Statistical analysis of geological factors controlling bed-bounded fracture density in heterolithic shale reservoirs: The example of the Woodford Shale Formation (Oklahoma, USA)

Natural fracture aperture-size, spacing, and stratigraphic variation in fracture density are factors determining the fluid-flow capacity of low-permeability formations. In this study, several facies were identified in a Woodford Shale complete section. The section was divided into four broad stratigraphic zones based on interbedding of similar facies. Average thicknesses and percentages of brittle and ductile beds in each stratigraphic foot were recorded. Also, five fracture sets were identified. These sets were split into two groups based on their trace exposures. Fracture linear intensity (number of fractures normalized to the scanline length [[Formula: see text]]) values were quantified for brittle and ductile beds. Individual fracture intensity-bed thickness linear equations were derived. These equations, along with the average bed thickness and percentage of brittle and ductile lithologies in each stratigraphic foot, were used to construct a fracture areal density (number of fracture traces normalized to the trace exposure area [[Formula: see text]]) profile. Finally, the fracture opening-displacement size variations, clustering tendencies, and fracture saturation were quantified. Fracture intensity-bed thickness equations predict approximately 1.5–3 times more fractures in the brittle beds compared with ductile beds at any given bed thickness. Parts of zone 2 and almost entire zone 3, located in the upper and middle Woodford, respectively, have high fracture densities and are situated within relatively organic-rich (high-GR) intervals. These intervals may be suitable horizontal well landing targets. All observed fracture cement exhibit a lack of crack-seal texture. Characteristic aperture-size distributions exist, with most apertures in the 0.05–1 mm (0.00016–0.0032 ft) range. In the chert beds, fracture cement is primarily bitumen or silica or both. Fractures in dolomite beds primarily have calcite cement. The average fracture spacing indices (i.e., bed thickness-fracture spacing ratio) in brittle and ductile beds were determined to be 2 and 1.2, respectively. Uniform fracture spacing was observed along all scanlines in the studied beds.

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Numerical Study on the Effects of Imbibition on Gas Production and Shut-In Time Optimization in Woodford Shale Formation

Energies ◽

10.3390/en13123222 ◽

2020 ◽

Vol 13 (12) ◽

pp. 3222 ◽

Cited By ~ 1

Author(s):

Zhou Zhou ◽

Shiming Wei ◽

Rong Lu ◽

Xiaopeng Li

Keyword(s):

Numerical Model ◽

Hydraulic Fracturing ◽

Field Data ◽

Gas Production ◽

Model Parameters ◽

Water Recovery ◽

Woodford Shale ◽

Capillary Suction ◽

Shale Formation ◽

The Relationship

In shale gas formations, imbibition is significant since the tight pore structure causes a strong capillary suction pressure. After hydraulic fracturing, imbibition during the period of shut-in affects the water recovery of flowback. Although there have been many studies investigating imbibition in shale formations, few papers have studied the relationship between gas production and shut-in time under the influence of imbibition. This paper developed a numerical model to investigate the effect of imbibition on gas production to optimize the shut-in time after hydraulic fracturing. This numerical model is a 2-D two-phase (gas and water) imbibition model for simulating an imbibed fluid flow and its effect on permeability, flowback, and water recovery. The experimental and field data from the Woodford shale formation were matched by the model to properly configure and calibrate the model parameters. The experimental data consisted of the relationship between the imbibed fluid volume and permeability change, the relative permeability, and the capillary pressure for the Woodford shale samples. The Woodford field data included the gas production and flowback volume. The modeling results indicate that imbibition can be a beneficial factor for gas production, since it can increase rock permeability. However, the gas production would be reduced when excessive fluid is imbibed by the shale matrix. Therefore, the shut-in time after hydraulic fracturing, when the imbibition happens in shale, could be optimized to maximize the gas production.

