Formation Pore Pressure Variation of the Neocomian Sedimentary Succession (the Fahliyan Formation) in the Abadan Plain Basin, SW of Iran

Abstract

The Neocomian Fahliyan Formation is one of the important oil reservoirs in the Abadan Plain Basin, SW of Iran. To evaluate the pore pressure regime of the Fahliyan reservoir, 164 in situ pressure data points (MDT, XPT, and RFT) were analyzed from seven wells belonging to six oilfields. The pressure versus depth plot revealed that the Fahliyan reservoir is highly overpressured in all fields. The formation was characterized as a multilayered stacked reservoir with different pore pressure decreasing downward in a step-wise manner. Also, there is a major pressure step in the middle part of the reservoir, suggesting the presence of a regional efficient seal dividing the reservoir into two stacked compartments, where the upper compartment is more overpressured than the lower one. The stepped pressure pattern of the Fahliyan Formation is a regional phenomenon controlled by a factor governed regionally, the depositional condition, and facies lateral changes during the deposition of shallowing upward sequence of the Fahliyan reservoir. In addition, direct relationship is observed between the reservoir pressure and burial depth. This matter could amplify the initially generated overpressure state more possible due to dewatering of sediments and by-pass product of oil migration from Garau source rock to the Fahliyan reservoir.

Stratigraphy, Tectonics and Hydrocarbon Habitat of the Abadan Plain Basin: A Geological Review of a Prolific Middle Eastern Hydrocarbon Province

“…A number of compartmentalized complex reservoirs both vertically and laterally, as a result of structural activity and subsequent depositional and post-depositional parameter interplay were evident in the Abadan Plain Basin [30].The depositional environment of the Dezful Embayment and Abadan Plain Basin can be classified into four distinct areas [9,19].…”

“…Major N-S trending Paleohighs in the Abadan Plain Basin are basement-cored complex horsts [30] that encompass some of the major oil fields in this region. Severe weathering has eroded parts of such structures, whilst the alluvial sediments cover most of the areas and the structures are explored by geophysical data.…”

“…Main structures of this basin are generated by differential compaction affected by reactivation of structural lineaments [30] that have made structural traps of compactional type (drape structures) [37]. The movement of the Afro-Arabia plate towards the Eurasia Plate during the Cretaceous, and subsequent closure of the Tethyan Ocean [27,38,39], have been followed by the continent-continent collision of the Zagros Orogen.…”

“…The Gadvan and Fahliyan formations exhibited different degrees of overpressure. The pore pressure tends to decrease at the bottom of the Fahliyan Formation, which creates additional complexity to the hydrology of the basin [30]. Similar to some other areas of the Zagros Structure [63], overpressure is often encountered in carbonate formations where none of the standard porosity responses to overpressure are observed, and thus, pore pressure is hard to predict.…”

Dynamic Evaluation Method of Caprock Microscopic Sealing in CO2 Sequestration Project

“…The caprock sealing mechanism mainly includes microsealing and macrosealing. In addition to strong microsealing ability, the caprock also needs to have a specific sufficient thickness and macrodistribution area to seal CO 2 in the formation system effectively [10][11][12][13][14]. At the present stage, most evaluation methods of caprock sealing property are multifactor evaluation methods based on statistics [15], such as the fuzzy evaluation method or weighted analysis method.…”