Advancement of Hydraulic Fracture Diagnostics in Unconventional Formations

Multistage hydraulic fracturing is a technique to extract hydrocarbon from tight and unconventional reservoirs. Although big advancements occurred in this field, understanding of the created fractures location, size, complexity, and proppant distribution is in its infancy. This study provides the recent advances in the methods and techniques used to diagnose hydraulic fractures in unconventional formations. These techniques include tracer flowback analysis, fiber optics such as distributed temperature sensing (DTS) and distributed acoustic sensing (DAS), tiltmeters, microseismic monitoring, and diagnostic fracture injection tests (DFIT). These techniques are used to estimate the fracture length, height, width, complexity, azimuth, cluster efficiency, fracture spacing between laterals, and proppant distribution. Each technique has its advantages and limitations, while integrating more than one technique in fracture diagnostics might result in synergies, leading to a more informative fracture description. DFIT analysis is critical and subjected to the interpreter’s understanding of the process and the formation properties. Hence, the applications of machine learning in fracture diagnostics and DFIT analysis were discussed. The current study presents an extensive review and comparison between different multistage fracture diagnostic methods, and their applicability is provided. The advantages and the limitations of each technique were highlighted, and the possible areas of future research were suggested.

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Post Discharge Clinically Overt Venous Thromboembolism in Orthopaedic Surgery Patients with Negative Venography -an Overview Analysis

Thrombosis and Haemostasis ◽

10.1055/s-0038-1650681 ◽

1996 ◽

Vol 76 (06) ◽

pp. 0887-0892 ◽

Cited By ~ 32

Author(s):

Serena Ricotta ◽

Alfonso lorio ◽

Pasquale Parise ◽

Giuseppe G Nenci ◽

Giancarlo Agnelli

Keyword(s):

Venous Thromboembolism ◽

Orthopaedic Surgery ◽

Diagnostic Methods ◽

Future Research ◽

Post Discharge ◽

Pharmacological Prophylaxis ◽

Vein Thrombosis ◽

Overview Analysis ◽

Major Orthopaedic Surgery

SummaryA high incidence of post-discharge venous thromboembolism in orthopaedic surgery patients has been recently reported drawing further attention to the unresolved issue of the optimal duration of the pharmacological prophylaxis. We performed an overview analysis in order to evaluate the incidence of late occurring clinically overt venous thromboembolism in major orthopaedic surgery patients discharged from the hospital with a negative venography and without further pharmacological prophylaxis. We selected the studies published from January 1974 to December 1995 on the prophylaxis of venous thromboembolism after major orthopaedic surgery fulfilling the following criteria: 1) adoption of pharmacological prophylaxis, 2) performing of a bilateral venography before discharge, 3) interruption of pharmacological prophylaxis at discharge in patients with negative venography, and 4) post-discharge follow-up of the patients for at least four weeks. Out of 31 identified studies, 13 fulfilled the overview criteria. The total number of evaluated patients was 4120. An adequate venography was obtained in 3469 patients (84.1%). In the 2361 patients with negative venography (68.1%), 30 episodes of symptomatic venous thromboembolism after hospital discharge were reported with a resulting cumulative incidence of 1.27% (95% C.I. 0.82-1.72) and a weighted mean incidence of 1.52% (95% C.I. 1.05-1.95). Six cases of pulmonary embolism were reported. Our overview showed a low incidence of clinically overt venous thromboembolism at follow-up in major orthopaedic surgery patients discharged with negative venography. Extending pharmacological prophylaxis in these patients does not appear to be justified. Venous thrombi leading to hospital re-admission are likely to be present but asymptomatic at the time of discharge. Future research should be directed toward improving the accuracy of non invasive diagnostic methods in order to replace venography in the screening of asymptomatic post-operative deep vein thrombosis.

