Previous studies have reported that chromosome synteny in Lepidoptera has been well conserved, yet the number of haploid chromosomes varies widely from 5 to 223. Here we report the genome (393 Mb) of the Glanville fritillary butterfly (Melitaea cinxia; Nymphalidae), a widely recognized model species in metapopulation biology and eco-evolutionary research, which has the putative ancestral karyotype of n ¼ 31. Using a phylogenetic analyses of Nymphalidae and of other Lepidoptera, combined with orthologue-level comparisons of chromosomes, we conclude that the ancestral lepidopteran karyotype has been n ¼ 31 for at least 140 My. We show that fusion chromosomes have retained the ancestral chromosome segments and very few rearrangements have occurred across the fusion sites. The same, shortest ancestral chromosomes have independently participated in fusion events in species with smaller karyotypes. The short chromosomes have higher rearrangement rate than long ones. These characteristics highlight distinctive features of the evolutionary dynamics of butterflies and moths.

In situ emulsion formation is an effective nonthermal method to improve conventional heavy-oil recovery. In this paper, a newly designed viscosity reducer (TPVR7) and a high-performance surfactant (dioctyl sodium sulfosuccinate, DSS) for enhanced conventional heavy-oil recovery have been introduced and evaluated. A dewatering rate test, emulsion droplet size measurement, multiple-light scattering, and interfacial tension measurement are carried out to evaluate the synergistic effect of the viscosity reducer and the surfactant on the emulsion stability and efficiency in enhancing heavy-oil recovery. The results show that adding a surfactant can significantly increase the emulsion stability by decreasing the size of the emulsion droplet and forming a tighter interfacial film. The optimum viscosity reducer−surfactant system is formulated as TPVR7-0.5% + DSS-0.5%. With the optimum system, the viscosity of heavy oil decreased from 350 to 9 mPa•s. The equilibrium interfacial tension of the oil/TPVR7-0.5% + DSS-0.5% solution is ∼0.092 mN/m, much lower than that of the oil/TPVR7 solution. The mechanisms of synergistic collaboration between the viscosity reducer and the surfactant include enhanced emulsion stability, viscosity reduction, and interfacial tension reduction. The sand-pack flooding experiments show that a viscosity reducer and surfactant could improve heavy-oil recovery by 21.89% after water flooding at the optimum concentration, which indicates that viscosity reducer and surfactant flooding has great potential to enhance heavy-oil recovery.

Profile modification of injection wells or water plugging of production wells are the most common ways to improve oil recovery with the continuous development of oil reservoirs. For high temperature and high‐salt oil and gas reservoirs, the plugging agent is required to have certain stability under high temperature and high‐salt conditions. Polymer gel is one of the commonly used plugging agents in oil fields. This article conducted detailed experimental research and mechanism analysis on six gel systems composed by two types of polymer (hydrolyzed polyacrylamide [HPAM] and terpolymer L‐1) and three types of cross‐linker systems (phenol/hexamethylenetetramine [HMTA], resorcinol/HMTA and bisphenol‐A/HMTA). The mechanisms of cross‐linker systems and polymer were studied, and the experimental researches were done on their gelation process, long‐term thermal stability, salt resistance, microstructure observation, rheological properties, and so on. The number of high‐temperature resistant cross‐linking points determines the performance of the gel system formed by cross‐linker systems with the polymer. The cross‐linker systems of bisphenol‐A/HMTA have four high‐temperature resistant cross‐linking points, and its performance was the best. Due to the introduction of ATBS and NVP groups on the polymer chain, the performance of gel system formed by the terpolymer L‐1 was significantly more stable than that of formed by HPAM. This study shows that the bisphenol‐A/HMTA‐L‐1 gel has excellent long‐term thermal stability and salt tolerance, and can be used in ultrahigh temperature (150°C) and high‐salt oil and gas reservoirs to improve oil recovery.

No abstract