International Journal of Advanced Engineering Research and Science (IJAERS) [Vol-4, Issue-11, Nov- 2017] https://dx.doi.org/10.22161/ijaers.4.11.9 ISSN: 2349-6495(P) | 2456-1908(O) www.ijaers.com Page | 62 Seismic Study at Subba Oil Field Applying Seismic Velocity Analysis Nawal Abed Al-Ridha 1 , Zahraa Shakir Jassim 2 Department of Geology, College of Science, University of Baghdad, Baghdad. Iraq Abstract— This research is seismic interpretation of two- dimensional seismic data from oil exploration company in Subba oil field. The field data process for the purpose of interpretation, synthetic seismogram was done for the well (Su-7) by using the sonic log and seismic velocity, where the seismic reflectors were picked up (Nhr Umr, Shuaiba, Zubair and Ratawi). Time and depth maps were prepared, showing convex structure with a north-south axis in the center of the study area, with two main dome at northern and southern of the study area. Velocity model from which velocity maps (Average velocity, and interval velocity) were drawn. Seismic inversion technique is used to shows the units within Formations and delineate the increase or decrease of porosity in the Nhr Umr and Zubair Formations. Keywords— Velocity analysis, Seismic attribute, Subba oil field. I. INTRODUCTION The geophysical techniques that most widely employed for exploration are the seismic, gravity, magnetic, electric, and electromagnetic methods. Less common method involves the measurement of radioactivity and temperature at or near the Earth's surface and in the air [1]. The reflection method is depending on the study of the elastic waves reflected from the interface between two geological layers. The reflection method is used exclusively for petroleum prospecting; it is more suitable in areas where the oil is in structural traps, but also it is useful for locating and detailing certain types of stratigraphic features [2], reflection technique measures the arrival time of seismic wave to travel from a source at the Earth's surface down into the ground where it's reflected back to a receiver which is located near the surface. The seismic wave can be generated on the ground by a near-surface explosion of dynamite, weight dropping and vibrate [3]. The studied area is located south Iraq between provinces of Basra, Dhi Qar and Almuthanna, as shown in Figure (1). The aim of this research is using velocity model and maps (vertical and horizontal average velocity slices) to show variation of seismic velocities, acoustic impedance and total porosity for Nahr Umr and Zubair Formations. Fig.1: Location map of study Area (Subba field ) II. DATA PROCESSING Geophysical data processing is the use of computers for the analysis of geophysical data. a major task in geophysics is to determine as much as possible about the constitution of the interior of the earth, [4]. we will explain how to obtain the field data used and how to process this data. Processing steps: 1. Reformat applications: Field data are recorded in a multiplexed mode using a certain type of format [5]. 2. Geometry update: is an update of the field records received from seismic teams in the field by sps file containing the information recorded in the field such as the values of (x , y , elevation and location …). 3. Static up date: is a correction of the delayed waves. and eliminates the effect of differences in earth's surface- level elevations. 4. Gain applications: is a time-variant scaling in which the scaling function is based on a desired criterion 5. Noise attenuation: is classified into two categories, random noise and coherent noise [6], as shown in Figure (2).