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The Effect of Perforation Spacing on the Variation of Stress Shadow

Energies ◽

10.3390/en14134040 ◽

2021 ◽

Vol 14 (13) ◽

pp. 4040

Author(s):

Weige Han ◽

Zhendong Cui ◽

Zhengguo Zhu

Keyword(s):

Compressive Stress ◽

Reservoir Rock ◽

Hydraulic Fractures ◽

Extended Finite Element ◽

Gas Reservoir ◽

Fracture Length ◽

Shadow Effect ◽

Stress Shadow ◽

Initiation Pressure ◽

Small Perforation

When the shale gas reservoir is fractured, stress shadows can cause reorientation of hydraulic fractures and affect the complexity. To reveal the variation of stress shadow with perforation spacing, the numerical model between different perforation spacing was simulated by the extended finite element method (XFEM). The variation of stress shadows was analyzed from the stress of two perforation centers, the fracture path, and the ratio of fracture length to spacing. The simulations showed that the reservoir rock at the two perforation centers is always in a state of compressive stress, and the smaller the perforation spacing, the higher the maximum compressive stress. Moreover, the compressive stress value can directly reflect the size of the stress shadow effect, which changes with the fracture propagation. When the fracture length extends to 2.5 times the perforation spacing, the stress shadow effect is the strongest. In addition, small perforation spacing leads to backward-spreading of hydraulic fractures, and the smaller the perforation spacing, the greater the deflection degree of hydraulic fractures. Additionally, the deflection angle of the fracture decreases with the expansion of the fracture. Furthermore, the perforation spacing has an important influence on the initiation pressure, and the smaller the perforation spacing, the greater the initiation pressure. At the same time, there is also a perforation spacing which minimizes the initiation pressure. However, when the perforation spacing increases to a certain value (the result of this work is about 14 m), the initiation pressure will not change. This study will be useful in guiding the design of programs in simultaneous fracturing.

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Wireless probes for measuring vertical temperature profiles in borehole heat exchangers (BHEs)

10.5194/egusphere-egu21-9948 ◽

2021 ◽

Author(s):

Simon Schüppler ◽

Roman Zorn ◽

Hagen Steger ◽

Philipp Blum

Keyword(s):

Measurement Uncertainty ◽

Fiber Optics ◽

Heat Exchangers ◽

Measurement Errors ◽

High Reliability ◽

Temperature Profiles ◽

Measured Temperature ◽

Distributed Temperature Sensing ◽

Vertical Temperature ◽

Borehole Heat Exchangers

<p>The measurement of the undisturbed ground temperature (UGT) serves to design low-temperature geothermal systems, in particular borehole heat exchangers (BHEs), and to monitor shallow aquifers. Wireless and miniaturized probes such as the Geosniff (GS) measurement sphere, which are characterized by an autarkic energy supply and equipped with pressure and temperature sensors, are increasingly being used for the measurement of highly resolved vertical temperature profiles. The measurement probe sinks along the course of the BHE with a selectable measurement frequency to the bottom of the BHE and is useable for initial measurements as well as long term groundwater monitoring. To ensure quality assurance and further improvement of this emerging technology, the analysis of measurement errors and uncertainties of wireless temperature measurements (WTMs) is indispensable. Thus, we provide an empirical laboratory analysis of random, systematic, and dynamic measurement errors, which lead to the measurement uncertainty of WTMs using the GS as a representative device. We subsequently transfer the analysed uncertainty to measured vertical temperature profiles of the undisturbed ground at a BHE site in Karlsruhe, Germany. The precision and accuracy of 0.011 K and -0.11 K, respectively, ensure a high reliability of the GS measurements. The largest measurement uncertainty is obtained within the first five meters of descent resulting from the thermal time constant &#964; of 4 s. The measured temperature profiles are qualitatively compared with common Distributed Temperature Sensing (DTS) using fiber optic cables and punctual Pt-100 sensors. Wireless probes are also suitable to correct temperature profiles recorded with fiber optics with systematic errors of up to -0.93 K. Various boundary conditions such as the inclination of the BHE pipes or changes of the viscosity and density of the BHE fluid effect the descent rate of the GS of up to 40 %. We additionally provide recommendations for technical implementations of future measurement probes and contribute to an improved understanding and further development of WTMs.</p>

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Hydraulic Fracturing Diagnostics Utilizing Near and Far-Field Distributed Acoustic Sensing DAS Data Correspondences

10.2118/204205-ms ◽

2021 ◽

Author(s):

Yinghui Wu ◽

Robert Hull ◽

Andrew Tucker ◽

Craig Rice ◽

Peter Richter ◽

...

