Predicting the Depositional Environments of Mishrif Formation from Seismic Isopach Map in the Dujaila Oil Field, Southeast-Iraq

Ahmed Muslim Khawaja,Jassim Muhammad Thabit

doi:10.24996/ijs.2021.62.6.19

Abstract

In this paper, we attempt to predict the depositional environments with associated lithofacies of the main reservoir of the late Cretaceous Mishrif carbonate Formation, depending on the analysis of the created seismic isopach map by integrating seismic and well data. The isopach map was created from a 3D-seismic reflection survey carried out at the Dujaila oil field in southeastern Iraq, which is of an area of 602.26 Km2, and integrated with the data of the two explored wells. Based on the interpretation of the seismic isopach map, the diagram of the 3D-depositional environment model of Mishrif Formation was constructed. It showed three distinguished depositional environments, which were graduated from a back reef lithofacies of a shallow open marine (shelf) environment in the west and NW, to a shoal environment of isolated Rudist reefal buildup in the middle, and a fore reef lithofacies of the deep open marine basin environment in the SE of the field. A 3D-instantaneous frequency model was generated to verify the capability of the seismic isopach map of predicting the depositional environments, which in turn showed that the low frequency was restricted in the region of the high thickness of Rudist reefal buildups (porous reservoir facies) in the vicinity of the productive well Dujaila-1.

Highlights

Modern three-dimensional (3D) seismic data assists in delineating reservoir geometry and in predicting petrophysical properties with variations away from those of the well control [1]
The use of the instantaneous frequency attribute confirmed the ability to predict the depositional environment from the seismic isopach map
A 3D-depositional environment model of Mishrif Formation was predicted directly from the seismic isopach map to illustrate the general configuration of the depositional basin architecture and horizontal lithofacies environments distribution

Summary

Introduction

Modern three-dimensional (3D) seismic data assists in delineating reservoir geometry and in predicting petrophysical properties (thickness, porosity, and lithology) with variations away from those of the well control [1]. The geologic model derived from combining the 3D seismic survey with available well data provides a degree of detail about the depositional environments of the producing reservoir that cannot be obtained from well data alone [2]. This research is interested in predicting the thickness and delineation of the depositional facies environments of Mishrif Formation (Cenomanian-Early Turonian), which is the main reservoir in Dujaila oil field, depending on the integration of the 3D post-stack time migrated seismic data and available data of two wells. The first well is Dujaila-1 (Du-1) that was drilled in 1960 and produced oil from Mishrif Formation. This study aims to estimate the depositional environments and associated lithofacies of the carbonate reservoir of Mishrif Formation from the seismic isopach map.

Objectives

Conclusion