Application of Research of the Relationship between Ground Stress and Fractures in the Trajectory Optimization of Horizontal Wells

2013 ◽  
Vol 765-767 ◽  
pp. 300-306
Author(s):  
Hui Zhang ◽  
Fang Jun Ou ◽  
Guo Qing Yin ◽  
Jing Bing Yi ◽  
Fang Yuan ◽  
...  
Keyword(s):  
Stress State ◽  
Stress Field ◽  
Trajectory Optimization ◽  
Horizontal Wells ◽  
Wellbore Stability ◽  
Natural Fracture ◽  
Fracture System ◽  
Well Trajectory ◽  
The Stability ◽  
The Relationship

From the perspective of improving single well production and wellbore stability, stress field and natural fractures are the factors which have to be taken into account in the development of horizontal wells of the complex carbonate oil and gas fields in Kuqa piedmont and platform-basin transitional area. On the one hand, as the present stress field is the key factor to control fracture permeability, the trajectory of horizontal wells should pass through fracture system with good permeability as much as possible, being conducive to the effective stimulation of the reservoir. On the other hand, at the state of specific stress, the stability of well trajectory varies with directions. Therefore, before drilling horizontal wells, it is necessary to fully analyze the quantitative relationship between the present stress state and natural fracture occurrence and mechanical characteristics, etc., to optimize and determine a well trajectory conducive to high yield and wellbore stability. In this study, firstly, the fundamental principles for evaluating the present stress state and analyzing the relationship between the stress and fractures were described. Then based on the relationship between them, the occurrence and longitudinal positions of permeability fractures were analyzed. Apart from that, the stability index and fracture opening pressure distribution of wells in different directions at given stress state and fracture system were also analyzed. Finally, the optimization scheme for trajectory of horizontal wells under complex conditions was discussed with three aspects taken into account, i.e. best drilling in permeability fractures, wellbore stability and drilled reservoir stimulation.

The in-situ stress state of the Rhine-Ruhr region and its implications for the geothermal energy utilization

2020 ◽  
Author(s):  
Michal Kruszewski ◽  
Giordano Montegrossi ◽  
Tobias Backers ◽  
Erik Saenger
Keyword(s):  
Stress State ◽  
Geothermal Energy ◽  
In Situ Stress ◽  
Wellbore Stability ◽  
Energy Utilization ◽  
Natural Fracture ◽  
Electricity Production ◽  
The Future ◽  
Ruhr Region

<p>The Rhine-Ruhr region is one of the largest metropolitan areas in Europe, with more than 10 million inhabitants, located in western Germany. The region is defined by the rich coal-bearing layers from the upper Carboniferous period, extracted as early as the 13<sup>th</sup> century and belonging to the sub-Variscan Trough. In 2018, after more than 700 years of exploration, the last black coal mine was closed in the area. One of the most promising re-uses of the abandoned coal mines is the exploitation of geothermal energy sources. Additionally, to the geothermal energy extracted from existing mines, potential deep geothermal reservoirs within the Rhine-Ruhr, may exist at depths between 4.5 and 6 km, where Devonian limestones were found. Based on the available temperature profiles from deep exploration wells in the area, geothermal gradient amounts to 36.8<sup>o</sup>C/km and results in reservoir temperatures between 170<sup>o</sup>C and 220<sup>o</sup>C, which will enable not only heat but even electricity production. This study provides a comprehensive investigation of the full in-situ stress state tensor with its anisotropy and presents crucial physical formation and natural fracture properties. The data for this investigation was acquired from the extensive borehole logging and geomechanical campaigns carried out in deep coal exploration wells throughout the 1980s as well as from the recent shallow geothermal research wells. Acquired data allowed assessing critically-stressed, i.e. hydraulically active, fractures undergoing shear displacement, being primarily responsible for the future geothermal reservoir permeability. Extensive sets of microseismic, subsidence and drilling data were used to confirm the results of the analysis. Additionally, wellbore stability analysis and potential drill paths for the future medium-to-deep geothermal wells in the region were assessed. This study is a part of the 3D-RuhrMarie project, which aims to assess the intrinsic seismic risk within the Rhine-Ruhr region to promote safer and economically more efficient exploration and exploitation of the future geothermal resources.</p>

THE OTWAY BASIN: EARLY CRETACEOUS RIFTING TO NEOGENE INVERSION

1995 ◽  
Vol 35 (1) ◽  
pp. 494 ◽  
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.

