Facies, Depositional Environment and Diagenesis of the Qom Formation in Rameh Section (Northeastern Garmsar)

Soraya Sardarabadi,Davood Jahani,Nader Kohansal Ghadimvand

doi:10.4236/ojg.2016.610091

Abstract

Deposits of the Qom Formation (Oligocene-Miocene) in Rameh section are located in northeastern Garmsar and contain dominantly 420 m Limestone, pebble-rich to sandy Limestone and marl Limestone. This formation is unconformably overlaid and underlaid with siliciclastic deposits of Upper Red Formation and Lower Red Formation. Field observations, along with laboratory investigations, have resulted in identifying tidal flat, lagoon, shoal and open marine environments in the studied formation. Open marine facies association consists of bioclast mudstone, bioclast wackestone, bioclast packstone and bioclast roadstone; shoal facies association consists of ooid grainstone, bioclast grainstone and coral boundstone; lagoon facies association is composed of dolomitic mudstone, intraclast bioclast wackestone and bioclast packstone; and tidal flat facies association is sandy dolomudstone and stromatolite boundstone. The qom formation rocks in Rameh section are deposited in a rimmed shelf carbonate ramp. This formation undergoes various diagenetic processes including dissolution, porosity, cementation, micritization, compaction and dolomitization.

Highlights

One of the requirements to safe drilling is the knowledge of the formation pore pressure gradient and the corresponding fracture gradient
This study focuses on comparing wire line log data with that of Wire line Formation Tester (WFT) in predicting the pore pressure in some selected wells in the Niger Delta oil field
Estimation of Pore Pressure by Different Methods Eaton’s exponential and Bowers pore prediction models were the fundamental pore pressure prediction approaches employed in this work

Summary

Introduction

One of the requirements to safe drilling is the knowledge of the formation pore pressure gradient and the corresponding fracture gradient. When the pore pressure of a formation at any depth is above the hydrostatic pressure for such formation, the pressure is considered to be over-pressured. On the other hand when the formation pressure is below the hydrostatic pressure at any depth, the formation is said to be under-pressured. The normal pressure is the hydrostatic pressure, or the pressure exerted by a column of water from the formation depth to sea level. When impermeable rocks such as shale sediments are compacted, their pore fluids cannot always escape and must support the total overlying rock column leading to anomalous formation pressure [1]

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