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پیش‌بینی فشار منفذی با استفاده از وارون‌سازی و تحلیل سرعت لرزه‌ای | ||
| فیزیک زمین و فضا | ||
| مقاله 5، دوره 38، شماره 4 - شماره پیاپی 1368843، اسفند 1391، صفحه 57-70 اصل مقاله (1.79 M) | ||
| شناسه دیجیتال (DOI): 10.22059/jesphys.2013.30206 | ||
| نویسندگان | ||
| حمیدرضا سلیمانی1؛ محمدرضا سکوتی دیارجان2؛ محمدعلی ریاحی3 | ||
| 1کارشناس ارشد، گروه علوم زمین، دانشگاه شهر نیویورک، ایالات متحده امریکا | ||
| 2کارشناس ارشد تعبیر و تفسیر داده‌های لرزه‌ای، مدیریت اکتشاف، شرکت ملی نفت ایران، تهران، ایران | ||
| 3دانشیار، گروه فیزیک زمین، موسسه ژئوفیزیک دانشگاه تهران، ایران | ||
| چکیده | ||
| فشار منفذی یا فشار شاره درون حفره‌های سنگ، از جمله کمیت‌های مهم در بحث اکتشاف و حفاری منابع نفت و گاز است. وجود فشار منفذی زیاد باعث ایجاد مشکلات عدیده‌ای از جمله فوران چاه، ناپایدار بودن چاه، گیرکردن لوله حفاری و یا از دست دادن چرخش گل حفاری می‌شود. به‌همین‌‌علت به‌نظر می‌رسد که پیش‌بینی عددی فشار منفذی، در سازند‌های با فشار زیاد، قبل از حفاری امری ضروری برای حفاری ایمن و اقتصادی است. همچنین در زمینه اکتشاف می‌توان از مفهوم فشار منفذی در تحلیل و بررسی مسیرهای مهاجرت نفت و در بررسی کیفیت پوش‌سنگ استفاده کرد. در این تحقیق به‌منظور پیش‌بینی کمی فشار منفذی از تبدیل سرعت- فشار منفذی، که با چاه‌های منطقه تنظیم شده، استفاده شده است لذا تولید مکعب سرعت لرزه‌ای مناسب در این تحقیق اهمیت ویژه‌ای دارد. باید توجه داشت که سرعت‌های به‌دست آمده از پردازش داده‌های لرزه‌ای معمولا به‌‌علت کم بودن وضوح و فرض‌های زمین لایه‌ای و برون‌راند هذلولی، دارای دقت کافی برای تحلیل فشار نیست. در تحقیق پیش رو سعی شده است تا با استفاده از داده‌های سرعت برانبارش و وارون‌سازی داده‌های لرزه‌ای، همچنین استفاده از داده‌های نگار سرعت صوتی در چاه‌های منطقه مدل سرعت مناسب بررسی فشار منفذی تولید شود. همچنین برای تبدیل داده‌های سرعت تولید شده به فشار موثر، از رابطه باورز (1995) تنظیم شده با چاه‌های منطقه استفاده شده است. درنهایت نتایج حاصل از اعتبارسنجی حاکی از مناسب بودن مدل فشار منفذی حاصل از این روش است. | ||
| کلیدواژه‌ها | ||
| زمین‌آمار؛ فشار روباره؛ فشارمنفذی؛ فشار هیدرواستاتیک؛ وارون‌سازی | ||
| عنوان مقاله [English] | ||
| Porepressure prediction using seismic inversion and velocity analysis | ||
| نویسندگان [English] | ||
| Hamidreza Soleymani1؛ Mohammadreza Sokooti2؛ Mohammad Ali Riahi3 | ||
| چکیده [English] | ||
| Pore pressure could be estimated prior to drilling using seismic velocities. Applying this approach, the final calculated pore pressure is highly affected by accuracy of the obtained velocity data. In order to generate an accurate velocity cube with proper resolution, velocities from well logs and post-stack 3-D seismic inversion are used along with stacking velocities from velocity analysis of 3-D seismic data. Using Bowers’s effective pressure method (1995), including known velocity and density values at well locations, the coefficients of Bowers’s equation could be calculated. Also, through applying Gardener’s equation, one could relate velocity to density in each well location and finally, it is possible to determine overburden stress for the entire survey. Pore pressure prediction is one of the most important stages in drilling of the new wells. According to Huffman 2002, “pressure prediction at the basin scale can be very powerful in (1) determining where the source rock is actively maturing (2) determining where large scale fluid migration is occurring in a basin (3) predicting the behavior of large regional faults and structures (4) identify the presence of secondary pressure area (5) constraining the porosity model and (6) evaluating the integrity of vertical seal in the basin”. Moreover, pressure information prior to drilling can insure economic advantages for safe drilling. Overpressure is referred to state where the pore fluid pressure exceeds