Certain types of silicon carbide (SiC) grains, e.g. SiC-X grains, and low density (LD) graphites are C-rich presolar grains that are thought to have condensed in the ejecta of core-collapse supernovae (CCSNe). In this work we compare C, N, Al, Si, and Ti isotopic abundances measured in presolar grains with the predictions of 21 CCSN models. The impact of a range of SN explosion energies is considered, with the high energy models favouring the formation of a C/Si zone enriched in 12C, 28Si, and 44Ti. Eighteen of the 21 models have H ingested into the He-shell and different abundances of H remaining from such H-ingestion. CCSN models with intermediate to low energy (that do not develop a C/Si zone) cannot reproduce the 28Si and 44Ti isotopic abundances in grains without assuming mixing with O-rich CCSN ejecta. The most 28Si-rich grains are reproduced by energetic models when material from the C/Si zone is mixed with surrounding C-rich material, and the observed trends of the 44Ti/48Ti and 49Ti/48Ti ratios are consistent with the C-rich C/Si zone. For the models with H-ingestion, high and intermediate explosion energies allow the production of enough 26Al to reproduce the 26Al/27Al measurements of most SiC-X and LD graphites. In both cases, the highest 26Al/27Al ratio is obtained with H still present at XH ≈ 0.0024 in He-shell material when the SN shock is passing. The existence of H in the former convective He-shell points to late H-ingestion events in the last days before massive stars explode as a supernova.

Reservoir stimulation by means of hydraulic fracturing has enhanced the production of hydrocarbons from shale. The latest methods concentrate on reducing the detrimental interference between fractures within the same well. The theory behind this is well understood, however the concept of constructive interference between fractures in adjacent wells is not so developed.In this paper, contemporary hydraulic fracturing techniques are numerically simulated to analyze both the rock and fluid mechanic effects on the generation of fractures within a reservoir. The techniques involve various geometrical patterns of well and fracture spacing, followed by methods of sequencing the different stages of stimulation. These methods aim to reduce the compressive stress normal to fractures and increase the size o f tensile regions between fractures in adjacent wells. To measure the performance of different methods, the simulated microseismic energy released is used to calculate the stimulated rock volume (SRV). Production profiles have been generated for several key hydraulic fracturing scenarios, with the results predominantly showing an optimum well spacing to exist.

No abstract