Executive Summary

It is with great pleasure that I write my first Executive Summary as Co-Executive Editor of SPE Reservoir Evaluation & Engineering. I accepted this post at the end of 2016 from former CEE Dr. Stephen Laubach. I want to thank Stephen for his dedicated service to SPE. Stephen is still part of our editorial team as Associate Editor. Since the beginning of my tenure, I have been working closely with the editorial office and the Associate and Technical Editors to provide readers with high-quality material for the upcoming issues. I truly appreciate the time and commitment of our volunteers performing critical reviews to ensure innovative and clear papers.

This issue of SPE Reservoir Evaluation & Engineering brings you 20 papers covering various topics, including enhanced oil recovery, reservoir simulation, fluid properties, formation evaluation, geostatistics, heavy oil, reservoir simulation, unconventional reservoirs, and well testing.

Enhanced Oil Recovery. The first paper of this section focuses on a new mathematical model, which could be used to simulate the combination of cocurrent and countercurrent imbibition, where one end face of the core is exposed to water and the other is exposed to oil. The second paper provides a comprehensive paleo-oil analysis for samples obtained from reservoir sponge cores. 

Fluid Properties. This paper is designed to provide a guideline for how to obtain reliable and consistent pressure/volume/temperature data from a laboratory. In addition, it reviews and extends existing consistency checks with a critical focus on the Y-function. 

Formation Evaluation (Petrophysics). This section presents several interesting papers geared toward improving our understanding of petrophysics. The first paper deals with the study of secondary mineralization and tortuosity within natural fractures, which is an important topic because morphology of the fractures indicates that they can be open or partially or completely mineralized. The second paper covers the application of reservoir surveillance with pulsed-neutron-capture (PNC) logs to provide time-lapse hydrocarbon saturations. It shows the importance of PNC logs in understanding reservoir fluid movement and chasing migrated hydrocarbons behind casing by showing a case study from the UK Central North Sea. A third paper studies the technical and economic factors to consider for calculating net pay. The proposed mobility cutoff is based on Darcy’s equation combined with profitability conditions to quantify the cutoff in hydrocarbon reservoirs. Another paper studies the effect of heterogeneous distribution of petrophysical properties in carbonate formations on injectivity loss during water-alternating-gas injection cycles. Finally, this section presents a case study of integration of old and new core and borehole measurements and 3D seismic data for effective reservoir characterization of a reservoir in the south-eastern Niger Delta. 

Geostatistics. Two papers on this topic are presented on this issue. The first paper presents a comprehensive approach to determine the number of appraisal wells, their sequence of drilling, and their justification by using a stochastic approach for optimal sequencing. A second paper proposes a new stochastic method to reconstruct a 3D image of a rock by use of only a 2D section of an imaged rock sample. The method is derived from a simple observation that the pores are gradually deformed from one section to the next. 

Heavy Oil. In this section one paper presents recent experimental studies on superheated solvent injection for heavy-oil recovery, which shows that when a solvent is injected into the reservoir, the process is highly sensitive to pressure and temperature. The paper formulates the optimal field-scale application conditions that yield maximum profit. Another paper focuses on contact-angle measurements to evaluate the wettability alteration on mineral plates and porous-rock samples, which included heavy-oil/bitumen containing carbonates using solvents, high-pH solutions, and nano/ionic liquids. This section closes with a paper proposing a practical methodology for consideration of anomalies during the integration of 4D seismic in steam-assisted-gravity-drainage reservoir characterization. 

Reservoir Simulation. This section presents three papers dealing with fractured reservoirs. The first paper considers space/time fractional diffusion in a linear, bounded region and derives an analytical expression for the pressure distribution in the bounded region in terms of the Mittag-Leffler function and the Laplace transformation. It deduces responses that may be expected in nanoporous reservoirs that are usually produced through horizontal wells containing multiple hydraulic fractures. The second paper describes an efficient method to model fractures with complex geometries with reservoir simulators. It demonstrates the accuracy of the approach by performing a series of case studies with two commercial reservoir simulators and comparing the results with local-grid-refinement models and a semi-analytical solution. The last paper of this section implements polymer transport and fluid rheology in a fully implicit hydraulic-fracturing and reservoir simulator. The simulator was used to investigate the effect on injectivity of shear thickening at high shear rates near the wellbore. 

Unconventional Reservoirs. One of the most popular topics these days is unconventional reservoirs (UR); here, we present four interesting UR papers. The first paper focuses on experimental measurements that visually and quantitatively investigate the hydraulic characteristics of rough fractures in the presence of proppants to optimize hydraulic-fracturing design in UR. The second paper examines the potential of the huff ’n’ puff gas-injection method to recover condensate in shale gas-condensate reservoirs by conducting experiments on a shale core. The study shows that condensate recovery was increased by applying huff ’n’ puff gas injection on a shale core. Another paper shows the development of a methodology that integrates decline curve analysis (DCA) models in UR with an approximate Bayesian probabilistic method that is based on rejection sampling to quantify the uncertainty associated with DCA models. The last paper of this section presents a workflow that uses microseismic (MS) to better characterize the stimulated reservoir volume in hydraulically fractured shale wells. The paper shows a spreadsheet-based method to divide the MS events from each fracture stage into three windows—the pad window, the proppant window, and the closure window—on the basis of the fracture-stimulation record of each stage

Well Testing. The lone paper in this section presents a case of harmonic pulse testing to identify non-Darcy effects in gas reservoir. Characterization and monitoring of the non-Darcy effects is key for defining an optimal reservoir exploitation strategy. 

The editorial committee made every effort to bring you a robust issue by selecting innovative and useful papers from industry and academia. All papers were carefully reviewed by knowledgeable technical editors under the coordination of the associate editors. However, conclusions and interpretation stemmed from these papers are opinions and observation of the authors. Because knowledge sharing and open discussions are important, SPE welcomes further discussion from our readers. I look forward to receiving discussion letters.

Happy reading!

Jesús M. Salazar,
SPE Res Eval & Eng Co-Executive Editor,
ConocoPhillips, Houston