normal hydrostatic pressure at the particular depth. This phenomenon usually results from restriction of the fluid flow due to rapid sedimentation or fluid expansion, which in turn results in increase in pore pressure. Since the pioneer work by Pennebaker (1968), many papers has begun to deals with the pressure prediction prior to drilling. A paper by Dutta (2002) provides a good insight into using seismic based methods and possible pitfalls of using different velocities in estimation of pore fluid pressure. Bowers (1995) suggested an outstanding empirical equation, using data from the Gulf of Mexico which governs the compaction and fluid expansion mechanisms. Since these two mechanisms are the most frequent causes of overpressure, the Bowers’s equation is an appropriate approach in most cases. It is important to note that to obtain the desired accuracy, constants A and B (i.e. the virgin curve parameters) in the Bowers’s equation should be determined using the available data from offset wells in every survey. In the process of pressure estimation, overburden pressure needs to be estimated. Hence, Gardner equation (Gardner et al., 1974) is calibrated by calculating related parameters, using available density and velocity logs. Knowing the velocity and having the calibrated Gardner’s equation in hand, one can calculate the overburden pressure. Moreover, effective pressure can be acquired with acceptable accuracy using calibrated Bowers’s equation. Eventually, porepressure could be estimated using Terzaghi’s equation (Terzaghi, 1943). It should be noted again, generating velocities from processing of 3-D seismic data, rock densities and calibrated Bowers’s equation are crucial steps, through our workflow. The final goal of this paper is to present a proper method to generate and validate the 3-D pore pressure model using conventional data for a large survey at Mansouri oil field (one of the Iranian south west oil fields). It is shown that the accuracy and resolution of the velocity model could be greatly enhanced by using available well logs and a proper geostatistical method. This high resolution velocity model results high resolution pore pressure model which reveals much information concerning reservoir integrity and characterization. The effective pressure is calculated using Bowers’s method which is calibrated using measured pressure data at some well locations and at the end; the porepressure is calculated using Terzaghi’s equation. Studying the final pore pressure map reveals that there are no major pressure anomaly within the Asmari reservoir. In addition, a bizarre looking low pressure anomaly in the beginning of the second segment is not due to a real drop in pressure (base on measured pressure in the well). In fact, this error is introduced due to changes in formation petrology at the reservoir seal. It should be noted that the geological study prior to pressure interpretation is an imperative stage in pressure estimation. Comparison of the predicted pore pressure with the measured pressure at well location which was not included in calibration phase reveals that final pressure estimation is reliable and it is in good agreement with the measured pressure data. The high resolution pressure data is suitable for well planning and provides detailed information on pressure variation along the future well trajectories. The 3-D pore pressure cube, along with effective pressure, overburden pressure and fracture pressures are obtained and used for regional geomechanical and pressure assessments. | ||
| کلیدواژه‌ها [English] | ||
| Effective Stress, Geostatistics, Overburden stress, Pore Pressure, Velocity model | ||
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