Executive Summary – May 2016

This issue of SPE Reservoir Evaluation and Engineering brings you 14 papers that reflect areas of current activity and interest in the industry. Four papers focus on topics related to formation evaluation, primarily well-log analysis. Four papers deal with various aspects of reservoir modeling, including history matching and production optimization. Another two papers deal with topics related to heavy oil and two more deal with topics related to core analysis and the use of gels to improve waterflood sweep in fractured reservoirs. The final two papers are related to unconventional resources.

With the discontinuation of the Journal of Canadian Petroleum Technology, in the future you can expect to see more papers related to unconventional resources and heavy oil in SPE Reservoir Evaluation and Engineering.

Formation Evaluation

Multiscale Imaging of Fixed-Cutter-Drill-Bit-Generated Shale Cuttings describes the application of recent developments in fabric-analysis techniques to analyze shale cuttings at the macro-, micro-, and nanolevels. These techniques are used to understand how shales break and deform under confining pressure and thus provide better understanding of drill-bit/rock interactions, especially in deep wells where confining pressure is high and rate of penetration is slow.

A Novel Work Flow of Density-Log Normalization for Coalbed-Methane Wells: An Example From the Surat Basin in Australia presents a new work flow for density-log normalization for coalbed-methane wells. It addresses two major challenges to current normalization methods: absence of a pervasive reference layer and removal of geological effects after normalization. The proposed work flow consists of six steps: data quality control (QC), geologic-area segmentation, subarea type-well selection, density-control points, variable linear transformation, and normalized-log result QC with box plots, matrix crossplots, and several histograms. The work flow was applied successfully to approximately 600 wells covering a large area in the Surat basin of Australia.

Matrix Permittivity Measurements for Rock Powders introduces a methodology for laboratory measurements of rock matrix permittivity using rock powders. The new methodology overcomes many of the limitations of conventional methods using solid plugs. It was applied to improve dielectric log interpretation in a carbonate reservoir offshore Sarawak. Application of the measured matrix permittivity values substantially improved the dielectric log interpretation in terms of water-filled porosity and also improved the correspondence between the measured cementation exponent and the MN parameter computed from the dielectric dispersion.

Lithofacies Classification of Thin-Layered Turbidite Reservoirs Through the Integration of Core Data and Dielectric-Dispersion Log Measurements describes a new probabilistic lithological facies-classification approach that integrates core data and a high-resolution dielectric-dispersion wireline log. Its 1-in. vertical resolution and a related fit-for-purpose petrophysical model make the log tool’s response suitable to describe the lithological heterogeneity of thinly laminated reservoirs (e.g., distal turbidites). The approach is illustrated by means of a study performed on the cored section of a well drilled into a laminated gas-bearing Pleistocene reservoir in the Adriatic basin.

Reservoir Modeling

Proactive Optimization of Intelligent-Well Production Using Stochastic Gradient-Based Algorithms provides guidelines on selecting a suitable proactive optimization strategy for intelligent wells (I-wells) to achieve long-term optimization objectives. Two state-of-the-art stochastic gradient-approximation algorithms, the simultaneous-perturbation stochastic approximation method and the ensemble-based optimization method, are evaluated. Both methods are shown to provide a fast solution to a large-scale and multiple I-well proactive optimization problem. Criteria for selecting one method over the other are identified based on the results of several synthetic test cases. Finally, the developed guidelines are used to perform proactive inflow control valve optimization in a large full-field model of a real oil field.

Probabilistic Reservoir-Property Modeling Jointly Constrained by 3D-Seismic Data and Hydraulic-Unit Analysis presents a new method for seismic reservoir characterization and reservoir-property modeling based on an integrated analysis of 3D-seismic data and hydraulic flow units. It is applied to an example of a producing reservoir offshore western Australia. The method combines hydraulic-unit analysis with a set of techniques for seismic reservoir characterization including rock-physics analysis, Bayesian inference, prestack seismic inversion, and geostatistical simulation of reservoir properties. Reservoir models constrained by both 3D-seismic data and hydraulic-flow-unit analysis using this method have the potential to improve the subsequent processes of reservoir characterization, fluid-flow performance forecasting, and production data or 4D-seismic history matching.

Streamline-Based Transport Tomography With Distributed Water Arrival Times presents an efficient approach to incorporate tracer-surveillance data and distributed water arrival-time information during history matching of high-resolution reservoir models. The approach relies on a streamline-based work flow that computes the sensitivity of water-arrival times analytically with respect to reservoir heterogeneity. The sensitivities are used in conjunction with an iterative inversion algorithm to update the reservoir models with techniques from seismic tomography. The proposed approach is demonstrated with both synthetic and field examples.

