Anisotropy analysis for optimized gas production in Coalbed Methane reservoir, Bokaro field, India

Abstract The efficient production of Coalbed Methane (CBM) gas is facing challenges due to the larger dewatering period from fracture connectivity to the aquifer zone. Also, commingled production from well makes it more difficult to identify the coal seam-wise problem. Therefore, prior knowledge of sub-surface fractures in coal seams is necessary to execute an accurate simulation model for planning hydraulic fracturing treatment. This paper highlights the studies in Bokaro CBM reservoir to mitigate challenges in few wells by characterizing anisotropy, determining fast shear wave polarization angle, maximum horizontal stress direction, fracture orientation, and analysis of low resistivity signature. Both the fast shear wave polarization angle and fracture orientation in resistivity image are observed in the same direction (N26°-35°E) in coal. The fast and slow shear slowness versus frequency plot concludes stress-induced anisotropy resulting from fractures that are supported by resistivity image and drilling core. Processing of the resistivity image log shows the maximum horizontal stress is along NE-SW direction, as identified from drilling-induced fractures. The observation of low resistivity signature with resistivity ranging from 0.4 to 0.8 ohm-m in few wells confirms the presence of conducting minerals such as siderite and pyrite from the x-ray diffraction studies of sidewall core. The present work guides in making production, drilling, and hydraulic fracturing design strategies to better understand the fluid propagation for optimized CBM production and will also help in future geomechanical studies.

Download Full-text

Predicting the azimuth of natural fractures and in-situ horizontal stress: A case study from Sichuan Basin, China

Geophysics ◽

10.1190/geo2020-0829.1 ◽

2021 ◽

pp. 1-97

Author(s):

kai lin ◽

Bo Zhang ◽

Jianjun Zhang ◽

Huijing Fang ◽

Kefeng Xi ◽

...

Keyword(s):

Hydraulic Fracturing ◽

Seismic Data ◽

Sichuan Basin ◽

Horizontal Stress ◽

Seismic Attributes ◽

Seismic Events ◽

Natural Fractures ◽

Microseismic Data ◽

Maximum Horizontal Stress

The azimuth of fractures and in-situ horizontal stress are important factors in planning horizontal wells and hydraulic fracturing for unconventional resources plays. The azimuth of natural fractures can be directly obtained by analyzing image logs. The azimuth of the maximum horizontal stress σH can be predicted by analyzing the induced fractures on image logs. The clustering of micro-seismic events can also be used to predict the azimuth of in-situ maximum horizontal stress. However, the azimuth of natural fractures and the in-situ maximum horizontal stress obtained from both image logs and micro-seismic events are limited to the wellbore locations. Wide azimuth seismic data provides an alternative way to predict the azimuth of natural fractures and maximum in-situ horizontal stress if the seismic attributes are properly calibrated with interpretations from well logs and microseismic data. To predict the azimuth of natural fractures and in-situ maximum horizontal stress, we focus our analysis on correlating the seismic attributes computed from pre-stack and post-stack seismic data with the interpreted azimuth obtained from image logs and microseismic data. The application indicates that the strike of the most positive principal curvature k1 can be used as an indicator for the azimuth of natural fractures within our study area. The azimuthal anisotropy of the dominant frequency component if offset vector title (OVT) seismic data can be used to predict the azimuth of maximum in-situ horizontal stress within our study area that is located the southern region of the Sichuan Basin, China. The predicted azimuths provide important information for the following well planning and hydraulic fracturing.

Download Full-text

Numerical Simulation and Laboratory Experiments of Hydraulic Fracturing of Highly Deviated Well

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.275-277.278 ◽

2013 ◽

Vol 275-277 ◽

pp. 278-281 ◽

Cited By ~ 4

Author(s):

Hai Yan Zhu ◽

Jing Gen Deng ◽

Song Yang Li ◽

Zi Jian Chen ◽

Wei Yan ◽

...

Keyword(s):

Numerical Simulation ◽

Hydraulic Fracturing ◽

Fracture Initiation ◽

Element Model ◽

Simulation Method ◽

Horizontal Stress ◽

Initiation Point ◽

Strength Failure ◽

Fluid Penetration ◽

Maximum Horizontal Stress

Considering the combined action of the fluid penetration and the casing, the seepage coupled deformation finite element model of the highly deviated casing perforation well is established by using the tensile strength failure criterion and applied on the BZ25-1 oil filed. The results show that the increasing of the perforation angle and the well azimuth and the decreasing of the inclination would lead to a higher fracture initiation pressure. The fracture initiation point always locates on the wellbore face when the influence of the casing is considered. When the casing is ignored: when the perforation angle is 0°-45°, the fracture initiation point locates on the root of the tunnel; when the angle is 45°-90°, the fracture initiation point may be on the wellbore face or the perforation biased toward the maximum horizontal stress direction; when the angle is near to 90°, the hydraulic fracturing difficultly fractures the rock through the perforation tunnels. The laboratory hydraulic fracturing simulation experiments of 45° deviated well are carried through 400mm3 cement specimen so as to obtain the fracture initiation point and geometric shape under different perforation angles, the results verify the accuracy of the numerical simulation method.

