Evaluation of the injection and plugging ability of a novel epoxy resin in cement cracks

Sustained casing pressure(SCP)is a crucial issue in the oil and gas production lifecycle.Epoxy resins,exhibiting exceptional compressive strength,ductility,and shear bonding strength,have the potential to form reliable barriers.The injectivity and sealing capacity of the epoxy resin is crucial parameters for the success of shallow remediation operations.This study aimed to develop and assess a novel solid-free resin sealant as an alternative to Portland cement for mitigating fluid leakage.The investigation evaluated the viscosity,compressive strength,and brittleness index of the epoxy resin sealant,as well as its tangential and normal shear strengths in conjunction with casing steel.The flow characteristics and sealing abilities of conventional cement and epoxy resin were comparatively analyzed in cracks.The results showed that the application of a viscosity reducer facilitated control over the curing time of the epoxy resin,ranging from 1.5 to 6 h,and reduced the initial viscosity from 865.53 to 118.71 m Pa,s.The mechanical properties of the epoxy resin initially increased with a rise in curing agent content before experiencing a minor decrease.The epoxy resin containing 30%curing agent exhibited optimal mechanical properties.After a 14-day curing period,the epoxy resin's compressive strength reached81.37 MPa,2.12 times higher than that of cement,whereas the elastic modulus of cement was 2.99 times greater than that of the epoxy resin.The brittleness index of epoxy resin is only 3.42,demonstrating high flexibility and toughness.The tangential and normal shear strengths of the epoxy resin exceeded those of cement by 3.17 and 2.82 times,respectively.In a 0.5 mm-wide crack,the injection pressure of the epoxy resin remained below 0.075 MPa,indicating superior injection and flow capabilities.Conversely,the injection pressure of cement surged dramatically to 2.61 MPa within 5 min.The breakthrough pressure of0.5 PV epoxy resin reached 7.53 MPa,decreasing the crack's permeability to 0.02 D,a mere 9.49%of the permeability observed following cement plugging.Upon sealing a 2 mm-wide crack using epoxy resin,the maximum breakthrough pressure attained 5.47 MPa,3.48 times of cement.These results suggest that epoxy resin sealant can be employed safely and effectively to seal cracks in the cement.

Robust and High-Wettability Pristine Poly(ether ether ketone) Nanofiber Separator for Heat-Resistant and Safe Lithium-Ion Battery

Separator is a pivotal component of lithium-ion batteries(LIBs)and determines the electrochemical performance and safety.However,with the increase in energy density and application scenarios,commercial polyolefin separators are increasingly unable to undertake heavy responsibility of battery safety protection.Herein,a new kind of nanofiber separator based on poly(ether ether ketone)(PEEK)with excellent thermal stability,self-extinguishing,and superior electrochemical properties is reported.Effective inheritance of intrinsic properties from raw PEEK materials and optimized hot-pressing operation endows the separator with high robustness and wettability,showing tensile strength of 15.8 MPa and a contact angle of 17.2°.The high thermal stability of PEEK can ensure the separator to preserve the structural integrity and microstructure at temperatures beyond 300℃,and the excellent self-extinguishing peculiarity of PEEK capacitates the high safety of LIB.Notably,benefitting from high porosity and polar surface,the PEEK separator shows high electrolyte uptake of 245.5%and exhibits a wider electrochemical window and faster lithium-ion transport number than commercial polyolefin separators.Furthermore,cells assembled with PEEK separator display better performance than the ones with PE separator,and the PEEK LIB has been successfully used to light up a lamp at a high temperature of 150℃.

Unusual Spherulitic Morphology of Poly(propylene fumarate)

Spherulites are the most common crystalline morphology and thus the visual expression of crystal structures for polymers.The diversified patterns have provided intuitive morphology probes for various crystallization behaviors,while the correlations between them are still needed to be enriched.In this work,the complicated spherulitic morphology of poly(propylene fumarate)(PPF),which is sensitive to crystallization temperature,is investigated.PPF melt,respectively,crystallizes into rough spherulites,regularly banded spherulites,and spherulites containing both two kinds of morphology at low,high,and mediate temperatures.By systematically assaying,it is clear that the growth axis along the radial direction changes from a-axis to b-axis as the crystallization temperature increases,which leads to the formation of unique crystallization-temperature-dependent spherulites.Based on detailed characterization of Fourier transform infrared spectroscopy,the packing state of the specific hydrogen bonds of"C=C-H…O=C-C=C"in PPF crystal lattices is determined,and furthermore,the mechanism for temperature-dependent selection of growth axes for PPF spherulites in melt is reasonably speculated.

