Continuous Innovation Achieves Better Zonal Isolation in Extended-Reach Wells
Authors: Wilson Adam 
Published: May 2018

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 188295, “Success Through Continuous Innovation To Achieve Better Zonal Isolation in Extended-Reach Wells in a UAE Field,” by Abdelkerim Doutoum Mahamat Habib, SPE, Yousif Saleh Al Katheeri, Sheldon Seales, SPE, Rayaz Evans Ramdeen, Romulo Francisco Bermudez, SPE, and Luis Eduardo Navas, SPE, ZADCO; and Saurabh Kapoor, SPE, Surya Pallapothu, Azza El Hassan, and Bipin Jain, SPE, Schlumberger, prepared for the 2017 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 13–16 November. The paper has not been peer reviewed.
Operators at a UAE field experienced several challenges while cementing production sections. A systematic approach was applied that used standard cementing best practices as a starting point. An advanced cement-placement software was used to model prejob circulation rates, bottomhole circulating temperatures, centralizer placement, and mud removal. To enhance conventional chemistry-based mud cleaning, an engineered fiber-based scrubbing additive was used in spacers with a microemulsion-based surfactant. Finally, real-time monitoring software was used to evaluate cement placement in real time.
Introduction
Artificial islands are built in the UAE to reduce life-cycle development costs and enable long-term maximum recovery levels by accommodating up to 300 wellheads on a single island. The wells drilled from these islands are complex extended-reach horizontal laterals with measured depths planned at more than 35,000 ft. Cementing these wells is extremely challenging, largely because of long open holes with high deviation, the use of nonaqueous fluids (NAFs) for shale stability, and lost circulation while drilling and cementing.
Additional stringent prerequisites, such as casing pressure tests at high pressures after the cement is set and the need to isolate narrowly separated sublayers of reservoir, increase the complexity of cementing these wells. This paper demonstrates the continuous improvements in the prevailing stepwise approach and the role of the improvements in attaining needed zonal isolation. These improvements can be divided into four main sections:
Advanced cement-placement modeling
Engineered fiber-based scrubbing agents in spacers
Engineered flexible expanding cement systems
Real-time cement-job monitoring
Advanced Cement-Placement Modeling
Good casing centralization during cementing operations is key to achieving proper mud displacement and obtaining hydraulic isolation in the annulus. To this end, centralizers are often placed along the casing to position it centrally in the borehole. The optimal number of centralizers and their spacing are determined through software simulations. Until now, the industry typically has used calculation methods derived from American Petroleum Institute Specification 10D to predict casing eccentricity in the wellbore. The calculations are based on an analytical soft-string method, which models an element of casing string between two centralizers as a bifixed beam. However, for extended-reach wells, the use of a numerical stiff-string method to compute torque-and-drag forces is becoming increasingly popular. It accounts for tubular bending stiffness and provides a more-realistic analysis of the stresses and loads acting on the drill-string and the borehole. The stiff-string technique, based on the finite-element method, is, therefore, proposed as an alternative and more-effective solution for computing casing centralization for cementing operations, especially in deviated sections.