Real-Time Pore and Fracture Pressure Prediction With FEWD in the Nile Delta
Authors: Mazzoni R. , Wahdan T. , Bassem A. , Ward C.D. 
Published: December 2007

Predicting pore and fracture pressures while drilling is essential for optimal mud weight and casing point selection. In the Nile Delta, offshore Egypt, rapid sediment deposition has resulted in a high overpressures which produce difficult drilling conditions. Traditional pore and fracture pressure prediction methods which use drilling data have recently been supported by a effective-stress method. This method uses FEWD data to measure formation properties directly and has helped the Operator to reduce drilling costs and the number of well sidetracks caused by drilling problems.

Introduction

Poor knowledge of the pore and fracture pressures in the Nile Delta has historically led to significant drilling downtime and well sidetracks. Typical drilling problems include well flow, differential sticking, lost circulation, and stuck pipe.

Traditional methods of pore pressure prediction (de-exponent, Sigmalog, gas indications) have limitations in the Nile Delta and elsewhere, because they use indirect pressure indications from drilling data and do not measure formation properties directly.

The advantage of using Formation Evaluation While Drilling (FEWD) data is that formation properties are measured directly. A mathematically linked pore and fracture pressure model that has been widely used with FEWD data to determine real-time pore and fracture pressures is an Effective Stress Loading (ESL) model. The theory and application of this method has been described previously.

This paper describes the application and experiences of applying the ESL approach with FEWD data, to real-time pore and fracture pressure prediction in the Operators Nile Delta drilling campaign.

Geological Setting & Overpressure-Generating Mechanisms

Geological Setting

No delta could be more classical in shape than that of the Nile river, which was compared by Herodotus in the fifth century BC to the shape of the Greek letter "Delta ()".

This region occupies a key position in the context of the Plate-Tectonic evolution of the Eastern Mediterranean and the Red Sea. It lies on the moderately deformed northern margin of the African plate, which extends well north of the Mediterranean coast.

This paper concentrates on the Operator's recent drilling campaign in two separate concessions; those of Baltim and Temsah (Fig. 1). A generalized stratigraphic column of the Nile Delta area is shown in Fig. 2. This part of the Mediterranean basin is characterized by two main depositional environments. The first, a 'deep marine' environment, is typified by the Temsah area. In this environment the Rosetta evaporites were deposited in the Late Miocene during the Messinian crisis when the Mediterranean Sea evaporated away. The second, a more sand prone 'deltaic' environment, is illustrated by the Baltim area.

Causes of Abnormally High Pressure

There is a basin-wide occurrence of over-pressure in the Nile Delta. A typical pressure profile is shown in Fig. 3. A number of mechanisms have been proposed to explain the generation of overpressure in this area, including:

High Sedimentation Rate. The occurrence of abnormally high pressures in the Nile Delta is primarily related to the rapid subsidence rate, beginning from the early Miocene and continuing to the present day.

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