Date of Award

January 2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Petroleum Engineering

First Advisor

Vamegh Rasouli

Abstract

The Cambro-Ordovician in the Algerian Saharan platform is characterized by tight sandstone formations with very low petrophysical characteristics where the natural fractures play an important role in their productivity. The Mouydir basin is the less explored basin in Algeria where no 3D seismic data exist and only low quality of seismic 2D surveys are available. In addition, few wells were drilled in the fifties exist in this basin. They were drilled based on the field observations, gravity data, geological maps, and seismic refraction data. Unfortunately, these wells were all negative. The Mouydir basin is limited in the west by the Ahnet and Timimoun basins, which are considered as the main gas provinces in the western part of the Saharan plate-form. In addition, The Mouydir basin is limited in the north and the east by Oued Mya and Illizi basins, which are considered as prospective oil provinces. These basins have the same petroleum system as the Mouydir basin where the Silurian hot shale is the principal source rock and Ordovician the main reservoirs, which produce tremendous quantity of oil and gas from naturally fractured reservoirs.

To overcome this lack of data, a specific and an innovative workflow is proposed to analyze and characterize the natural fractures in the Cambro-Ordovician reservoir by using an analog that appears in the southern edge of the Mouydir basin in order to bring a new insight and guide the future exploration wells in this basin. This workflow integrates multiple data that help to build a deterministic fracture model. This model highlights the major and minor fractures that aid to understand the basin’s geological evolution as well as the impact of the basement’s fractures on the basin structuration and on the sedimentary cover. The 3D fracture model is used to understand the fractures’ distribution, fractures’ connectivity, and fractures’ kinematics. The outcomes could be used to predict fractures’ extension and occurrence in the subsurface and could be used to explain the negative results of the drilled wells. Different scales of observation have enabled to highlight a fractal dimension of natural fracturing in these unconventional reservoirs.

The fracture characterization using core and borehole imagery data including the fracture attributes, breakouts, and induced fractures help to determine the in-situ stress, fracture morphology, and fracture typology. The 3D seismic attributes and the interpretive criteria of seismic 2D support to determine the intensity, density and fracture kinematics of natural fractures. These approaches allow up understanding the geological processes that affect the area of study, which are responsible for the generation of the complex fracture patterns. These approaches will aid to predict the occurrence of these fracture patterns in the area where no data is available.

The drilling of a horizontal pilot well on the positive structures already discovered, perpendicular to the Maximum Horizontal stress, having as target the Cambro-Ordovician reservoir in the depocenter of the Mouydir basin, could be a decelerator of a new exploration era in this unexplored basin.

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