Conglomerate oil reservoirs have reserves exceeding 2 billion tonnes in China and are one of the important replacement fields for oil and gas energy in China. However, conglomerate reservoirs contain a large amount of gravel, which is very heterogeneous mechanically and has significant differences in crack propagation paths. It is difficult to achieve balanced distribution of fractures in fracturing, and it is difficult to effectively explain using existing theories of uniform rock crack propagation. Therefore, it is necessary to explore relevant theories and methods applicable to conglomerate. In response to the characteristics of conglomerate reservoirs and the difficulties in development engineering, this article explores the difficulties and countermeasures in conglomerate development from five aspects:rock characteristics, research methods, mechanical characteristics, fracture propagation and hydraulic fracturing technology. Based on this, a multi-scale analysis method was proposed for comprehensive mesoscale, conventional scale, large scale model, meter scale, and field scale, and the laboratory research results were applied to oilfield sites through scale upgrading; Clarifying the gravel, mixed base, and cementation surface is the key to controlling rock mechanical parameters and fracture patterns. It is necessary to establish a weak cementation surface model to improve the accuracy of mechanical parameter prediction; It has been clarified that there are two modes of conglomerate fracture propagation:through gravel and around gravel, with obvious process zone characteristics. A fracture propagation model suitable for conglomerate can be constructed based on the double K fracture criterion to predict the initiation and propagation parameters; The compressibility evaluation should be guided by the integration of geological engineering, integrating rock fabric characteristics and multi-scale mechanical parameters to establish, and optimize fracturing plans.

Due to the existence of gravel, glutenite is heterogeneous and different from fine-grained rocks such as sandstone and shale in structure. To fully understand the effect of gravel on failure mode in glutenite, we performed triaxial compression tests on different glutenites. The results indicate that failure modes of glutenite are complex due to the existence of gravel. Under different confining pressures, three failure modes were observed. The first failure mode, a tensile failure under uniaxial compression, produces multiple tortuous longitudinal cracks. In this failure mode, the interaction between gravels provides the lateral tensile stress for rock splitting. The second failure mode occurs under low and medium confining pressure and produces a crack band composed of micro-cracks around gravels. This failure mode conforms to the Mohr-Coulomb criterion and is generated by shear failure. In this failure mode, shear dilatancy and shear compaction may occur under different confining pressures to produce different crack band types. In the second failure mode, gravel-induced stress concentration produces masses of initial micro-cracks for shear cracking, and gravels deflect the fracture surfaces. As a result, the fracture is characterized by crack bands that are far broader than in fine-grained rocks. The third failure mode requires high confining pressure and produces disconnected cracks around gravels without apparent crack bands. In this failure mode, the gravel rarely breaks, indicating that the formation of these fractures is related to the deformation of the matrix. The third failure mode requires lower confining pressure in glutenite with weak cement and matrix support. Generally, unlike fine-grained rocks, the failure mode of glutenite is not only controlled by confining pressure but also by the gravel. The failure of glutenite is characterized by producing cracks around gravels. These cracks are produced by different mechanisms and distributed in different manners under different confining pressures to form different fracture patterns. Therefore, understanding the rock microstructure and formation stress state is essential in guiding glutenite reservoir development.