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Variation of Porosity and Permeability of Nahr Umr and Yammama Formations in South of Iraq

The study of the project focused on the fields of Nasiriyah in southern Iraq to study porosity and permeability variation between Nahr Umr reservoir and Yamamma reservoir this will be done in two parts, the first one is theoretical which will depends
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  Republic of Iraq Ministry of Higher Education and Scientific Research University of Technology Petroleum Technology Department Variation of Porosity and Permeability in Nahr Umr and Yammama Formations in South of Iraq Dr. Hussain Al-Sudani  Abstract The study of the project focused on the fields of Nasiriyah in southern Iraq to study  porosity and permeability variation between Nahr Umr reservoir and Yamamma reservoir this will be done in two parts, the first one is theoretical which will depends on definition of  petrophysical properties, and the second part is practical which includes using surfer program to draw map and study the variation of these properties (Porosity and Permeability). Finally, the best production reservoirs will be identifying by comparing between these properties. 1. Introduction Engineers typically required an estimation of the rock properties in order to compute oil reserves, production capacity, and recovery efficiency of the reservoir. The rock  properties which are called petrophysical properties are very important because the amount of hydrocarbon present in a reservoir is a function of its petrophysical properties, and these  properties include porosity, permeability and fluid saturation. These properties and their relationships are used to identify and evaluate: hydrocarbon reservoir, hydrocarbon sources, seals, and aquifers. The reservoir and fluid characteristics to be determined are: thickness (bed  boundaries), Lithology (rock type), Porosity, Fluid saturations and pressures, Fluid identification and characterization, Permeability (absolute) and Fractional flow (oil, gas, water). It is easy to define these characteristics and to appreciate their part in the assessment of reserves. The difficult part comes in determining their actual value at a level of certainty needed to make economic decisions leading to development and production. The best source of petrophysical properties data is the well logging technique, which is the primary source of petrophysical evaluation of reservoirs in the oil and gas wells. Well logging define as the technique of making petrophysical properties measurements in the subsurface earth formations through the drilled borehole, in order to determine both the  physical and chemical properties of rocks and the fluid its contain. 2. Aim of Study Comparison of change in petrophysical properties between two rock reservoirs (Nahr Umr and Yammama ) to be oil producing reservoirs and this done by using the available data and formation for several chosen wells within Nasiriyah oilfield. 3. Area of study  Nasiriyah oilfield lies east of the River Euphrates, about 38 kilometers northwest of the city of Nasiriyah [1]. It is around 34 km length and 13 km width at Mishrif surface reflection [2]. The Nasiriyah oil field was investigated by the Iraq National Oil Company (INOC) in 1975. The field is assembled inside the Gharraf axis, which incorporates the undeveloped Gharraf and Rafidain field [3].   Figure (1): location map shows Nasiriyah oilfield [4]. 4. Stratigraphy of Nahr Umr Structure: There are 18 wells drilled in Nahr Umr Structure. The deepest well are (NR1, NR3,  NR7, NR9, NR10 and NR12) and they reached Sulaiy Formation. The Oil is present in many formations, these are from bottom to top: Zubair and Yamama Formation (Early Cretaceous), Mishrif, Nahr Umr (Middle Cretaceous), Sa'di, Khasib (Late Cretaceous). Fatha, Ghar (Early- Middle Miocene).The best reservoirs are Yamama, Zubair, and Mishrif [3]. 4.1 Nahr Umr formation  Nahr Umr Formation widespread throughout the Mesopotamian Zone. The lower Cretaceous sedimentary cycle in Iraq divided into two sub-sedimentary cycles: the first started from the Late Berriasian to the Aptian, the second one is the Alpian which covered  Nahr-Umr and Maudud formations. Nahr-Umr Formation in its type locality consists of black shales, interbeded with medium to fine-grained sands and sands. The depositional environments generally are pro-delta and delta-front which is considered as a deltaic environment affected by sea currents. The average thickness of the formation is about 119 m; the reserved oil is approximately 68 million tons. The porosity ranged from 10 to 23 % and  permeability from 50 to 400 md in the upper part of the formation [5]. 