Seismic azimuthal anisotropy analysis after hydraulic fracturing

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.

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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.

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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.

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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.

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Fracability Evaluation Method and Influencing Factors of the Tight Sandstone Reservoir

Geofluids ◽

10.1155/2021/7092143 ◽

2021 ◽

Vol 2021 ◽

pp. 1-15

Author(s):

Jiageng Liu ◽

Lisha Qu ◽

Ziyi Song ◽

Jing Li ◽

Chen Liu ◽

...

Keyword(s):

Hydraulic Fracturing ◽

Horizontal Stress ◽

High Fracture Toughness ◽

Hydraulic Fractures ◽

Anisotropy Coefficient ◽

Natural Fractures ◽

Fracture Networks ◽

Tight Sandstone ◽

Stress Anisotropy ◽

Sandstone Reservoir

Fracability evaluation is the basis of reservoir fracturing and fracturing zone optimization. The tight sandstone reservoir is characterized by low porosity and low permeability, which requires hydraulic fracturing to improve industrial productivity. In this study, a systematic model was proposed for the fracability evaluation of tight sandstone reservoirs. The rock mechanics tests and sonic tests demonstrated that tight sandstone reservoir is characterized by high brittleness, high fracture toughness, and weak development of natural fractures. Numerical simulation was used to analyze the change of reservoir parameters during hydraulic fracturing and the influence of in situ stress on fracture propagation. The results showed that when the horizontal stress anisotropy coefficient is small, natural fractures may lead hydraulic fractures to change direction, and complex fracture networks are easily formed in the reservoir. The horizontal stress anisotropy coefficient ranges from 0.23 to 0.52, and it is easy to produce fracture networks in the reservoir. A new fracability evaluation model was established based on the analytic hierarchy process (AHP). The fracability of tight sandstone reservoir is characterized by the fracability index (FI) and is divided into three levels. Based on the model, this study carried out fracability evaluation and fracturing zone optimization in the study area, and the microseismic monitoring results verified the accuracy of the model.

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Utilizing Microseismic to Monitor Fracture Geometry in a Horizontal Well in a Tight Sandstone Formation

10.2118/204736-ms ◽

2021 ◽

Author(s):

Abu M. Sani ◽

Hatim S. AlQasim ◽

Rayan A. Alidi

Keyword(s):

Horizontal Well ◽

Fracture Propagation ◽

Horizontal Stress ◽

Height Growth ◽

Tight Sandstone ◽

Fracture Geometry ◽

Fracture Length ◽

Sandstone Formation ◽

Fracture Height ◽

Maximum Horizontal Stress

Abstract This paper presents the use of real-time microseismic (MS) monitoring to understand hydraulic fracturing of a horizontal well drilled in the minimum stress direction within a high-temperature high-pressure (HTHP) tight sandstone formation. The well achieved a reservoir contact of more than 3,500 ft. Careful planning of the monitoring well and treatment well setup enabled capture of high quality MS events resulting in useful information on the regional maximum horizontal stress and offers an understanding of the fracture geometry with respect to clusters and stage spacing in relation to fracture propagation and growth. The maximum horizontal stress based on MS events was found to be different from the expected value with fracture azimuth off by more than 25 degree among the stages. Transverse fracture propagation was observed with overlapping MS events across stages. Upward fracture height growth was dominant in tighter stages. MS fracture length and height in excess of 500 ft and 100 ft, respectively, were created for most of the stages resulting in stimulated volumes that are high. Bigger fracture jobs yielded longer fracture length and were more confined in height growth. MS events fracture lengths and heights were found to be on average 1.36 and 1.30 times, respectively, to those of pressure-match.

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Geomechanical Approach in Classification of Borehole Failures in Fractured Carbonates of Boca De Jaruco Field

10.2118/208065-ms ◽

2021 ◽

Author(s):

Anna Vladimirovna Norkina ◽

Iaroslav Olegovich Simakov ◽

Yuriy Anatoljevich Petrakov ◽

Alexey Evgenjevich Sobolev ◽

Oleg Vladimirovich Petrashov ◽

...