Download Full-text

Seismic Anisotropy at the Rotokawa and Ngatamariki Geothermal Fields in the Taupo Volcanic Zone

10.26686/wgtn.17141978.v1 ◽

2021 ◽

Author(s):

◽

Stefan Mroczek

Keyword(s):

Shear Wave ◽

Delay Time ◽

Seismic Anisotropy ◽

Horizontal Stress ◽

Shear Wave Splitting ◽

Taupo Volcanic Zone ◽

Volcanic Zone ◽

Geothermal Fields ◽

Wave Splitting ◽

Maximum Horizontal Stress

<p>In order to investigate the cracks/fractures in the geothermal fields of Rotokawa and Ngatamariki, we measure seismic anisotropy across both fields and interpret the results in the context of stress aligned microcracks. Cracks aligned perpendicular to the direction of maximum horizontal stress close and their fluid is forced into cracks aligned with maximum horizontal stress (SHmax). Seismic anisotropy is the directional dependence of a seismic wave's velocity and provides a measure of crack orientation and density. To measure seismic anisotropy we conduct shear wave splitting measurements on 52,000 station-earthquake pairs across both Rotokawa and Ngatamariki from earthquakes recorded during 2015. Both fields are the subject of other geophysical and geological studies. Thus they are excellent subjects for studying seismic anisotropy. We cluster our measurements by their station-event path and fit the parameters from these clusters to those from theoretical crack planes. We also apply 2-D tomography to shear wave splitting time delays (𝛿t) and spatial averaging to shear wave splitting fast polarisations (∅). In addition, we compare time delays with P-wave to S-wave velocity ratios (νP / vS). Local measurements of stress within Rotokawa and regional measures of stress within the Taupo Volcanic Zone provide a comparison for the shear wave splitting measurements. We measure ∅ which agrees with the NE-SW regional direction of SHmax across Ngatamariki and parts of Rotokawa. Within Rotokawa, we observe a rotation of ∅ away from NE-SW toward N-S that agrees with borehole measurements of direction of SHmax of 023° and 030°. Spatial averaging of ∅ reveals mean orientations close to the strike of nearby active faults. The theoretical crack planes, that fit best to the shear wave splitting measurements, correspond to aligned cracks striking 045° outside of both fields, 035° within Ngatamariki, and 035° through to 0° within Rotokawa. The average percent anisotropy for the full dataset, approximately 4%, is close to the upper bound for an intact rock. Delay time tomography shows regions of higher delay time per kilometre of path length (s=km) within both fields and possibly associated with the production field fault in Rotokawa. vP =vS shows a wide range of normally distributed values, from 1.1 through to 2.4 with a mean of 1.6, indicating a mixture of gas filled and saturated cracks. A positive correlation between delay time per kilometre (𝛿tpkm) and νP /νS indicates that the majority of the cracks are saturated.</p>

Download Full-text

Integration of Advanced Borehole Sonic and Resistivity Image Analysis for Fracture and Stress Characterisation - Implications to Carbon Sequestration Feasibility

10.2118/204696-ms ◽

2021 ◽

Author(s):

Debashis Konwar ◽

Abhinab Das ◽

Chandreyi Chatterjee ◽

Fawz Naim ◽

Chandni Mishra ◽

...

Keyword(s):