Keyword(s):

Hydraulic Fracture ◽

Near Field ◽

Fracture Propagation ◽

Cost Effective ◽

Hydraulic Fractures ◽

Far Field ◽

Distributed Temperature Sensing ◽

Acoustic Sensing ◽

Distributed Acoustic Sensing ◽

Multiple Fibers

Abstract Distributed fiber-optic sensing (DFOS) has been utilized in unconventional reservoirs for hydraulic fracture efficiency diagnostics for many years. Downhole fiber cables can be permanently installed external to the casing to monitor and measure the uniformity and efficiency of individual clusters and stages during the completion in the near-field wellbore environment. Ideally, a second fiber or multiple fibers can be deployed in offset well(s) to monitor and characterize fracture geometries recorded by fracture-driven interactions or frac-hits in the far-field. Fracture opening and closing, stress shadow creation and relaxation, along with stage isolation can be clearly identified. Most importantly, fracture propagation from the near to far-field can be better understood and correlated. With our current technology, we can deploy cost effective retrievable fibers to record these far-field data. Our objective here is to highlight key data that can be gathered with multiple fibers in a carefully planned well-spacing study and to evaluate and understand the correspondence between far-field and near-field Distributed Acoustic Sensing (DAS) data. In this paper, we present a case study of three adjacent horizontal wells equipped with fiber in the Permian basin. We can correlate the near-field fluid allocation across a stage down to the cluster level to far-field fracture driven interactions (FDIs) with their frac-hit strain intensity. With multiple fibers we can evaluate fracture geometry, the propagation of the hydraulic fractures, changes in the deformation related to completion designs, fracture complexity characterization and then integrate the results with other data to better understand the geomechanical processes between wells. Novel frac-hit corridor (FHC) is introduced to evaluate stage isolation, azimuth, and frac-hit intensity (FHI), which is measured in far-field. Frac design can be evaluated with the correlation from near-field allocation to far-field FHC and FHI. By analyzing multiple treatment and monitor wells, the correspondence can be further calibrated and examined. We observe the far-field FHC and FHI are directly related to the activities of near-field clusters and stages. A leaking plug may directly result in FHC overlapping, gaps and variations in FHI, which also can be correlated to cluster uniformity. A near-far field correspondence can be established to evaluate FHC and FHI behaviors. By utilizing various completion designs and related measurements (e.g. Distributed Temperature Sensing (DTS), gauges, microseismic etc.), optimization can be performed to change the frac design based on far-field and near-field DFOS data based on the Decision Tree Method (DTM). In summary, hydraulic fracture propagation can be better characterized, measured, and understood by deploying multiple fibers across a lease. The correspondence between the far-field measured FHC and FHI can be utilized for completion evaluation and diagnostics. As the observed strain is directly measured, completion engineering and geoscience teams can confidently optimize their understanding of the fracture designs in real-time.

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Novel Near-Wellbore Fracture Diagnosis for Unconventional Wells Using High-Resolution Distributed Strain Sensing during Production

SPE Journal ◽

10.2118/205394-pa ◽

2021 ◽

pp. 1-10

Author(s):

Ge Jin ◽

Gustavo Ugueto ◽

Magdalena Wojtaszek ◽

Artur Guzik ◽

Dana Jurick ◽

...

