Comparison between Rafidhiya and Shuaiba Domes within the properties of Mishrif Formation in Zubair Field; the implication of structural Geology and petrophysical analyses

Abstract

The current study combined both concepts of structural geology and petrophysical to understand the structural feature of Mishrif Formation and its implication on the petrophysical characterization of the formation in Shuaiba and Rafidhiya Domes (or culminations) in Zubair Field. Shuaiba and Rafidhiya are adjacent domes and these domes belong to the same Field but the domes separated by saddle may related to Basra – Zubair basement fault.
 The domes have different petrophysical properties of Mishrif Formation; consequently, influenced in water and oil saturation. Therefore, the study tries to understand the structural and petrophysical position of Mishrif Formation of the domes. The structural analysis included geometric and genetic analysis, whereas petrophysical analysis used open hole logs interpretation to determine the petrophysical characteristics (especially the distribution of porosity, permeability, and water saturation.
 It was concluded that may a variation in porosity and permeability of Mishrif Formation for Shuaiba and Rafidhiya domes because each dome was formed by a different folding mechanism effected on the petrophysical properties. The structural geology analysis detects that may be Shuaiba dome formed by bending fold mechanism (vertical force of salt structure), while Rafidhiya dome by buckling fold mechanism (parallel force of collision of Arabian and Eurasian plate). These mechanisms may directly be affected in permeability distribution, and consequently on oil and water saturation of Mishrif Formation. Thus, Shuaiba Dome has thinning in hinge area and extensional force leads to create fractures and karst phenomena, and as a result, high permeability in upper Mishrif. On the contrary, Rafidhiya Dome has a thickening feature and there is no indication of karst phenomena and low permeability. Therefore, the Mishrif of Shuaiba dome permeable and oil-saturated, while, it flooded with water in Rafidhiya Dome. The disconnection in reservoir pressure confirmed by difference in initial reservoir pressure of Mishrif Formation of Shuaiba Dome and recent reservoir pressure of Mishrif Formation of Rafidhiya Dome

Structural Geology Study of Tuba Oilfield, Southern Iraq

“…The lower part of the Mishrif Formation of the study area is the most important in terms of oil saturation and petrophysical properties (porosity and permeability) (Samir, 2011). On the contrary, the upper part of the Mishrif formation in the Zubair oilfield is the main one, and this is compatible with the bending and buckle mechanisms' strain pattern (Lazim, et al, 2020;Dawood, 2019, 2020). In addition, the facies of Mishrif formation of Tuba oilfield are less quality than North Rumaila oilfield, although they are homogenous (Jalayh, 1979).…”

“…This could be noticed by the occurrence of normal faults in the Rumaila oilfield (Jaffar and Abdulnaby, 2018) and Zubair oilfield (Lazim et al, 2020b), while there is no fault in the study area according to 2D seismic interpretation (Samir, 2011). The NW-SE fold axis direction may be due to the counterclockwise motion of the Arabian plate and this direction is equivalent to surrounding fold axes of oilfields in southern Iraq, such as Rumaila oilfield (Jaffar and Abdulnaby, 2018), Zubair oilfield (Lazim and Dawood, 2020), West Qurna oilfield (Lazim et al, 2020a), and Nahr Umr oilfield (Al-Kubaisi and Lazim, 2016).…”

Characterization of Structural Geology of Faihaa Oilfield, Southern Iraq

“…There is no interpretation for gravity and magnetic geophysical data of the study area, but depending on the results of adjacent Oilfields and structures within the Zubair subzone (like Nahr Umr and Zubair Oilfields) the salt structures of Hormuz salt and basement faults has been indicated [11], [13], [14]. These geophysical results are linked with the oilfields' structural pictures and folding mechanisms (bending and buckle) [23]- [25]. Therefore, the bending mechanism could be attributed to the influence of salt structure-activity of Hormuz salt and/or reactivated basement faults as vertical force, while buckling mechanism to the collision between Arabian Plate and Eurasian Plate as a parallel force.…”

“…Oilfield [23]- [25]West Qurna Oilfield [27]. The fold axis of the study area has almost 3⁰ from center to south, and for north part approximately ≈ 30⁰ for Lower Cretaceous, ≈ 45⁰ from Lower Cretaceous to Miocene, and ≈ 60⁰ for early and middle Miocene.…”