Petrophysical Characteristics and Reservoir Modeling of Mishirf Formation at Noor Oil Field, South of Iraq

Petrophysical properties of the Mishrif reservoir at Noor oil field have been done. Based on the interpretation of the open hole data from wells (No-1, 2, 3, 4, and 5) . Which have been calculated total porosity, effective and secondary porosity, water and hydrocarbon saturation (moveable and residual hydrocarbon) in invaded and uninvaded zones. Depends on the calculated of petrophysical properties, Mishrif Formation can be divided into eight reservoir units (RU-1 to 8), separated by eight caped rock units (barrier) (Bar-1 to Bar8). Threedimensional reservoir model of oil saturation was constructed using the Petrel Software, (2009). Distribution of these petrophysical properties for each reservoir unit within the studied field has been done. The results showed that the best reservoir units are the second, fourth and first reservoir unit. It’s worth mentioned here that the heterogeneity of the thicknesses of these units and its individual direction. In addition, observed that the oil saturation increases towards the north of the field at the well (No-5) and the center of the field at the well (No-4). Introduction Mishrif Formation represents one of the important Cretaceous formations. As distinguished by its lithological and geographic spread makes it a good storage of hydrocarbons. It is the second oil storage after the Zubair Formation in southern Iraq (AlNaqib, 1967). As well as the importance it represents a unique lithological architectural derivative of multi-environments within a shallow shelf. Stratigraphic succession of Mishrif Formation at study wells shows that this formation deposits between the ages of (Late CenomanianEarly Turonian). Rabanit (1952) was first describing of this formation at type section in a well (Zb-3) in southern Iraq. Where the deposition of this formation gradually within environmental from the outer shelf to shallow No.13 Journal of Petroleum Research & Studies (JPR&S) E211 open shelf environments at the lower part of the formation, whereas, organic reefal complex deposited at the middle part, the upper part deposits under restricted lagoon environment condition (Razoian, 1995). The study area represented by five oil wells within the field (No-1, 2, 3, 4, and 5) note that the well (No-4) is not fully penetrated of drilling to study formation. The field is located in the province of Amara. Structural map on top of Mishrif Formation indicated that the dimensions of the field are about 20 km long and 7.5 km wide. The axis of structure extend to northwest – southeast direction, and it turned out that dip slope of the north-east flank approximately (2°), either southwest flank has reached the degree of inclination of about (1.5 °) (Figure 1). Mishrif Formation lays gradually contact with Rumaila Formation from the bottom and the unconformable contact with Khasib Formation at the top. The main goal of the study to determine petrophysical properties of Mishrif reservoir units in Noor oil field and detailed review of the most important petrophysical properties to clarify their changes vertically and laterally within the wells by using programs (Techlog and Petrel). Fig.(1) Structural contour map on top of Mishrif Formation at Noor Oil Field. No.13 Journal of Petroleum Research & Studies (JPR&S) E212 Research methods 1 Petrophysical characteristics have been calculated through the use of open hole logs, such as (Gamma Ray (GR), Neutron (NPHI), Density (RHOB), Sonic, Shallow and Deep Resistivity Logs (Rxo and Rt). 2 Mishrif rocks was divided into reservoir units and other unreservoir units dependent on the results of petrophysical properties account for (Computer Processes Interpretation (CPI)) using the program (Techlog). 3 Reservoir characteristics for reservoir units within the wells of the field were done by use the Petrel Software (2009). Petrophysical parameters 1Calculated of shale volume Gamma ray log is the best tool using to identify and calculate the volume of shale. Because of its so sensitive to the response of radioactive material. This tool concentrates on the appearance of shale and argillaceous carbonate rocks. Calculated of shale volume in the following equation: . (1) Where: IGR: Coefficient of gamma rays index. GRLog: read the gamma rays of the formation. GRmin: minimum gamma rays read opposite clean layers. GRmax: maximum gamma rays read opposite shale layers. It is then calculating the volume of shale (Vsh) using the following equation: No.13 Journal of Petroleum Research & Studies (JPR&S) E213 . (2) Depends on the percentage of the shale volume extracted from previous equation (2) for studied wells were identified free shale zones (clean zone), which is by the volume of shale less than (Vsh <% 10) and zones containing volume shale large from (Vsh ≥% 10) as shally zone (no clean zone). 2Calculation of porosity: Porosity can be divided into two classes depends on the time of their formation. The first class represents initial porosity (primary porosity) and the second represents a porous secondary (secondary porosity). There are several methods of calculation of porosity; it is possible to calculate the primary porosity of the sonic log, as in equation Wyllie et al. (1958) which are used in the depths of the shale-free (clean Zone): . (3) Where: ØS: porosity calculated from sonic log. ∆t log: Full-wave interval of the formation and registration of the log is measured directly (μsec/ ft). ∆t ma: wave interval transit thought matrix (47.5 μsec/ ft to limestone rocks). ∆tf: wave interval transit thought the pore fluid (185 μsec/ ft to saline water). But in the depths that exceed Shale volume by about (10%), a zones bearing shale (Shally zone) are used equation (Dresser Atlas, 1979) to remove the effect of shale and correct, as in the following equation: . (4) Where: ∆t sh : Full-wave interval of the adjacent shale. No.13 Journal of Petroleum Research & Studies (JPR&S) E214 To correct the effect of hydrocarbons are used equation Hilchie, (1978):