Keyword(s):

Stress State ◽

Horizontal Wells ◽

Horizontal Stress ◽

In Situ Stress ◽

Vertical Wells ◽

Stress Regime ◽

Geophysical Information ◽

The Republic ◽

Maximum Horizontal Stress

Abstract This article is a continuation of the work on geomechanically calculations for optimizing the drilling of horizontal wells into the productive reservoir M at the Boca de Haruco field of the Republic of Cuba, presented in the article SPE-196897. As part of the work, an assessment of the stress state and direction was carried out using geological and geophysical information, an analysis of the pressure behavior during steam injections, cross-dipole acoustics, as well as oriented caliper data in vertical wells. After the completion of the first part of the work, the first horizontal wells were successfully drilled into the M formation. According to the recommendations, additional studies were carried out: core sampling and recording of micro-imager logging in the deviated sections. Presence of wellbore failures at the inclined sections allowed to use the method of inverse in-situ stress modeling based on image logs interpretation. The classification of wellbore failures by micro-imager logging: natural origin and violations of technogenic genesis is carried out. The type of breakout is defined. The result of the work was the determination of the stress state and horizontal stresses direction. In addition, the article is supplemented with the calculation of the maximum horizontal stress through the stress regime identifier factor.

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Improving the efficiency of hydraulic fracturing treatment in CBM reservoirs by stimulating the surrounding natural fracture system

The APPEA Journal ◽

10.1071/aj14028 ◽

2015 ◽

Vol 55 (1) ◽

pp. 351

Author(s):

Alireza Keshavarz ◽

Alexander Badalyan ◽

Raymond Johnson ◽

Pavel Bedrikovetski

Keyword(s):

Hydraulic Fracturing ◽

Mathematical Modelling ◽

Gas Production ◽

Natural Fracture ◽

Productivity Index ◽

Coal Bed ◽

Natural Fractures ◽

Core Flooding ◽

Induced Fractures ◽

Water Gas

A method is proposed for enhancing the conductivity of micro-fractures and cleats around the hydraulically induced fractures in coal bed methane reservoirs. In this technique, placing ultra-fine proppant particles in natural fractures and cleats around hydraulically induced fractures at leak-off conditions keeps the coal cleats open during water-gas production, and this consequently increases the efficiency of hydraulic fracturing treatment. Experimental and mathematical studies for the stimulation of a natural cleat system around the main hydraulic fracture are conducted. In the experimental part, core flooding tests are performed to inject a flow of suspended particles inside the natural fractures of a coal sample. By placing different particle sizes and evaluating the concentration of placed particles, an experimental coefficient is found for optimum proppant placement in which the maximum permeability is achieved after proppant placement. In the mathematical modelling study, a laboratory-based mathematical model for graded proppant placement in naturally fractured rocks around a hydraulically induced fracture is proposed. Derivations of the model include an exponential form of the pressure-permeability dependence and accounts for permeability variation in the non-stimulated zone. The explicit formulae are derived for the well productivity index by including the experimentally found coefficient. Particle placement tests resulted in an almost three-times increase in coal permeability. The laboratory-based mathematical modelling, as performed for the field conditions, shows that the proposed method yields around a six-times increase in the productivity index.

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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.

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THE OTWAY BASIN: EARLY CRETACEOUS RIFTING TO NEOGENE INVERSION

The APPEA Journal ◽

10.1071/aj94031 ◽

1995 ◽

Vol 35 (1) ◽

pp. 494 ◽

Cited By ~ 1

Author(s):

A.J. Buffin ◽

A.J. Sutherland ◽

J.A. Gorski

Keyword(s):