Wave Attenuation ◽

Horizontal Stress ◽

Open Fractures ◽

Earth Model ◽

Natural Fractures ◽

Mechanical Earth Model ◽

Induced Fractures ◽

Maximum Horizontal Stress ◽

Fracture Stability ◽

Resistivity Image

Abstract Borehole resistivity images and dipole sonic data analysis helps a great deal to identify fractured zones and obtain reasonable estimates of the in-situ stress conditions of geologic formations. Especially when assessing geologic formations for carbon sequestration feasibility, borehole resistivity image and borehole sonic assisted analysis provides answers on presence of fractured zones and stress-state of these fractures. While in deeper formations open fractures would favour carbon storage, in shallower formations, on the other hand, storage integrity would be potentially compromised if these fractures get reactivated, thereby causing induced seismicity due to fluid injection. This paper discusses a methodology adopted to assess the carbon dioxide sequestration feasibility of a formation in the Newark Basin in the United States, using borehole resistivity image(FMI™ Schlumberger) and borehole sonic data (SonicScaner™ Schlumberger). The borehole image was interpreted for the presence of natural and drilling-induced fractures, and also to find the direction of the horizontal stress azimuth from the identified induced fractures. Cross-dipole sonic anisotropy analysis was done to evaluate the presence of intrinsic or stress-based anisotropy in the formation and also to obtain the horizontal stress azimuth. The open or closed nature of natural fractures was deduced from both FMI fracture filling electrical character and the Stoneley reflection wave attenuation from SonicScanner monopole low frequency waveform. The magnitudes of the maximum and minimum horizontal stresses obtained from a 1-Dimensional Mechanical Earth Model were calibrated with stress magnitudes derived from the ‘Integrated Stress Analysis’ approach which takes into account the shear wave radial variation profiles in zones with visible crossover indications of dipole flexural waves. This was followed by a fracture stability analysis in order to identify critically stressed fractures. The borehole resistivity image analysis revealed the presence of abundant natural fractures and microfaults throughout the interval which was also supported by the considerable sonic slowness anisotropy present in those intervals. Stoneley reflected wave attenuation confirmed the openness of some natural fractures identified in the resistivity image. The strike of the natural fractures and microfaults showed an almost NE-SW trend, albeit with considerable variability. The azimuth of maximum horizontal stress obtained in intervals with crossover of dipole flexural waves was also found to be NE-SW in the middle part of the interval, thus coinciding with the overall trend of natural fractures. This might indicate that the stresses in those intervals are also driven by the natural fracture network. However, towards the bottom of the interval, especially from 1255ft-1380ft, where there were indications of drilling induced fractures but no stress-based sonic anisotropy, it was found that that maximum horizontal stress azimuth rotated almost about 30 degrees in orientation to an ESE-WNW trend. The stress magnitudes obtained from the 1D-Mechanical Earth Model and Integrated Stress Analysis approach point to a normal fault stress regime in that interval. The fracture stability analysis indicated some critically stressed open fractures and microfaults, mostly towards the lower intervals of the well section. These critically stressed open fractures and microfaults present at these comparatively shallower depths of the basin point to risks associated with carbon dioxide(CO2) leakage and also to induced seismicity that might result from the injection of CO2 anywhere in or immediately below this interval.

Download Full-text

Fracture detection in a carbonate reservoir using a variety of seismic methods

Geophysics ◽

10.1190/1.1444633 ◽

1999 ◽

Vol 64 (4) ◽

pp. 1266-1276 ◽

Cited By ~ 42

Author(s):

Maria A. Pérez ◽

Vladimir Grechka ◽

Reinaldo J. Michelena

Keyword(s):

Structural Changes ◽

Horizontal Stress ◽

Azimuthal Anisotropy ◽

Carbonate Reservoir ◽

P Wave ◽

Regional Trend ◽

Wave Data ◽

Fracture Orientation ◽

Geological Conditions ◽

Maximum Horizontal Stress

We combine various methods to estimate fracture orientation in a carbonate reservoir located in southwest Venezuela. The methods we apply include the 2-D rotation analysis of 2-D P-S data along three different azimuths, amplitude‐variation‐with‐offset (AVO) of 2-D P-wave data along the same three azimuths, normal‐moveout (NMO) analysis of the same 2-D data, and both 3-D azimuthal AVO and NMO analysis of 3-D P-wave data recorded in the same field. The results of all methods are compared against measures of fracture orientation obtained from Formation microScanner logs recorded at four different locations in the field, regional and local measures of maximum horizontal stress, and the alignment of the major faults that cross the field. P-S data yield fracture orientations that follow the regional trend of the maximum horizontal stress, and are consistent with fracture orientations measured in the wells around the carbonate reservoir. Azimuthal AVO analysis yields a similar regional trend as that obtained from the P-S data, but the resolution is lower. Local variations in fracture orientation derived from 3-D AVO show good correlation with local structural changes. In contrast, due to the influence of a variety of factors, including azimuthal anisotropy and lateral heterogeneity in the overburden, azimuthal NMO analysis over the 3-D P-wave data yields different orientations compared to those obtained by other methods. It is too early to say which particular method is more appropriate and reliable for fracture characterization. The answer will depend on factors that range from local geological conditions to additional costs for acquiring new information.

