Executive Summary

Cosan Ayan, Schlumberger

With the new peer-review system that we started using last year, the paper-submission process for meetings and for peer review has been decoupled. Many of us are now familiar with the new system and I am taking this chance to remind this to our colleagues who may not be aware of the process. For any paper to be peer reviewed, a separate submission has to be made using Scholar One, the web-based submission and peer-review system. Please check SPE.org for the details.

This issue of SPE Res Eval & Eng starts with a well-placement paper ,"Improved Geosteering by Integrating in Real Time Images From Multiple Depths of Investigation and Inversion of Azimuthal Resistivity Signals." The authors use a deep reading azimuthal resistivity imaging tool that provides images at multiple depths of investigation. Coupled with a series of transverse electromagnetic measurements specific to azimuthal resistivity in real time, the integrated images help geosteering engineers remain at planned distances from formation and fluid boundaries. Carbon capture and storage is an area of active research and its implications extend beyond the oil and gas industry. The paper, "Lithological and Petrophysical Core-Log Interpretation in CO2SINK, the European CO2 Onshore Research Storage and Verification Project," studies an injection and three observation wells where core-log integration was conducted for the Middle Keuper saline aquifer at Ketzin near Berlin. In the paper,"Detecting Thief Zones in Carbonate Reservoirs by Integrating Borehole Images With Dynamic Measurements: Case Study From the Mauddud Reservoir, North Kuwait," the authors combine conventional logs, borehole images, and production logging results to identify vuggy or fractured thief zones ("superpermeability zones") in the Mauddud reservoir of northern Kuwait. Thief zones in this reservoir are the culprit for early water breakthrough and their characteristics are quite important for flood management. Liquid-condensate blockage is an important factor affecting well deliverability--and eventual hydrocarbon recovery--in gas gas/condensate fields. In the paper, "Gas-Condensate Pseudopressure in Layered Reservoirs," the authors verify gas-condensate pseudopressure for layered systems including the effects of capillary number and high velocity flow. Their examples show that the three-region formulation can model well performance in numerical models that use coarse grid-blocks. Continuing with gas condensates, the paper, "Gas/Condensate Relative Permeability of a Low Permeability Core: Coupling vs. Inertia," studies the coupled effects of capillary number and high-velocity gas flow on relative permeability of tight sandstones. At low capillary numbers, inertial effects were dominant at high liquid-condensate-to-gas-flow-rate ratios and gas relative permeability reduces with increasing velocity. At higher flow-rate ratios, the relative permeability increased at low capillary numbers. When capillary numbers were high, inertial effects had a negative impact on relative permeability for all flow rate ratios. In a closely related paper, "Effect of Salinity on Wettability Alteration to Intermediate Gas Wetting," the authors study the change of wettability from water-wet to intermediate-gas-wet with decreasing NaCl salinity, which also decreases gas permeability. The authors suggest displacement of brine with water before treatment and subsequent drainage by Nitrogen. Delineation of thin reservoir units of 10 to 15 m is the focus of the paper,"Detection and Spatial Delineation of Thin-Sand Sedimentary Sequences With Joint Stochastic Inversion of Well Logs and 3D Prestack Seismic Amplitude Data." In this study, the authors use a new stochastic inversion algorithm that effectively combines high resolution well logs with dense horizontal-coverage 3D-prestack seismic amplitude data. They demonstrate the merits of this approach using data from a fluvial-deltaic sequence that had insufficient vertical seismic resolution. Lyons outcrop of Colorado sandstone exhibits natural transverse rock-matrix anisotropy with fine-layered dipping beds. In the paper,"Pore-Pressure-Coefficient Anisotropy Measurements for Intrinsic and Induced Anisotropy in Sandstone," the authors identify and isolate the effects of stress-induced anisotropy from the natural transverse anisotropy on measured stiffness components, elastic modulii, and Biot’s pore-pressure coefficients. Nuclear magnetic resonance (NMR) data is currently used to determine near-wellbore fluid types and viscosities. A quantitative method and procedure to determine gas/oil ratio and live-oil viscosity for volatile oils from NMR-log data is described in the paper, "A Mixing Rule of Self