Welcome to the December issue of this 30th volume of SPE Drilling & Completion journal. As my term comes to an end with this issue, I would like to say that it has been my pleasure to serve these past 3 years as executive editor. I am very glad to announce that the next executive editor for our journal is Christoph Zerbst of Petroleum Development Oman LLC. I know that this journal is in excellent hands with Christoph and that he will do an outstanding job of managing changes and improvements to SPEDC. I look forward to reading next year’s issues… I hope that you do, too.
Journal Performance Statistics
SPEDC continues to show generally favorable metrics, with notable improvements in time to render a decision to authors and in citation index. The following are highlights of performance statistics for the period July 2014 to June 2015:
• 160 papers were submitted for review, 70% as direct-to-peer and 30% from conferences
• 20% acceptance rate
• 171 technical reviewers participated
• 355 reviews submitted
• 61 days average time to initial decision
• 150 initial decisions
• 117 final dispositions
• 3523 subscribers
• Impact Factor has increased by 80% to 0.46
And now, on to the papers…
Our first paper for this issue of SPEDC presents how an in-depth understanding of the mechanical properties and in-situ stresses of the Keshen reservoir was obtained and subsequently applied to optimize stimulation designs. In Geomechanical-Evaluation Enabled Successful Stimulation of a High-Pressure/High-Temperature Tight Gas Reservoir in Western China, an integrated geomechanical evaluation was conducted with core evaluations and well-logging data obtained from within the field. The authors present a laboratory investigation into the mechanical behavior of the reservoir’s sandstone under realistic in-situ stresses, pore pressures, and temperature. The mechanical behaviors observed were used to calibrate and augment mechanical-earth models, whose validity was shown through comparisons between wellbore stability predictions and the field-based observations of microresistivity images.
Controlling fluid loss properties is an important parameter for certain fracturing fluids. One method to reduce fluid loss is to add silica flour, which may introduce potentially damaging, insoluble materials to the fluid formulation. Development of Polyglycolic- and Polylactic-Acid Fluid-Loss-Control Materials for Fracturing Fluids presents the investigations and conclusions drawn from laboratory testing and subsequent numerical modeling for polyglycolic acid (PGA) and polylactic acid (PLA) fluid loss agents. The authors found that powdered, granular, and fibrous materials made of PGA or PLA are suitable for fluid loss agents, because of their favorable mechanical properties along with the capability of dissolution after application.
The suspension of lost circulation materials in a drilling fluid is as important during general wellbore circulation as it is during special operations, such as hesitation-squeezes. Managing Suspension Characteristics of Lost-Circulation Materials in a Drilling Fluid presents an experimental study of the suspension of a range of lost-circulation materials (LCMs) in various drilling fluids. From experimental data, semiempirical models were developed to help predict the influence of suspending aids upon LCMs in drilling fluids. The design parameters used in these models include fiber concentration, fiber density, number of fibers per unit volume, and the average fiber length and diameter. The study focuses on the LCM/fluid-interaction aspect, and provides novel methods to address the suspension challenge presented by large LCM particulates.
The rheological properties of cement slurries may vary greatly with the change of temperature, which not only increases the complexity of cementing job design but may detrimentally affect cement quality. Cement Slurries With Rheological Properties Unaffected by Temperature presents us with solutions for this problem through cement slurries improved by the addition of a thermosensitive viscosity controller. This cement slurry exhibits temperature stable rheological properties between 20 and 120°C, yet still exhibits performances needed to address the demands of well cementing. It has been used successfully in the oil field and the results show that the cementing job quality is acceptable.
Cement Evaluation—A Risky Business teaches us that cement evaluation is much more than just the running of a cement bond log. We are presented with the view that to properly evaluate a cement sheath one must understand all knowledge of the cement job, slurry designs, and the limitations of the evaluation techniques applied. The author reviews various methods of cement evaluation—from job data, casing- and formation-pressure testing, through sonic and ultrasonic logging. The assumptions associated with each technique are outlined, and the discussion includes some of the limitations of the various techniques, along with cautions on how misinterpretation of the results can lead to assumptions of cement integrity that may not be appropriate.
Lightweight cement can present unique challenges to efficient and accurate evaluation of cement-sheath integrity. Ultrasonic-Log Response in Lightweight-Cement Conditions details these unique challenges, such as how standard bond-log tools require high compressional bonding to the casing in order to observe an attenuation of the sonic signal that is set up inside the casing. Lightweight cement exhibits high amplitude and little alteration in the log waveform on conventional bond logs because of lower fluid density when pumped and lower compressive strength after being set up. These properties can make the log appear as if no cement is present. This paper demonstrates the application of ultrasonic cement evaluation tools under these difficult conditions. Examples of conventional cement, lightweight cement, and settable efficiency fluids are considered.
Designing a polycrystalline-diamond-compact (PDC) bit with higher drilling efficiency and longer bit life is almost always the objective during PDC bit design optimization. In our final paper, a newly developed PDC cutter-force model and a new bit model are presented and discussed within The Role of Rock-Chip Removals and Cutting-Area Shapes in Polycrystalline-Diamond-Compact-Bit Design Optimization. The authors present how almost all previous cutter-force models assumed that cutting force was proportional to cutting area and why cutting-area-based bit models failed to properly predict bit forces. In this new cutter force model, cutting force is a function of the shape of the cutting area. Three-dimensional rock chips created in front of the cutting face are modeled, meshed, and removed from the hole’s bottom by updating the hole bottom at each timestep. Laboratory test results of four PDC bits confirmed that the new bit model is able to predict the sensitivity of bit drilling efficiency to the changes of bit design variables (e.g., cutter-layout methods). Successful field applications demonstrated the usefulness of the new bit model in PDC bit design optimization.