scholarly journals The Research on Influence of Unloading on Borehole Stability in Clay-Rich Shale Formation

2017 ◽  
Vol 10 (1) ◽  
pp. 204-219 ◽  
Author(s):  
Yi Ding ◽  
Xiangjun Liu ◽  
Pingya Luo ◽  
Lixi Liang
Keyword(s):  
Stress State ◽  
Influence Factor ◽  
Wellbore Stability ◽  
Clay Shale ◽  
New Model ◽  
Rock Structure ◽  
Well Trajectory ◽  
Shale Formation ◽  
Mud Pressure

Introduction: Unloading phenomenon happens in the beginning of drilling and is able to change stress state around borehole. This change of stress state causes impact on rock structure and strength, thus affecting the evaluation of wellbore stability. Especially for determining initial mud pressure, unloading is a significant influence factor. Clay-rich shale formation is well-known for high risk of borehole collapsing, appropriate mud pressure is necessary to stabilize wellbore. Therefore, the unloading influence needs to be considered when it comes to selection of initial mud pressure. Materials and Methods: In this paper, based on the triaxial test, unloading situation has been simulated to investigate the influence of unloading on rock mechanical property. It is shown that clay-shale strength declines with increasing unloading range. Also, note that in comparison with internal friction angle, cohesion has larger decline caused by unloading. Results: Taking account of the unloading influence, new model has been established to investigate wellbore stability. These results demonstrate that unloading creates variable strength decrease at the wall of borehole due to different in-situ stress and well trajectory. This strength decrease gives rise to increasing collapse pressure. In particular, unloading has relatively larger impact in the formation with strong anisotropy and high in-situ stress. Besides, inappropriate well trajectory will increase unloading impact. Conclusion: Finally, this model has been applied to several cases in clay-shale formation, Northern China. And the new model in each case is well consistent with oilfield experience, indicating its practicability and proving unloading is a non-negligible factor for the assessment of wellbore stability.

scholarly journals A New Simulation Approach to Model Complex Fracture Networks in the Shale Formation Considering Gas Desorption

2016 ◽  
Author(s):  
Xinfang Ma
Keyword(s):  
Shale Gas ◽  
Horizontal Wells ◽  
Production Performance ◽  
Natural Fracture ◽  
Fracture System ◽  
Gas Reservoir ◽  
Fine Grid ◽  
Stimulated Reservoir Volume ◽  
Shale Gas Reservoir ◽  
Reservoir Volume

Hydraulic fracturing in shale gas reservoirs has usually resulted in complex fracture network. The results of micro-seismic monitoring showed that the nature and degree of fracture complexity must be clearly understood to optimize stimulation design and completion strategy. This is often called stimulated reservoir volume (SRV). In the oil & gas industry, stimulated reservoir volume has made the shale gas exploitation and development so successful, so it is a main technique in shale gas development. The successful exploitation and development of shale gas reservoir has mainly relied on some combined technologies such as horizontal drilling, multi-stage completions, innovative fracturing, and fracture mapping to engineer economic completions. Hydraulic fracturing with large volumes of proppant and fracturing fluids will not only create high conductivity primary fractures but also stimulate adjacent natural fractures. Fracture network forming around every hydraulic fracture yields a stimulated reservoir volume. A model of horizontal wells which was based on a shale gas reservoir after volume fracturing in China was established to analyze the effect of related parameters on the production of multi-fractured horizontal wells in this paper. The adsorbed gas in the shale gas reservoir is simulated by dissolved gas in the immobile oil. The key to simulate SRV is to accurately represent the hydraulic fractures and the induced complex natural fracture system. However, current numerical simulation methods, such as dual porosity modeling, discrete modeling, have the following limitations: 1) time-consuming to set up hydraulic and natural fracture system; 2) large computation time required. In this paper, the shape of the stimulated formation is described by an expanding ellipsoid. Simplified stimulated zones with higher permeability were used to model the hydraulic fracture and the induced complex natural fracture system. In other words, each primary fracture has an enhanced zone, namely SRV zone. This method saves much developing fine-grid time and computing time. Compared with the simulation results of fine-grid reference model, it has shown that this simplified model greatly decreases simulation time and provides accurate results. In order to analyze the impacts of related parameters on production, a series of simulation scenarios and corresponding production performance were designed. Optimal design and analyses of fracturing parameters and the formation parameters have been calculated in this model. Simulation results showed that the number of primary fractures, half length, SRV half-width and drop-down have great effects on the post-fracturing production. Formation anisotropies also control the production performance while the conductivity of the primary fractures and SRV permeability do not have much impact on production performance. The complexity of stimulated reservoir volume has strong effect on gas well productivity. Fracture number mainly affects the early time production performance. The increase of SRV width cannot enlarge the drainage area of the multi-fractured horizontal wells, but it can improve the recovery in its own drainage region. Permeability anisotropies have much effect on production rate, especially the late time production rate. The results prove that horizontal well with volume fracturing plays an irreplaceable role in the development of ultra-low permeability shale gas reservoir.

