پديد آورندگان :
صفاكش فريده نويسنده دانشجوي دكتري ژيومورفولوژي، دانشكده علوم جغرافيايي، دانشگاه خوارزمي، ايران , مقصودي ياسر نويسنده دانشكده مهندسي ژئودزي و ژئوماتيك ,دانشگاه صنعتي خواجه نصيرالدين طوسي,تهران,ايران Maghsoudi Yasser
كليدواژه :
ميدانهاي نفتي , زاگرس , نيوتكتونيك , شاخصهاي ژيومورفيك , جراحي- زهره
چكيده لاتين :
Introduction
With 6.8 percent oil reservoirs, Zagros is one of the most prolific oil sedimentary basins. The greater part of its hydrocarbon reservoirs are concentrated in anticlinal traps, which they are also the subsets of the structural traps. In addition to rich and vast hydrocarbon reservoirs, Zagros have been also considered well in terms of itʹs the Neotectonic activities. Studies of Neotectonic activities as an important factor in the control of landforms in tectonic regions, Apart from its social and economic interest, studies of active tectonics follow a multi disciplinary approach, integrating data from structural geology, geomorphology, stratigraphy, geochronology, seismology, and geodesy.The unrelenting competition between tectonic processes that tend to build topography and surface processes that tend to tear them down represents the core of tectonic geomorphology.Since so Most effective morphometric indices have been related to erosional and depositional processes associated with fluvial systems.Rivers are highly sensitive to subtle landscape fluctuations induced by tectonic activity and can assist in differentiating active segments of geologic structures. Because Drainage basins represent dynamic systems that may retain records of formation and progression since most tectono-geomorphic processes occur within its confines. Therefore, Morphometric analyses of river networks, drainage basins and relief using geomorphic indices, as well as geostatistical analyses of topographical data, have become useful tools for investigating landform evolution. In recent studies related to morphotectonics, a mixture of geomorphologic and morphometric analyses of landforms and topographic analyses are utilized to obtain active tectonics and they have been tested in different tectonically active areas and provide insight about particular areas that are subject to active tectonic deformation.Therefore, since so many of geomorphologic effects are highly susceptible to tectonic movements and their changes are happening at the same time, we should be looking for forms and shapes that have retained these changes over the years. With regard to the abovementioned matter and using geomorphologic indices, the current study attempts to consider Neotectonic activities and its impact on the positioning of the oil fields in the Jarahi and Zohre sub-basins.
Materials and methods
In order to achieve the goals of this research, documentary information,1:50000-1:25000 topographic maps and 1:100000-1:250000 geological map, a digital elevation model (DEM) related to SRTM topographic data and landsat 8 satellite images have been the important research tools. For the analysis of Neotectonic activities in the case study area, have been used such geomorphologic indices as Stream Length-Gradient index, River Sinuosity, Relief Amplitude, Hypsometric Integral, Basin Shape Factor and Drainage Basin Asymmetry Factor Index.Arc GIS software was used to digitize the topographic maps and drawing of river networks for calculating these indices.
Results and discussion
Results of the calculation of geomorphologic indices:
The SL values in the study area range from 0 to 573, The S values in the study area range from `1.1 to 2.46, The RA values in the study area range from 31 to 3254, The HI values in the study area range from 0.04 to 0.56, The values in the study area range from 0.19 to 2.49 and The |AF–50| values in the study area range from -28.83 to 32.59. The classification used in this paper for each geomorphic index is calculated from El Hamdouniʹs method.According to Relative Tectonic Activity (lat) index, three class high active(1.6 ? LAT < 2), 12.2%, moderate active (2 ? LAT < 2.5), 34.5% and low active (lat ? 2.5), 53.2% were identified.
Finally, with stratum overlaying of oilfield and the obtained final layer from geomorphologic indices of the studied basin, it was found that in the Class I areas, there was no oil fields with high level of tectonic activity, but 38/3 percent of oil fields are located in Class II areas with their average tectonic activity and 61/6 percent of oil fields are located in Class III areas with their low tectonic activity.
Conclusion
The obtained quantitative values from the results of the geomorphic indices in the 38 sub – basin led to divide the studied basin into three tectonic areas with low, medium, and high tectonic activity. It was also shown that the Neotectonic activity level in different parts of the basin is not the same and the forces act with greater intensity in the eastern half. This activity caused to more oil fields of Jarahi – Zohre basin, i.e. 61.6 percent located in the region with the lowest Neotectonic activity. In fact, being in the lowest Neotectonic Class acted as the factor to emerge the oil traps and to maintain the hydrocarbons. On the other hand, in the areas with the highest Class of Neotectonic, there was virtually no oil field. The results indicated that Neotectonic has important role in the running or migration of oil traps and the extent of tectonic is necessary to create small fractures to oil running and finally oil production. In fact, it can be attributed to Neotectonic both destructive and inhibiting role in addition to constructive and transferring hydrocarbons.
