Bayesian Optimization for Field-Scale Geological Carbon Storage

We present a framework that couples a high-fidelity compositional reservoir simulator with Bayesian optimization(BO)for injection well scheduling optimization in geological carbon sequestration.This work represents one of the first at tempts to apply BO and high-fidelity physics models to geological carbon storage.The implicit parallel accurate reservoir simulator(IPARS)is utilized to accurately capture the underlying physical processes during CO_(2)sequestration.IPARS provides a framework for several flow and mechanics models and thus supports both stand-alone and coupled simulations.In this work,we use the compositional flow module to simulate the geological carbon storage process.The compositional flow model,which includes a hysteretic three-phase relative permeability model,accounts for three major CO_(2)trapping mechanisms:structural trapping,residual gas trapping,and solubility trapping.Furthermore,IPARS is coupled to the International Business Machines(IBM)Corporation Bayesian Optimization Accelerator(BOA)for parallel optimizations of CO_(2)injection strategies during field-scale CO_(2)sequestration.BO builds a probabilistic surrogate for the objective function using a Bayesian machine learning algorithm-the Gaussian process regression,and then uses an acquisition function that leverages the uncertainty in the surrogate to decide where to sample.The IBM BOA addresses the three weaknesses of standard BO that limits its scalability in that IBM BOA supports parallel(batch)executions,scales better for high-dimensional problems,and is more robust to initializations.We demonstrate these merits by applying the algorithm in the optimization of the CO_(2)injection schedule in the Cranfield site in Mississippi,USA,using field data.The optimized injection schedule achieves 16%more gas storage volume and 56%less water/surfactant usage compared with the baseline.The performance of BO is compared with that of a genetic algorithm(GA)and a covariance matrix adaptation(CMA)-evolution strategy(ES).The results demonstrate the superior performance of BO,in that it achieves a competitive objective function value with over 60%fewer forward model evaluations.

Characterization of deformation stability of in-situ TiB2/6351 composites during hot compression based on Murty criterion

In situ TiB2 reinforced 6351 Al alloy composites were subjected to compression testing at strain rates and temperatures ranging from 0.001 to 10 s -1 and from 300 to 550？欲espectively,using Gleeble-1500D system.And the associated microstructural transformations and instability phenomena were studied by observations of the optical and transmission electron microscope.The power dissipation efficiency and instability parameter were calculated following the dynamic material model and plotted with the temperature and logarithm of strain rate to obtain processing maps for strains of 0.2,0.4,and 0.6.The processing maps present the instability zones at higher strain rates.The result shows that with increasing strain,the instability zones enlarge.The microstructural examination shows that the interface separates even the particle cracks or aligns along the shear direction of the adiabatic shear band in the instability zones.Two domains of higher efficiencies correspond to dynamic recovery and dynamic recrystallization during the hot deformation.Using the processing maps,the optimum processing parameters of stain rates and temperatures can be chosen for effective hot deformation of TiB2/6351 composites.

Picoplankton and virioplankton abundance and community structure in Pearl River Estuary and Daya Bay, South China

By using flow cytometry techniques, we investigated the abundance and composition of the heterotrophic prokaryotes, virioplankton and picophytoplankton community in the Pearl River Estuary and Daya Bay in the summer of 2012. We identified two subgroups of prokaryotes, high nucleic acid（HNA） and low nucleic acid（LNA）, characterized by different nucleic acid contents. HNA abundance was significantly correlated with larger phytoplankton and Synechococcus（Syn） abundance, which suggested the important role of organic substrates released from primary producers on bacterial growth. Although LNA did not show any association with environmental variables, it was a vital component of the microbial community. In contrast to previous studies, the total virioplankton concentration had a poor relationship with nutrient availability. The positive relationship between large-sized phytoplankton abundance and the V-I population confirmed that V-I was a phytoplankton-infecting viral subgroup. Although the V-II group（bacteriophages）was dominant in the virioplankton community, it was not related with prokaryotic abundance, which indicated factors other than hosts controlling V-II abundance or the uncertainty of virus-host coupling. With respect to the picophytoplankton community,our results implied that river input exerted a strong limitation to Syn distribution in the estuary, while picoeukaryotes（Euk） were numerically less abundant and showed a quite different distribution pattern from that of Syn, and hence presented ecological properties distinct from Syn in our two studied areas.

Pressure transient analysis for a fractured well in a stress-sensitive tight multi-medium oil reservoir

Tight multi-medium oil reservoirs are the main source of hydrocarbon resources around the world.Acid fracturing is the most effective technology to improve productivity in such reservoirs.As carbonates are primarily composed of dolomite and calcite,which are easily dissolved by hydrochloric acid,high-permeability region will be formed near the well along with the main artificial fracture when acid fracturing is implemented in tight multi-medium oil reservoirs.In this study,a comprehensive composite linear flow model was developed to simulate the transient pressure behavior of an acid fracturing vertical well in a naturally fractured vuggy carbonate reservoir.By utilizing Pedrosa's substitution,perturbation,Laplace transformation and Stehfest numerical inversion technol-ogy,the pressure behavior results were obtained in real time domain.Furthermore,the result of this model was validated by comparing with those of previous literature.Additionally,the influences of some prevailing parameters on the type curves were analyzed.Moreover,the proposed model was applied to an acid fracturing well to evaluate the effectiveness of acid fracturing measures,to demonstrate the practicability of the proposed model.