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High-Resolution Stratigraphy and Diagenesis of Upper Khartam Member, Khuff Formation: Implication on Reservoir Quality and Architecture. Outcrop Analog from Central Saudi Arabia

l High-Resolution Stratigraphy and Diagenesis of Upper Khartam Member, Khuff Formation: Implication on Reservoir Quality and Architecture. Outcrop Analog from Central Saudi Arabia. PhD thesis, King Fahd University of Petroleum and Minerals.

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Arabic Abstract

تعرف مكامن الخف في حقول النفط في شرق شبه الجزيرة العربية بعدم التجانس من ناحية التتابع الطبقي وجودة المكمن. عضو الخرطم التابع لتكوين الخف في وسط المملكة العربية السعودية يتيح فرصة جيدة لدراسة عدم التجانس الهندسي وجودة مكامن الخف. تمت دراسة أربعة مواقع بصورة تفصيلية من ناحية الخصائص الرسوبية والطبقية كما تم تحليل المسامية والنفاذية لحوالي 1000 عينة. تم تحديد سبعة عشر سحنة صخرية، يشكل حجر الأوليت الحبيبي, والحجر الجيري المتبلور وحجر الدولوميت النسبة الأكبر من هذه السحنات. هذه السحنات ترسبت في سبع بيئات مختلفة أدت إلى تكوين مكمن معقد من ناحية التتابع الطبقي والشكل الهندسي. من ناحية أخري, عمليات مابعد الترسيب أثرت وبشكل كبير على مسامية ونفاذية هذا المكمن. هذه العمليات تشمل وبصورة كبير عمليات الإذابة والسمنتة والدلمتة والكسور والإستيلوليتس. والأهم من ذلك، أن مسامية ونفاذية طبقات المكمن وعلى امتدادات صغير تتغير وبشكل كبير. هذا التغير عزي لعمليات مابعد الترسيب والتي بدورها أثرت وبشكل تفاضلي على جودة طبقات المكمن. من المعتقد أن الكسور والإستالوليتس هي المتحكم الرئيسي في عمليات التغيير التفاصلي لعمليات مابعد الترسيب حيث أنها لعبت دور القنوات والحواجز لسوائل عمليات التغير. من المتوقع وجود درجة عالية من التشابه بين المماثل السطحي ومكامن الخف، هذا مستدل من طبيعة التتابع والترتيب الطباقي. ولذلك، فإن عضو الخرتم العلوي في وسط المملكة العربية السعودية ربما يمثل تماثلا ممتازاً لمكامن الخف في شرق شبه الجزيرة العربية. وبالتالي، فإن نتائج هذه الدراسة يمكن أن تعزز المعرفه النوعية والتقييمية لمكامن الخف.

English Abstract

The Khuff reservoirs are known for having complex heterogeneities and these were described to occur at inter-well and sub-seismic scale. We therefore studied the high-resolution stratigraphic framework of the Upper Khartam Member of the Khuff reservoirs in outcrop analogues. Four outcrop localities were logged and about 100 representative samples were collected for microfacies, micropaleontology, and porosity and permeability analysis. Furthermore high-resolution photo-mosaics of the outcrops were made. The latter cover an extension of about 7 kms, mostly along dip direction. Centimetre-thick beds are followed laterally and logged for detailed sedimentology and sequence stratigraphy. Seventeen lithofacies were defined, with coarse-grained oolitic grainstone, interlaminated quartz-bearing recrystallized limestone, recrystallized limestone, interlaminated quartz-bearing fine-grained oolitic grainstone, bioclastic grainstone/packstone, and marlstone making up the bulk of the successions. These lithofacies are occurring as sheet-like and channelized bodies. The former range in thicknesses from 5 to 40 cm and possess a lateral extension varying between 5 and 300 m, while channelized bodies have two anatomies, i.e. small tidal creeks (1m in width by 30cm in height) and large tidal channels (3m in width by 50cm in height). Accordingly, seven depositional settings were distinguished, including intertidal-subtidal flats, supratidal settings, intertidal channels and creeks, shoal ridges, reef complex, and outer ramp settings. Four stratigraphic identities were defined, these include; beds, bedset, high-frequency fifth-order sequences, and fourth-order sequences. About 20,000 beds are defined and traced laterally, ranging in thickness from 5 to 40 cm and extending between 5 and 300 m. The beds are stacked into well-developed bedsets composed of a complex internal amalgamation with relatively large lateral extension of several thousand of metre and thickness ranging between 1 and 5 m. These are genetically stacked into six high-frequency sequences with prominent flooding surfaces linked to shifts in shoreline position. The high-frequency sequences likely represent fifth-order cycles and possibly relate to Milankovitch cycles (i.e. eccentricity cycles of 100,000 year). Six major diagenetic processes could be differentiated in the studied outcrops, namely: dissolution, pore lining and pore blocking calcite cementation, dolomitization, fracturing, and stylolitization. Ten porosity types could be differentiated in the studied outcrops, namely: intergranular, intragranular, shelter, dissolution-enlarged, moldic, vuggy, micro-porosity, and porosity in relation to dolomite–dedolomite, dolomite-leaching, and fracture development. The oolitic grainstones of the intertidal sheets, intertidal creeks, and intertidal channels are dominated by dissolution, moldic, and vuggy porosity, whereas intercrystalline and fracture porosity prevails in the recrystallized limestone. The interplayed diagenetic processes have impacted the ultimate reservoir quality. Most critically, reservoir quality of the studied reservoir units along their lateral extension, as defined in their sequence stratigraphic framework, was influenced differentially by diagenesis, which resulted in a lateral segmentation of single bodies into different, hydraulic units. XRD data show a control of certain mineralogical associations (such as SiO2 and SrSO4) on the lateral intermittence of the intra-reservoir body. SEM observations reveal a textural control on porosity and permeability. The differential mold-filling calcite cements of the oolitic grainstones of the intertidal sheets and channels have significantly reduced porosity and permeability. Generally, mineral content has little impact on the reservoir quality, although clay minerals have played a central role in lining the pore space and affecting reservoir quality. Overall, the lateral segmentation most likely was caused by a differential diagenetic evolution, and most critically, this evolution seems to have been controlled by fractures and stylolites which respectively acted as conduits to and barriers for vertical fluid flow and, hence, controlled the differential cementation and dissolution processes. The lithofacies models are critically valid and consistent with the detailed sedimentological and sequence stratigraphic data. The short-scale property heterogeneity models were established. Porosity of intertidal sheets has relatively great horizontal ranges (300 m) compared with the intertidal channels and creeks (150 m). A high degree of similarity is expected between the studied outcrops and the Khuff reservoirs, as inferred from the nature of high-resolution sequence stratigraphy. Therefore, the studied succession of the Upper Khartam Member in central Saudi Arabia is possibly represents an excellent analogue for the Khuff reservoirs in Eastern Arabia. And thus, my results could enhance the quantitative and the qualitative assessment of the Khuff reservoirs heterogeneities



Item Type:Thesis (PhD)
Subjects:Earth Sciences
Divisions:College Of Sciences > Earth Sciences Dept
Committee Advisor:Kaminski, Michael
Committee Co-Advisor:Abdullatif, Osman
Committee Members:Hariri, Mustafa and Abdulraheem, Abdulazeez and Mahmoud, Mohamed
ID Code:140482
Deposited By:AMMAR ADAM (g201104010)
Deposited On:15 Oct 2017 10:14
Last Modified:15 Oct 2017 10:18

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