Infill-Well Fracturing Optimization in Tightly Spaced Horizontal Wells

SPE Journal ◽  
2016 ◽  
Vol 22 (02) ◽  
pp. 582-595 ◽  
Author(s):  
Reza Safari ◽  
Richard Lewis ◽  
Xiaodan Ma ◽  
Uno Mutlu ◽  
Ahmad Ghassemi
Keyword(s):  
Stress State ◽  
Stress Field ◽  
Hydraulic Fracture ◽  
Fracture Propagation ◽  
Horizontal Wells ◽  
In Situ Stress ◽  
Work Flow ◽  
Treatment Schedule ◽  
Reservoir Geomechanics

Summary Cost-effective production from unconventional reservoirs relies on creating new reservoir surface area where fractures are extended into and produce from undepleted zones. Field observations indicate that infill-well fractures could propagate toward nearby producers and depleted zones. This communication between infill and producer wells has been seen to cause casing collapse, and negatively affect current production levels. In this paper, an integrated reservoir/geomechanics/fracture work flow is established to optimize infill-well treatment schedule and to minimize fracture communication between wells. In particular, the paper presents: (i) numerical evaluation of depletion-induced stress changes between tightly spaced producers, (ii) hydraulic-fracture curving in a perturbed stress field, and (iii) hydraulic-fracture communication between wells, and infill-well treatment-design optimization to maximize production. A systematic study of depletion effects and the key parameters that control fracture curving allows us to improve the infill-well fracture design by minimizing the communication between wells while maximizing the hydraulic-fracture extent. Depletion perturbs the in-situ stress tensor in the formation around fractured horizontal wells. The analysis shows that the perturbed-stress field is a function of stress/formation anisotropy, fluid mobility, pore pressure, operating bottomhole pressure (BHP), and Biot's constant. A fracture-propagation model, coupled with the altered in-situ stress field, is used to predict the hydraulic-fracture propagation path(s) and their radius of curvature (i.e., if the stress state dictates that the fractures should curve). The analyses are performed for different infill-well treatment schedule(s), and yield the most-likely fracture geometries (taking into account uncertainties in a shale formation). Resulting infill-well fracture geometries are imported into a reservoir simulator to quantify the production and to identify the optimal design parameters. The coupled work flow (reservoir/geomechanics/fracture) is then applied to a field example to demonstrate the feasibility of its application at the reservoir scale. The results show that (a) infill-well fractures between tightly spaced horizontal wells can intentionally be curved and (b) communication between wells and fracture-coverage area can be controlled by adjusting stimulation parameters to maximize recovery. Forward coupled modeling can be useful in guiding when to drill infill wells before the altered-stress state negatively affects production outcome.

An Experimental Investigation on Thermal Conductivity and Viscosity of Graphene doped CNTs /TiO2 Nanofluid

2020 ◽  
Vol 17 (3) ◽  
Author(s):  
A.M. Zetty Akhtar ◽  
M.M. Rahman ◽  
K. Kadirgama ◽  
M.A. Maleque
Keyword(s):  
Thermal Conductivity ◽  
Zeta Potential ◽  
Base Fluid ◽  
Minimum Quantity Lubrication ◽  
Cutting Fluid ◽  
Cutting Zone ◽  
Observation Method ◽  
The Stability ◽  
The Relationship ◽  
Zeta Potential Analysis

