Novel Approach for Rate Transient Analysis of Fractured Wells from Carbonate Reservoirs with Heterogeneous Natural Fractures.

This paper developed a new methodology for rate transient analysis of fractured wells in carbonate reservoirs. Both the heterogeneity and dual-permeability flow behavior are incorporated into the proposed model, and the fractured carbonate reservoir was simulated with a two-zone composite model. In each zone, a traditional dual-porosity model was applied to describe the characteristics of the natural fractures and matrix. With the Laplace transform, we derived the solution of the mathematical model and plotted new type curves for transient rate decline analysis. Then, the flow regimes were divided and analyzed based on the new type curves. The influences of several critical parameters on transient rate response were also examined. A field case was studied further to demonstrate the precision and application of the proposed method. The results show that the new type curves are mainly composed of eight flow stages. The difference in physical properties (k 2,1, η2,1) between the two zones significantly impacts the transition and boundary-dominated flow regimes. When the values of k 2,1 and η2,1 are smaller, the derivative curve of the transition flow stage will move down, and the duration of this stage on the derivative curve is longer, while the duration of the boundary dominant flow stage will decrease. The dimensionless radial radius of the inner zone (r 1D) can significantly influence the transition flow regime. When r 1D is larger, the production rate and its derivative curve of the transition flow stage will move up, and the duration of this stage will be longer. The results also show that the proposed methodology can effectively fit the field production data. This method can be applied in well productivity evaluation for fractured carbonate reservoirs.

Synthesis and Characterization of an Novel Intercalated Polyacrylamide/Clay Nanocomposite.

Solving the problem of the low temperature and low salt resistances of conventional polyacrylamide and the high cost of functional monomers, and thus, introducing it to the interlayer space provided by a layered structure for polymer modification, is a promising option. In this study, montmorillonite was used as the inorganic clay mineral, and an intercalated polyacrylamide/clay nanocomposite was synthesized via in situ intercalation polymerization. The optimal synthesis conditions were a clay content of 10.7%, preparation temperature of 11 °C, initiator concentration of 2.5 × 10-4 mol/L, and chain extender concentration of 5%. The IR results showed that the polymer was successfully introduced to the nanocomposite. The synthesized intercalated polyacrylamide/clay nanocomposite exhibited a better thickening effect, good viscoelasticity, and better salt resistance and thermal stability than polyacrylamide. In addition, the thickening capacity and thermal stability were superior to the salt-resistant polymer, with a 16.0% higher thickening viscosity and a 15.1% higher viscosity retention rate at 85 °C for 60 d. The intercalated polyacrylamide/clay nanocomposite further expanded the application of polyacrylamide in petroleum exploitation.

Highly efficient thermoelectric air conditioner with kilowatt capacity realized by ground source heat-exchanging system.

The enormous need for refrigeration of modern human life has inevitably aggravated the environmental crisis worldwide. To date, there are very few refrigeration technologies available beholding both harmless refrigerants and high efficiency. Here, we proposed a geothermal-thermoelectric air conditioning system (GeoTEAC) with refrigerant-free and high energy efficiency through synergistically combining the merits of thermoelectric effect and ground source heat exchanging system. The system showed competitive cooling and heating COPs of 5.83 and 2.92, respectively, with kilowatt capacity, which are 3-4 times higher than that of previously reported thermoelectric air-conditioning setups. For a conceptual scenario, we demonstrated the lowest TEWI values for the GeoTEAC system among different air-conditioning types. Our work provides sustainable and climate-friendly solutions to realize worldwide emission peaks and carbon neutralization.

A CO2-responsive smart fluid based on supramolecular assembly structures varying reversibly from vesicles to wormlike micelles.

