Executive Summary

Anil Ambastha, Chevron

Papers in this issue of SPE Res Eval & Eng focus primarily on streamline simulation, water-injection situations, reservoir-characterization issues, and production-data analysis. The following is a brief outline of the papers in this issue.

Streamline Simulation

"Thermal Streamline Simulation for Hot Waterflooding" extends streamline simulation to hot waterflooding by taking into account advective parts of mass balance and energy equations, temperature-dependent viscosity, thermal expansion of the fluids, and gravity effects. The authors tested their streamline simulation results against commercial thermal simulators for 2D, heterogeneous, quarter five-spot pattern problems. "Parallelization of a Commercial Streamline Simulator and Performance on Practical Models" presents parallelization to multicore architectures on the basis of the OpenMP programming model and its performance on a variety of large models including SPE10, Forties, a UK oil/water model, Judy Creek, a Canadian waterflood/water-alternating-gas model, and a South American black-oil model. The authors parallelized streamline-transport step that represents approximately 40–80% of the total run time as well as additional runtime code, including the gravity-line solver and some simple routines required for constructing the pressure matrix, resulting in overall speedup factors between 1.8 and 3.3x for eight threads.

Performance Optimization

"Results of the Brugge Benchmark Study for Flooding Optimization and History Matching"describes results from nine participating groups in a unique benchmark project to test the combined use of waterflooding optimization and history-matching methods in a closed-loop workflow discussed at the SPE Applied Technology Workshop held in Brugge, Belgium in June 2008. The goal set for the exercise was to create a set of history-matched reservoir models and then to find an optimal waterflooding strategy for an oilfield containing 20 producers and 10 injectors, which can each be controlled by three inflow control valves. "Field Applications of Waterflood Optimization via Optimal Rate Control With Smart Wells" presents waterflood optimization by means of rate control using streamlines that rely on equalizing the arrival time of the waterfront at all producers for maximizing the sweep efficiency. Optimization is performed under operational and facility constraints using a sequential quadratic programming approach for two field examples: "Brugge" and a super-giant Middle Eastern field.

Dispersion in Porous Media

"Theoretical and Experimental Investigation of Water-in-Oil Transverse Dispersion in Porous Media" reports on mechanisms causing the expansion of the water-saturation transition zone (transverse dispersion) in a segregated flow of oil and water approaching a vertical well’s completion. The mechanisms--including nonlinear flow, turbulence, shear rate, flow baffling at grains--all contribute to the instability of the oil/water interface resulting in hydrodynamic mixing. In this work, the authors have modeled mathematically the effect of flow baffling and demonstrated transverse dispersion experimentally using a linear physical sand pack.

Water Injection

"A New Laboratory Method for Evaluation of Sulphate Scaling Parameters From Pressure Measurements" describes the determination of coefficients for the mathematical model that predicts permeability and well productivity reduction caused by the reaction of sulphate from the injected seawater with metals from the formation water using pressure measurements during coreflood experiments. The tests show that the proposed method is more precise for artificial cores than for the natural reservoir cores. "A Model for Water Injection Into Frac-Packed Wells" discusses how the frac pack and the formation is plugged because of the deposition of particles from the injected water and their effective permeability to water is continuously reduced. Cases of frac packs with large proppant size and narrow frac packs are both considered. It is shown that frac packs are expected to maintain higher injectivities in comparison to any other completions such as openhole, cased hole, and perforated or gravel packs. "In-Situ Phase Pressures and Fluid Saturation Dynamics Measured in Waterfloods at Various Wettability Conditions" describes the simultaneous measurement of local pressures and in-situ fluid saturations during waterfloods of six outcrop chalk coreplug samples prepared at various wettabilities. Using high spatial resolution magnetic resonance imaging to image fluid saturations and pressure taps with semipermeable discs to measure individual phase pressures allowed calculations of relative permeabilities and the dynamic capillary pressure curves for the imbibition processes as well as in-situ Amott-Harvey indices.


"Analytical Upgridding Method To Preserve Dynamic Flow Behavior" proposes a new upgridding method that preserves the pressure profile at the upscaled level. The new method is currently developed for single-phase flow; however, authors have used it for both single- and two-phase flows for 2D and 3D cases.

Reservoir Characterization

"Support-Vector Regression for Permeability Prediction in a Heterogeneous Reservoir: A Comparative Study" develops a permeability prediction model using support-vector regression from well logs in a heterogeneous sandstone reservoir. To demonstrate the potential of the proposed support-vector machines regression technique in predicting permeability, a comparative study was carried out to compare its performance with multilayer perceptron neural network, generalized neural network, and radial basis function neural networks. "Integration of Well-Test Pressure Data Into Heterogeneous Geological Reservoir Models" presents an application of the ensemble Kalman filter (EnKF) method. The method is tested with synthetic heterogeneous single- and two-layer reservoirs. Excellent data matches are obtained with EnKF in a small fraction of the time that would be required for a gradient-based history-matching process and the observed data fall within the uncertainty bounds of the ensemble data predictions."Characterization of Reservoir Heterogeneity Through Fluid Movement Monitoring With Deep Electromagnetic and Pressure Measurements" presents a novel technique to characterize detailed formation heterogeneity for a carbonate reservoir using measurements from electrode resistivity array (ERA) installed on tubing in a barefoot well, a wireline formation tester, and a permanent downhole pressure sensor. The ERA measurements were carried out in conjunction with low-salinity water injection and oil and water production in the same well. The time-lapse ERA voltages near a source electrode represented local formation heterogeneity within the length of the ERA string vertically and approximately 100-ft laterally.

Production Data Analysis

"Production Performance of a Constant-Pressure Well in an Orthogonally Fractured Reservoir"has developed formulas for production forecasting and for analyzing historical production decline during three distinct production modes identified by the time when the effects of the reservoir boundary vs. the influx from the matrix blocks are observed. "Production-Data Analysis--Challenges, Pitfalls, Diagnostics" provides a "state-of-the-technology" review of current production-data-analysis techniques/tools--particularly tools to diagnose the reservoir model and assess the reservoir condition."Steady-State Productivity Equations for a Multiple-Wells System in Sector Fault Reservoirs"uses fully-penetrating vertical wells as uniform line sinks and solves a square matrix of dimension n, where nis the number of wells, to develop simple, reasonably accurate multiple-wells system productivity equations. The analytical solutions are verified with numerical simulation in several examples. This paper also gives an equation for calculating skin factors of each well in steady state. "Analysis of Production Data From Hydraulically Fractured Horizontal Wells in Shale Reservoirs" models the stimulated volume around the well as a naturally-fractured region. A semianalytical model incorporating the key features of reservoir heterogeneity and the details of hydraulic fracture and wellbore flow is used to present production decline characteristics in terms of transient productivity index. Production decline analysis of fractured horizontal wells in shale-oil and -gas formations by transient productivity index is explained and demonstrated by field applications.

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Anil Ambastha, Chevron