The science of the provenance, sedimentary system, and distribution of sand bodies is unclear, limiting oil and gas exploration. Here, we combined heavy mineral, rare earth element, petrographic, and outcrop data to shed new light on the provenance, depositional environment, and paleoclimatic conditions of the Permian Jiamuhe Formation. The provenance is characterized by “a main provenance system, and four provenance zones,” and this result could be interpreted from analyses of its seismic reflection, clastic composition, REE_S, and heavy minerals. A detailed sedimentological study performed in the excellent outcrops, a comprehensive analysis of logging, and the legalistic cores of this formation allowed for the identification of ten lithofacies and three lithofacies associations. Four distributary/underwater channels were observed. Furthermore, the redox and paleoclimatic conditions based on trace elements (Th/U, V/(V + Ni), V/Cr, Cu/Zn, Sr/Ba, and Sr/Cu) suggested a weak reduction in the environment, as well as semi-humid and semi-dry conditions of the Jiamuhe Formation. These conditions are also supported by the mudstone color and plant fossils. The tectonic setting belongs to the acid island arc area based on the trace element discrimination diagram of La-Th-SC and the values of the La, Ce, ΣREE, L/H, La/Yb, and (La/Yb)N criteria. The research results further confirm that there are differences in the mineral compositions in the same provenance area, and they provide a geological basis for the fine sedimentary facies characterization and a favorable zone prediction in this area.

The Jiamuhe Formation in the northwest margin of the Shawan Sag comprises tight sandstone reservoirs, and its distribution has obvious regional differences, but the reasons for this difference are not clear. This study aims to clarify the diagenetic facies and pore evolution patterns by integrating petrographic thin sections, fluorescence thin sections, X-ray diffraction, porosity-permeability data. The objective is to identify the causes of these differences, establish a theoretical evolutionary model, and quantitatively characterize pore evolution. The study area is dominated by lithic sandstone, feldspar lithic sandstone, and lithic feldspar sandstone. These rocks are characterized by relatively low textural and compositional maturity. The primary storage space is predominantly composed of secondary pores formed through dissolution, with minor microfractures present. The findings indicate that dissolution is the principal factor contributing to the physical properties of reservoirs observed between the delta plain and delta front. The texture of the cement and secondary pores govern the variations in physical properties within the same facies zone. The diagenetic sequence includes compaction→early chlorite coating→early meteoric water dissolution→early calcite/kaolinite cementation→middle-stage analcime/philipsite/zeolite cementation →middle-stage organic acid dissolution→microfractures. Quantitative analysis indicates that the original porosity decreased 23.89% by compaction and 7.94% by cementation. Conversely, dissolution and tectonic fracturing enhance porosity by 5.87% and 5.10%, respectively. The theoretical calculations align well with the experimental results. Based on the cementation-sedimentation-pore type, the Jiamuhe Formation in the study area is classified into four distinct diagenetic facies, type I is strong cementation – outer delta front – dissolution pores. Type II is strong cementation – inner delta front – intra granular dissolution pores with moderate dissolution. Type III is poor cementation – delta plain – intergranular pores with strong dissolution. Type IV is strong compaction – delta plain – intergranular dissolution pores with moderate cementation. The evolutionary history of each facies was reconstructed by using porosity evolution curves. Type I and Type III were demonstrated significant reservoir potential, offering a reference for predicting favorable reservoir distribution in future studies.

Introduction: The sediment genetic mechanisms have always been an important branch of the “source-sink” system, and it is also a research hotspot.Methods: Conglomerate, sandstone, and coal are developed of Middle-Lower Jurassic in the Junggar Basin, and the genetic mechanism is not clear, which restricts further exploration of oilfield. Based on the core carefully, test data, and outcrop sections, Badaowan and Xishanyao formations are analyzed.Results: Five types of conglomerate lithofacies and sandstone lithofacies, two kinds of mudstone lithofacies, and one type of coal are identified. Based on the structural-genetic mechanism, the debris flow and traction current with conglomerate are developed, and a method of the semi-quantitative identifying index is proposed based on the sedimentary sequence of lithological characteristics, MPS/BTh, and grain size characteristics as the identification criteria. Depending on fluvio-delta, the genetic bodies of the distribution channel, subaqueous distribution channel, mouth bar, braided channel, and overbank sandstone are divided.Discussion: By integrating structural, paleoclimatic, and sedimentary environment, it was observed that coal in the Badaowan Formation has the characteristics of continuous and stable distribution of thick layers, whereas multiple sets of discontinuous and instable distribution are observed in the in Xishanyao Formation. Finally, the filling model is established, and the superposition and distribution of sandbodies are clarified.

This study aims to refine the fracture characterization of three-point bending semi-circular specimens used in rock fracture toughness assessments. The primary objective is to improve the accuracy of such evaluations by developing numerical simulations of specimens with pre-engineered cracks of varying geometries. Numerical simulations were conducted using the finite element method. The interaction integral method was employed to quantify the stress intensity factors (SIFs) and T-stress at crack tips. Initially, the model’s accuracy was validated by replicating stress singularities at crack tips in a benchmark circular disk with a central straight crack. Following validation, dimensionless fracture parameters specific to the three-point bending semi-circular specimens were calibrated. The numerical results demonstrate that the dimensionless stress intensity factor (Y_I) increases with both the relative crack length (a/R) and the spacing between support points. Notably, for relative crack lengths a/R ≤ 0.5, the dimensionless T-stress assumes negative values, initially decreasing and then increasing as the relative crack length increases. The findings of this study provide valuable insights into the fracture behavior of three-point bending semi-circular specimens with pre-engineered cracks. Based on the observed trends in the dimensionless fracture parameters, it is recommended that relative crack lengths within the range of 0.2–0.6 be used to maintain the accuracy of rock fracture toughness tests. The finite element method used in this study serves as a robust tool for calibrating fracture parameters, thereby laying a strong foundation for the application of these specimens in rock fracture toughness evaluations.