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sequential gaussian simulation

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تکرار جستجوی کلیدواژه sequential gaussian simulation در مقالات مجلات علمی
  • Beheshte Nakhaie Sarvedani, Reza Jahanshahi *, Amin Assari
    The Gohar-Zamin mine is located in the southwest of Sirjan city in Kerman province, Iran. Geology condition showed that two fault categories played an important role in the formation of crushed and weathered regions in the southern part of the pit. The spatial analysis of the Lugeon variable indicated that the hydraulic conductivity in the rock mass is very low and the groundwater flow is concentrated only in a limited number of high-transmission main gaps. The mine needs to the designing a proper system for dewatering. Hence, a Gaussian simulation method was used to determine the suitable location of the dewatering wells in the vicinity of the pit. Exploratory spatial data analysis (ESDA) was used to examine location maps, histograms, correlations, and variogram of the Lugeon and RQD data. The relationship between Lugeon and RQD with depth demonstrated that the minimum of RQD and maximum of Lugeon were concentrated in certain elevations. The calculated variograms of RQD and Lugeon showed good spatial continuity. Variograms of the normalized values were performed to carry out the Gaussian simulation of the RQD and Lugeonn variables. Probability and uncertainty maps of RQD and Lugeon indicated that the south-eastern parts of the pit play an important role in permeability.
    Keywords: Permeability, Geostatistics, Lugeon, RQD, sequential Gaussian simulation
  • علی آدیم، محمدعلی ریاحی، مجید باقری *
    برای بهینه سازی تصمیمات حفاری و برنامه ریزی محل چاه ها در مناطق فشار بالا، تخمین فشار منفذی بسیار ضروری می باشد. به عبارت دیگر در مراحل مختلف مهندسی نفت، پیش بینی قابل اعتماد فشار منفذی، قبل از حفاری بسیار مهم می باشد. پیش بینی فشار منفذی، جهت انتخاب مناسب لوله جداری و وزن گل حفاری بسیار مهم می باشد. هدف اصلی این مطالعه تخمین فشار منفذی به روش های ایتون و باورز و مقایسه دقت و کارایی آنها می باشد. جهت دستیابی به این هدف، در روش باورز، محقیقین جهت ارتباط مستقیم بین سرعت و تنش موثر تلاش کردند. یکی از این مدل ها توسط باورز گسترش داده شد. داده های سرعت و چگالی موجود در محل چاه ها با استفاده از تکنیک ترکیبی شبیه سازی گوسی پی در پی و کوکریجینگ هم مختصات، در فواصل بین چاه ها پراکنده شد. سپس با استفاده از رابطه بین سرعت و تنش موثر، مکعب تنش موثر و رابطه بین چگالی و فشار روباره، مکعب فشار روباره تولید می شود. در نتیجه فشار منفذی سازند با توجه به رابطه ترزاقی تخمین زده می شود. در روش دیگر )ایتون( فشار منفذی با استفاده از اطلاعات چاه نگاری با به کار بردن روش پیش بینی ایتون با اصلاحات مورد نظر در محل چاه ها تخمین زده می شود. در این روش، خط روند زمان گذر صوتی با استفاده از روش ژانگ و با توجه به لیتولوژی تقسیم بندی می شود. نتایج این مطالعه، نشان می دهد که فشار منفذی تخمین زده شده به وسیله روش اصلاح شده ایتون با ضریب نمایی 0. 4 بیشترین شباهت را با داده های فشار اندازه گیری شده دارند.
