Correlation Analysis of Fracture Intensity Descriptors with Different Dimensionality in a Geomechanics-constrained 3D Fracture Network

Summary The Duvernay Formation is an unconventional reservoir characterized by induced seismicity and fluid migration, with natural fractures likely contributing to both cases. An alpine outcrop of the Perdrix and Flume formations, correlative with the subsurface Duvernay and Waterways formations, was investigated to characterize natural fracture networks. A semiautomated image-segmentation and fracture analysis was applied to orthomosaics generated from a photogrammetric survey to assess small- and large-scale fracture intensity and rock mass heterogeneity. The study also included manual scanlines, fracture windows, and Schmidt hammer measurements. The Perdrix section transitions from brittle fractures to en echelon fractures and shear-damage zones. Multiple scales of fractures were observed, including unconfined, bedbound fractures, and fold-relatedbed-parallel partings (BPPs). Variograms indicate a significant nugget effect along with fracture anisotropy. Schmidt hammer results lack correlation with fracture intensity. The Flume pavements exhibit a regionally extensive perpendicular joint set, tectonically driven fracturing, and multiple fault-damage zones with subvertical fractures dominating. Similar to the Perdrix, variograms show a significant nugget effect, highlighting fracture anisotropy. The results from this study suggest that small-scale fractures are inherently stochastic and that fractures observed at core scale should not be extrapolated to represent large-scale fracture systems; instead, the effects of small-scale fractures are best represented using an effective continuum approach. In contrast, large-scale fractures are more predictable according to structural setting and should be characterized robustly using geological principles. This study is especially applicable for operators and regulators in the Duvernay and similar formations where unconventional reservoir units abut carbonate formations.

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Analyzing the Impacts of Meshing and Grid Alignment in Dual-Porosity Dual-Permeability Upscaling

SPE Reservoir Evaluation & Engineering ◽

10.2118/208573-pa ◽

2021 ◽

pp. 1-20

Author(s):

Ziming Xu ◽

Juliana Y. Leung

Keyword(s):

Fracture Network ◽

Fracture Plane ◽

Fracture Density ◽

Shape Factors ◽

Stimulated Reservoir Volume ◽

Reservoir Volume ◽

Multiple Length Scales ◽

Fracture Intensity ◽

Cumulative Production ◽

The Difference

Summary The discrete fracture network (DFN) model is widely used to simulate and represent the complex fractures occurring over multiple length scales. However, computational constraints often necessitate that these DFN models be upscaled into a dual-porositydual-permeability (DPDK) model and discretized over a corner-point grid system, which is still commonly implemented in many commercial simulation packages. Many analytical upscaling techniques are applicable, provided that the fracture density is high, but this condition generally does not hold in most unconventional reservoir settings. A particular undesirable outcome is that connectivity between neighboring fracture cells could be erroneously removed if the fracture plane connecting the two cells is not aligned along the meshing direction. In this work, we propose a novel scheme to detect such misalignments and to adjust the DPDK fracture parameters locally, such that the proper fracture connectivity can be restored. A search subroutine is implemented to identify any diagonally adjacent cells of which the connectivity has been erroneously removed during the upscaling step. A correction scheme is implemented to facilitate a local adjustment to the shape factors in the vicinity of these two cells while ensuring the local fracture intensity remains unaffected. The results are assessed in terms of the stimulated reservoir volume calculations, and the sensitivity to fracture intensity is analyzed. The method is tested on a set of tight oil models constructed based on the Bakken Formation. Simulation results of the corrected, upscaled models are closer to those of DFN simulations. There is a noticeable improvement in the production after restoring the connectivity between those previously disconnected cells. The difference is most significant in cases with medium DFN density, where more fracture cells become disconnected after upscaling (this is also when most analytical upscaling techniques are no longer valid); in some 2D cases, up to a 22% difference in cumulative production is recorded. Ignoring the impacts of mesh discretization could result in an unintended reduction in the simulated fracture connectivity and a considerable underestimation of the cumulative production.

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Stochastic Sensitivity Analysis for effective Parameters Ranges on 3D Fracture Network Using Stress Distribution, Outcrops and Wellbore Data Adjusted to Well Production History in Mature Field

10.2118/169417-ms ◽

2014 ◽

Author(s):

E.J. Bustamante ◽

V. Cabello Rios ◽

D. Escobedo Cabrera ◽

P. Manrique Cáceres ◽

L. Choque ◽

...