Integration of Cumulative-Distribution-Function Mapping With Principal-Component Analysis for the History Matching of Channelized Reservoirs proposes a work flow to integrate cumulative-distribution-function (CDF) mapping with principal-component analysis (PCA) for assisted history matching on channelized reservoirs. The CDF/PCA method is first applied to a real-field case with three facies to quantify the quality of the reconstructed models. Compared with traditional PCA results, the integration of CDF-based mapping with PCA can improve the quality of the reconstructed reservoir models significantly. Results for the real-field case also reveal some limitations of the proposed method, especially when it is applied to reservoirs with three or more facies. Next, the CDF/PCA method is applied together with an effectively parallelized derivative-free optimization method to history matching of a synthetic case with two facies. The geological facies, reservoir properties, and uncertainty characteristics of production forecasts of models reconstructed with CDF/PCA are consistent with those of the original models.

Heavy Oil

Swelling and Viscosity Reduction of Heavy Oil by CO2-Gas Foaming in Immiscible Condition describes a laboratory study of foamy oil created by depressurization of heavy oil saturated with CO2. Swelling and apparent viscosity characteristics in bulk are correlated with measurements of bubble size distribution. 

Development of a Thermal Wellbore Simulator With Focus on Improving Heat-Loss Calculations for Steam-Assisted-Gravity-Drainage Steam Injection describes the development of a standalone fully implicit thermal wellbore simulator to improve estimation of heat loss from the wellbore to the surrounding formation. A series of computational-fluid-dynamics (CFD) models are run to characterize the buoyancy-driven flow for different annulus sizes and lengths and numbers of tubing strings. On the basis of the CFD models, correlations are derived that can be used conveniently for the more-accurate heat-loss estimation for steam-assisted-gravity-drainage injection wells with single or multiple tubing strings. The correlations are embedded in the wellbore simulator, and results are compared with other heat-loss-modeling methods to demonstrate the improved capabilities. A series of validations against commercial simulators and field data are also presented.

Core Analysis

Intercept Method—A Novel Technique To Correct Steady-State Relative Permeability Data for Capillary End Effects describes the intercept method, a modified steady-state approach for relative permeability measurement in which corrections for capillary end-effect (CEE) artifacts are applied as data are measured. The method requires running a steady-state relative permeability test with several different flow rates for each fractional flow, which allows for assessment and correction of CEE artifacts. Because the corrections are made during the test rather than after the test is complete, any discrepancies can be resolved by additional measurements before moving on to the next fractional flow. The method is validated by theoretical calculations.

Sweep Improvement

Low-Salinity Chase Waterfloods Improve Performance of Cr(III)-Acetate Hydrolyzed Polyacrylamide Gel in Fractured Cores describes laboratory testing of a method to mitigate rupture of polymer gels when they are used to reduce water channeling in fractured reservoirs. The method involves injecting low-salinity water after gel placement in the fractures. Coreflood tests demonstrate that the low-salinity water swells conventional Cr(III)-acetate hydrolyzed polyacrylamide gels, thereby improving gel-blocking performance significantly after gel rupture. Low-salinity water subsequently flooded the matrix during chase floods, which provided additional benefits to the waterflood.

Unconventional Resources

Appraising Unconventional Resources: How Many Wells To Drill and Where To Place Them? proposes a value-of-information (VOI) methodology that is tuned to the nature of the subsurface uncertainties in unconventional plays and is capable of assessing a wide range of appraisal strategies. The methodology assumes that spatial dependencies exist between the performance levels of individual wells. The methodology is illustrated by application to a typical unconventional pay to optimize the VOI of an appraisal program in terms of the number of appraisal wells to be drilled and the placement of those wells. The study results demonstrate how the VOI of each incremental appraisal well decreases with the number of appraisal wells and how an optimal number of appraisal wells can be determined.

Effect of Fracture Characteristics on Behavior of Fractured Shale-Oil Reservoirs by Cyclic Gas Injection uses a numerical-simulation approach to evaluate the enhanced-oil-recovery potential in fractured shale-oil reservoirs by cyclic gas injection. Simulation results indicate that the stimulated fracture network contributes significantly to the well productivity by means of its large contact area with the matrix, which prominently enhances the macroscopic sweep efficiency in secondary cyclic gas injection. Sensitivities to fracture spacing, the size of the fracture network, fracture connectivity, and stress-dependent fracture-network conductivity on well-production performance are investigated.

 

The above papers were all reviewed and ultimately approved in the peer-review process. However, the conclusions presented in these papers are not cast in stone. Because the sharing of knowledge and experiences is essential, SPE welcomes further “discussion” of any paper published in any SPE journal. Therefore, I again urge you to submit a discussion of a paper to SPE if you have alternative views on methods, interpretations, and/or conclusions presented or if the authors and reviewers have missed publications that either support or invalidate results.


Gary Teletzke

Executive Editor, SPE Reservoir Evaluation & Engineering-Reservoir Engineering