Executive Summary

Cosan Ayan, Schlumberger
Anil Ambastha, Chevron

April brings a number of significant changes to the online versions of SPE's peer-reviewed journals. Those of you who rarely visit the online journals might find it rewarding to do so, as a number of new features are available that will greatly enhance your use of the journals. I'll outline a few of these developments, and then we'll review the 15 papers in the April issue of the SPE Reservoir Evaluation & Engineering Journal.

To begin with, you may be interested to know that the online journals now feature a page that displays the most downloaded papers from the journal in the past 30 days, an important reflection of what our readers value, and a potential indication of current research needs. This information includes all data collected since SPE began tracking download information in May of 2007.

Next, SPE is moving toward an article-based journal publication system, in which papers will be published online first, thus guaranteeing that information is released in a timely manner. Then, after online publication, papers will be selected for inclusion in print issues of the peer-reviewed journals. This new process allows the journals some freedom to concentrate on themes and topics of current interest, thereby better serving our readers, while further improving the time between acceptance and publication.

Individual papers in the online journals include a bevy of new features you’ll appreciate. Author names are hyperlinked to conduct a search on the author's name in OnePetro, so you can easily see what else this person has written. Discipline categories and author-supplied keywords are shown where available (a feature that is expected to expand over time as authors become used to supplying keywords). Furthermore, a proper citation for the paper itself is provided; citations can be downloaded to EndNote or other format for use in a bibliographic program. Finally, tools are available to easily transfer information on a paper to one of the online reference tagging and sharing sites, including citeulike2collabConnoteaBibSonomy, and deli.cio.us. I encourage you to visit the online journals and look into these exciting new features and functions.

Now, however, we turn our focus to the April issue, which includes some papers on multiphase transfer functions for naturally fractured reservoirs. The paper "Verification and Proper Use of Water-Oil Transfer Function for Dual-Porosity and Dual-Permeability Reservoirs" uses 3D fine-grid numerical modeling of a matrix block and compares the results with a simple transfer function for a water/oil system. The approach can be extended to dual-permeability systems and requires matrix capillary pressure curves, fluid densities, and block dimensions. In a closely related paper, "A Critical Review for Proper Use of Water/Oil/Gas Transfer Functions in Dual-Porosity Naturally Fractured Reservoirs: Part I," the authors use a similar approach to investigate oil/water and oil/gas transfer functions. For immiscible flow, capillary and gravity forces provide the main control for oil drainage from a matrix block, whereas viscous displacement is, in general, negligible. In the second part of the paper, "A Critical Review for Proper Use of Water/Oil/Gas Transfer Functions in Dual-Porosity Naturally Fractured Reservoirs: Part II," the authors study the flow of a low-concentration, water-soluble surfactant in the fracture and modify the transfer function to account for the early slow mass transfer into matrix. They also give an analytical approximation to the differential equation of fracture to matrix mass transfer and a method of solution to predict oil drainage performance. Continuing the theme of fractured reservoirs, the paper "Multiphysics and Multiscale Methods for Modeling Fluid Flow Through Naturally Fractured Carbonate Karst Reservoirs," models fluid flow in porous rock as well as in vugs and caves by combining Stokes and Darcy flows in a single system of equations. The equations also allow accurate scale-up for flow modeling. In still another paper related to fractured reservoirs, the authors develop 2- and 3D fractal discrete fracture networks; their paper "Estimation of Fracture Porosity of Naturally Fractured Reservoirs With No Matrix Porosity Using Fractal Discrete Fracture Networks" outlines the algorithms which are applicable for reservoirs where fractures provide the main storage capacity and permeability, while matrix contributions to both are negligible. In fields with reservoir scale faults, it is common to see secondary faults and fracture networks near the major fault zones.

Surfactant selection and screening for EOR studies are the focus of the paper "Identification and Evaluation of High Performance EOR Surfactants," in which the authors outline an efficient methodology using phase behavior and coreflood experiments to screen various surfactants for SP or ASP EOR applications. They find that addition of sodium carbonate is beneficial, reducing the adsorption of surfactant both in sandstone and in carbonate rock. In the paper "A New Approach for Reliable Estimation of Hydraulic Fracture Properties Using Elliptical Flow Data in Tight Gas Wells," the authors present an iterative method to compute formation permeability and fracture half-length using data from the elliptical flow regime observed between linear and pseudoradial flow regimes.

The next paper, "Experimental Determination of Relative Permeabilities for a Rich Gas/Condensate System Using Live Fluid," outlines computation of gas and condensate liquid relative permeabilities using live rich gas/condensate fluids. Using live single-phase gas condensate samples, the authors conducted two-phase flow tests and showed a significant increase in both gas and liquid relative permeabilities with increasing capillary numbers. In addition, the measured condensate relative permeabilities were higher than gas relative permeabilities for the fluids considered.

"A New Azimuthal Deep-Reading Resistivity Tool for Geosteering and Advanced Formation Evaluation," outlines geosteering and petrophysical applications using data from a new LWD azimuthal resistivity tool. As the tool rotates, it records phase shift and attenuation data at 32 azimuthally located bins, which are then converted to phase shift and attenuation resistivities at multiple spacings and frequencies.

Condensate recovery factor was increased from the originally planned value of 50% to an estimated ultimate value of 81% as outlined in the paper "Dry Gas Reinjection in a Strong Waterdrive Gas/Condensate Field Increases Condensate Recovery--Case Study: the Sleipner Ty Field, South Viking Graben, Norwegian North Sea." The original reservoir pressure was only tens of psi higher than the dewpoint pressure of this strong water-drive gas/condensate field. Dry gas injection increased the reservoir pressure and helped revaporize the dropped condensate as the reservoir pressure increased. Concerns about trapping the injected gas resulted in the halting of gas injection, and blowdown phase started. In the paper "Stress-Dependent Directional Permeabilities of Two Analog Reservoir Rocks: A Prospective Study on Contribution of µ-Tomography and Pore Network Models," the authors outline an integrated method which combines experimental investigation of directional permeabilities measured using a triaxial cell and pore network modeling with data obtained from computed micro-tomography imaging. A vertical observation well equipped with an array of microseismic sensors were used to monitor a SAGD process involving a horizontal injector-producer pair as described in the paper"Monitoring SAGD Steam Injection Using Microseismicity and Tiltmeters." Coupled with data from surface tiltmeters, the data was analyzed for monitoring the warm-up phase, which indicated thermally induced fracturing and deformation of the wellbore caused by thermal expansion.

In the paper "Modeling of Equalizer Production System and Smart Well Applications in Full-Field Studies," the authors considered single-well, sector, and full-field models to study the merits of inflow control devices (ICD). The authors also present a new well equation which incorporates the pressure drop across an ICD with the pressure drop caused by drawdown.

The Valhall field in the North Sea is a well-known chalk reservoir undergoing compaction. In "Improved Compaction Modeling in Reservoir Simulation and Coupled Rock Mechanics: Flow Simulation With Examples From the Valhall Field," the authors present an efficient method to improve compaction calculations by a flow simulator which is based on results from a simplified coupled flow–stress simulation. The method is aimed to reduce total computer time in iterative coupled simulations without loss of accuracy, focusing on two mechanistic models from the Valhall field. Finally, in the paper "A New Diagnostic Analysis Method for Waterflood Performance," the author introduces a new waterflood performance analysis method which starts with Buckley-Leverett equation and uses a semilogarithmic approximation between oil to water relative permeability ratio and water saturation. The analytical approach can be used to assess waterflood performance, including production decline and ultimate recovery.

Cosan Ayan, Schlumberger