کاربرد لاگ‌های تصویری در‌ بهبود ضریب سیمان‬شدگی مخزن آسماری یکی از میادین نفتی فروافتادگی دزفول‬‬‬‬‬‬‬‬‬‬‬‬‬‬

نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه زمین‌شناسی، دانشکده علوم زمین، دانشگاه خوارزمی، تهران، ایران

2 پژوهشگاه صنعت نفت، تهران، ایران

چکیده

محاسبه دقیق اشباع شدگی، به ضریب سیمان شدگی (m) وابسته است که به­طور رایج به صورت یک عدد ثابت در نظر گرفته میشود. با توجه به ساختار ناهمگون در سنگهای کربناته، استفاده از مقادیر ثابت میتواند منجر به خطای زیادی در محاسبات اشباع سیالات شود. در این پژوهش به منظور بهبود ضریب سیمانشدگی و محاسبه دقیق اشباع آب مخزن کربناته شکافدار آسماری ارزیابی پتروفیزیکی یک بار با دیدگاه مرسوم و با در نظر گرفتن مقدار ثابت برای m و بار دیگر با میزان m متغیر مشخص شده توسط لاگهای تصویری انجام شد. در این راستا ابتدا تفسیر پتروفیزیکی لاگ­های متداول چاه مورد مطالعه با استفاده از مدل Multimin در نرم افزار Geolog صورت پذیرفت. در ادامه داده­های لاگ­های تصویری FMI چاه مذکور برای استخراج پدیده­های مختلف ساختمانی به ویژه شکستگی­ها مورد استفاده قرار گرفت. در نهایت ضریب سیمانی شدگی متغیر با در نظر گرفتن چگالی شکستگی­های زون­های مختلف به دست آمد و ارزیابی پتروفیزیکی مجددا با در نظر گرفتن تاثیر آن صورت گرفت. نتایج ارزیابی پتروفیزیکی نشان داد که میزان و الگوی شکستگی­ها یکی از فاکتورهای مهم کنترل­کننده ضریب سیمان­شدگی مخزن مورد مطالعه هستند. مقایسه نتایج ارزیابی پتروفیزیکی به دو روش مرسوم و روش استفاده از نتایج لاگهای تصویری و تطابق با دادههای مغزه حاکی از آن است که علیرغم تغییرات ضریب سیمانشدگی، تغییرات زیادی بر روی میزان تخلخلهای مخزن آسماری در میدان نفتی مورد مطالعه مشاهده نمیشود. در حالی که تغییرات کمی در ضریب سیمانشدگی، منجر به تغییرات وسیعی در میزان فاکتور اشباع شدگی این مخزن میگردد. 

کلیدواژه‌ها


عنوان مقاله [English]

Application of image logs to improve cementation exponent of the Asmari reservoir in an oilfields of Dezful Embayment

نویسندگان [English]

  • Seyede Nadia Hosseini 1
  • Elham Asadi Mehmandosti 1
  • Farhad Khoshbakht 2
1 Department of Geology, Faculty of Earth Sciences, Kharazmi University, Tehran, Iran
2 Research Institute of Petroleum Industry, Tehran, Iran
چکیده [English]

Introduction
Determination of petrophysical properties is the most important part of hydrocarbon reservoirs characterization. Accordingly, by obtaining total and effective porosity, the volume of shale, and the saturation of the fluids, the reservoir regions are determined. Identification of fluid saturation as a petrophysical characteristic has an important effect in hydrocarbon reservoir studies. The exact calculation of this factor depends on the cementation exponent (m) which is commonly considered as a constant number. Due to the heterogeneous structure of carbonate rocks, the use of constant values can lead to a large error in the fluid saturation calculations.
In this study, in order to improve the cementation exponent and to accurately calculate the saturation of the fractured Asmari reservoir in one of the wells south of Dezful Embayment oilfields, petrophysical, core and image log data (FMI) were used.
Material & Methods
Petrophysical evaluation was performed once with a conventional method, taking into account the constant value for m and again with the variable m value specified by image logs. In this regard, firstly, the petrophysical interpretation of full set logs of the studied well were made, using the Multimin model in Geolog software. Then, the FMI image logs of the well were used to extract various structural phenomena, especially fractures. Finally, the variable cementation exponent was calculated by taking into account the density of fractures of different zones and the petrophysical evaluation was again considered with consideration of its effect.
Results and discussion
Based on image log analysis in studied reservoir, three major fractures, including open and semi-open fractures, filled fractures and breakout fractures -due to borehole collapse- have been identified. These fractures are more commonly observed in the lower part of the Asmari carbonate reservoir in the studied well. Image log analysis showed that with increasing the open and semi-open fractures’ density, variation of cementation exponent also increased. So, the effect of this exponent on petrophysical evaluation is important. Also, the results of petrophysical evaluation showed that the amount and pattern of fractures are important factors controlling the cementation exponent of the studied reservoir. As the fractures increase, the cementation exponent decreases and as a result, the water saturation decreases.
Conclusions
Comparison of petrophysical evaluation with conventional and image log methods and correlation with the core data indicate that despite the changes in cementation exponent, porosities of Asmari reservoir did not change significantly in the studied oil field. On the contrary, small changes in the cementation exponent, can lead to large variations in the saturation factor in this reservoir.
Therefore, the correct estimation of the cementation exponent in each zone is necessary for an accurate estimation of the saturation factor in the reservoirs. Therefore, using image logs to evaluate petrophysical properties in order to improve the evaluation of reservoir quality can be a precise and relatively rapid method in reservoir studies.

کلیدواژه‌ها [English]

  • Petrophysical assessment
  • Water saturation
  • Cementation exponent (m(
  • Image logs
  • Asmari fractured carbonate reservoir.‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬
-چهرازی، ع. و رضایی، م.ر.، 1393. اصول برداشت و تفسیر نگاره­های چاه­پیمایی، انتشارات دانشگاه تهران، 699 ص.
-کاظم زاده، ع.، نبی ­بیدهندی، م.، کرامتی معزآباد، م.، رضایی، م.ر. و سعادت، ک.، 1386. تعیین ضرایب آرچی در پتروفاسیس های متفاوت سنگ­های کربناته با استفاده از لاگ­های انحراف سرعت امواج لرزه­ای، مجله فیزیک زمین و فضا، 33، ص 51-66.
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