No abstract

The significant heat loss and severe thermal fluctuations inherent in steam-assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS) impose considerable constraints on well cementing. In order to obtain better energy efficiency and mechanical robustness, there is considerable interest in the development of low-thermal-conductivity cement that can provide a combination of enhanced thermal insulation and mechanical resilience upon thermal cycling. However, the current palette of thermal cements is exceedingly sparse. In this article, we illustrate a method for decreasing the thermal conductivity of cement by inclusion of hydroxyethylcellulose-functionalized halloysite nanotubes. Halloysite/hydroxyethylcellulose inclusions offer an abundance of disparate interfaces and void space that can effectively scatter phonons, thereby bringing about a pronounced reduction of thermal conductivity. The microstructure of the nanocomposite cementitious matrix is strongly modified even as the compositional profile remains essentially unaltered. Modified cement nanocomposites incorporating halloysite nanotubes along with hydroxyethylcellulose in a 8:1 ratio with an overall loading of 2 wt.% exhibit the lowest measured thermal conductivity of 0.212 ± 0.003 W/m.K, which is substantially reduced from the thermal conductivity of unmodified cement (1.252 W/m.K). The ability to substantially decrease thermal conductivity without deleterious modification of mechanical properties through alteration of microstructure, inclusion of encapsulated void spaces, and introduction of multiple phonon-scattering interfaces suggests an entirely new approach to oilwell cementing based on the design of tailored nanocomposites.

Ac hallenge in anion control in periodic solids is to preserve the crystal lattice while substituting for different anions of widely varying sizea nd hardness.P ost-synthetic modification routes that place cations or anions in nonequilibrium configurations are promising;h owever,s uch methods remain relatively unexplored for anion placement. Here,w er eport the synthesis of LaOI nanocrystals by an onhydrolytic sol-gel condensation reaction and their transformation into LaOBr,LaOCl, and LaOF nanocrystals along hardsoft acid-base principles using post-synthetic metathesis reactions with ammonium halides.A nion displacement proceeds along halide planes,p reserving the tetragonal matlockite structure.E nergy-variant X-raye xcited optical luminesce signatures of alloyed Tb 3+ -ions is asensitive quantum reporter of the preservation of the cation sublattice and hardening of the crystal structure upon anion replacement.

An increasing global population and a sharply upward trajectory of per capita energy consumption continue to drive the demand for fossil fuels, which remain integral to energy grids and the global transportation infrastructure. The oil and gas industry is increasingly reliant on unconventional deposits such as heavy crude oil and bitumen for reasons of accessibility, scale, and geopolitics. Unconventional deposits such as the Canadian Oil Sands in Northern Alberta contain more than one-third of the world’s viscous oil reserves and are vital linchpins to meet the energy needs of rapidly industrializing populations. Heavy oil is typically recovered from subsurface deposits using thermal recovery approaches such as steam-assisted gravity drainage (SAGD). In this perspective article, we discuss several aspects of materials science challenges in the utilization of heavy crude oil with an emphasis on the needs of the Canadian Oil Sands. In particular, we discuss surface modification and materials’ design approaches essential to operations under extreme environments of high temperatures and pressures and the presence of corrosive species. The demanding conditions for materials and surfaces are directly traceable to the high viscosity, low surface tension, and substantial sulfur content of heavy crude oil, which necessitates extensive energy-intensive thermal processes, warrants dilution/emulsification to ease the flow of rheologically challenging fluids, and engenders the need to protect corrodible components. Geopolitical reasons have further led to a considerable geographic separation between extraction sites and advanced refineries capable of processing heavy oils to a diverse slate of products, thus necessitating a massive midstream infrastructure for transportation of these rheologically challenging fluids. Innovations in fluid handling, bitumen processing, and midstream transportation are critical to the economic viability of heavy oil. Here, we discuss foundational principles, recent technological advancements, and unmet needs emphasizing candidate solutions for thermal insulation, membrane-assisted separations, corrosion protection, and midstream bitumen transportation. This perspective seeks to highlight illustrative materials’ technology developments spanning the range from nanocomposite coatings and cement sheaths for thermal insulation to the utilization of orthogonal wettability to engender separation of water–oil emulsions stabilized by endogenous surfactants extracted during SAGD, size-exclusion membranes for fractionation of bitumen, omniphobic coatings for drag reduction in pipelines and to ease oil handling in containers, solid prills obtained from partial bitumen solidification to enable solid-state transport with reduced risk of damage from spills, and nanocomposite coatings incorporating multiple modes of corrosion inhibition. Future outlooks for onsite partial upgradation are also described, which could potentially bypass the use of refineries for some fractions, enable access to a broader cross-se...

The increasing reliance on steam-assisted gravity drainage (SAGD) to access unconventional bitumen deposits within the sub-Arctic necessitates the development of robust cement sheaths for oilwell cementing. Such cement sheaths can potentially increase the energy efficiency of the SAGD process by reducing heat loss while maintaining mechanical integrity upon prolonged exposure to cyclic thermal stress. Modifying oilwell cement by the inclusion of hydroxyethylcellulose-functionalized halloysite nanotubes (HEC-HNTs) within the cementitious matrix results in a high density of enclosed void space and disparate interfaces, which serve to scatter phonons and reduce thermal conductivity. In this study, we have systematically evaluated the influence of HEC-HNT loading on the thermomechanical properties of cement with and without the addition of calcium chloride as an accelerator and have correlated the reduction of thermal conductivity to the distinctive microstructure of the nanocomposite cement. The incorporation of HEC-HNTs in thermal cement reduces the thermal conductivity from 0.856 W m −1 •K −1 to 0.206 W m −1 •K −1 without substantially altering the compressive strength. Model systems mimicking SAGD oilwell cement sheaths have been prepared from umodified and modified (incorporating HEC-HNT) cement and subjected to cyclic thermal stress emulative of SAGD conditions. Cement sheaths constructed from the modified cement with CaCl 2 maintain a higher temperature gradient as compared to unmodified cement with CaCl 2 ; a 12 °C increased temperature differential between hot and cold surfaces is observed for a 4.5 cm thick sheath with a considerably shallower rate of increase in temperature. Aggressive thermal cycling (20 h at 250 °C followed by 4 h at 25 °C) for 20 days brings about a 20% reduction of compressive strength. The combination of additives facilitating thermal insulation and mitigating differential shrinkage provides an attractive means of oilwell cementing for SAGD applications wherein cyclic thermal stresses are operational and energy efficiency is of paramount importance. Extrapolating the considerably increased temperature differentials between hot and cold ends within model systems to entire wells portends significant energy savings and reduction in amounts of injected steam.