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Chemostratigraphic, palynostratigraphic, and sequence stratigraphic analysis of the Woodford Shale, Wyche Farm Quarry, Pontotoc County, Oklahoma

Interpretation ◽

10.1190/int-2014-0089.1 ◽

2015 ◽

Vol 3 (1) ◽

pp. SH1-SH9 ◽

Cited By ~ 10

Author(s):

Bryan W. Turner ◽

Carlos E. Molinares-Blanco ◽

Roger M. Slatt

Keyword(s):

Gamma Ray ◽

Data Sets ◽

Well Log ◽

Woodford Shale ◽

Sequence Stratigraphic ◽

Base Level ◽

Area Of Interest ◽

Significant Area ◽

Shale Reservoirs ◽

Well Log Analysis

Understanding mudrocks and shale reservoirs has become a significant area of interest within industry and academia in recent years. Of particular interest is understanding the pervasive variability present within these units. This variability became apparent when conventional approaches, such as lithostratigraphic analysis and well log correlation, were coupled with recent developments in palynostratigraphy and chemostratigraphy. A single shallow Woodford Shale research core in the western Arkoma Basin from Pontotoc County, Oklahoma, was used to identify three scales of stratigraphic cyclicity. By comparing the relative abundances of continental sourced pollen and spores to marine-derived acritarchs over a stratigraphic interval, it was possible to extrapolate the overall trends in shoreline trajectory. Conventional well log analysis, such as gamma ray logs, provided a balanced understanding of the interplay between localized changes in sedimentation and regional shifts in the stratigraphic base level, in addition to providing a means to tie these analyses to extensive subsurface data sets. Chemostratigraphic correlations resolved subtle, but stratigraphically significant, shifts in localized patterns in sedimentation. Using these approaches, the Lower and Middle Woodford Shale can be divided into four chemostratigraphic parasequences within a transgressive systems tract defined by well log and core analysis. The Upper Woodford can be separated into an additional four chemostratigraphic parasequences within a highstand systems tract. Chemostratigraphic data also revealed the changing bottom water conditions present at the time of deposition, with a period of localized anoxic conditions recorded in the Lower and Upper Woodford in this part of the basin. These localized changes in sedimentation and environmental conditions can be nested into two longer term regional transgressions and regressions.

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Statistical analysis of lake sediment geochemical data for understanding surface geological factors and processes: An example from Amazonian upland lakes, Brazil

CATENA ◽

10.1016/j.catena.2018.12.003 ◽

2019 ◽

Vol 175 ◽

pp. 47-62 ◽

Cited By ~ 7

Author(s):

Prafulla Kumar Sahoo ◽

José Tasso Felix Guimarães ◽

Pedro Walfir Martins Souza-Filho ◽

Mike A. Powell ◽

Marcio Sousa da Silva ◽

...

Keyword(s):

Statistical Analysis ◽

Lake Sediment ◽

Geochemical Data ◽

Geological Factors

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Diffraction imaging in fractured carbonates and unconventional shales

Interpretation ◽

10.1190/int-2014-0080.1 ◽

2015 ◽

Vol 3 (1) ◽

pp. SF69-SF79 ◽

Cited By ~ 10

Author(s):

Ioan Sturzu ◽

Alexander Mihai Popovici ◽

Tijmen Jan Moser ◽

Sudha Sudhakar

Keyword(s):

Natural Fracture ◽

Small Scale ◽

Fracture Density ◽

New Approach ◽

Field Development ◽

Time Migration ◽

The Us ◽

Diffraction Imaging ◽

Resolution Imaging ◽

Shale Reservoirs

Diffraction imaging is recognized as a new approach to image small-scale fractures in shale and carbonate reservoirs. By identifying the areas with increased natural fracture density, reservoir engineers can design an optimal well placement program that targets the sweet spots (areas with increased production), and minimizes the total number of wells used for a prospective area. High-resolution imaging of the small-scale fractures in shale reservoirs such as Eagle Ford, Bakken, Utica, and Woodbine in the US, and Horn River, Montney, and Utica in Canada improves the prospect characterization and predrill assessment of the geologic conditions, improves the production and recovery efficiency, reduces field development cost, and decreases the environmental impact of developing the field by using fewer wells to optimally produce the reservoir. We evaluated several field data examples using a method of obtaining images of diffractors using specularity filtering that could be performed in depth and time migration. Provided that a good migration velocity was available, we used the deviation of ray scattering from Snell’s law to attenuate reflection energy in the migrated image. The resulting diffraction images reveal much of the structural detail that was previously obscured by reflection energy.

