بررسی فرونشست زمین در اثر استخراج مواد نفتی با استفاده از روش تداخل سنجی رادار

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشجوی کارشناسی ارشد ژئودزی دانشگاه تهران

2 گروه سنجش از دور / دانشکده مهندسی نقشه برداری و اطلاعات مکانی/ دانشگاه تهران

3 استادیار گروه معدن، دانشکده مهندسی معدن، پردیس دانشکده های فنی، دانشگاه تهران

10.22131/sepehr.2018.31470

چکیده

تولید از مخازن هیدروکربوری، سبب افت فشار منفذی در این مخازن میشود. این افت فشار، تنش ناشی از رسوبات روبارهی سنگ مخزن را که پیش از عملیات برداشت، توسط فشار سیال داخل مخزن و سنگهای پوششی کنترل میشد افزایش داده و موجب تراکم محیط متخلخل اطراف میشود. در صورتی که میزان تراکم مخزن از حدی فراتر رود، سنگهای روباره در اثر وزن خود شروع به فرونشست خواهند کرد که این امر میتواند تأثیرات مخربی از جمله شکستگی چاهها، مچاله شدگی لولههای جداری و خسارات سرچاهی را به دنبال داشته و در نتیجه فرآیند تولید از این مخازن را با مشکل جدی مواجه کند. بنابراین مطالعه پدیدهی فرونشست ناشی از بهرهبرداری منابع هیدروکربوری، حائز اهمیت بوده و نیاز به توجه و بررسی دقیق دارد. برای این منظور روشهای متعددی میتواند مورد استفاده قرار گیرد؛ لذا روشی که دارای سرعت و دقت بالا و هزینهی پایین باشد همواره در اولویت خواهد بود. بدلیل هزینهبر بودن روشهای ترازیابی دقیق و نقشهبرداری زمینی و نیز عدم دسترسی به مشاهدات آنها در برخی شرایط خاص، بکارگیری روشی سریعتر و ارزانتر پیشنهاد میشود. خوشبختانه پیشرفت در زمینهی ماهواره و تکنولوژی رادار باعث شده است که قادر به اندازهگیری جابجاییهایی بسیار کوچک سطح زمین در نواحی مستعد جابجایی از جمله میدانهای تحت برداشت سیالهای زیرسطحی باشیم. روش تداخلسنجی تفاضلی رادار (InSAR) فناوری نوینی است که از تصاویر ماهوارهای جهت آشکارسازی دگرریختی شکل سطح زمین استفاده میکند. در این راستا دو میدان بزرگ نفتی یکی واقع در منطقهی جنوب غربی ایران و دیگری در کالیفرنیای مرکزی توسط تکنیک تداخلسنجی راداری مورد بررسی قرار گرفت. نتایج بدست آمده بیانگر کارایی مناسب این روش به منظور بررسی جابجایی ناشی از فرونشست در میادین مذکور میباشد.

کلیدواژه‌ها


عنوان مقاله [English]

Study of land subsidence due to the oil extraction using Radar Interferometry (InSAR)

نویسندگان [English]

  • narges fatholahi 1
  • Mehdi Akhoondzadeh Hanzaei 2
  • Abbas Bahroudi 3
1 M.Sc. Student, Geodesy Department, School of Surveying and Geospatial Engineering, College of Engineering, University of Tehran
2 Assistant professor, University of Tehran
3 Mining Engineering Faculty, The university of Tehran
چکیده [English]

Extended Abstract
Land subsidence is a vertical movement of the earth surface relative to a stable reference level. It occurs as a result of plate tectonic and human activities. The common causes of subsidence from human activities are pumping under-ground water, oil and gas from overlying reservoirs. Withdrawal of fluids from hydrocarbon reservoirs causes their pressure to decrease. This pressure reduction rises the stress of reservoir’s overburden sediments which was previously controlled by the pressure of inside fluids before exploitation, and consequently increases the density of their porous surroundings. If the reservoir’s density exceeds a specific threshold, overburden rocks start to subside because of their weight. Therefore pressure drawdown leads to reservoir compaction, movement of the overburden and subsidence over the reservoir. This subsidence can prove costly for production and surface facilities. So study of the subsidence caused by hydrocarbon exploitation is an important task which needs precise considerations. Several methods are available to monitor land subsidence. Classical surveying such as Leveling and global positioning system (GPS) can produce some related data whereas they are expensive and cannot also produce the needed map at a particular period of time. Recent advances in satellite and Radar technology have made it possible to measure very small movements of the earth surface. Interferometric Synthetic Aperture Radar (InSAR) is a novel technology for measuring the surface deformation. Using the InSAR technique at relatively large subsidence areas can be monitored. The pros of InSAR are that it is not necessary to physically access the deformation areas and also the high spatial and temporal resolution of its data. Sub-centimeter accuracy has been reported for InSAR derived surface deformations. Interferometric Synthetic Aperture Radar relies on repeated imaging of a given geographic location by space-borne radar platforms. Synthetic Aperture Radar sensors measure both magnitude and phase of the transmitted electromagnetic signal that is backscattered from the earth surface. The phase measurement is used to derive information on heights and deformations of the terrain. This phase represents a combination of the distance scattering effect. If a second SAR data set is collected then from comparing the phase of the second image with the phase of the first, an interferogram can be formed. The basic principle of interferometric SAR is that if the surface characteristics are identical for both images, the phase differences are sensitive to topography and any intrinsic change in position of a given ground reflector. The interferogram can be corrected for topographic information using an external digital elevation model (DEM). The change in distance is along the line of sight to the satellite, preventing it from directly distinguishing vertical and horizontal movement. As geometrical and temporal baseline de-correlations and atmospheric noise are limitation factors to assess slow movements in subsidence areas, recent developments in multi temporal InSAR (MTI) algorithms have enabled the detection and monitoring of the slow deformation with millimetric precision. In this paper, Marun oil field; the second-largest oil field which is located in the south west of Iran has been studied. The Small Base Line Subset (SBAS) approach that is an (InSAR) algorithm has been performed for generating mean deformation velocity map and displacement time series from a data set of subsequently acquired SAR images. SBAS technique identifies coherent pixels with phase stability over a specific observation period which has been implemented in StaMPS software. This method which is based on multiple master interferograms, works with interferograms with small spatial baselines and short temporal intervals to overcome de-correlations by increasing spatial and temporal sampling and coherent areas. For this study, we have used 10 ASAR images acquired by the ENVISAT satellite from European Space Agency (ESA) during 2003 to 2006 and have generated 22 interferograms by the SBAS method. All interferometric processing were implemented using DORIS software. A SRTM Digital Elevation Model (DEM) with 3-arcsecond geographical resolution has been used to remove the topographic phase. SBAS processing was then implemented using the Stanford Method for Persistent Scatterers (StaMPS) software. As a result, the mean velocity map obtained through InSAR time series analysis which is in the Line-Of-Sight (LOS) direction of satellite to the ground. The time series analysis results of InSAR have been then compared with field production data. This sampled data allows us to evaluate potential of non-tectonic effects such as petroleum extraction on surface displacements and the relationship between both deformation and oil production rate. The results of InSAR analysis reveal the maximum subsidence on order of 13/5 mm per year over this field due to the extraction and geological characteristics in the time period of 2003-2006.

کلیدواژه‌ها [English]

  • SAR Interferometry
  • Land Subsidence
  • Withdrawal of Fluids
  • Hydrocarbon reservoir

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