An Integrated Appraisal of Burgan Reservoir in Soroosh Oil Field, Using Petrographic and Petrophysical Approaches

The Burgan Formation in northwest of the Persian Gulf is applied to lower part of Albian age Kazhdumi Formation, where is dominated by coarse to medium terrigenous facies. It is the most susceptible siliciclastic unit in the area to hydrocarbon reservoir. This reservoir is studied in a well of Soroosh oil field with best available data to determine its facies characteristics, sequence stratigraphy and reservoir quality. Based on the petrographic results and log data, 7 facies are determined in the formation, which are mainly composed of sandstone and shale. These facies are classified into three facies associations (FA) based on their sedimentological properties and environmental conditions. The first FA consists of sandstone, siltstone and shale, mostly developed in the lower part of formation, and is related to a fluvial environment. The second FA consists of fluvial sandstones and sandwich by marine shales and is related to fluvial-dominated shallow marine setting (estuary to delta). The third FA consists of limestones of chemical and biochemical origin and is related to a marine condition. According to their reservoir quality, these facies associations show a decreasing trend in porosity and permeability values from FA1 to FA3. The first FA is more abundant in the lower part of the Burgan Formation where causes a good reservoir quality trait. FA2, presenting a medium reservoir quality, is more frequent in the middle parts of studied formation and FA3 is found almost in the upper parts. Based on the results from this study, three 3rd order sequences have been identified. Sequences 1 and 3 are partial but the sequence 2 is the main and most complete one of the formation in the studied area. The paleosol horizons are used for relative sea level change analysis of the formation in sequence stratigraphic studies.

Structural Control on the Salmas Geothermal Region, Northwest Iran, from Fractal Analysis and Paleostress Data

The Salmas geothermal field is located in NW Iran. Subduction of Neo-Tethys oceanic crust beneath the Iranian microcontinent caused to propagation of the magmatic-Arc. Fractures and faults in the convergent zone have created path-ways for the circulation of geothermal fluid. Fracture concentration in the Salmas geothermal field has been characterized using of the fractal method and creation of a fracture density map that shows the highest concentration in the central part of the study area. The permeability of fractures has been evaluated by analyzing their orientation in respect to the paleostress axes. Also, the fractal analyzing result indicates the maximum fractal dimension（1.96） is around the thermal spring outlet. Paleostress analyzing revealed that in the central part of the study area, σ1 axes orientation is S90°W/10° and the σ2 dip is near to the vertical in this stress field, where strike slip faults can be propagated. In the SE part near the recharge of the thermal springs, the σ3 plunge increases to 70？ and σ1 orientation is N15°E/20°, in this local tectonic regime thrust fault developed. Fractures have an important role in the circulation of fluid and the fractal dimension increases near the thermal springs in the Salmas geothermal field. Regarding the paleostress data fracture with N-S direction such as the F1 fault zone（parallel to the σ1 axes）, a suitable pathway for deep circulation of geothermal fluid flow has been created.

Inspecting the Reservoir Characteristics of the Burgan Formation of Soroosh Oil Field Applying Rock Typing Methods in the Context of Geological Studies

The Albian age Burgan Formation is one of the most important siliciclastic reservoirs in the Arabian Plate. Northwest of Persian Gulf is the main area in Iran invaded by these siliciclastic sediments. This study uses a new and comprehensive procedure to identify the reservoir characteristics of the Burgan Formation in Soroush oil field (NW Persian Gulf). Results from core and petrographic studies led identification of 7 microfacies (MF1 to MF7) that are grouped into 3 main facies association (FA1, to FA3). Results from reservoir characterization indicate a dramatic decrease in reservoir quality from bottom to top (FA1 toward FA3). Using the Flow Zone Indicator (FZI) method, 5 Hydraluic flow units (HFUs) were recognized in the formation. The HFUs are in a notable accordance with facies associations. The HFUs 1 and 2 correlate with theFA1, the HFUs 3 and 4 with the FA2 and the HFU5 cover intervals defined by FA3. Cluster analysis of wireline logs resulted in determination of 5 electrofacies (EF1 to EF5) which are in agreement with the ascertained HFUs. Inspecting the vertical distribution of FAs, HFUs and EFs, three distinct zones are determined. The lower zone is characterized by good reservoir quality, abundance of FA1, HFUs1 and 2 and also EFs 1 and 2 is observed there. The middle zone with a moderate reservoir quality and upper zone presents the poorest quality. In the middle zone FA2, HFUs3 and 4 and also EFs 3 and 4 are more abundant while in the upper one interval are clearly correlated with FA3, HFU5 and also EF5.