Executive Summary

As before, I would like to take this opportunity to cordially thank all of our editors, without whom this journal would simply not be possible. The Executive Editor distributes the incoming manuscripts, corresponds with the authors, and represents SPE Drilling & Completion, but the majority of work with the peer reviews (the “heavy lifting” behind the scenes) is performed by our associate editors (AEs). Therefore, it is my privilege and pleasure to recognize the team of industry experts currently serving as AE, volunteering their scarce spare time to manage our peer reviews, identifying quality papers for publication (only main areas of expertise are listed below):

  • Bernt Aadnøy - Drilling Design and Analysis, Wellbore Design/Construction, Research
  • Ramadan Ahmed - Well Control, MPD and Underbalanced Drilling, Hole Cleaning, Research
  • Mark Brinsden - Perforating, Completion Planning, Design and Installation, Interventions
  • Curtis Cheatham - Directional Drilling, Drillstring Dynamics, Drilling Equipment
  • Shilin Chen - Bit Design and Optimization, Drillstring Dynamics, Bit Selection
  • Alexander Crabtree - MPD and Underbalanced Drilling, Downhole Tools and Equipment
  • Barkim Demirdal - Drilling Fluid Rheology, Heavy Oil, Shale Gas, Drilling Design
  • Simon James - Cement, Remedial Cementing, Zonal Isolation, Downhole Operations
  • Vassilios Kelessidis - Cutting Transport, Drilling Hydraulics, Multiphase Systems
  • John Mason - Completion Planning, Design and Installation, Intervention Operations
  • Stephane Menand - Drillstring Design and Dynamics, Bit Selection and Performance
  • Kaibin Qiu - Geomechanics, Wellbore Stability, Compaction and Subsidence
  • David Stiles - Cement, Wellbore Integrity, Lost Circulation, Downhole Operations
  • Carl Thaemlitz - Fluid Chemistry, Drilling Fluids, Handling, Processing and Treatment
  • John Thorogood - Real-Time Operations, Drilling Automation, Directional Drilling
  • Claas van der Zwaag - Completion Planning, Design and Installation, Sand Control, Impairment
  • “Joe” Yunxu Zhou - Drilling Design and Analysis, Telemetry, Automation, Drilling Hydraulics 

Together with our more than 160 technical editors and, not least, the staff in the SPE office that make this journal happen with their energy and dedication: 

Many thanks to you all!

And now on to our articles, which are hoped to provide you with some useful ideas for the various professional targets aspired.

Completion. Maximizing long-term production (or injection) by applying suitable and cost-effective completion technologies is a top priority and constant challenge for many of us. And I encourage reading of our first article in this issue because it offers a useful case history showing what respective optimization measures have been investigated in an oil field on the Alaskan North Slope.

In paper Completion Optimization Provides Step Changes in Horizontal Well Performance in the Oooguruk Field, Alaska, the authors start by introducing the field, its reservoirs (developed by horizontal wells with longitudinal fracturing and waterflooding), and the logistical challenges on a man-made island in the Beaufort Sea. They further share the historical development of completion techniques for the production [openhole (OH) unstimulated, OH liner with external packers and dynamic diversion fracturing, OH dual-lateral unstimulated, OH liner with external packers and fracture sleeves] and water-injection wells and compare respective production rates from the different completion designs. 

The authors conclude that in their circumstances OH liners with external swell packers, ball-actuated fracture sleeves, and resin-coated proppant are a promising way forward and will also be implemented for future water-injection wells. Perhaps the insights shared here can be helpful for your own completion optimization program.

Drilling. Our second paper in this issue discusses an important rig safety feature—the automated detection of mud gains or losses and the potential limitations to it. This is a topic that is highly relevant, especially for casing schemes with reduced kick margins, relying on the ability to detect smaller influx volumes than previously required in more-conservative well designs.

In Insights Into the Physical Phenomena That Influence Automatic Gain/Loss Detection During Drilling Operations, currently used detection strategies (variation of active volume, delta-flow, pressure variations in/out, processed differential flow out) are described, followed by a discussion of the transient phenomena during flow-rate changes, the effects of fluid compressibility or of mud retention in the return lines, and the situation when making connections. An example for a kick taken at connection time is also shared to demonstrate detection accuracy.

The authors conclude that transient effects potentially limiting existing detection techniques can be accounted for by respective “high-fidelity” hydraulic modelling, provided an accurate description of the drilling fluid’s rheological properties is used and constant model updates are performed. This may be something worth considering for your rigs to improve influx or loss-detection reliability

If you are working in one of the hydrocarbon provinces where the pay zone is located below a salt structure, our next article is for you because it investigates some fundamental questions about drilling salt [i.e., the manner in which rate of penetration (ROP) and mechanical specific energy (MSE) are related to bottomhole pressure]. 

