Cambrian-Ordovician and Upper Cretaceous reservoir formations, the primary producing formations in the Sirte Basin, Libya have complex structures which affect the performance of the reservoirs. It is critical to understand the complicated relationships between fault networks, fractures, and stratigraphy of the area for future field development. However, detecting faults especially subtle faults and fractures is a challenging task using conventional seismic data due to the low signal-to-noise ratio. Seismic attributes provide effective tools in identifying and enhancing fault and fracture interpretation beyond the seismic resolution of the conventional seismic data. In this study, we focus on coherence and curvature attributes extracted from the poststack 3D seismic data acquired in the central Sirte Basin to delineate subtle fault and fracture zones. We applied a median filter and spectral whitening to enhance the data quality and remove noise resulted from acquisition and processing effects. We utilized these methods to produce high-resolution data and preserve structural features. A total of 17 faults have been identified in the study area. The most common fractures in the Cambrian-Ordovician reservoir formations are in the northwest and southeast of the field. Seismic data conditioning and seismic attribute analyses applied on the 3-D seismic data effectively increased our understanding of the reservoir complex and help detect and identify subtle faults and fracture zones in the study area.
The Cambrian-Ordovician and Upper Cretaceous formations, which are the main oil-producing formations in the central Sirte Basin, are structurally complex. The lateral and vertical heterogeneity of the reservoir formations is not well-understood, which negatively affects the performance of the reservoirs. We constructed efficient full-field static models that incorporate the lateral and vertical variation of those reservoir formations by integrating geologic and geophysical data. We determined lithology and reservoir properties by selecting appropriate petrophysical techniques that suit the available well data and overcome issues with unreliable well-log measurements. In the process of building structural models, defining and mapping the base of the Cambrian-Ordovician Gargaf Formation was very challenging because wells did not penetrate the basal formation, and the quality of the seismic data decreases with depth. Therefore, we applied techniques of adding isochore maps of the overlying Upper Cretaceous of the Bahi and Waha Formations to map basal contact and determine the thickness of the Gargaf Formation for the first time in the area. The constructed isochore maps showed the thickness variation and the distributions of the Bahi and Waha Formations and explained the influence of Gargaf paleotopography and faults on them. The fault models combined with facies and property models suggested an interconnection among the three main reservoirs. They also indicated that the quality of the Waha reservoir enhances as the lithology varies from limestones to calcareous sandstones, whereas the quality of the Gargaf reservoir was primarily controlled by fractures. The total estimate of the original oil in place with the largest contribution of hydrocarbon volume from the Waha Formation was [Formula: see text] stock tank barrel. The created model with a fine-scale geocellular covering an area of [Formula: see text] is unique to the study area and it can be updated and refined at any time with new data production and drilling activities.
Cambrian-Ordovician and Upper Cretaceous reservoir formations are found in the central western Sirte Basin, the main oil producing region in the Sirte Basin, Libya. As a result of changes in sedimentary environments and structural activities, a number of irregularities in reservoir continuity have developed, which negatively affected the overall performance of the reservoir. Effective simulation of such complex reservoirs can be achieved by integrating geophysical, geological, and petrophysical data to construct a reliable full-field static model, which has the potential to simulate the vertical and lateral variations in the reservoir formations. In this study, 2D and 3D seismic data acquired in central western Sirte Basin are used to construct a fault and structural model which is an important component of the static model. Well data are incorporated with core data to construct a property model that integrates a range of reservoir properties including facies, porosity, permeability, and net-to-gross ratio. A fine-scale geo-cellular model is created by integrating the fault, structural, and property models for the entire field. The model consists of three main zones, which are subdivided into 23 lithologically and petrophysically distinct subzones and are further divided by adding layers to prepare for property distribution. This results in the development of a static model that contains 30.6 million cells. A total of ten facies are identified using well-log and core data and are distributed through the model using sequential index simulation method. Porosity, permeability, and net-to-gross ratio are estimated and distributed through the model using sequential Gaussian simulation method. The total original oil in place for the full field is estimated to be 2.548 × 10 9 STB.
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