Horizontal-Well Correlation in Geosteering Complex Reservoirs of Saudi Arabia
Authors: Carpenter Chris 
Published: February 2015

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 164151, ’Horizontal-Well Correlation Using Real-Time Data and Log Prediction in Geosteering Complex Reservoirs of Saudi Arabia,’ by Abdul Mohsen A. Al-Maskeen, Roger R. Sung, and Sadaqat S. Ali, Saudi Aramco, prepared for the 2013 SPE Middle East Oil and Gas Show and Conference, Manama, Bahrain, 10-13 March. The paper has not been peer reviewed.
A new workflow technology has been launched that uses real-time logging-while-drilling (LWD) data and a new horizontal well-correlation technique to dynamically update a structural framework that can be used to geosteer an active drilling well. The benefits of this new approach include faster well-log interpretation and the ability to dynamically and more-accurately update the subsurface model during drilling to efficiently steer the wellbore into the most productive parts of conventional and unconventional reservoirs.
Introduction
With increased competition in the energy market, oil companies face the constant challenge of improving accuracy while reducing cycle time. This goal has driven the advancement of technologies in horizontal drilling, real-time monitoring, and geological interpretation significantly during the last few years.
Previous well-correlation work-flows used by Saudi Aramco were typically limited to applying the vertical-well approach even when drilling horizontal wells. This approach involved transforming the well logs from a measured-depth domain to a true-vertical-depth (TVD) domain and introducing some degree of uncertainty. However, accurate correlations using TVD can be obtained only in vertical wells or wells drilled through beds with no structural dip. TVD well correlations become meaningless when deviated wells penetrate dipping beds. This approach poses another problem in that the subsurface layers and the structural-framework model are not dynamically updated while drilling, which may negatively affect the accuracy of well planning, interpretation, and geosteering.
Additionally, the percentage of highly deviated and long horizontal wells in Saudi Aramco’s field portfolio has increased significantly in order to maximize reservoir contact for optimal development. Therefore, the shortcomings of the traditional well-correlation technique have become a major issue. Improvement of technology and tools for making accurate log correlations while geosteering to keep the well in the production zone on a real-time basis is not only critical but also essential.
The technology and methodology demonstrated in this paper enable real-time horizontal-well correlation, greatly enhancing the geologist’s ability to steer the well placement accurately and update the subsurface layers dynamically. This workflow has been applied successfully in several Saudi Aramco fields, including the largest onshore oil field in the world. By use of this technique, many long-reach horizontal wells achieving maximum reservoir contact have been drilled. Not only has accuracy been enhanced, but also the turn-around time has been reduced by an order of magnitude.