Diffusivities in Methane Hydrocarbon Mixtures and the Determination of GOR and Oil Viscosities From NMR Log Data." The technique is based on the analysis of diffusivity distribution of the hydrocarbon fluid containing multiple components using a new mixing rule for methane/oil binary systems. Splitting the C7+ components was the key focus of the paper, "An Approach for Characterization and Lumping of Plus Fractions of Heavy Oil." The authors outline a method to split the plus fraction into single carbon numbers, generating the mole fraction and the respective molecular weight. The technique is based on the relationships between three parameter gamma distribution, experimental mole fraction, molecular weight, and single carbon-number data. In the paper, "Quantifying Nonuniform Aquifer Strength at Individual Wells," the authors describe a method that allows defining the strength of the aquifer for each particular well. The technique combines capacitance-resistance and analytical aquifer models. The formulation allows for unsteady-state and pseudosteady-state flows. It allows for each individual well to be connected to a different aquifer model through the capacitance-resistance model. A new method to compute absolute permeabilities from two-phase transient-well tests is described in the paper, "Use of Transient Data To Calculate Absolute Permeability and Average Fluid Saturations." In addition to absolute permeability, the method also gives the average phase saturations in the area influenced by the well test. Though the method does not address which relative permeabilities to use, the same set of relative permeability curves can be used for well-test analysis and for reservoir simulation, making the input values consistent. Streamline simulation of polymer flooding is discussed in the paper, "Polymer Flood Modeling Using Streamlines." The authors use the well-known physical models for polymer flooding in 1D to represent the displacement efficiency. They couple this with a 3D streamline simulator to capture the sweep efficiency caused by well rates and reservoir heterogeneity. They show that the nonlinearity introduced by the dependence of the polymer/water phase viscosity on the distribution of the polymer in the reservoir is captured. In the continuous quest for restoring productivity of gas wells with liquid blocks, the authors in the paper, "A New Solution To Restore Productivity of Gas Wells With Condensate and Water Blocks," propose a chemical treatment. The treatment consists of a fluorinated material delivered in a glycol-alcohol solvent mixture. The mechanism is wettability alteration, making the water-wet sandstone more neutral wet and to increase the gas relative permeability. In the paper "Investigation of the Effect of Rock Mechanical Properties and In-Situ Stresses on Seismic Velocity Through a Coupled Geomechanical Reservoir Model," the authors integrate reservoir engineering, geomechanics, and rock physics in 3D. They model deformation and stresses induced by exploitation by using the pressures obtained from simulation in a geomechanical model. A sensitivity analysis with different mechanical parameters is performed on a 3D model. The mean effective stress resulting from each geomechanical simulation is used to update seismic velocities and time shifts associated with seismic horizons. The study shows that the time-shift values of the seismic horizons determined using this approach would be detectable on 4D seismic data. In the paper, "A Semianalytical Approach To Model Pressure-Transients in Heterogeneous Reservoirs," the authors describe a semianalytical approach to model pressure transients in heterogeneous systems including composite, layered, and compartmentalized reservoirs. The reservoir is divided into blocks corresponding to locally homogeneous regions and analytical pressure-transient solutions for adjacent blocks are coupled at the boundaries. This approach is an alternative to full numerical modeling of pressure-transient responses in heterogeneous formations. Accurate measurement of shale and coal-bed gas content is key to a successful project. Such measurements are done on fresh cut cores in which the determination of "lost-gas" content is usually made by extrapolation. In the paper, "A New Regression-Based Method for Accurate Measurement of Coal and Shale Gas Content," the authors describe a new method to determine the "lost-gas", which is a regression based technique that takes diffusivity with time into account. The accuracy of the technique is only dependent on the data collection in the field in the early stage and compared to linear and polynomial regression methods, the new technique is not dependent on the number of points selected.

Cosan Ayan, Schlumberger