Executive Summary

Anil Ambastha, Chevron
Cosan Ayan, Schlumberger

Papers in this issue of SPE Res Eval & Eng focus on naturally-fractured reservoirs, chemical methods, CO2 sequestration, cold heavy-oil production, gas-hydrate reservoirs, and various specific modeling situations. The following is a brief outline of the papers in this issue.

"Modeling Wettability Alteration by Surfactants in Naturally Fractured Reservoirs" describes adaptation of a chemical flooding simulator to model improved-oil-recovery processes involving surfactants in fractured reservoirs. Multiple relative permeability and capillary pressure curves corresponding to different wetting states have been used to model wettability alteration. "An Approach to Fracture Characterization Using Borehole Seismic Data" discusses a method using median velocity and F-K filtering in addition to special enhancement techniques on the zero-offset vertical seismic profile data with the objective of enabling improved prediction of fracture clusters or swarms away from the wellbore."Gravity-Drainage and Oil-Reinfiltration Modeling in Naturally Fractured Reservoir Simulation" uses refined-grid, single-porosity simulations to develop pseudofunctions needed in a dual-porosity formulation for modeling of gravity drainage and oil reinfiltration processes that occur in the gas-cap zone of naturally-fractured reservoirs. "The Effect of Pressure-Decline Rate and Pressure Gradient on the Behavior of Solution Gas Drive in Heavy Oil" describes solution-gas drive experiments for heavy oil in which the pressure-decline rate and pressure gradient are independently varied by changing confining pressure and production rate, respectively. This paper concludes that the effect of pressure gradient on gas mobility and oil recovery is much more significant than the effect of pressure-decline rate. "Eliminating Buoyant Migration of Sequestered CO2 Through Surface Dissolution: Implementation Costs and Technical Challenges" discusses various aspects of injection of CO2-saturated brine into deep saline aquifers as a viable means of eliminating the risk of buoyancy-driven CO2leakage for large-scale CO2 sequestration operations. "Updating the Geomechanical Model and Calibrating Pore Pressure From 3D Seismic Using Data From the Gnu-1 Well, Dampier Subbasin, Australia" presents verification of the predrill pore pressure prediction previously undertaken using 3D seismic velocity data and offset well data. Post-mortem analysis after the drilling of Well Gnu-1 also allowed refinement of the predrill geomechanical model for continued future use. "Retention of CO2-Foaming Agents Onto Chalk-Effects of Surfactant Structure, Temperature, and Residual Oil Saturation" describes results of flow-through retention experiments conducted with CO2-foaming agents (two different branched ethoxylated sulphonates were used) on outcrop Leige chalk plugs, representative of North Sea chalk reservoirs, at two different temperatures, 55°C and 70°C. "A New Polymer Application for North Sea Reservoirs"  discusses laboratory work carried out using colloidal dispersion gels (CDG) at high temperatures (85°C) and salinity (~35,000 μg/g). On average, 40% of the remaining oil after waterflooding was produced by CDG injection in linear corefloods, and a mechanism of microscopic diversion is proposed to explain these results. "An Integrated Methodology for Calibrating a Heterogeneous/Fractured Reservoir Model From Wellbore Flow Measurements: Case Study" proposes a sequential application of gradient-based inversion loop followed by global and local gradual deformation methods to refine a geostatistical facies model for a water-bearing, fractured reservoir located near Poitiers, France. "Local Update of Object-Based Geomodels" presents new algorithms that allow rapid local updating of static reservoir models when new wells are drilled, while preserving as much of the existing history match as possible. "A Sensitivity Analysis for Effective Parameters on 2D Fracture Network Permeability" proposes a new and practical approach to estimate fracture network permeability (FNP) using statistical and fractal characteristics of fracture networks. This paper also provides a detailed sensitivity analysis to determine the relative importance of fracture network parameters on the FNP using an experimental design approach in comparison to a single fracture conductivity. "Review of Practical Experience by Polymer Flooding at Daqing" describes successful practices applied during polymer flooding at Daqing that will be of considerable value to future chemical floods, both in China and elsewhere. "Prediction of Gas Productivity from Eastern Nankai Trough Methane-Hydrate Reservoirs" presents numerical simulation results on the applicability of a variety of methane-hydrate dissociation/production methods and the feasibility of the future development in terms of gas production and economics.

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Anil Ambastha, Chevron