    کلید واژگان: فشار منفذی، روش ایتون، روش باورز، مقاومت صوتی، شبیه سازی گوسی پی درپی، کوکریجینگ هم مختصات
    Ali Adim, Mohammad Ali Riahi, Majid Bagheri*
    Summary: Pore pressure is defined as the pressure of the fluid inside the pore space of the formation that is also known as the formation pressure. When the pore pressure is higher than hydrostatic pressure, it is referred to as overpressure. Knowledge of this pressure is essential for cost-effective drilling, safe well planning, and efficient reservoir modeling. To optimize drilling decisions and well planning in overpressure areas, it is essential to predict pore pressure in the first step. Before drilling, reliable prediction of pore pressure is critically important at different stages of petroleum engineering investigations. Pore pressure prediction has an important application in proper selection of casing and reliable mud weight. Currently pore pressure prediction in carbonate reservoir is still far from satisfaction, and there is no specific method widely accepted. The existing methods and theories in the pore pressure prediction community are almost all based on the shale properties. Although these methods are not the proper way to predict pore pressure in carbonates and may probably lead to dangerous errors, they are still used in the field practice of carbonate reservoirs. Introduction: The generation of abnormal pore pressure in carbonate formation is different from a reservoir to another reservoir because of different depositional and geological conditions. Although most studies currently point out that under-compaction mechanism is the dominant mechanism of abnormal pore pressure generation, the role of this mechanism in carbonate formations needs further study and discussion. Over-pressure can be identified by direct and indirect methods. Direct methods such as measured pressure data obtained from drill stem test (DST), repeat formation tester (RFT), modular dynamic test (MDT) and mud weight, and they are reliable evidences that reflect the over-pressure phenomenon in permeable reservoirs. Methodology and Approaches: Pressure coefficient, which is the ratio of the actual fluid pressure versus corresponding normal hydrostatic pressure at the same depth, has also been proposed and applied to investigate over-pressure. On the contrary, indirect methods, such as well logging, seismic and rock mechanic data, can identify abnormal pressure zones based on various response anomalies compared with the normal pressure system. The main objective of this study is to determine pore pressure using Eaton’s and Bowers’ methods and to compare their accuracy and usage. To obtain this goal in Bowers’ method, researchers try to directly link the formation velocity to the effective stress. One of these models was developed by Bowers (1995). Results and Conclusions: Sonic and density data in the distance between wells have been predicted using a combination of sequential Gaussian simulation and collocated cokriging techniques. Then, effective stress cube and overburden pressure cube have been predicted using velocity to effective stress transform and density to overburden pressure relation. Eventually, formation pore pressure has been predicted using Terzaghi’s method. Another way to estimate pore pressure is used from well logging data by applying Eaton's method (1975) with some modifications. In this way, sonic transient time trend line is separated by lithology changes determined from Zhang’s method. Our results show that the best correlation with the measured pressure data is obtained by the modified Eaton’s method with the Eaton’s exponent of about 0.4. Pore
    Keywords: Pore Pressure , Eaton’s Method , Bowers’ Method , Acoustic Impedance, Sequential Gaussian Simulation , Collocated Cokriging
  • بهشته نخعی سرودانی، رضا جهانشاهی*، امین عصاری