The Effect of Polymer-Substrate Interaction on the Nucleation Property:Comparing Study of Graphene and Hexagonal Boron Nitride Nanosheets

Hexagonal boron nitride nanosheets （BNNSs） can work as a more efficient nucleating agent for two polyesters compared to graphene. Studies on the crystallization and dewetting processes of two polyesters, poly（butylene succinate） and poly（butylene adipate）, on the two substrate surfaces prove that the interaction between BNNSs and the polyesters is stronger than that between graphene and the polyesters. This strong interaction induces the pre-ordered conformation of molten PBA which has been identified by the in situ FTIR spectra. Thus BNNSs possess higher nucleation property than graphene. Finally, a new polymer-substrate interaction induced nucleation mechanism was proposed to explain the nucleation efficiency difference between graphene and BNNSs.

Melting and Annealing Peak Temperatures of Poly(butylene succinate) on the Same Hoffman-Weeks Plot Parallel to Tm=Tc Line

The crystallization and melting behavior of polymers is of theoretical importance.In this work,poly(butylene succinate)(PBS)was selected as an example to study such behavior at low supercooling via introduction of the extended-chain crystal(ECC)of the same polymer as nucleating agent.The crystallization of PBS with its ECC as nucleating agent in a wide temperature range(90–127°C)and the following melting behavior were studied.It is revealed that the melting point(Tm',for Tc≥113°C)and the annealing peak temperature(Ta',for Tc=90–100°C)show similar asymptotic behavior.Both Tm and Ta approach to a value of ca.3.3°C higher than the corresponding Tc when the crystallization time tc approaches the starting point.That is to say,the Hoffman-Weeks plot is parallel to Tm=Tc line.The crystallization line became parallel to the melting line when PBS was crystallized at Tc higher than 102°C.Based on these results,we propose that the parallel relationship and the intrinsic similarity between the Ta and the Tm observed at the two ends of the Tc range could be attributed to the metastable crystals formed at the beginning of crystallization.

Distinctive Polymorphism-like Isodimorphism in Poly(propylene succinate-ran-propylene fumarate)

Co-crystallization of different monomeric units fundamentally contributes to the versatile and tunable performance of random copolymers.At present,the crystallization manners of random binary copolymers have been divided into three categories:isomorphism,isodimorphism and comonomer exclusion.Each category,however,has its own advantages and disadvantages.Therefore,it is challenging to design and prepare random copolymer sharing the advantages of isomorphism and isodimorphism through a new co-crystallization manner beyond the ones already exist.On the basis of previous study on poly(alkylene succinate-ran-alkylene fumarate)whose co-crystallization can be extensively and finely regulated by simply varying the chemical structure of alkylene,random copolymers of poly(propylene succinate-ranpropylene fumarate)(PPSF)are synthesized using 1,3-propanediol as the diol source.The thermal properties and crystal structure of PPSF are investigated,and,intriguingly,it is proved that PPSF is an isodimorphism system while displays similar composition-dependent thermal properties and crystallinity as isomorphism.That is,PPSF exhibits a novel co-crystallization behavior that has rarely been discovered,which would combine the advantages of both isomorphism and isodimorphism.Consequently,PPSF could be termed as a new-type,special compositiondependent polymorphism.Besides,the altering of PPS-like to PPF-like crystal structure of PPSF when changing chain composition has been proved to originate from the shift of dominant inter-segment interaction from van der Waals forces to strong hydrogen-bonding interaction.This work enriches the co-crystallization manner of random copolymers,leading to more diverse performance design of polymer materials.

Prominently Promoting the Formation of Poly(butylene adipate) α-Form Crystals by Coalescing from Inclusion Complex

We successfully use a co-precipitation method to prepare inclusion complex between poly（butylene adipate） （PBA） chains （guest component） and urea molecules （host component）. The PBA/urea inclusion complex is confirmed to adopt a hexagonal crystal modification with lattice parameters ofa = 8.14 A and c = 10.92 A, and the interaction between PBA chains and urea is van der Waals force. The singly isolated PBA chains are suggested to take some gauche conformation, which is different from the all-trans conformation in r-form PBA. Furthermore, we employ the isolated PBA chains which are uniformly pre-established in a specific conformation in urea channels to regulate the crystal form of PBA for the first time. After removing the host urea molecules, the coalesced PBA chains are found to solely crystallize into a-form crystals at different coalescing temperatures. By comparing the FTIR spectra, it is found that PBA chains in inclusion complex plausibly contain some similar conformers as those in a-form crystal, which is suggested to be the intrinsic reason for the sole formation of a-form crystals. This research proves that inclusion complex can be used as a very effective method to regulate polymorphism of semi-crystalline polymers.

Isomorphism in ternary complex:Poly(ethylene oxide),urea and thiourea

Herein,we demonstrated that poly（ethylene oxide）（PEO）,urea and thiourea can crystallize into novel ternary complex with the molar ratio of guest polymer and host small molecule as 3：2,and proved that the ternary complex behaves isomorphism phenomenon by varying the ratio between urea and thiourea for the first time.This observation gives a boost to prepare co-crystals of different small molecules that cannot be obtained by direct mixing without the aid of polymer chains.