مشروع البحث: DEPOSITONAL ENVIRONMENT PETROGRAPHY AND RESER PROPERTIES OF THE GIALO LIMESTONE GIALO FIELD SIRT BASIN LIBYS
تحميل...
المساهمين
الممولين
رقم التعريف
6938
الباحث
عبد الفتاح علي الزوبي
الوصف
This study investigates the petrography, sedimentology, diagenetic evolution of the Middle Eocene Gialo Formation in the subsurface of the north-central Sirt Basin based on data from core samples from three boreholes in the Assumood and Sahl gas-fields. The reservoir quality of Middle Eocene carbonates in the intracratonic Sirt Basin (at the northern margin of the African continent) is strongly influenced by depositional facies and various diagenetic modifications. This formation is a prolific hydrocarbon-producing unit. Presented in this thesis is a review of the Gialo Formation, an evaluation of the facies and an interpretation of the depositional environment. During this Master project, diagenesis was also evaluated with the aim of better understanding reservoir development of the Gialo Formation. On the basis of detailed core description and petrographic study five facies have been distinguished. These are: (1) Nummulite facies, (2) Discocyclina nummulite facies, (3) Nummulite Operculina Discocyclina facies, (4) Operculina nummulite facies, (5) Operculina facies. These are interpreted as having been deposited in an open-marine, upper mid ramp, lower mid ramp, outer ramp environments. Nummulitie wackestone packstone, dominated by B-forms with minor A-forms, comprise the upper part in mid ramp, and packstone form the lower part of the mid ramp. The type and distribution of the Gialo depositional facies were influenced by basin-floor architecture and environmental controls. Middle ramp facies were deposited across three facies: (1) Upper mid ramp, dominated by Nummulite wackestone/packstone, and Discocyclina nummulitic mudstone. (2) Lower mid-ramp, dominated by nummulitie Operculina Discocyclina wackestone packstone and Operculina nummulite wackestone packstone. (3) outer ramp, dominated by fragmented Operculina mudstone. Present-day reservoir characteristics of the Gialo Formation are the net result of modification to the original depositional characteristics caused by diagenesis processes. This diagenesis took place on the seafloor, under burial, and in the meteoric diagenetic environment. Early marine diagenetic processes affecting the Middle Eocene Gialo carbonates resulted in micritization of bioclasts. Later diagenesis in meteoric to burial environments resulted in dissolution of bioclasts, cementation, pressure dissolution, compaction and fracturing. Generally the porosity in the Gialo sedmnts is either primary or secondary, enhanced by dissolution and fracturing of the sediments. Reduction in porosity in the investigated sediments is mainly due to cementation and compaction. The common pore-types in the Gialo Formation are intergranular, moldic, intragranular, vuggy and scattered fractures. These variations in porosity and permeability are strongly related to facies changes, which were influenced by depositional environment and diagenetic processes.
الكلمات الدالة
DEPOSITONAL ENVIRONMENT PETROGRAPHY AND RESER PROPERTIES OF THE GIALO LIMESTONE GIALO FIELD SIRT BASIN LIBYS