Abstract
Shales reservoirs have a high degree of anisotropy due to the presence of natural fractures (NFs) and also the orientation of beddings. Thus, hydraulically induced fractures (HFs) interact with natural fractures and generate a network of fractures with complex geometry. The existence of NFs modifies the stress field in the shale and directly influences the geomechanical behaviour of the HFs during the fracturing operation, generating branches in the dominant fracture and contributing to the complex network of fractures. The construction of a network of fractures increases significantly the conductivity of the formation, as it connects previously isolated fractures and pores, thus increasing the productivity index of the wells and providing greater economic viability in the shale gas/oil reservoir designs. This work presents a sensitivity analysis of the influence of fracturing spacing in the construction of the network of complex fractures generated in shales, aiming to understand how this parameter modifies the volume of stimulated reservoir (SRV) and the distribution of propant in the network of fractures, in order to avoid problems in this step of the design and thus, maintain the economic viability of the network. The literature review includes the main published works on this subject and the unconventional fracture models (UFM) used to model the network of complex fractures. Sensitivity analysis will be performed using the MShale software, which uses a stochastic model of the discrete fracture network (DFN) method and numerically solves the equilibrium equations and pore elasticity for shales in terms of effective stresses, in addition to mass conservation equations, linear momentum and energy with viscous dissipation for stokes creeping flow. For the analysis, the other parameters that influence the construction of the network will be kept constant and only the spacing between fracturing will have variation.
Highlights
The generation of oil occurs in sedimentary basins such as lakes, oceans, rivers and marshes, where sedimentary rocks with large amounts of fine grains, clay and silt are deposited over millions of years and carrying a certain volume of organic matter accumulated in the interior of their pores [1], Such rocks are called source rocks [2]
The shale gas /shale oil system is different from the conventional reservoirs (CR) mentioned above, since shales are part of a group known in the literature as unconventional reservoirs (NCR), because the primary migration has not yet occurred and because the shales have low permo-porous properties
In fragile shale gas/shale oil reservoirs, with low values of dynamic viscosity of the fracturing fluid, the construction of the network of complex fractures occurs with greater ease;
Summary
The generation of oil occurs in sedimentary basins such as lakes, oceans, rivers and marshes, where sedimentary rocks with large amounts of fine grains, clay and silt are deposited over millions of years and carrying a certain volume of organic matter accumulated in the interior of their pores [1], Such rocks are called source rocks [2]. Its formation is by means of transport by water or air Such rocks are usually composed of silica, combined with other common minerals such as feldspar and clay minerals, e.g. quartz, limestone and feldspar, which have low granulometry, making it difficult to explore shale gas /shale oil without use stimulation techniques. Another characteristic of the shales is to possess high total organic content, TOC [5].
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