Keyword(s):

Sensitivity Analysis ◽

Stress Distribution ◽

Fracture Network ◽

Effective Parameters ◽

Well Production ◽

Stochastic Sensitivity ◽

Production History ◽

Mature Field ◽

Stochastic Sensitivity Analysis ◽

3D Fracture Network

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The Stratigraphy of Pre-Tertiary Economic Basement in South Jambi B Block, South Sumatra Basin

10.29118/ipa21-g-271 ◽

2021 ◽

Keyword(s):

Significant Contribution ◽

Fracture Network ◽

Natural Fracture ◽

Fracture Density ◽

The South ◽

The North ◽

Fracture Intensity ◽

Parent Rocks ◽

Major Fault ◽

Essential Function

As one of the most promising plays, the Pre-Tertiary basement play holds a significant contribution to the latest success of exploration efforts in the South Sumatra Basin, which then includes the South Jambi B Block. Yet, the natures of the Pre-Tertiary unit in this block remains unsolved. Lithology variability, spatial irregularity, genetic ambiguity, and different reservoir characteristic are indeterminate subjects in the block are the main focus here. The ultimate goals of this study are to better characterize the unit and gain more understanding in calibrating the remaining potential. Based on this study, The Pre-Tertiary units are mainly originated from layered marine-deltaic sedimentary parent rocks with carbonate, intruded by spotty granite where the concentration of each parent rocks varies at the north, the middle, and southern part. Secondly, both lithology heterogeneity and natural fracture density create distinctive reservoir deliverability at each structure. The storage concept is an essential function of natural fracture intensity and diversity, supported by matrix porosity that varies across a different succession of lithology. Lastly, this study observes that major fault orientation is essential in constructing the fracture network. Evidence from several image logs across the study area concludes that most of the interpreted fractures are oriented subparallel to the major faults. The northern belt area is relatively affected by NW-SE Neogene structure, where the southern area is recognized to be affected by both Neogene compression and pre-existing Paleogene structure.

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Fracture intensity attribute for the Tensleep reservoir at Teapot Dome, Wyoming, USA

Interpretation ◽

10.1190/int-2014-0258.1 ◽

2015 ◽

Vol 3 (3) ◽

pp. SZ41-SZ48 ◽

Cited By ~ 6

Author(s):

Payam Kavousi Ghahfarokhi ◽

Thomas H. Wilson

Keyword(s):

Oil Recovery ◽

Negative Curvature ◽

Fracture Network ◽

Fracture Zones ◽

Tight Sandstone ◽

Teapot Dome ◽

Discrete Fracture ◽

Fracture Intensity ◽

Small Fault ◽

Seismic Scale

The Tensleep oil reservoir at Teapot Dome, Wyoming, USA, is a naturally fractured tight sandstone reservoir that has been considered for carbon dioxide enhanced oil recovery ([Formula: see text]-EOR) and sequestration. Interpretation of open fractures identified in wireline image logs from the field suggests that the reservoir fracture network is dominated by early formed structural hinge-oblique fractures with interconnectivity enhanced by hinge-parallel and hinge-perpendicular fracture sets. Previous studies show that 3D seismic scale discontinuity attributes are dominated by more recent hinge-parallel and strike slip trends. The most negative curvature attribute that we used highlights concave features attributed to subtle traveltime delay through fracture zones and small faults or flexures associated with the fracture swarms. The poststack discontinuity extraction workflow incorporated seismic spectral blueing (SSB) to enhance the resolution of the seismic data. The SSB process is followed by computation of the short-wavelength most negative curvature. Subsequently, the minimum similarity attribute is applied to accentuate regions with minimum similarity of curvature. An edge-illumination process is then applied to the minimum similarity of the most negative curvature output. Discontinuities extracted through edge illumination locate regions of minimal similarity in curvature along fracture zones or small fault boundaries. This workflow enhances hinge-oblique discontinuities without azimuthal filtering and provides a fracture intensity attribute, which is used as an input to distribute the fracture intensity through the model discrete fracture network. Qualitative correlation of production data to extracted discontinuities suggests that wells located on hinge-oblique discontinuities are more productive than other wells in the field.