Download Full-text

Distinguishing between Stress-induced and Structural Anisotropy at Mount Ruapehu Volcano

10.26686/wgtn.13876058 ◽

2021 ◽

Author(s):

J Johnson ◽

Martha Savage ◽

John Townend

Keyword(s):

Shear Wave ◽

Seismic Anisotropy ◽

Horizontal Stress ◽

Structural Features ◽

Spatial Variations ◽

Induced Anisotropy ◽

Structural Anisotropy ◽

Mount Ruapehu ◽

Stress Induced Anisotropy ◽

Maximum Horizontal Stress

We have created a benchmark of spatial variations in shear wave anisotropy around Mount Ruapehu, New Zealand, against which to measure future temporal changes. Anisotropy in the crust is often assumed to be caused by stress-aligned microcracks, and the polarization of the fast quasi-shear wave (φ) is thus interpreted to indicate the direction of maximum horizontal stress, but can also be due to aligned minerals or macroscopic fractures. Changes in seismic anisotropy have been observed following a major eruption in 1995/96 and were attributed to changes in stress from the depressurization of the magmatic system. Three-component broadband seismometers have been deployed to complement the permanent stations that surround Ruapehu, creating a combined network of 34 three-component seismometers. This denser observational network improves the resolution with which spatial variations in seismic anisotropy can be examined. Using an automated shear wave splitting analysis, we examine local earthquakes in 2008. We observe a strong azimuthal dependence of φ and so introduce a spatial averaging technique and two-dimensional tomography of recorded delay times. The anisotropy can be divided into regions in which φ agrees with stress estimations from focal mechanism inversions, suggesting stress-induced anisotropy, and those in which φ is aligned with structural features such as faults, suggesting structural anisotropy. The pattern of anisotropy that is inferred to be stress related cannot be modeled adequately using Coulomb modeling with a dike-like inflation source. We suggest that the stress-induced anisotropy is affected by loading of the volcano and a lithospheric discontinuity. Copyright 2011 by the American Geophysical Union.

Download Full-text

Stress filed data visualization by using earthquake focal mechanism and shear wave splitting results in the Makran region northern Iran

Nexo Revista Científica ◽

10.5377/nexo.v34i02.11570 ◽

2021 ◽

Vol 34 (02) ◽

pp. 825-834

Author(s):

Shahrokh Pourbeyranvand

Keyword(s):

Shear Wave ◽

Data Visualization ◽

Focal Mechanism ◽

Horizontal Stress ◽

Shear Wave Splitting ◽

Northern Iran ◽

Earthquake Focal Mechanism ◽

Study Results ◽

Wave Splitting ◽

Maximum Horizontal Stress

In this study, a new method is introduced for stress data visualization. As an example, the SHmax variations in the Makran region are mapped by using this new approach. Maximum horizontal stress directions in the study area are extracted from earthquake focal mechanism data. The anisotropy study results in terms of shear wave splitting fast direction axes are added to the dataset to show its effect. The results show substantial variation in SHmax directions, which reflects the complicated tectonic nature of the region. Adding the shear wave splitting data improved the results' accuracy and showed the correlation between the two quantities in the study area.

Download Full-text

Investigation on the CBM Extraction Techniques in the Broken-Soft and Low-Permeability Coal Seams in Zhaozhuang Coalmine

Geofluids ◽

10.1155/2021/1163413 ◽

2021 ◽

Vol 2021 ◽

pp. 1-9

Author(s):

Zhaoying Chen ◽

Xuehai Fu ◽

Guofu Li ◽

Jian Shen ◽

Qingling Tian ◽

...

Keyword(s):

Coal Seam ◽

Hydraulic Fracturing ◽

Coalbed Methane ◽

Research Result ◽

Horizontal Stress ◽

Gas Production ◽

Vertical Stress ◽

Low Permeability ◽

Coal Seams

To enhance the coalbed methane (CBM) extraction in broken-soft coal seams, a method of drilling a horizontal well along the roof to hydraulically fracture the coal seam is studied (i.e., HWR-HFC method). We first tested the physical and mechanical properties of the broken-soft and low-permeability (BSLP) coal resourced from Zhaozhuang coalmine. Afterward, the in situ hydraulic fracturing test was conducted in the No. 3 coal seam of Zhaozhuang coalmine. The results show that (1) the top part of the coal seam is fractured coal, and the bottom is fragmented-mylonitic coal with a firmness coefficient value of less than 1.0. (2) In the hydraulic fracturing test of the layered rock-coal specimens in laboratory, the through-type vertical fractures are usually formed if the applied vertical stress is the maximum principal stress and is greater than 4 MPa compared with the maximum horizontal stress. However, horizontal fractures always developed when horizontal stress is the maximum or it is less than 4 MPa compared with vertical stress. (3) The in situ HWR-HFC hydraulic fracturing tests show that the detected maximum daily gas production is 11,000 m3, and the average gas production is about 7000 m3 per day. This implies that the CBM extraction using this method is increased by 50%~100% compared with traditional hydraulic fracturing in BSLP coal seams. The research result could give an indication of CBM developing in the broken-soft and low-permeability coal seams.