This paper presents the findings of the stability, thermal conductivity and viscosity of CNTs (doped with 10 wt% graphene)- TiO2 hybrid nanofluids under various concentrations. While the usage of cutting fluid in machining operation is necessary for removing the heat generated at the cutting zone, the excessive use of it could lead to environmental and health issue to the operators. Therefore, the minimum quantity lubrication (MQL) to replace the conventional flooding was introduced. The MQL method minimises the usage of cutting fluid as a step to achieve a cleaner environment and sustainable machining. However, the low thermal conductivity of the base fluid in the MQL system caused the insufficient removal of heat generated in the cutting zone. Addition of nanoparticles to the base fluid was then introduced to enhance the performance of cutting fluids. The ethylene glycol used as the base fluid, titanium dioxide (TiO2) and carbon nanotubes (CNTs) nanoparticle mixed to produce nanofluids with concentrations of 0.02 to 0.1 wt.% with an interval of 0.02 wt%. The mixing ratio of TiO2: CNTs was 90:10 and ratio of SDBS (surfactant): CNTs was 10:1. The stability of nanofluid checked using observation method and zeta potential analysis. The thermal conductivity and viscosity of suspension were measured at a temperature range between 30˚C to 70˚C (with increment of 10˚C) to determine the relationship between concentration and temperature on nanofluid’s thermal physical properties. Based on the results obtained, zeta potential value for nanofluid range from -50 to -70 mV indicates a good stability of the suspension. Thermal conductivity of nanofluid increases as an increase of temperature and enhancement ratio is within the range of 1.51 to 4.53 compared to the base fluid. Meanwhile, the viscosity of nanofluid shows decrements with an increase of the temperature remarks significant advantage in pumping power. The developed nanofluid in this study found to be stable with enhanced thermal conductivity and decrease in viscosity, which at once make it possible to be use as nanolubricant in machining operation.

A FORECAST OF PRODUCTIVE LONGEVITY OF HOLSTEIN COWS BY INDIRECT SIGNS

2020 ◽  
Author(s):  
З.С. САНОВА
Keyword(s):  
Correlation Coefficient ◽  
Aging Process ◽  
Direct Relationship ◽  
Stability Index ◽  
Age At First Calving ◽  
Group I ◽  
Predicted Values ◽  
The Stability ◽  
Relationship Of ◽  
The Relationship

В статье представлены материалы о взаимосвязи продолжительности продуктивного использования коров с характеристикой устойчивости к деградации, с возрастом отела и удоем. В исследованной, разнородной по происхождению, группе животных для прогноза продуктивного периода коров, обусловленного устойчивостью к деградации и возрастом первого отела, пригодно уравнение регрессии, аргументами в котором являются индекс устойчивости, возраст первого отела в первой и второй степенях. Коэффициент корреляции межу предсказанными значениями продуктивного периода и его фактическими величинами в I группе составляет 0,502, во II - 0,604. При этом крайние варианты прогнозируются со статистическими ошибками 5 мес при оценке индекса устойчивости по 2 лактациям и 4,1 мес по 3, а средние варианты, соответственно, 1,6 и 1,51 мес. Индекс устойчивости к процессу старения является важной характеристикой биологических особенностей коров, определяющий их продуктивное долголетие. Его оценка по первым 2 и 3 лактациям имеет прямолинейную связь с продуктивным периодом (r=0,4109 и r=0,5270), соответственно. Зависимость продуктивного периода от возраста первого отела криволинейная — с увеличением возраста первого отела сокращается срок продуктивного использования, при возрасте первого отела более 1400 дней срок продуктивного использования колеблется от 1,33 до 1,41 лактации. Коэффициент корреляции между этими характеристиками коров составляет - 0,2164 в I и - 0,2620 во II группах. The article presents materials about the relationship of the duration of productive use of cows with the characteristic of resistance to degradation, with the age of calving and milk yield. In the studied group of animals, which is heterogeneous in origin, the regression equation is suitable for predicting the productive period of cows due to resistance to degradation and the age of the first calving, the arguments of which are the stability index, the age of the first calving in the first and second degrees. The correlation coefficient between the predicted values of the productive period and its actual values in group I is 0.502, in group II - 0.604. At the same time, the extreme variants are predicted with statistical errors of 5 months when evaluating the stability index for 2 lactations and 4.1 months for 3, and the average variants, respectively, are 1.6 and 1.51 months. The index of resistance to the aging process is an important characteristic of the biological characteristics of cows, which determines their productive longevity. Its estimate for the first 2 and 3 lactations has a direct relationship with the productive period (r=0.4109 and r=0.5270), respectively. The dependence of the productive period age at first calving curvilinear with increasing age at first calving reduces the time to productive use, while age at first calving of more than 1400 days, the period of productive use ranges from 1.33 to 1.41 lactation. The correlation coefficient between these characteristics of cows is-0.2164 in I and-0.2620 in II groups.

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