CO2-responsive smart fluids have been widely investigated in the past decade. In this article, we reported a CO2-responsive smart fluid based on supramolecular assembly structures varying from vesicles to wormlike micelles. Firstly, oleic acid and 3-dimethylaminopropylamine reacted to form a single-chain weak cationic surfactant with a tertiary amine head group, N-[3-(dimethylamino)propyl]oleamide (NDPO). Then, 1,3-dibromopropane was used as the spacer to react with NDPO to form a gemini cationic surfactant, trimethylene α,ω-bis(oleate amide propyl dimethyl ammonium bromide) (GCS). By controlling the feed ratio of 1,3-dibromopropane and NDPO, we found that the mixtures of GCS and NDPO with the molar ratio of 7 : 3 approximately could form vesicles in aqueous solution by supramolecular self-assembly. After bubbling CO2, the tertiary amine of NDPO was protonated. The packing parameter of the mixed surfactants reduced accordingly, accompanied by the transition of aggregates from vesicles to wormlike micelles. As a result, the zero-shear viscosity of the solution increased by more than four orders in magnitude. When the solid content of GCS/NPDO mixtures was higher than 5 wt% in solution, the sample treated by CO2 behaved as a gel over a wide frequency range with shear-thinning and self-healing properties. In addition, the sol-gel transition could be repeatedly and reversibly switched by cyclically bubbling CO2 and N2. Our effort may provide a new strategy for the design of CO2-responsive smart fluids, fostering their use in a range of applications such as in enhanced oil recovery.

Correction: A CO2-responsive smart fluid based on supramolecular assembly structures varying reversibly from vesicles to wormlike micelles.

[This corrects the article DOI: 10.1039/D0RA03854G.].

A Novel Supercritical CO2 Foam System Stabilized With a Mixture of Zwitterionic Surfactant and Silica Nanoparticles for Enhanced Oil Recovery.

In order to improve the CO2 foam stability at high temperature and salinity, hydrophilic silica nanoparticles (NPs) were added into a dilute zwitterionic surfactant solution to stabilize supercritical CO2 (SC-CO2) foam. In the present paper, the foaming capacity and stability of SC-CO2 foam were investigated as a function of NP concentration at elevated temperatures and pressures. It was observed that the drainage rate of SC-CO2 foam was initially fast and then became slower with NPs adsorption at the gas-liquid interface. The improved foam stability at high temperature was attributed to the enhanced disjoining pressure with addition of NPs. Furthermore, an obvious increase in the foam stability was noticed with the increasing salinity due to the screening of NP charges at the interface. The rheological characteristics including apparent viscosity and surface elasticity, resistance factor, and microstructures of SC-CO2 foam were also analyzed at high temperature and pressure. With addition of 0.7% NPs, SC-CO2 foam was stabilized with apparent viscosity increased up to 80 mPa·s and resistance factor up to 200. Based on the stochastic bubble population (SBP) model, the resistance factor of SC-CO2 foam was simulated by considering the foam generation rate and maximum bubble density. The microstructural characteristics of SC-CO2 foam were detected by optical microscopy. It was found that the effluent bubble size ranged between 20 and 30 µm and the coalescence rate of SC-CO2 foam became slow with the increasing NP concentration. Oscillation measurements revealed that the NPs enhanced surface elasticity between CO2 and foam agents for resisting external disturbances, thus resulting in enhanced film stability and excellent rheological properties.

Mechanism of Polyacrylamide Hydrogel Instability on High-Temperature Conditions.

A gel system composed of acrylamide (AM), N,N'-methylenebisAM (BIS), and ammonium persulfate ((NH4)2S2O8) was developed and applied extensively in reservoirs to reduce water cut and increase oil production in mature fields. However, this gel system suffers from thermal stability loss and syneresis at high temperatures that reduces its ability to control water flow. It has been widely accepted that the loss of gel thermal stability can be explained via three aspects: the rupture of polymer chains, the breakage of cross-linker chains, and hydrolysis of polymer. The mechanism of hydrogel syneresis through polymer hydrolysis has been investigated extensively in other publications. However, research on the other two mechanisms is quite limited. In this article, we conduct a series of experiments to demonstrate how the rupture of polymer and cross-linker chains leads to the hydrogel instability at high temperatures. Viscosity and energy-dispersive system measurements suggested that polyAM chains were disrupted by the oxidation reactions involving free radicals. The method to measure the cross-linking degree was established and in combination with X-ray photoelectron spectroscopy measurements, the results showed that cross-linker chains were broken as a result of weaker C-N bond resulting from positively charged mesomethylene carbon and hydrolysis of amide groups on the cross-linker. Because of the application of deionized water in the experiments, nuclear magnetic resonance and FTIR measurements showed that the hydrolysis degree of polymer was weak. Hence, our results verified that breakage of polymer and cross-linker chains led to the rupture of the gel network at high temperature. Besides, cross-linker chains may play a more important role in the thermal stability of the gel, which explains some work into high-temperature-resistant gels.