but also to use them for assessing effective properties of the material by numerical methods. We have studied the pore structure of three samples of permeable porous ceramics by X-ray microtomography and numerically determined the permeability by solving the Stokes equation in the three-dimensional geometry of the pore structure. The data thus obtained are in excellent agreement with results of laboratory measurements. Morphological analysis of the pore structure (pore size distribution) allowed us to explain the results obtained for three samples of ceramics produced from granules of various sizes and shapes.

Studying of Shale Organic Matter Structure and Pore Space Transformations During Hydrocarbon Generation

In this study, we focus on organic matter structure and its interaction with the pore space of shales during hydrocarbon (HC) generation. Rock samples collected from Domanic horizon of South-Tatar arch were heated in the pyrolyzer to temperatures closely corresponding to different catagenesis stages. X-ray microtomography method was used to monitor changes in the morphology of the pore space and organic matter structure within studied shale rocks. By routine measurements we made sure that all samples had similar composition of organic and mineral phases. All samples in the collection were grouped according to initial structure and amount of organics. They were processed separately to: (1) study the influence of organic matter content on the changing morphology of the rock under thermal effects; (2) study the effect of initial structure on the primary migration processes for samples with similar organic matter content. After heating the morphology of altered rocks was characterized by formation of new pores and channels connecting primary voids. However, it was noted that the samples with a relatively low content of the organic matter had less changes in pore space morphology, in contrast to rocks with a high organic content. Second part of the study also revealed significant differences in resulting pore structures depending on initial structure of the unaltered rocks and connectivity of original organics.

Transformation of the pore space during the simulation of the generation of hydrocarbon fluids in the Domanik horizon of the South-Tatar crest as an example

The main purpose of this paper is to study the factors that control changes in rock structure during catagenetic transformation of organic matter. Hydrocarbon generation and primary migration can be controlled by numerous parameters; the most important are temperature, pressure, hydrocarbon composition, and organic matter type and content. The influences of most of these parameters have been studied and experimentally demonstrated. However, there are a few works that are dedicated to the investigation of the texture features of rocks, as well as the quantitative content of the organic matter on the pore space transformation of rocks. Therefore, these parameters are the most important when studying the primary migration processes. It was found experimentally that the rock pore space after each stage of heating is transformed, forming new pore spaces and channels that connect the primary pores. A sample with a relatively low content of organic matter has been found to undergo fewer changes in pore-space morphology in comparison to rock that is saturated in organic content. It has been found that that the change of pore-space morphology depends on the original structure of the rocks. Most of the structural changes were observed during rock heating within 260–430°C; the most intense formation of hydrocarbons was revealed within this interval.