Fracture Detection Using Azimuthal P-wave Amplitude Variation with Offset (AVOA) in a Carbonate Reservoir, Khurais Field, Saudi Arabia

(2009) Fracture Detection Using Azimuthal P-wave Amplitude Variation with Offset (AVOA) in a Carbonate Reservoir, Khurais Field, Saudi Arabia. Masters thesis, King Fahd University of Petroleum and Minerals.

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Arabic Abstract

أصبح وصف شقوق المكامن شرطا أساسيا للإدارة المثلى للمكامن البترولية. هذه الدراسه تقدم وصفا للشقوق في مكمن العرب في حقل خريص, المملكه العربيه السعوديه. ولوصف الشقوق تم استشعار الشقوق عن طريق .(Azimuthal Amplitude Variation with offset) " تقنية " تباين مطال الموجه السيزميه هذه الدراسه استعملت البيانات السيزميه آمدخل لحساب اتجاه و حدة الشقوق في المكمن و آمخرج نحصل على خريطتين. الأولى لوصف اتجاهات الشقوق و الثانية لوصف حدة التشقق. البيانات السيزميه المستخدمة تغطي مساحة 300 آيلو متر مربع من حقل خريص. هذه البيانات السيزميه تم تحصيلها و معالجتها بطريقة تلائم .(AVOA) تطبيقات تباين مطال الموجه السيزميه اظهرت امكانية تقسيم اتجاهات الشقوق الى قسمين القسم الاول (AVOA) نتائج التباين مطال الموجه السيزميه موازي لطي حقل الخريص, والقسم الثاني عمودي على اتجاة الطي. أما حدة التشقق فقد تبين من الدراسة اعلى حدية على حافة الطي. وللتحقق من نتائج هذه الدراسه فقد تم استخدام بيانات بتروفيزيائيه من الآبار الموجوده في منطقة الدراسة. و حيث تطابقت و بشكل ,(AVOA) تبين من هذه المقارنه امكانية الاعتماد على التقنية المستخدمه في هذه الدراسه آبير آل من اتجاهات و حدة الشقوق من البيانات السيزمية بتلك من الآبار. بعد تحليل النتائج تبين تأثير السوائل الموجودة في المكمن. أيضا تبين امكانية تأثر النتائج بسماآة متكون العرب. يمكن الاعتماد عليها آوسيلة لوصف شقوق (AVOA) وبالرغم من ذلك فإن تقنية تباين مطال الموجه السيزميه المكامن.

English Abstract

Fracture characterization has increasingly become an essential requirement for optimum management of hydrocarbon reservoirs. And to gain insight into the fracturing that occurs within the Upper Jurassic, Arab-D carbonate reservoir of Khurais field, seismic anisotropy, which is presumably induced due to the presence of vertically aligned fractures, is investigated. In order to practically infer fracture orientations and anisotropy magnitude, the azimuthal P-wave amplitude variation with offset (AVOA) technique is applied. In this case study, the AVOA technique is applied using an input of non-migrated 3D pre-stack seismic data acquired over the western flank of the Khurais field, Saudi Arabia, with a total study area of approximately 300 km2. The seismic data were acquired with wide-azimuth survey parameters that allowed for a uniform amplitude sampling of the Arab-D along all azimuths within a maximum offset of 1800 meters. This maximum offset allows for a reliable AVOA analysis since the depth of the Arab-D reservoir inside of the study area does not go below 1700 meters. Furthermore, the seismic data used for this study were previously processed in a flow that is designed to include only processes appropriate for AVOA analysis including surface consistent amplitude gain and deconvolution. And for this case study, the pre-stack common midpoint (CMP) gathers are binned into 4 by 4 super-gathers. To infer fracture parameters, the ellipse-fitting method of Grechka and Tsvankin (1998) is used to calculate both the fracture-induced anisotropy orientation, and also anisotropy magnitude (fracture intensity). AVOA analysis results indicate that the inferred fracture orientations, in this case study, can be clustered into two dominant orientations. The first dominant orientation is parallel to axis of the Khurais fold structure (North-South). The second dominant orientation of fractures is East-West which is perpendicular to the fold axis and in the direction of the established regional stress field. Such results followed very closely the fracture orientations obtained from available borehole image logs acquired in four horizontal wells. The orientation trends are also consistent with the structural geology studies conducted for the Khurais field using post-stack seismic data, image logs, kinematic models, and core analyses. AVOA results also show higher magnitude of fracture-induced anisotropy (fracture intensity) along the fold hinge zone and the fold forelimb but relatively lower intensities over the backlimb of the fold. Such trend is confirmed by the loss of circulation trends encountered by the horizontal wells drilled within the study area, and also by the structural geology studies conducted for the Khurais field. In this case study, it is observed that the fracture-fluid content as well as bed thickness variation (tuning) appears to have an effect on the anisotropy magnitude. Although there are no available deterministic relationships to relate anisotropy magnitude with neither fluid-content or bed thickness, however, such observations were noted previously in AVOA related literature. Overall, the AVOA results obtained using the ellipse fitting approach proved to be a reliable source of information for mapping subsurface fractures when the input seismic data are properly acquired and processed. Master of Science Degree King Fahad University of Petroleum and Minerals Dhahran, Saudi Arabia July 2009

Item Type: Thesis (Masters)
Subjects: Earth Sciences
Divisions: College Of Sciences > Earth Sciences Dept
Committee Advisor: Al-Shuhail, Abdullatif A.
Committee Members: Al-Shuhail, Abdullatif A. and Hariri, Mustafa and Al-Dajani, Abdulfattah
Depositing User: HADI M BALHARETH (g200301230)
Date Deposited: 05 Oct 2009 13:27
Last Modified: 01 Nov 2019 17:11