    آبخوان دربرگیرنده پیت معدن گهرزمین از دو بخش آبرفتی و سنگی تشکیل شده است. لایه فوقانی از آبرفت های کواترنری و سازند سخت زیرین عمدتا از سنگ های دگرگونی مربوط به کمپلکس گل گهر ساخته شده است. در سازند سخت، به دلیل وضعیت تکتونیکی منطقه و درزها و شکاف ها و بازشدگی ها، آب های زیرزمینی به سمت پیت معدن تمرکز یافته اند. وجود این آب در پیت معدن، علاوه بر مزاحمتی که در عملیات استخراج ایجاد می کند، سبب ناپایداری دیواره های پیت و ایجاد هزینه های اضافی در عملیات انفجار می شود. بنابراین، ضروری است محل زون های تراوا با استفاده از روش های زمین آمار شناسایی شوند و در طراحی آینده سیستم زهکشی پیت معدن مدنظر قرار گیرند. در این پژوهش روش شبیه سازی زمین آماری گاوسی متوالی جهت نیل به این هدف به کار رفت. تعداد 87 گمانه اکتشافی در لایه متراکم آبرفت کواترنری و سازند سخت موجود است که داده های شاخص کیفیت مغزه حفاری (RQD) از آن ها برداشت شد. در این مطالعه تحلیل اکتشافی مکانی داده ها، شامل بررسی آمار مقدماتی و نقشه موقعیت مکانی و نمودار فراوانی و تغییرنما روی داده های متغیر RQD، انجام شد. بررسی آمار مقدماتی نشان داد این متغیر از توزیع نرمال تبعیت نمی کند. اعمال وزن دکلاسترینگ تاثیر چندانی بر توزیع آماری داده ها نداشت. بنابراین، داده ها با یک تبدیل گاوسی به مقادیر نرمال تبدیل شدند و تغییرنمای بدون جهت و جهت دار مقادیر نرمال متغیر مذکور ترسیم شد. سه جهت Azimuth 0-Dip 0، Azimuth 90- Dip 0، و Dip 90 بهترین پیوستگی مکانی را نشان دادند. این سه جهت با یک دیگر تلفیق شدند و یک مدل واحد به آن ها برازش یافت. بررسی تغییرنمای سه بعدی نشان داد بیشترین پیوستگی مکانی در جهت شرقی غربی نسبت به دو جهت دیگر وجود دارد. در نهایت شبیه سازی گاوسی متوالی متغیر RQD با استفاده از تغییرنمای سه بعدی مقادیر نرمال صورت گرفت و نقشه عدم قطعیت شبیه سازی ها رسم شد. نتایج نشان داد قسمت های جنوب شرقی، جنوب غرب، و غرب پیت بیشترین احتمال وجود زون های تراوا را دارند.
    کلید واژگان: تراوایی، زمین آمار، شبیه سازی گاوسی متوالی، نرم افزار ایساتیس، RQD
    Beheshteh Nakhae Sarvdani, Reza Jahanshahi *, Amin Asari
    In this research, a sequential Gaussian simulation method has been used to determine the permeable zones in the hard-rock aquifer of the Gohr-Zamin open pit mine. For this purpose, 4946 RQD data from eighty-seven exploratory boreholes was used and exploratory-spatial data analysis of these data was performed using the preliminary statistics, location maps, histograms and variograms. Results of preliminary statistics show that this variable has not a normal distribution and that the statistical parameters are not significantly affected considering the declustering weights. The RQD data was transformed to a normal distribution with a Gaussian transform. In the next step, the omnidirectional/directional experimental variograms of RQD data were calculated and modeled using the standard models. Three directions of (1) Azimuth 0-Dip 0, (2) Azimuth 90- Dip 0 and (3) Dip 90 show the best spatial continuity. These variograms were combined together in a one single model. The highest spatial continuity is in the east-west direction compared to the other two directions. Finally, the sequential Gaussian simulation of RQD variable was performed using the 3D modeled variogram and normalized data. A probability map was generated using the results of 100 simultaions. Results show that the southeastern, southwest, and western parts of the mine pit are the best places for drilling new pumping wells.
    Introduction
    Gohar-Zamin iron ore mine is located in 50 km southwest of Sirjan city in Kerman province. Due to the tectonic condition, fracture and fissure in the hard-rock aquifer of area, the groundwater has been concentrated on the pit mine. Therefore, identifying the permeable zones is essential to mine dewatering process.
    Materials and methods
    In this research, ISATIS software has been used to sequential Gaussian geostatistical simulation. The exploratory-spatial data analysis was performed including preliminary statistics, location map, histogram and variograms of RQD values. Then the cell declustring method is used to decluster the RQD variable. Moreover, Gaussian transform method is applied to data normalization. In order to investigate the spatial continuity of the RQD variable, the omnidirectional and directional variograms were generated. Finally, sequential Gaussian simulation as well as simulation uncertainty analysis have been performed using three-dimensional variograms of the RQD normal values.