Keyword(s):

Oil And Gas ◽

Fiber Optic ◽

Fracture Network ◽

Production Performance ◽

Hydraulic Fractures ◽

Fracture Aperture ◽

Strain Sensing ◽

Extensional Strain ◽

Cluster Efficiency ◽

Distributed Strain

Summary The characteristics of hydraulic fractures in the near-wellbore region contain critical information related to the production performance of unconventional wells. We demonstrate a novel application of a fiber-optic-based distributed strain sensing (DSS) technology to measure and characterize near-wellbore fractures and perforation cluster efficiency during production. Distributed fiber-optic-based strain measurements are made based on the frequency shift of the Rayleigh scatter spectrum, which is linearly dependent on strain and temperature changes of the sensing fiber. Strain changes along the wellbore are continuously measured during the shut-in and reopening operations of a well. After removing temperature effects, extensional strain changes can be observed at locations around the perforation cluster during a shut-in period. We interpret that the observed strain changes are caused by near-wellbore fracture aperture changes caused by pressure increases within the near-wellbore fracture network. The depth locations of the measured strain changes correlate well with distributed acoustic sensing (DAS) acoustic intensity measurements that were measured during the stimulation of the well. The shape and magnitude of the strain changes differ significantly between two completion designs in the same well. Different dependencies between strain and borehole pressure can be observed at most of the perforation clusters between the shut-in and reopening periods. We assess that this new type of distributed fiber-optic measurement method can significantly improve understanding of near-wellbore hydraulic fracture characteristics and the relationships between stimulation and production from unconventional oil and gas wells.

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Experience in Optimizing the Location and Parameters of Multistage Hydraulic Fractures for a Multilateral Well Based on Reservoir Simulation

10.2118/206541-ms ◽

2021 ◽

Author(s):

Vil Syrtlanov ◽

Yury Golovatskiy ◽

Konstantin Chistikov ◽

Dmitriy Bormashov

Keyword(s):

Hydraulic Fracturing ◽

Reservoir Simulation ◽

Optimal Placement ◽

Hydraulic Fractures ◽

Low Permeability ◽

Advantages And Disadvantages ◽

Modeling Methods ◽

Multistage Hydraulic Fracturing ◽

Determination Of Parameters

Abstract This work presents the approaches used for the optimal placement and determination of parameters of hydraulic fractures in horizontal and multilateral wells in a low-permeability reservoir using various methods, including 3D modeling. The results of the production rate of a multilateral dualwellbore well are analyzed after the actual hydraulic fracturing performed on the basis of calculations. The advantages and disadvantages of modeling methods are evaluated, recommendations are given to improve the reliability of calculations for models with hydraulic fracturing (HF)/ multistage hydraulic fracturing (MHF).

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Microseismic monitoring using a fibre-optic Distributed Acoustic Sensor (DAS) array

Geophysics ◽

10.1190/geo2019-0752.1 ◽

2020 ◽

pp. 1-48

Author(s):

James P. Verdon ◽

Steve A. Horne ◽

Andrew Clarke ◽

Anna L. Stork ◽

Alan F. Baird ◽

...

Keyword(s):

Time Windows ◽

Microseismic Monitoring ◽

P Wave ◽

Hydraulic Fractures ◽

Fibre Optic ◽

S Wave ◽

Simple Method ◽

Waveform Data ◽

Zero Offset ◽

Optic Array

We present a case study demonstrating the use of an “L”-shaped downhole fibre-optic array to monitor microseismicity. We use a relatively simple method to detect events from continuous waveform data, and develop a workflow for manual event location. Locations are defined with a cylindrical coordinate system, with the horizontal axis of the DAS cable being the axis of symmetry. Events are located using three manual “picks”, constraining (1) the zero-offset “broadside” channel to the event (2) the P-S wave arrival time difference at the broadside channel, and (3) the angle, ? of the event from the array. Because the one-component DAS array is unable to record P-wave energy on the broadside channel, the P-wave pick is made indirectly by ensuring that the modeled P- and S-wave moveout curves match the observed data. The ? angle requires that signal is observed on the vertical part of the array, in our case this is possible because an engineered fiber, rather than standard telecommunications fiber, provided a significant reduction in the noise level. Because only three picks need to be made, our manual approach is significantly more efficient than equivalent manual processing of downhole geophone data, where picks for P- and S-waves must be made for each receiver. We find that the located events define a tight cluster around the injection interval, indicating that this approach provides relatively precise and accurate event locations. A surface microseismic array was also used at this site, which detected significantly fewer events, the locations of which had significantly greater scatter than the DAS array locations. We conclude by examining some other aspects of the DAS microseismic data, including the presence of multiple events within very short time windows, and the presence of converted phases that appear to represent scattering of energy from the hydraulic fractures themselves.