4.2 Yamamma Formation The Yamamma formation, which is a heterogeneous carbonate reservoir, is one of the most important oil production reservoirs in southern Iraq , which was deposited during the lower cretaceous period within the main retrogressive depositional cycle (Berriasian –Aptian) south of Iraq ,and from its stratigraphic position an age of late berriasiam to early valanginian age is expected ,yamama formation contains hydrocarbons at 26 structures in southern Iraq including West Qurna ,North Rumaila and Majnoon fields [5].  5 Petrophysical Properties: Petrophysics is the study of physical rock properties and their contained fluids. It comes from the Greek Petra means "rock" and physic means “nature". The word petophysics was coined by Archie and Thomeer. Petrophysical properties are required for typical reservoir engineering purposes include porosity, permeability, and saturation of liquids. A  procedure for identifying and characterizing petrophysical flow units helps to resolve some of the key challenges faced in exploration and production of carbonate reservoirs. The application of this model shows a key to understand and predict the performance of carbonate reservoirs is to represent them as combinations of different flow units, each of them with uniform pore-throat size distribution and similar performance. If a relationship exists between depositional faces and flow units, one can develop a common geological and engineering zonation [2]. 6. Methodology The research includes two main parts, the first one is theoretical where we collect all information regarding Nahr Umr formation, Yammama formation and the second part of this research is the practical approach where we used information of well logs. The data obtained for each oil well in Nasiriyah oilfield where used to draw several maps using Surfer program with two and three dimensions in order to create a suitable picture of the variation of  petrophysical properties in Nahr Umr and Yammama reservoirs. Surfer is a grid-based mapping program that interpolates irregularly spaced XYZ data into a regularly spaced grid. Grids may also be imported from other sources, such as the United States Geological Survey (USGS). The grid is used to produce different types of maps including contour, vector, image, shaded relief, 3D surface, and 3D wireframe maps. Many gridding and mapping options are available allowing you to produce the map that best represents your data [6]. Figure (2): Surfer software user interface [6].  7. Result and Discussion In this section, the results concluded in the research will be demonstrated and discussed. The wells that are included in this study are (NS-1, NS-2, NS-3, NS-4, NS-5) of  Nasiriyah oilfield which penetrate Nahr Umr Reservoir and Yamamma reservoir. Table (1) and table (2) consists of general information of Nasiriyah oilfield in order to better understand this oilfield and have an overview of the two reservoir and their petrophysical  properties distribution. A horizontal comparison was made between the data of the porosity,  permeability and water saturation for each well to choose the best zone for production of these reservoirs. Table (1) Information and data of Nahr Umr reservoir in Nasiriyah oilfield. X Y Well no. Elevation Thickness all (m) Porosity Permeability all (mD) 596.655 3465.833 NS-1 5.4 117.2 0.200481 131.4576 592.255 3468.133 NS-2 5.5 121.8 0.222641 353.4071 599.155 3467.033 NS-3 5.1 117.8 0.200318 132.142 588.405 3466.508 NS-4 5.53 120.1 0.226024 412.5013 582.755 3470.933 NS-5 5.7 120.6 0.215502 261.1306 Table (2) Information and data of Yamamma reservoir in Nasiriyah oilfield. X Y Well no. Elevation Thickness all (m) Porosity Permeability all (mD) 596.655 3465.833 NS-1 5.4 109.25 0.1445 5.388 592.255 3468.133 NS-2 5.5 106.45 0.1459 5.639 599.155 3467.033 NS-3 5.1 73.31 0.1287 2.921 588.405 3466.508 NS-4 5.53 106.41 0.1504 5.611 582.755 3470.933 NS-5 5.7 97.89 0.1429 4.801 Depending on table (1 and 2), the thickness of Nahr Umr and Yamamma reservoirs was illustrated in figure 3 and 4.
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