    Results and discussion
    It is clear from the indicator maps that high RQD values are concentrated in the south of pit and deeper levels. It is influenced by the shape of the iron ore deposit. According to the value of skewness and kurtosis coefficients of RQD, it seems that this variable do not has the normal distribution. The 3D variogram on the XY, XZ and YZ planes indicate (a) lower spatial continuity in the north-south direction relative to the east-west direction, (b) spatial continuity in the eastern-western axis is greater than the Z axis and (c) spatial continuity in the Y direction is greater than the Z direction. The final floor level in the pit is very important for designing and determining the position of pumping wells to dewatering process. Therefore, results of 100 simulations were overplayed. The mean values of simulations calculated from the final floor level in the pit to the top of hard-rock aquifer. It was observed that at each elevation, minimum of RQD were concentrated in certain regions. These maps can be used to determine the high permeable zone.
    Also, two main strike-slip faults with an almost NW-SE and E-W trend, pass through the southern part of pit. These fults and crush zones are located almost in the same direction.
    Conclusion
    According to the results of study, the RQD variable does not follow the standard distribution and declustering weight on the data did not have much effect on the mean value. It indicats a fairly uniform distribution of RQD data in the study area. Omindirectional and directional variograms of the RQD variable (normal values) showed that this variable has good spatial continuity. Moreover, the three-dimensional variogram of the RQD indicated that the E-W direction has the highest spatial continuity relative to the two N-S and Z directions. While, the spatial continuity in the N-S direction is more than the spatial continuity in Z direction. Results showed two straight-slip faults with NW-SE and E-W trends are located in the south of pit and These have important role in greating the crushed and permeable zones. Sequential Gaussian simulation and uncertainty maps in various parts of the pit showed that regions of southeast, southwest, and west of the pit have the highest probability is the low RQD and the high permeability.
    Keywords: Permeability, Geostatistics, RQD, Sequential Gaussian Simulation, ISATIS software
  • شیما سلیمانی، امید اصغری، محمدکاظم حفیظی
    مسئله نفوذ آب شور به داخل آب شیرین در مناطق ساحلی، بسیاری از کشورها را نگران کرده است. با توجه به اهمیت تامین منابع آب شیرین در چنین مناطقی و مخاطره موجود در احتمال برخورد چاه های آب حفر شده به زون های آب شور، داشتن مدل سه بعدی دقیقی از نحوه توزیع آب های شور و شیرین حائز اهمیت است. برای دستیابی به چنین مدلی، اندازه گیری های قابل اطمینان و تفسیر های کامل و جامع مورد نیاز است. هدف از این تحقیق، استفاده از روش های زمین آماری برای سه بعدی سازی نتایج تحقیقات مقاومت ویژه و بارز سازی زون های آب شور و شیرین در آبخوان است. داده های مقاومت ویژه ظاهری مورد نیاز در این تحقیق با آرایه شلومبرژه در دشت برازجان بوشهر برداشت شد. پس از تفسیر های صورت گرفته روی داده های اولیه، مقادیر مقاومت ویژه واقعی آبخوان، درحکم ورودی های الگوریتم شبیه سازی پی درپی گاوسی معرفی و داده ها 100 بار شبیه سازی شدند. اعتبارسنجی صورت گرفته روی نتایج نشان می دهد که 100 بار تحقق مقادیر مقاومت ویژه، معتبر هستند. سپس نقشه هایE-type و احتمال مقاومت ویژه آبخوان رسم شد. این نقشه ها مدلی سه بعدی از توزیع مقاومت ویژه واقعی آبخوان و احتمال وجود آب شور و شیرین را نمایش می دهند. مقایسه مدل به دست آمده از شبیه سازی و چاه موجود در منطقه حاکی از تطبیق زیاد مدل با واقعیت است.