Stress Field ◽

Normal Fault ◽

Horizontal Wells ◽

Horizontal Stress ◽

Natural Fracture ◽

Water Flooding ◽

Hydraulic Fractures ◽

Vertical Wells ◽

Minimum Horizontal Stress ◽

Maximum Horizontal Stress

Borehole breakouts and hydraulic fractures inferred from dipmeter and formation microscanner logs indicate that the minimum horizontal stress (σh) is oriented 035°N in the South Australian sector of the Otway Basin. Density and sonic check-shot log data indicate that vertical stress (σv) increases from approximately 20 MPa at a depth of one km to 44 MPa at two km and 68 MPa at three km. Assuming a normal fault condition (i.e. σy > σH > σh), the magnitude of σh is 75 per cent of the magnitude of the maximum horizontal stress (σH), and the magnitude of σH is close to that of av. Sonic velocity compaction trends for shales suggest that pore pressure is generally near hydrostatic in the Otway Basin.Knowledge of the contemporary stress field has a number of implications for hydrocarbon production and exploration in the basin. Wellbore quality in vertical wells may be improved (breakouts suppressed) by increasing the mud weight to a level below that which induces hydraulic fracture, or other drilling problems related to excessive mud weight. Horizontal wells drilled in the σh direction (035°N/215°N) should be more stable than those drilled in the σH direction, and indeed than vertical wells. In any EOR operations where water flooding promotes hydraulic fracturing, injectors should be aligned in the aH (125°N/305°N) direction, and offset from producers in the orthogonal σh direction. Any deviated/horizontal wells targeting the fractured basement play should be oriented in the σh (035°N/215°N) direction to maximise intersection with this open, natural fracture trend. Hydrocarbon recovery in wells deviated towards 035°N/215°N may also be enhanced by inducing multiple hydraulic fractures along the wellbore.Considering exploration-related issues, faults following the dominant structural trend, sub-parallel to σH orientation, are the most prone to be non-sealing during any episodic build-up of pore pressure. Pre-existing vertical faults striking 080-095°N and 155-170°N are the most prone to at least a component of strike-slip reactivation within the contemporary stress field.

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Lithology-controlled stress variations and pad-scale faults: A case study of hydraulic fracturing in the Woodford Shale, Oklahoma

Geophysics ◽

10.1190/geo2017-0044.1 ◽

2017 ◽

Vol 82 (6) ◽

pp. ID35-ID44 ◽

Cited By ~ 7

Author(s):

Xiaodong Ma ◽

Mark D. Zoback

Keyword(s):

Hydraulic Fracturing ◽

Horizontal Wells ◽

Horizontal Stress ◽

Strike Slip ◽

Woodford Shale ◽

Stress Regime ◽

Component Content ◽

Microseismic Events ◽

Minimum Horizontal Stress ◽

Stress Variations

We have conducted an integrated study to investigate the petrophysical and geomechanical factors controlling the effectiveness of hydraulic fracturing (HF) in four subparallel horizontal wells in the Mississippi Limestone-Woodford Shale (MSSP-WDFD) play in Oklahoma. In two MSSP wells, the minimum horizontal stress [Formula: see text] indicated by the instantaneous shut-in pressures of the HF stages are significantly less than the vertical stress [Formula: see text]. This, combined with observations of drilling-induced tensile fractures in the MSSP in a vertical well at the site, indicates that this formation is in a normal/strike-slip faulting stress regime, consistent with earthquake focal mechanisms and other stress indicators in the area. However, the [Formula: see text] values are systematically higher and vary significantly from stage to stage in two WDFD wells. The stages associated with the abnormally high [Formula: see text] values (close to [Formula: see text]) were associated with little to no proppant placement and a limited number of microseismic events. We used compositional logs to determine the content of compliant components (clay and kerogen). Due to small variations in the trajectories of the horizontal wells, they penetrated three thin, but compositionally distinct WDFD lithofacies. We found that [Formula: see text] along the WDFD horizontals increases when the stage occurred in a zone with high clay and kerogen content. These variations of [Formula: see text] can be explained by various degrees of viscous stress relaxation, which results in the increase in [Formula: see text] (less stress anisotropy), as the compliant component content increases. The distribution of microseismic events was also affected by normal and strike-slip faults cutting across the wells. The locations of these faults were consistent with unusual lineations of microseismic events and were confirmed by 3D seismic data. Thus, the overall effectiveness of HF stimulation in the WDFD wells at this site was strongly affected the abnormally high HF gradients in clay-rich lithofacies and the presence of preexisting, pad-scale faults.

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