Executive Summary

Cosan Ayan, Schlumberger
Behrooz Fattahi, Aera Energy

In this issue, I would like to give a brief summary from the recent reader survey concerning the quality of SPE Reservoir Evaluation & Engineering. The SPE staff conducted the survey by contacting members worldwide. As of June 2008,SPEREE journal had 4,207 total subscribers with 52% from North America and 25% from Europe/Russian Federation. After those large groups, readers from the Asia/Asia-Pacific region make up 10% of the subscribers, followed by 6, 5, and 2% for the Middle East, South America/Caribbean, and Africa, respectively. Oil company subscribers lead with 55% of the readers, followed by service/manufacturing companies with 19%, while 14% of the subscribers were consultants, and 7% were from academia.

With this subscriber profile, most of the response on journal quality comes from North America and Europe/Russian Federation. Out of the 229 responses received to the question "Overall, how do you rate the technical content of SPE Reservoir Evaluation & Engineering?", 27% of readers answered with "excellent," 56% "very good," 14% "good," 2% "fair," and 1% "poor." Eight percent of the attendees thought that the value of the journal "improved significantly" and 40% responded as "improved" over the last 2 years, while 37% thought it was the "same." Some of the respondents also read a non-SPE journal that covers similar topics to SPE Reservoir Evaluation & Engineering. When asked to compare our journal with non-SPE journals, 23% of responses endorsed SPEREE as "significantly better," 37% thought it is "somewhat better," 35% said it is "about the same" and 5% responded as "somewhat worse." None thought that our journal is "significantly worse."

The respondents stressed the importance of the peer-review process and 51% thought that "Peer-review added significant value to a paper and were willing to wait for the review process." 29% said that "peer-review was valuable, but the content of the paper becomes less valuable if the review process took too long." The "timeliness was very important" for 8% of the respondents and 12% said "rapid access to the best papers, regardless of whether they were peer-reviewed was most important."

The spread of respondents per company type and profession are shown in Tables 1 and 2, respectively.

The survey gives us a glimpse of information on how the journal is perceived by a limited number of respondents and by no means puts the review committee and SPE staff at ease. The whole review system, both in quality and quantity, is going through a continuous improvement process. While we see some results already, we hope to speed up the peer-review process further along with assuring a quality journal.