    کلید واژگان: ژئوالکتریک، زمین آمار، آب شور و شیرین، شبیه سازی، تغییرنما (واریوگرام)
    S. Soleimani, O. Asghari, M. K. Hafizi
    Saltwater intrusion into freshwater in coastal areas has been a serious concern for many countries. Providing fresh water in some regions is very crucial. In fact، the areas that are prone to encountering salt water zones should be checked meticulously. The preferred method for such investigation is a precise 3-D model of distribution of fresh and salt water In order to reach such a model، reliable measurements and comprehensive resistivity interpretations are needed. The purpose of this study is to use geostatistical simulations in order to provide a 3-D aquifer model from the results of the resistivity studies. This means to delineate the boundary of saltwater and freshwater in the aquifer. Geostatistical simulation provides a robust tool for presentation of the results achieved from interpretation of resistivity data. Geostatistical simulations by assessing the risk and uncertainties regarding the measurements at hand، provides a method for a precise economical study and therefore a more detailed financing and planning scheme. Most of the prediction/estimation methods involve، in some way، an averaging method in which smoothing and reducing the amplitude of fluctuations among their characteristics are happened. However، geostatistical simulation methods are able to reproduce the minor and local differences more precisely than other methods. In other words، the simulation does not reduce the variance of the data so the minimum and maximum values are reproduced. The required data for this study were acquired in Borazjan plane in the Boushehr province، south of Iran. 82 Vertical Electrical Sondage (VES) with Schlumberger array were conducted along with 6 profiles in the Study area. The distance between 2 subsequent measurements are 200 m، and lateral distance between 2 neighbor profiles is 1000 m. Distances between current electrodes (AB) are increased from 1. 5 m to 1000 m. Each logarithmic decade contains 6 different measurements. Direction of survey oriented North-West to South-East in each profile. After the data gathering، with the use of electrical software، apparent resistivity sections are provided. In the next step، data are inverted using a software and the standard curves. The best multi-layered ground for the Earth is obtained. After the interpretation of the initial data، the real resistivity values of the aquifer are introduced to sequential Gaussian simulation algorithm as input data. Regarding the concept of 1D resistivity inversion، those maps and sections are considered important that manifest coherent amplitude of resistivity variations. In this study، those simulations are considered and used that are capable to reproduce coherent amplitude of resistivity values. For this reason، we use Sequential Gaussian Simulation method which includes such a characteristic in nature، for simulation of the aquifer. For this reason، data are normalized into Gaussian distribution. In order to investigate the anisotropy in the region، a directional variography is done; then the best variogram model is chosen using the cross validation test. The anisotropy shows range/sill variations of the variogram in different orientations; thus the variogram is a useful tool for identification the heterogeneities in the investigation area. Using 50 m×50 m×10 m blocks and the sequential Gaussian simulation algorithm، 100 times simulations were performed and 100 realizations were obtained. The simulation results (realizations) are only acceptable when they can reproduce the identical histogram/variogram، which in this case is the histogram and the variogram of the raw data of the aquifer. After the simulation results were validated the E-type map is derived. This map shows the average value simulated for each block by averaging the values of the 100 realizations. This map is a 3-D model of the real resistivity distribution within the aquifer. The increase of the resistivity values can be observed in this map. Among the most important results، obtained from the realizations، are the probability maps. These maps show the probability of exceeding a defined value، and are driven by counting the number of times that the resistivity value of a block has passed a certain resistivity value in the all realizations. In fact، the probability map can be assumed as a good factor for determination of drilling position for freshwater exploitation. Using the probability maps، the freshwater positions can be identified with the probability of 1 or very close to 1. In order to make a comparison between the data of the drilled well which is placed in the farthest distance between the two profiles، and the estimated model، a network was designed by which it was possible to estimate the aquifer resistivity values at the position of the well. The acquired resistivity values، using the Geostatistical simulation within the designed network and the resistivity values in the aquifer in the position of the well، proves the accurate estimation of the model in accordance with the reality of the aquifer.
    Keywords: Geostatistics, Sequential Gaussian simulation, Freshwater, Saltwater, Resistivity, Variogram
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