Narrow-Margin Drilling and Operational Geosciences in Egypt and Syria
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 152893, ’Narrow-Margin Drilling and Operational Geosciences in Egypt and Syria,’ by Bart W. Tichelaar, Hisham F. Salem, Sandy A. Amin, and Ramy M. Shafik, Shell Egypt N.V., prepared for the 2012 North Africa Technical Conference and Exhibition, Cairo, 20-22 February. The paper has not been peer reviewed.

The ability to drill exploration objectives safely and efficiently requires knowledge of the available drilling margin. Operational geosciences were applied in two recent exploration wells in Egypt and Syria where predrilling pore-fluid-pressure and fracture-pressure models were built to enable well design. While drilling the well, these models were updated continuously in real time to make the correct operational decisions. Before drilling the more-challenging well sections, learning from shallower sections in the well was used to prepare a look-ahead assessment of the available drilling margin to select a strategy to drill the next section.

Introduction

The drilling margin, defined as the pressure range (or pressure interval) from the formation pore-fluid pressure to the fracture pressure, is important for well engineering, well-cost estimation, and exploration evaluation. During well operations, a narrow drilling margin that is assessed improperly can lead to unexpected influx of reservoir fluid into the wellbore or to sudden downhole loss of drilling mud. The geosciences offer concepts and technologies to assess the drilling margin in the predrill phase. Downhole real-time data-acquisition and -transmission technologies make it possible to operationalize many of the existing predrill approaches such that real-time updates of the available drilling margin (i.e., pore pressure and fracture gradient) can be produced to reduce the uncertainty in predrill models. These real-time updates facilitate operation-al decisions during well execution and make drilling more efficient.

From a drilling-technology perspective, there are several ongoing developments that can be integrated with real-time pore-pressure/fracture-gradient prediction. Examples include ruggedized managed-pressure-drilling (MPD) systems, the emergence of real-time mud-hydraulics modeling, and the design of downhole lithium batteries with high temperature ratings to power logging-while-drilling (LWD) tools.

Recently, Shell Egypt’s Geosolutions Team had the opportunity to work on narrow-margin exploration projects in the Nile delta and on the South Syrian platform. Although not all data from these projects have been released for publication, two examples of applying real-time geosciences are described. Both wells are in near-crestal locations, and a narrow drilling margin was recognized early in the exploration phase such that proper regional data analysis could take place for the entire well in the predrill phase. Also, options for real-time data acquisition were investigated so that geoscience-data interpretation could form a key operational element during drilling. The Zerzura well in Egypt targeted clastic rocks of Miocene and Oligocene age to a depth of nearly 6 km in a high-pressure/high-temperature regime in shallow water in the Nile delta. The Wadi Saeed well on the South Syrian platform is less than 2 km deep in Paleozoic rocks of mixed clastic and carbonate origin in a land setting with low pressure and temperature. Also, not all required equipment and software were available for the Syrian-platform well because of export controls.