JOURNAL OF THE EARTH
Year:2010 | Volume:4 | Issue:4|Papers Count:10

The mudstone is main Caprock in the Gachsaran Field. This Field is located at 220 km south east of AhwazThis Caprock iuvistigated by Gamma, Sonic log, Sem whit Edx. This Caprock divided by 6 keybeds the thiknes in some area is decreased that is related to tectonic activity. The more thikness of Caprock is on the north limb of field and in some wells, This thickness get 60 meter. The more thicknes is related to C Keybed. The comparision of changes whith dip formation shows that chang of thickness always is not submission dip formation. Anhydrit crystals is effected diagenestic and replacement calcitization processes is best marks to show that. The petrophysical studies and lithological changes are cases studied at he sobkha –lagon that is suggested for Gachsaran formation litological changes can be a sign alternactiv climates of warm and dry in depositional urrent of Caprock.

The study area is a part of Folded-Zagros Zone which its geomorphologic position is located in middle part of Zagros, South Pole-Dokhtar city in Lorestan province. Investigations in this area indicate a mega failure at north Limb Kabir-Kuh Range. This phenomenon to called Seymareh Landslide by learned people. In the studied area a part of north limb of Kabir-Kuh which including Ilam, Sarvak and Pabdeh-Gurpi formations and also some parts of the Asmari and Shahbazan formations by various reasons such as urgent of stress (earthquake), geology and topography in a area with average 8 km. width, 15 km. length, and 300 meters thickness was displacement about 20 km. over adjacent area and settled in a wide region. This failure is the largest one in north hemisphere in the world that can be introduced changing in the derange system of area, creation the big artificial lakes in Pole-Dokhtar and Dareh-Shahr and probably disappear historical civilization in the area as its results.

The Kangan Formation of Early Triassic age is one of the important carbonate reservoir rocks in the southwest of Iran and Persian Gulf. This Formation has been studied for recognition of sedimentary environment, type of carbonate platform and recognition and determination of sedimentary sequences in Nar-1 and Asl-1 wells in southwest of Iran. Microscopic studies and also analysis of gamma ray and neutron logs led to recognition of four facies belts that related to tidalflat, lagoon, shoal and open marine environments. These facies were deposited in a carbonate ramp. The important diagenetic process of the facies is dolomitization. Besed on sequence stratigraphy, the Kangan Formation in the studied sections consists of one sequence (3rd-order cycle). In both of studied sub-surface sections, the lower contact of sequence is type 1 unconformity (SB1) and the upper contact of sequence is type 2 unconformity (SB2).

Porosity is one of the most important parameters, which is considered as one of the fundamental factors in reservoir engineering. By knowing this parameter, specialists are able to design and manage, effectively, the process of oil and gas fields development. One of the oldest procedure in porosity and permeability evaluation is, using the core samples, but this method has its own short come, namely only indicated the reservoir parameters/properties at the well or well vicinity. In this regards 3D seismic data has ability in combination with the core and well log data to define/estimate these result far away from the well location. To achieve this result seismic attributes especially the seismic inversion method are powerful tolls. In this paper 3D seismic data in the study area (an oil field in South West of Iran) has been interpreted using well data. In addition seismic inversion has been conducted in order to estimate the porosity distribution based on acoustic impedance within the study area.

Geoelectrical study designation has been done on the basis of pre knowledge about study area (on the basis of visiting have been done), process of buried fault, after shock data of Bam earthquake, remote sensing study and the process of recognized fault of Bam. The aim of this study is the investigation of faults and fractures location.Methods which are used in these studies are consist of electrical sounding with schlomberger array, 3 electrode MN (3MN method), CRP and cross (perpendicular) arrangement around Bam city. The assessment of electrical sounding point shows that the main result of this project is made by electrical sounding points which consist of 213 sounding.Estimating the strike of the lateral discontinuity was used too.In 3MN method of measurement, 3 measurements of electrical resistance with 3 different lengths of potential electrodes for each current electrode space were done and 3 separate curves for each station were produced. Investigation of these curves was very useful in direction determination and the strike of lateral discontinuities. In another profile and for 21 stations measurements CRP method which has high capability in determination of faults and fractures location was used.In another profile and in the middle of studied area and in 21 stations of cross perpendicular sounding was performed. In this method the location of lateral discontinuity (faults and) in relation with measurement point was determined. Coordination of all sounding point was picked up by GPS equipment.

Seismic hazard assessment is carried out for 48.5 - 51 oE and 33 – 36 N o including Markazi province (central province). To do this, seismotectonic map of the region has been provided by using geology maps 1:2500000, tectonic maps, satellite images, available reports, earthquake and minor earthquake catalogues. Five potential seismic sources have been identified by analyzing geology, seismology and geophysics data in the studying area. At last, peak ground 10 iso-acceleration maps for return period have been displayed by probability method. Seisrisk III program in a network of dots with the distance of 0.1 degree has been utilized in seismic hazard assessment. Seismic zone map of Markazi province shows peak horizontal acceleration for 10% probability in 10 years is 0.2g. Markazi province can be divided into different zone with relative risk. The quietest zone is in west. There are regions in north with high relative risk around Indes, kushk Nosrat, Khoshk rud Fault. There is the same situation for a small zone in west north which is in east north of Dorud Fault.

Seismic waves would be attenuated while transmitting in the earth layers. Determination of attenuation mechanism in the earth and analysis of seismic data are very important. One of the most significant parameters in attenuation of seismic waves is attenuation coefficient (1/Q). Attenuation is limited by quality factor which describe the scattering in media. By increasing of attenuation, quality factor would be decreased. One of the newest ways for estimation of Q is using VSP data (Vertical Seismic Profiling) by considering the decrease of frequency and amplitude in different depths for down going waves. In this research quality factor would be estimated by using zero-offset VSP data of two exploration wells in the south of Iran. Q would be estimated by amplitude decay method and analytical signal method. We show that decreasing of Q maybe due to gas hydrocarbon existence.

In this study, fault-lines of northwestern-southeastern trend have been tectonics structures. Besides the mentioned trend, the northwestern southwestern trends also had outcrop in the studied range. Recent seismic data indicate the fact that in the studied range the active presence of North Firouzabad transpressure fault-line has been caused formation of fault scarps. So that, very deep valleys and creates seismotectonics potential in a place where it is jointed with Firouzabad synthetic fault line with northwestern-southwestern trend. More over Firouzabad Kojour earthquake has been the first turning point which has been recorded in Central Alborz mountains after the earthquake which occurred on 2nd July (measuring Mw=6.8). Since earthquake, occurrence and specifications of its epicenter are applied to identification of depth-related and kinematical structures of active fault lines. Study of Firrouzabad Kojour earthquake would be useful in being familiar and acquainted with tectonic structures of Central Alborz region. 5000 data have been recorded in 19 short period stations of Institute of Geophysics, University of Tehran (IGUT) and 3 broadband stations of International Institute of Earthquake Engineering and Seismology (IIEES), since 2004. We use geological map of 1:100000 and 1:250000 scale and topography map with 1:250000 scale in this study. Observed discontinue on the map are related to the faults in the area which are proved by area geology map.