A Fully Completed Solution With Zonal Isolation In Norway
Authors: Carpenter Chris 
Published: February 2015

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 166209, ’Intelligent Completions and Uncemented Liners Combine To Provide a Fully Completed Solution With Zonal Isolation in Norway,’ by A.W. Kent, D.W. Burkhead, R.C. Burton, K. Furui, S.C. Actis, K. Bjornen, J.J. Constantine, W.W. Gilbert, R.M. Hodge, L.B. Ledlow, M. Nozaki, A. Vasshus, and T. Zhang, ConocoPhillips, prepared for the 2013 SPE Annual Technical Conference and Exhibition, New Orleans, 30 September-2 October. The paper has not been peer reviewed.

This paper describes the design, testing, installation, and performance of the first fully completed well using an intelligent inner completion inside an uncemented liner with openhole packers for zonal isolation. The term “fully completed” implies full reservoir access along the pay length for production and high-rate matrix acid stimulation using limited entry for fluid diversion within well segments. The well-design concept evolved from technical challenges associated with completing long cased-and- cemented laterals in the mature Ekofisk waterflood.

Introduction

To improve acid stimulation and reduce casing deformation and well failures in the Ekofisk field, a new class of wells was introduced to the field (please see the complete paper for a discussion of field characteristics and associated challenges). These new fully completed wells were perforated along the entire horizontal section and used limitedentry techniques to distribute acid more evenly over the reservoir intervals. Perforations were generally spaced at one hole every 10 ft of reservoir net pay along the horizontal section, with stimulation volumes on the order of 20 bbl of 28% hydrochloric acid (HCl) per perforation. These new completion techniques proved successful in providing high-productivity completions with low well-failure rates. Post-stimulation skin values have been found to be in the -4 to -4.5 range, while liner deformation and well failures have decreased.

The new fully completed designs were first implemented in horizontal wells with cemented liners, but as confidence in the designs increased, conceptual planning moved to openhole designs with uncemented liners. To improve the fully completed well designs further, it was desired to combine the benefits of a surface-operated intelligent-well system (IWS) for downhole flow control with limited-entry diversion to provide uniform acid distribution along pay intervals in an uncemented liner. This led to the Ekofisk 2/4-B-19C (hereafter referred to as the B-19C) well design. For a discussion of the functional requirements, design features, and modeling and testing of the uncemented-liner completion and all of its components, please see the complete paper.

Operational Highlights

The complex nature of the naturally fractured chalk in the Ekofisk field makes it challenging to predict the pattern of the waterflood, leaving the details of the final completion to be decided only after the well has been drilled. A sophisticated logging plan was implemented to characterize the wellbore better and improve hole-conditioning efforts. Among the logging-while-drilling (LWD) tools used was a deep directional electromagnetic (DDEM) tool, which helped with trajectory planning while drilling. Approximately halfway into the Tor formation, the DDEM readings indicated that the well was being drilled into the lower, wet layers of the target Upper Tor formation near the border of deeper Tor layers. After passing through a fault, higher resistivity values were seen above the well and the decision was made to increase the hole angle from 90 to 94°, steering up and into an oil-filled formation. The presence of subseismic faults and layers with high water saturations also plays an important role in the decision on where to blank off sections with openhole packers and solid liner joints vs. where to expose the liner to the reservoir by use of acid-soluble plugs. Fig. 1 shows the point at which the decision was made to build to 94° in an effort to remain in the oil-saturated Tor interval.