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Statistical analysis and significance of pyrite in the Wufeng-Lower Longmaxi Shale Formation in South China

Arabian Journal of Geosciences ◽

10.1007/s12517-020-06190-0 ◽

2020 ◽

Vol 13 (22) ◽

Author(s):

Ke Jiang ◽

Wen Zhou ◽

Naier Deng ◽

Weiguo Song

Keyword(s):

Statistical Analysis ◽

South China ◽

Longmaxi Shale ◽

Shale Formation

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Lithofacies and stratigraphy of a complete Woodford Shale outcrop section in South Central Oklahoma: Geologic considerations for the evaluation of unconventional shale reservoirs

Interpretation ◽

10.1190/int-2017-0074.1 ◽

2018 ◽

Vol 6 (1) ◽

pp. SC15-SC27 ◽

Cited By ~ 4

Author(s):

Henry Galvis ◽

Daniela Becerra ◽

Roger Slatt

Keyword(s):

High Frequency ◽

Local Source ◽

Woodford Shale ◽

Quartz Content ◽

Potential Target ◽

South Central ◽

Lower Member ◽

Bed Thickness ◽

Shale Reservoirs ◽

Multiple Scenarios

We have developed a detailed rock-based documentation of a previously undescribed Woodford Shale outcrop in South Central Oklahoma. The complete exposed section provided the opportunity to investigate lithologic attributes across the complete Woodford Shale thickness, as well as on its under- and overlying formational contacts. Within the Woodford Shale strata, seven lithofacies were recognized honoring textural and compositional attributes, and they were grouped based on their weathering response into soft (incompetent) and hard (competent) beds. Internally, across the Woodford interval, there is an overall upward increase in quartz content, represented by higher proportions of siliceous shales and chert around the middle and upper members, whereas the lower member is mostly dominated by organic and clay-rich shales interbedded with minor proportions of cherty beds. However, most notable was the rhythmic cyclicity between hard (brittle) and soft (ductile) lithofacies throughout the Woodford, from which systematic measurements of bed thickness and soft-to-hard ratios are examined to illustrate multiple scenarios of stratigraphic anisotropy. The geologic assessment of reservoir quality was assessed using the vertical arrangement of lithofacies, from which we hypothesized that potential target zones are interpreted to be composed by high-frequency interbeddings of organic-rich “soft” beds (acting as a local source) and “hard” brittle beds (acting as more frackable or fractured rocks). According to this model and the vertical stratigraphy, a potential target zone is interpreted to lie in between the upper half of the middle Woodford and lower half of the upper Woodford member, where the soft-to-hard ratio is approximately 50/50 and the beds are thinner.

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The role of reservoir modelling in unlocking unconventional (resource) plays

The APPEA Journal ◽

10.1071/aj12051 ◽

2013 ◽

Vol 53 (2) ◽

pp. 440

Author(s):

Hiwa Sidiq ◽

Eli Silalahi ◽

Grant Skinner ◽

Perdana Noverda Pamurty

Keyword(s):