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Integrated study of a fractured granitic basement reservoir with connectivity analysis and identification of sweet spots: Cauvery Basin, India

The Leading Edge ◽

10.1190/tle38040254.1 ◽

2019 ◽

Vol 38 (4) ◽

pp. 254-261

Author(s):

Deepa ◽

J. Nagaraju ◽

Binod Chetia ◽

Rajeev Tandon ◽

P. K. Chaudhuary ◽

...

Keyword(s):

Fracture Network ◽

Earth Model ◽

Connectivity Analysis ◽

Fracture Permeability ◽

Cauvery Basin ◽

Well Production ◽

Fracture Intensity ◽

Mechanical Earth Model ◽

Well Data ◽

Sweet Spots

Basement exploration in India has seen increased interest after the recent discovery of a field in the Cauvery Basin in southeastern India, with an average individual well production of 700 b/d from a fractured basement reservoir. The field is presently under development, with several development well locations identified for drilling. Optimized development of a fractured basement reservoir requires identification of areas with a permeable fracture network. To meet this objective, we adopted a comprehensive integrated workflow involving the use of common reflection angle migrated seismic data, fracture modeling, a 1D mechanical earth model (MEM), identification of critically stressed fractures in 3D space, fracture permeability/connectivity analysis, and sweet spot identification. The workflow yielded a robust discrete fracture network model based on 3D directional fracture intensity, a 1D MEM that gave regional stress gradients (pore pressure, overburden, Shmin, and SHmax), and rock strength and elastic properties. In addition, we generated a critically stressed 3D fracture model and performed sequential stratal surface restoration for predictive strain modeling that was calibrated at wells. Our fracture permeability and connectivity analysis showed that existing hydrocarbon-producing wells are located within areas that have a fracture cluster/swarm with associated good fracture connectivity. A 3D basement facies model constructed by integrating well data and a poststack inversion impedance volume showed that major flow zones occur in weathered basement associated with low impedance. This model, in combination with fracture intensity data, provides good indication of the location of basement sweet spots in the Cauvery Basin. The understanding gained on the controls of occurrence of basement fractures explains why some wells in the field are producers and others are dry. This led to greater confidence in optimizing the locations of previously proposed new development wells.

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Fracture distribution on the Swift Reservoir Anticline, Montana: Implications for structural and lithological controls on fracture intensity

Geological Society London Special Publications ◽

10.1144/sp487.9 ◽

2019 ◽

Vol 487 (1) ◽

pp. 209-228 ◽

Cited By ~ 1

Author(s):

Hannah Watkins ◽

Clare E. Bond ◽

Adam J. Cawood ◽

Mark A. Cooper ◽

Marian J. Warren

Keyword(s):

Fracture Network ◽

Structural Factors ◽

Fractured Reservoir ◽

Hydrocarbon Production ◽

Fracture Intensity ◽

Porosity And Permeability ◽

Primary Porosity ◽

Rock Mechanical Properties ◽

Fracture Distribution ◽

Reservoir Potential

AbstractWhere primary porosity and permeability of a rock are unfavourable for hydrocarbon production, fractures can improve reservoir potential by enhancing permeability. Higher fracture intensity may create a better-connected fracture network, improving fractured-reservoir quality. Investigations into the controls on fracture intensity commonly conclude that either structural or lithological factors have the greatest influence on fracture abundance. We use the Swift Reservoir Anticline in northwestern Montana to investigate how fracture intensity varies throughout the structure and determine that although structural factors do influence fracture intensity, lithology is the main control at outcrop.The Swift Reservoir Anticline exposes bedding surfaces of the Mississippian Castle Reef Formation dolomite. Field data indicates that fracture intensity is highest in the fold forelimb, decreasing into the backlimb except in outcrops of coarse dolomite where fracture intensity is low, regardless of structural position. Field fracture intensity correlates with whole-rock quartz, kaolinite and porosity percentages. We suggest porosity and composition influence bulk-rock mechanical properties, which, in turn, control the fracture intensity at outcrop. Fracture intensity has a stronger relationship with lithological than structural factors, therefore we suggest that the key to predicting fracture intensity in the subsurface here is understanding how lithology varies spatially.

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