This issue starts with a simulation paper and modeling carbonate reservoirs is often a challenge. Al Shaheen field in Qatar, which had broken a few "longest horizontal well" records at the time is no exception with varying fluid properties, wettability changes, several long horizontal wells, reservoir complexities, tilted oil/water contact, and separate gas caps. The paper "The Application of Unstructured Gridding Techniques for Full Field Simulation of a Giant Carbonate Reservoir Developed with long Horizontal Wells," outlines the challenges and how a 2.5D PEBI grid around horizontal wells helped overcome some computational issues and increased interwell resolution. Net-sand, net-thickness, net-to-gross, cut-off(s) have been used extensively in our literature and often experts put different meanings on these terms. In the paper "The Application of Cutoffs in Integrated Reservoir Studies," the author focuses on rock typing, scale, and depletion mechanism dependency of cut-off determination. It outlines a workflow for the application of cut-offs in integrated reservoir studies. "A Parametric Study on the Benefits of Drilling Horizontal and Multilateral Wells in Coalbed Methane Reservoirs," presents a study on coalbed methane reservoirs considering horizontal and multilateral completions. Using permeability, desorption characteristics, and gas content as parameters with net present value as an evaluation yardstick, the authors show quadmultilaters as the optimum drilling configuration. In the paper "Seismic Facies Identification and Classification Using Simple Statistics," the authors propose a statistical approach to identify and classify facies using seismic amplitude data. The method was applied to a synthetic and a real data set to estimate facies types along with their probabilitistic spatial distributions. In a related paper, "Seismic Reducing Reservoir Prediction Uncertainty by Updating a Stochastic Model Using Seismic History Matching," the authors outline an automated history matching method that includes 4D seismic and production data. The method was used in the Schiehallion-UK Continental Shelf turbidite reservoir. The time-lapse data was shown to reduce the uncertainty in predictions of the areal sweep and the pressure distribution. Low-salinity waterflooding has been studied in the literature and shown to increase the recovery factor in clastics, mainly resulting from a wettability change toward a more water-wet rock. The paper, "Modeling Low-Salinity Waterflooding," proposes an extension to waterflood simulators in which salt is treated as a component and saturation functions are expressed as a function of salinity, also considering hysteresis and a dispersion model in the aqueous phase. Saturation-height models were developed for each hydraulic unit in the paper "Relative Permeability Coupled Saturation-Height Models on the Basis of Hydraulic (Flow) Units in a Gas Field." Depositional-and diagenetic-rock-fabric information were linked to hydraulic units and the hydraulic units with similar capillary pressure relationships were then associated. Hydraulic-unit-based relative permeability models have been developed for the gas field under study, which agreed with steady-state relative permeability data. Loss of injectivity in a pilot waterflood project prompted the authors to study reactive transport modeling and core floods. In the paper, "Using Laboratory Flow Experiments and Reactive Chemical Transport Modeling for Designing Waterflooding of the Agua Fría Reservoir, Poza Rica-Altamira Field, Mexico,"the authors conducted laboratory coreflood experiments studying the sensitivity of mineral dissolution and precipitation effects to water composition. Untreated native reservoir water was found to cause serious porosity and permeability reduction because of calcite precipitation. Using treated water that performed well in the laboratory flow experiments allowed injection to proceed. The paper, "Streamline-Assisted Ensemble Kalman Filter for Rapid and Continuous Reservoir Model Updating,"brings an active research topic with fast assimilation of new information in existing reservoir models. Using synthetic and field data, the authors show the merits of streamline assisted ensemble Kalman filter (EnKF) to overcome some of the existing limitations of the EnKF approach. By conditioning the cross-covariance matrix using information obtained from streamline simulation, the approach retains key geological features, decreasing the severity of the overshooting problem reported in earlier implementations of the EnKF. Fracture corridors are subvertical, fault-related fracture swarms that intersect the reservoir and have considerable lateral extension. The paper "Using Probabilistic Decision Trees to Detect Fracture Corridors From Dynamic Data in Mature Oil Fields," describes a method that uses direct and indirect fracture indicators in dynamic data. The probabilistic decision trees can be useful in mapping fracture corridors in mature fields with insufficient image log data and in cases in which only major faults could be identified by seismic-map attributes. Continuing with another study focusing on fractures, the paper "An Integrated Geologic and Engineering Assessment of Fracture-Flow Potential in the Ratawi Reservoir of the Wafra Field, Partitioned Neutral Zone," shows that only a limited number of fractures have a significant effect on the production behavior of the Ratawi reservoir. Fractures were encountered throughout the field, but fracture-influenced reservoir behavior was confined to the periphery. The study suggests that for the largest part of the field, explicit fractures are not necessary in the flow-simulation models. "Using Drillstem and Production Tests to Model Reservoir Relative Permeabilities," first shows that relative permeabilities, rather than fluid saturations and fluid properties, are usually the least certain data during history matching. Next, the authors investigate why relative permeabilities have the greatest uncertainty and conclude that the answer is the inability to prepare core samples, which properly consider oil emplacement in the reservoir and the subsequent geological history. The authors then suggest greater reliance on drillstem testing and production data to derive relative permeabilities, showing a case from an abandoned North Sea reservoir. Using the Devonian Antrim shale gas case, the paper, "Economic Decision Making and the Application of Nonparametric Prediction Models," shows the uses of local nonparametric regression models to estimate remaining resources of unconventional gas in untested areas. The methods also helps in the strategic ordering of drilling prospects and has the benefit of updating predictions as new drilling results become available. In a highpressure air injection project, air is injected at high pressure into an oil reservoir and combustion is initiated. The paper "Recovery Factors in High-Pressure Air Injection Projects Revisited," presents a technique based on the "volume-burned method" to compute the recovery factor which uses laboratory results and field data mostly gathered from the Buffalo field. A new downhole fluid analysis tool is described in the paper "New Downhole-Fluid-Analysis Tool for Improved Reservoir Characterization,"  that has two different optical spectrometers with 36 channels in total. The spectrum is used for analysis of fluid hydrocarbon composition, CO2 content, GOR, water content, water pH, and mud-filtrate contamination. It also has fluorescence,density-viscosity, pressure, and temperature sensors. In "Key Aspects of Project Design for Polymer Flooding at the Daqing Oilfield," the authors summarize the extensive polymer flooding experience from Daqing oilfield in China, which started polymer injection in late 1995. Design procedures were outlined, covering profile modification, zone isolation, optimum polymer formulations, injection rates, and time-dependence of the molecular weight of the polymer used in the injected slugs.