Seismic Data ◽

Fracture Network ◽

Fracture Density ◽

Reservoir Modelling ◽

Technical Developments ◽

Well Spacing ◽

Shale Reservoirs ◽

Unconventional Resource ◽

Sweet Spots

There has been a recent focus on the insight that reservoir modelling provides into devising the best workflows and its ability to include reservoir attributes that affect recovery factors in shale. This extended abstract examines recent technical developments in reservoir modelling and how such modelling can identify sweet spots in shale reservoirs. An accurate characterisation of a pre-existing fracture network and its structural complexities, however, requires the gathering of a large amount of data. In addition, investigating sweet spots at the presently low gas prices sometimes prevents the acquisition of such data that is essential as an input to drilling strategies, fracture program design, well spacing, and understanding stimulated reservoir volumes (SRV) in shale. The pre-existing fractures may also have a limited impact on recovery rates. The transport along a wellbore is mainly controlled by the drained volume, not only by the fractures around the well. In such cases, the pre-existing fractures and their reactivation during the fracturing stage are not sufficient to determine the amount of gas that can be recovered during production. This volume is effectively not only a function of the fracture density, but also of the propped fractures. The challenge, therefore, becomes the ability to have a good estimation of the size of the SRV and be able to calibrate this volume using relevant data such as micro-seismic data and the recovery from previous fraccing stages. This extended abstract also discusses how reservoir modelling can play a key role in this area.

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Statistical analysis of classification

Symposium - International Astronomical Union ◽

10.1017/s0074180900053420 ◽

1966 ◽

Vol 24 ◽

pp. 188-189

Author(s):

T. J. Deeming

Keyword(s):

Multivariate Analysis ◽

Statistical Analysis ◽

Classification Scheme ◽

Analytical Procedure ◽

Narrow Band ◽

Scientific Research ◽

Maximum Amount ◽

Amount Of Information

If we make a set of measurements, such as narrow-band or multicolour photo-electric measurements, which are designed to improve a scheme of classification, and in particular if they are designed to extend the number of dimensions of classification, i.e. the number of classification parameters, then some important problems of analytical procedure arise. First, it is important not to reproduce the errors of the classification scheme which we are trying to improve. Second, when trying to extend the number of dimensions of classification we have little or nothing with which to test the validity of the new parameters.Problems similar to these have occurred in other areas of scientific research (notably psychology and education) and the branch of Statistics called Multivariate Analysis has been developed to deal with them. The techniques of this subject are largely unknown to astronomers, but, if carefully applied, they should at the very least ensure that the astronomer gets the maximum amount of information out of his data and does not waste his time looking for information which is not there. More optimistically, these techniques are potentially capable of indicating the number of classification parameters necessary and giving specific formulas for computing them, as well as pinpointing those particular measurements which are most crucial for determining the classification parameters.

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Quantitative parallel EELS spectrum imaging developed as a new tool in AEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010013064x ◽

1992 ◽

Vol 50 (2) ◽

pp. 1202-1203

Author(s):

Gianluigi Botton ◽

Gilles L'espérance

Keyword(s):

Statistical Analysis ◽

Spatial Resolution ◽

Personal Computer ◽

Systematic Study ◽

Present Author ◽

Chemical Elements ◽

Detection Limits ◽

Research Groups ◽

Quantitative Performance ◽

Spectrum Imaging

As interest for parallel EELS spectrum imaging grows in laboratories equipped with commercial spectrometers, different approaches were used in recent years by a few research groups in the development of the technique of spectrum imaging as reported in the literature. Either by controlling, with a personal computer both the microsope and the spectrometer or using more powerful workstations interfaced to conventional multichannel analysers with commercially available programs to control the microscope and the spectrometer, spectrum images can now be obtained. Work on the limits of the technique, in terms of the quantitative performance was reported, however, by the present author where a systematic study of artifacts detection limits, statistical errors as a function of desired spatial resolution and range of chemical elements to be studied in a map was carried out The aim of the present paper is to show an application of quantitative parallel EELS spectrum imaging where statistical analysis is performed at each pixel and interpretation is carried out using criteria established from the statistical analysis and variations in composition are analyzed with the help of information retreived from t/γ maps so that artifacts are avoided.

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