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A new approach to evaluate the performance of partially propped hydraulic fractures

The APPEA Journal ◽

10.1071/aj12030 ◽

2013 ◽

Vol 53 (1) ◽

pp. 355 ◽

Cited By ~ 1

Author(s):

Luiz Bortolan Neto ◽

Aditya Khanna ◽

Andrei Kotousov

Keyword(s):

Sensitivity Study ◽

Economic Benefits ◽

Productivity Index ◽

Hydraulic Fractures ◽

Fracture Geometry ◽

Fracture Conductivity ◽

New Approach ◽

Fracture Length ◽

Compressive Stresses ◽

Initial Fracture

A new approach for evaluating the performance of hydraulic fractures that are partially packed with proppant (propping agent) particles is presented. The residual opening of the partially propped fracture is determined as a function of the initial fracture geometry, the propped length of the fracture, the compressive rock stresses, the elastic properties of the rock, and the compressibility of the proppant pack. A mathematical model for fluid flow towards the fracture is developed, which incorporates the effects of the residual opening profile of the fracture and the high conductivity of the unpropped fracture length. The residual opening profile of the fracture is calculated for a particular case where the proppant pack is nearly rigid and there is no closure of the fracture faces due to the confining (compressive) stresses. A sensitivity study is performed to demonstrate the dependence of the well productivity index on the propped length of the fracture, the proppant pack permeability, and the dimensionless fracture conductivity. The sensitivity study suggests that the residual opening of a fracture has a significant impact on production, and that partially propped fractures can be more productive than fully propped fractures. Application of this new approach can lead to economic benefits.

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Plants that cause photosensitivity in ruminants in Brazil

Semina Ciências Agrárias ◽

10.5433/1679-0359.2016v37n4p2009 ◽

2016 ◽

Vol 37 (4) ◽

pp. 2009 ◽

Cited By ~ 3

Author(s):

Sheila Nogueira Ribeiro Knupp ◽

Leonardo Sidney Knupp ◽

Franklin Riet-Correa ◽

Ricardo Barbosa Lucena

Keyword(s):

Pyrrolizidine Alkaloids ◽

Clinical Signs ◽

Mechanisms Of Action ◽

Diagnostic Methods ◽

Future Research ◽

Steroidal Saponins ◽

Poisonous Plants ◽

Toxic Compounds ◽

Toxic Compound ◽

Ammi Majus

This study aimed to review the mechanisms of action, clinical signs, pathology, and toxic compounds of plants that cause photosensitivity in ruminants. In addition, we sought to clarify the diagnostic methods and prophylaxis of photosensitivity-induced plants. Photosensitizing plants constitute an important group of poisonous plants in Brazil and there are at least seventeen species distributed in nine genera. Some of these plants have well known toxic compounds; in others, the substance responsible for the disease is unknown. In general, the photosensitivity can be classified as primary or secondary. Among the plants causing primary photosensitivity in Brazil, Ammi majus contains furocoumarins, while the compound in Froelichia humboldtiana remains uncertain. The known toxic compounds causing secondary photosensitivity include pyrrolizidine alkaloids, furans sesquiterpenes, triterpenes, and steroidal saponins. In other plants causing secondary photosensitization, including Stryphnodendron spp. and Enterolobium spp., the toxic compound is still unknown. Future research should be conducted in order to determine the various mechanisms of action of each toxic compound to assist the diagnosis of photosensitivity, to develop less toxic or non-toxic cultivars, or even to find new ways of preventing photosensitization.

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