Fractured Reservoirs Elective I PDF

Fractured Reservoirs Elective I Dr. Mahmoud Badawy Lecturer of Geophysics, and Geo-Modeling Department of Petroleum Engineer, College of Engineering, 1 Almaaqal National University,...

Fractured Reservoirs Elective I Dr. Mahmoud Badawy Lecturer of Geophysics, and Geo-Modeling Department of Petroleum Engineer, College of Engineering, 1 Almaaqal National University, Page Basra, Iraq  Fractured Reservoirs-Elective I Fractures are three-dimensional (3D) features and their distribution, in general, is heterogeneous. Fractures seen in the wellbore can be analyzed to determine aperture and probable production rates. Well logs, in particular imaging logs such as borehole micro-scanners (Formation Micro-Scanner and FMI tools). This kind of study is most successful where the reservoir is formed almost entirely of fracture porosity (as in fractured basement). In general, fractures are important because of their influence on tight reservoirs, not because of their actual oil storage capability. Although fracture volume may be negligible in comparison with the total reservoir volume, they provide an interface with the matrix that is much larger than the borehole. Factors controlling the occurrence of natural, open, permeable fractures include the nature and degree of folding and/or faulting, in-situ stresses and changes in rock properties such as porosity and bedding. Fractures are usually formed during folding or doming of a reservoir, with the most intense fracturing concentrated in low-porosity rocks. In areas where the reservoirs have little matrix permeability fractures are critical to productivity. This is especially true of basement reservoirs where fracture porosity makes up most of the reservoir. 2 Page Dr. Mahmoud Badawy  Fractured Reservoirs-Elective I Borehole imaging and 3D seismic surveys have improved fault mapping, and horizontal wells are providing a new insight into the fracturing associated with reservoir faulting. Fracturing typically occurs in one of two ways, either parallel or perpendicular to normal or reverse faults. Oblique orientations are associated with wrench or shear movements. Fracture density, or the “intensity” of fracturing, is defined as the number of fractures per unit length inside an interval of a defined height. This value must be corrected for the orientation created by changes in angle of the fracture planes and the borehole axis. Fracture orientations can be related to specific geological parameters and structural events. Changes in orientation can be caused by later fault movement associated with variations in tectonic stress through time. Fractures related to faults are much less abundant than fractures related to the folding or doming of a field, but the vertical continuity of faults often results in significant fluid movements through fault-associated fracture systems. Recognizing faults depends on our ability to detect the bedding plane above and below the feature. Natural fractures are usually assumed to have been created by tectonic stresses. They are more common in brittle rocks such as carbonates, igneous and metamorphic rocks than in sandstones and typically occur in specific directions which are dictated by the regional tectonic stresses. 3 Page Dr. Mahmoud Badawy  Fractured Reservoirs-Elective I Large fractures induced-from drilling conditions perpendicular to the direction of borehole enlargement are usually long straight cracks in an axial position on opposite sides of the borehole. These induced cracks are extensional fractures that form and are propagated in front of the bit during drilling. Fractures are often detected while drilling by massive lost circulation, sudden pressure kicks or drilling breaks. High-resolution logs (ideally electrical imaging logs such as the Formation Micro- Scanner or FMI tool) are the best means of describing the fracture geometry. The fracture inclination, θ, and spacing, h, can be determined directly from inspection of the images. The fracture opening or aperture, ε, requires some computation. The main differences between electrical images and acoustic images for this kind of work relate to the resolution and depth of investigation of the measurements. Whereas electrical imagers have a high vertical resolution. 4 Page Dr. Mahmoud Badawy  Fractured Reservoirs-Elective I PROBLEMS: 1- Define fractured reservoirs. 2- Mention the tools used in detecting fractures. 3- What are the important of fractures. 4- Fracture intensity is ……………………………………………………… 5- The most common fractures are exist in ………………… Lithology. 6- True or False: - Fracture related to faults is more abundant than folding ( ) - Fractures induced is horizontal to bit drilling borehole ( ) - Mud circulation can not detect fracture ( ) and mention why? 5 Page Dr. Mahmoud Badawy