Executive Summary

Dean Oliver, University of Oklahoma, Norman

Although SPEJ sometimes appears to focus on research related to flow in porous media, its true breadth of coverage is illustrated by the content of this month’s issue, which includes papers from reservoir, production, and drilling and completions engineering.

SPEJ has a long history of publishing innovative papers on the development of new methods for history matching. Many of the classic papers of the “first golden age” of history matching were published in the predecessor of the current SPEJ. Research in the area of automatic or assisted history matching slowed for a number of years, but has had a strong resurgence in the past 10 years, owing at least partly to increases in computational power, but also to developments in geostatistics and the interest in uncertainty quantification.

This month’s issue of SPEJ contains three papers on history matching and one on well testing. Although well testing might not seem to be closely related to history matching, the goals of both are in fact quite similar—to estimate properties of the reservoir from measurements of rates and pressures at wells. In well testing, the estimation is typically done through comparison of observed pressure data with standard analytical solutions for constant production rate wells in reservoirs that are initially at equilibrium. If these limitations are not valid because of rate variation during production or the influence of rate variations at other wells, those effects must usually be removed before the data can be analyzed. In “Deconvolution of Multiwell Test Data,” Levitan discusses a generalization of standard single-well deconvolution to multiwell pressure and rate data.

A major difference between well-testing and history matching is the number of parameters that are estimated. When experimental design methods are used for history matching, the goal is often to identify the parameters that have the greatest effect on the quality of the history match. In “Semi-Automatic Multiple Resolution Design for History Matching,” Li and Friedmann introduce a methodology for selecting sampling points to improve the accuracy of response surface approximations to the objective function. The approximation to the objective function is iteratively improved until adequate accuracy is achieved. In the second paper on history matching, “An Iterative Ensemble Kalman Filter for Multiphase Fluid-Flow Data Assimilation,” Gu and Oliver extend the applicability of the ensemble Kalman filter to problems of greater nonlinearity. Finally, in “Compressible Streamlines and Three-Phase History Matching,” Cheng, Oyerinde, Datta-Gupta, and Milliken introduce the concept of an effective density of total fluids to generalize the definition of streamlines in compressible flow. This formulation allows efficient streamline sensitivity computation to be performed for three-phase flow problems.

Four additional papers in this issue relate to various aspects of reservoir engineering and evaluation. The first two describe improvements in oil recovery. In “Wettability Alteration to Intermediate Gas-Wetting in Gas-Condensate Reservoirs at High Temperatures,” Fahes and Firoozabadi describe the use of a water-soluble fluorocarbon polymer to permanently alter reservoir wettability from liquid-wetting to intermediate gas-wetting at high temperatures, resulting in an improvement of flow of oil and gas condensates around the wellbore. In the second paper, “Impact of Viscous Fingering on the Prediction of Optimum WAG Ratio,” Juanes and Blunt investigate variation in the displacement efficiency and the mobility ratio with WAG ratio across the solvent front in a miscible flood, when fingering is included in the analysis. Although their prediction of the optimum WAG ratio is not greatly different from that estimated by Stalkup’s method, the authors’ method, which includes the effects of fingering, suggests that it is beneficial to inject more solvent.

The third and fourth reservoir papers describe improvements in laboratory measurement techniques and understanding of physical phenomena of the near-well region. In “Capillary Wicking in Gas Wells,” Mahadevan, Sharma, and Yortsos investigate the fundamental issue of changes in water saturation owing to evaporation caused by gas expansion in the near-wellbore region during production of gas wells. The authors model the evaporation process by accounting for the capillary driven film flow of saline brines to the wellbore region and the effect of gas expansion. In “Acid Number Measurements Revisited,” Fan and Buckley propose an improved procedure for measuring acid numbers of crude oil samples. They suggest that acid number measured with the new procedure can be used with other crude oil properties to evaluate interfacial properties of oils.

Three of the last papers might be classified as geomechanics and fluid mechanics of petroleum engineering problems. Based on results of a numerical analysis of flow in coiled tubing, Zhou and Shah develop a new friction factor correlation applicable to the flow of a wide range of fluids in coiled tubing operations. The authors compare the predictions with experimental data from recent full-scale experiments in their paper “Theoretical Analysis of Turbulent Flow of Power-Law Fluids in Coiled Tubing.” In the first geomechanics paper, “Feeling the Pulse of Drill Cuttings Injection Wells—A Case Study of Simulation, Monitoring, and Verification in Alaska,” Guo, Abou-Sayed, and Engel describe the monitoring and analysis of data from continuous deep disposal of drill cuttings and open pit materials on the North Slope of Alaska. The large capacity of the injectors and the increase in system storage indicated that previous fractures were open during subsequent injections, and part of the injected slurry went to previous fractures.

The final paper of this issue, “Comprehensive Transient Modeling of Sand Production in Horizontal Wellbores,” by Nouri, Vaziri, Belhaj, and Islam, models the initiation and rate of sand production in horizontal wells. Their model indicates that removal of the failed material during production may trigger additional shear failure of the formerly intact material. Results from the numerical model are compared with experimental data on large block tests.

Three new Review Chairs join us with the December issue. Hisham Nasr-El-Din is currently a senior PE consultant with the Saudi Arabian Oil Company. His areas of expertise include facilities operations, oilfield chemistry, and production enhancement. Kassem Ghorayeb is currently a principal reservoir engineer with Schlumberger in the North Kuwait Jurassic Project. He has conducted research on numerical simulation and mathematical modeling of compositional variation and fluid flow in homogeneous and fractured hydrocarbon reservoirs. Kristian Jessen is an assistant professor in the Mork Family Department of Chemical Engineering at the University of Southern California. His research interests include flow and transport in porous media, phase behavior, transport properties of nonideal mixtures, and CO2 sequestration.