Download Full-text

Design of Horizontal Wellbore in Dadas Shales of Turkey by Considering Wellbore Stability and Reservoir Geomechanics

10.2118/202183-ms ◽

2021 ◽

Author(s):

Sukru Merey ◽

Can Polat ◽

Tuna Eren

Keyword(s):

Hydraulic Fracturing ◽

Horizontal Well ◽

Oil And Gas ◽

Horizontal Wells ◽

Horizontal Stress ◽

Wellbore Stability ◽

Horizontal Drilling ◽

Horizontal Wellbore ◽

Reservoir Geomechanics ◽

Maximum Horizontal Stress

Abstract Currently, many horizontal wells are being drilled in Dadas shales of Turkey. Dadas shales have both oil (mostly) and gas potentials. Thus, hydraulic fracturing operations are being held to mobilize hydrocarbons. Up to 1000 m length horizontal wells are drilled for this purpose. However, there is not any study analyzing wellbore stability and reservoir geomechanics in the conditions of Dadas shales. In this study, the directions of horizontal wells, wellbore stability and reservoir geomechanics of Dadas shales were designed by using well log data. In this study, the python code developed by using Kirsch equations was developed. With this python code, it is possible to estimate unconfined compressive strength in along wellbore at different deviations. By analyzing caliper log, density and porosity logs of Dadas shales, vertical stress of Dadas shales was estimated and stress polygon for these shale was prepared in this study. Then, optimum direction of horizontal well was suggested to avoid any wellbore stability problems. According to the results of this study, high stresses are seen in horizontal directions. In this study, it was found that the maximum horizontal stress in almost the direction of North-South. The results of this study revealed that direction of maximum horizontal stress and horizontal well direction fluid affect the wellbore stability significantly. Thus, in this study, better horizontal well design was made for Dadas shales. Currently, Dadas shales are popular in Turkey because of its oil and gas potential so horizontal drilling and hydraulic fracturing operations are being held. However, in literature, there is no study about horizontal wellbore designs for Dadas shales. This study will be novel and provide information about the horizontal drilling design of Dadas shales.

Download Full-text

Seismic azimuthal anisotropy analysis after hydraulic fracturing

Interpretation ◽

10.1190/int-2013-0013.1 ◽

2013 ◽

Vol 1 (2) ◽

pp. SB27-SB36 ◽

Cited By ~ 11

Author(s):

Kui Zhang ◽

Yanxia Guo ◽

Bo Zhang ◽

Amanda M. Trumbo ◽

Kurt J. Marfurt

Keyword(s):

Hydraulic Fracturing ◽

Anisotropy Field ◽

Horizontal Wells ◽

Horizontal Stress ◽

Azimuthal Anisotropy ◽

Barnett Shale ◽

Natural Fractures ◽

Tight Sandstone ◽

Induced Fractures ◽

Maximum Horizontal Stress

Many tight sandstone, limestone, and shale reservoirs require hydraulic fracturing to provide pathways that allow hydrocarbons to reach the well bore. Most of these tight reservoirs are now produced using multiple stages of fracturing through horizontal wells drilled perpendicular to the present-day azimuth of maximum horizontal stress. In a homogeneous media, the induced fractures are thought to propagate perpendicularly to the well, parallel to the azimuth of maximum horizontal stress, thereby efficiently fracturing the rock and draining the reservoir. We evaluated what may be the first anisotropic analysis of a Barnett shale-gas reservoir after extensive hydraulic fracturing and focus on mapping the orientation and intensity of induced fractures and any preexisting factures, with the objective being the identification of reservoir compartmentalization and bypassed pay. The Barnett Shale we studied has near-zero permeability and few if any open natural fractures. We therefore hypothesized that anisotropy is therefore due to the regional northeast–southwest maximum horizontal stress and subsequent hydraulic fracturing. We found the anisotropy to be highly compartmentalized, with the compartment edges being defined by ridges and domes delineated by the most positive principal curvature [Formula: see text]. Microseismic work by others in the same survey indicates that these ridges contain healed natural fractures that form fracture barriers. Mapping such heterogeneous anisotropy field could be critical in planning the location and direction of any future horizontal wells to restimulate the reservoir as production drops.

Download Full-text