The influence of brittleness and ductulity of shale formations on the efficiency of hydraulic fracturing
Oil- and gas-saturated clay-carbonate pays of Eagle-Ford formation are simultaneously hydrocarbon source rocks, reservoir and cap rocks. Shale formations have a significant quartz (silicate) or the carbonate component, that make them more brittle and as a result subject to fracturing. Syngenetic organic matter (OM) is the source of hydrocarbons. Kerogen structure affects the elastic and mechanical properties of the reservoir. Oil and gas accumulations in clay-carbonate formations are formed in the closed thermodynamic systems, the movement of the front edge of the hydrocarbon reservoir, as shown above, has its own (internal) causes of movement. Reservoir volume increase in such a system occurs due to appearance of new fractures and growth of already available ones in deadlocks zones of fluid fractures, where there happens increase of the non-anticline (catagenetic) oil deposit. After assessing lithogenesis of formations it can be possible to predict the more brittle and more ductile areas. The exact determination of brittle rocks’ area is important for effective implementation of hydraulic fracturing. Brittleness depends on the component composition of the rock, temperature and pressure. Correction factor is proposed to be introduced for the reliable assessment of this parameter. Based on the proposed dependence, the diagram that allows assessing the physical component of the rock components’ composition is applied. The main way of shale formations develop is hydraulic fracturing of a formation, namely, creation of additional artificial (secondary, technogenic) fractures in brittle and compacted rocks to provide effective movement of the fluid to the wellbore. In this context, knowledge about brittleness and ductility of rocks allows estimating the degree of the required impact on the formation and defining the amount of water and proppant necessary for hydraulic fracturing as well as areas inefficient for conducting of fracturing. Showings of brittleness and ductility of shale formations can be used for qualitative-quantitative prediction of fractures’ spatial position and stresses’ anisotropy as well as estimation of water and proppant demand needed after conducting of a formation hydraulic fracturing. When developing productive intervals of shale deposits it is proposed to apply the cyclic method with repeated hydraulic fracturing of a formation tested and approved when used in vertical well of the Eagle Ford formation that extends the life-time of a well operation and, consequently, maintaining the high level of production without drilling new producing wells.