Electromagnetic Measurement While Drilling System Enabled the Operator to Reach Beyond the Limits in a Multiphase Foam Drilling Medium

Abstract

In this era of low oil price, it is vital for the operators to deliver low cost wells with enhanced production. A continuous technological advancement in the oil and gas industry has played a pivotal role in establishing high returns on investments. Many techniques have been developed so far in this aspiration to improve the quality of the reservoirs, enhanced production mechanisms and efficient drilling operations.

Situated in Sulaiman fold belt of Pakistan a large Gas field was discovered by one of the NOCs in 2011. It was a carbonate reservoir, laterally extended on a large portion resulting in a big volumetric reservoir. When discovered it was observed that being naturally fractured and having low reservoir pressure it was plagued with massive loss of circulation and associated drilling challenges. Conventional drilling technique has also resulted in immense reservoir damage. To overcome the challenges of overbalanced drilling the operator started drilling with underbalanced drilling methodology in this formation, which resulted in efficient drilling, saving time and cost.

In order to improve the field economics, the operator decided to drill horizontally into this formation to maximize the production potential of each well. As a pilot project a well was designed to drill a horizontal leg of almost 504 m into this carbonate reservoir. It was obvious that this formation could not be drilled with conventional overbalanced mud system so it would be drilled with underbalanced multiphase foam drilling system. The biggest challenge in this gaseous foam drilling medium is to control the trajectory of the well as the measurement while drilling (MWD) system works through mud pulse telemetry that could only be done in an incompressible drilling fluid.

To address this major glitch an electromagnetic (EM) MWD system was suggested that can transmit the signals via electromagnetic waves and is independent of the drilling medium being used. Based on the resistivity analysis of the formations laying above this reservoir, modeling was performed to design the most suitable measuring system. As the lateral was long and deep so the requirement of extended range antenna system was also incorporated so that signal transmission remain uninterrupted throughout the drilling operation.

Through the application of this unconventional MWD technique the operator was able to drill the longest horizontal well in this block. The well was completed without any NPT in an excellent fashion and tested to evaluate the maximum flow potential of this reservoir. This application has shown the operators how to reach beyond the limits in such troublesome formations.