The Effect of Borehole Pressure on the Drilling Process in Salt starts with a literature review and continues with a description of the experiments performed (tri-axial compression of core plugs, visual single PDC cutter tests, full scale 8 ¾-in. PDC bit drilling tests), presents the results obtained (forces, friction coefficient, ROP, MSE), and discusses these in detail (including cutting structure). The authors show that the effects of increased borehole pressure on ROP and MSE are smaller than observed in sedimentary rocks such as shale, sandstone, or limestone. 

Because the disadvantages from using a high mud density (i.e., for borehole stability) are limited, it is recommended to optimize bit design (“lowest-tolerable cutter density”) and other drilling fluid properties to increase ROP and lower MSE requirements for salt drilling. 

Especially in slot-constrained environments, but not only there, multilateral (ML) wells can be a viable option for field development. But with some of us, they might have a reputation of being highly complex, complicated, and therefore prone to failure. In case you are open to challenging this perception by digesting some facts, please read on.

In the paper Study of Multilateral-Well-Construction Reliability, the authors perform a detailed analysis of the worldwide data base from one service provider for three different ML systems installed (22 year period, 951 junctions in 778 wells, 82% TAML level 4/5, 18% TAML level 2/3) under different aspects such as reliability improvement over time, subsea vs. nonsubsea, common root causes for failure, risk increase with number of junctions per well, or reliability vs. efficiency.

They conclude that the investigated ML systems have a reliability of 93 to 99.6%, comparable with published reliability data for other technologies such as sand control or intelligent wells. And, at least, I have to admit that these figures are much higher than I initially thought.

Tools allowing quick engineering judgements can be a useful addition for the fast assessment of specific situations, and not only in times of high work load. Therefore, we offer here an “easy-to-use” approach to check hole cleaning efficiency in directional wells.

The fifth paper of this issue, A Fast Graphic Approach To Estimate Hole Cleaning for Directional Drilling, provides an introduction to cuttings transport and describes how the presented lookup charts have been developed, taking into account aspects such as well-inclination angle, density difference between mud and cuttings, fluid viscosity, ROP, and drillpipe rotation. Examples for a single hole section or the complete wellbore are provided, the chart estimations are compared with experimental results from other authors, and limitations for the use of these charts are stated (assumed parameter ranges).

It is shown that the charts have an accuracy of ± 20%, considered acceptable for practical drilling operations. Perhaps this is something you will find helpful for a quick screening in the well-design phase or the daily monitoring of your drilling operations, be it in the office or on the rig (potentially without access to sophisticated hydraulics-modeling software). 

In (offshore) wells with narrow pressure windows, the conventional pumping of cement slurry (down the string) can become a challenge because of equivalent-circulation-density (ECD) limitations. One potential solution could be reverse circulation of the slurry (down the annulus), historically used only in some special cases, and our following paper helps to assess the ECD reductions to be expected. 

A Comparative Hydraulic Analysis of Conventional- and Reverse-Circulation Primary Cementing in Offshore Wells starts with a literature review and a description of the different slurry placement techniques [conventional- and reverse-circulation primary cementing (CCPC, RCPC)] for both traditional and deepwater scenarios (the latter with a crossover tool at the wellhead below the riser). Subsequently, the authors perform a hydraulic analysis for each technique, discuss the results and provide an example calculation in the appendix.

It is concluded that the pressure difference between CCPC and RCPC is caused only by changes in frictional pressure and that potential ECD advantages from RCPC depend on the location of the “critical depth” ( zC, Eq. 23) relative to the previous casing shoe. If zC is less than shoe depth, the complete openhole section can be exposed to less pressure with RCPC, but if zC is greater than shoe depth, any weak formation to be protected would need to be located deeper than zC to benefit from lower ECD.

Our next paper is highly recommended for all colleagues concerned with designing and testing complex (offshore drilling) machinery, because it describes how computer simulations can help to evaluate control algorithms early in the design phase and reduce the scope of actual onsite tests of full-scale equipment.

In Modeling and Simulation of a Cylinder Hoisting System for Real-Time Hardware-in-the-Loop Testing, the authors provide an introduction to modeling-and-simulation software (“virtual prototyping”) and technical information about the investigated hoisting system before the mathematical modeling of mechanical and control systems is described. They share how simulation results with a complex model and a simplified model were benchmarked against data (pressure, velocity) measured on a hoisting system during actual operations and any limitations associated with the simplified (“low-fidelity”) modeling approach. 

The simulation results of both complex and simplified modeling are able to reproduce the actual reference measurements with sufficient accuracy. But, because the “high-fidelity” model is computationally very demanding (hence, slow), only the developed simplified model could be used on a commercially available PC for real-time testing.

Conclusion. That’s it for this first issue in 2017. On behalf of the entire Editorial Review Committee, I thank you for your continued support of SPE Drilling & Completion.

Christoph Zerbst, SPE Drill & Compl Executive Editor;
Petroleum Development Oman