Executive Summary

The second issue of Volume 22 of SPE Reservoir Evaluation & Engineering comes with a lineup of 28 papers, one of the largest in a while. The papers cover a diverse number of topics in reservoir engineering, formation evaluation, and oil and gas economics. Seven papers deal with the always growing research on unconventional reservoirs. We are also featuring two papers in the spotlight of the trending topic of machine learning and data analytics (MLDA). We will be spotlighting papers on MLDA throughout the year to highlight the importance of its application in the oil and gas industry.

I would like to welcome new Associate Editor Chicheng Xu, an energetic young professional who brings a breadth of experience in formation evaluation and data analytics, two of the main topics covered by this journal. The staff and editorial committee of the journal truly appreciate the contribution of our volunteers who step up as associate editors, technical reviewers, and authors.

Below you will find brief summaries of the papers comprising this issue of SPE Reservoir Evaluation & Engineering.

Spotlight on Machine Learning and Data Analytics. This section presents two papers that describe the application of MLDA for production data classification to select restimulation candidates and to interpret flow-rate, pressure, and temperature data from permanent downhole gauges. 

Petrophysics of Unconventional Reservoirs. Understanding the pore-scale structure and fluid transport in tight rocks is fundamental to optimal development of unconventional resources. This section brings you three papers dealing with multiscale experimental studies on interactions between aqueous-based fracturing fluids and tight organic-rich source rocks; a laboratory study on water weakening of Marcellus, Woodford, Eagle Ford, and Wolfcamp shales; and a new method using high-field-core nuclear-magnetic resonance to characterize source-rock porosity and fluids.

Analysis of the Stimulated Reservoir Volume. Prediction of unconventional reservoir performance is critical; in this vein, two papers deal with characterization and modeling of the stimulated reservoir volume associated with multistage hydraulically fractured horizontal wells, namely, long-period, long-duration seismic events and their probable role in reservoir stimulation and stage productivity and a practical methodology for production-data analysis of single-phase unconventional wells with complex fracture geometry.

Enhanced Oil Recovery in Unconventional Reservoirs. Oil recovery from tight reservoirs under primary production is less than 10% at best; improving recovery is a very active area of investigation. Two papers describe emerging technologies for improving recovery from tight liquid reservoirs, which includes an interpretation of proppant transport within the stimulated reservoir volume in the Permian Basin and a compositional simulation of CO2 huff ’n’ puff in the Eagle Ford formation with CO2 molecular diffusion.

Formation Evaluation. The various papers on this section study wettability estimation using surface-complexation simulations, laboratory study of ultrasonic velocity variations during CO2 flooding, real-time borehole fluid-sampling-contamination prediction using inversion techniques, and determination of maximum allowable safe-core-retrieval rates.

Chemical Enhanced Oil Recovery. Continuing with the enhanced-oil-recovery theme, four papers describe different research projects on chemical enhanced oil recovery, including quality assurance and quality control of surfactants for field-scale enhanced-oil-recovery pilot projects, polymer-flood field implementation, field oil-production response of injection-well gel treatments, and an improved method of moment to determine mobile-phase saturations using a single-well chemical-tracer test.

Phase Behavior. Thermodynamics is a science that we see in our everyday life just by looking at the water cycle: evaporation, condensation, rain, etc. Two papers present phase-behavior studies on hydrocarbons—an experimental study of emulsion phase-behavior of Athabasca bitumen/diethylamine/brine mixtures and an evaluation of steady-state-based pressure-saturation predictions in gas-condensate reservoirs under various reservoir and well-operating conditions.

Reservoir Simulation. Numerical reservoir simulation allows us to understand how a reservoir behaves by using first principles and physics of fluid flow. This section brings you a description and quantification of truncation errors produced by local-grid refinement in reservoir simulation and a Darcy-scale simulation of boundary-condition effects during capillary-dominated flow in high-permeability systems.

Production Optimization Modeling. Two papers describe new approaches for dynamic production modeling. The first paper describes a workflow to characterize waterflood-induced fractures by integrating real-time monitoring, formation test, and dynamic production analysis applied to Changqing Field in China. The second paper introduces a method of network-constrained production optimization by means of multiple shooting.

Pressure-Transient Analysis. This section features two relevant papers covering field-wide determination of directional permeability using transient well testing and pressure-transient responses of fractures with variable conductivity and asymmetric well location.

Oil and Gas Economics and Uncertainty. The last section of this issue presents a topic that is relatively new to our journal, economics and uncertainty. The first paper studies value of information of a horizontal polymer pilot under uncertainty incorporating the risk attitude of the decision maker, the second paper evaluates the technical efficiency of upstream companies of different size in Nigeria, and the third paper studies the single-tier and dual-tier tax systems and their implication for petroleum project economics in Nigeria.

As in every issue, the editorial board has made every effort to bring you a robust selection of manuscripts from industry and academia. All papers were carefully reviewed by at least two technical reviewers under the coordination of an associate editor. However, conclusions and interpretations stemming from these papers are opinions and observation of the authors. I would like to express my appreciation to the technical reviewers who selflessly dedicate their time to perform outstanding reviews to maintain the quality of our journal.

We at SPE always welcome further discussion from our readers. I look forward to receiving your comments and suggestions. Hope you enjoy these outstanding papers!

Jesús M. Salazar, SPE Res Eval & Eng Executive Editor,
Marathon Oil, Houston