An improved geomechanical model for the prediction of fracture generation and distribution in brittle reservoirs

Abstract

It is generally difficult to predict fractures of low-permeability reservoirs under high confining pressures by data statistical method and simplified strain energy density method. In order to establish a series of geomechanical models for the prediction of multi-scale fractures in brittle tight sandstones, firstly, through a series of rock mechanics experiments and CT scanning, we determined 0.85 σc as the key thresholds for mass release of elastic strain energy and bursting of micro-fractures. A correlation between fracture volume density and strain energy density under uniaxial stress state was developed based on the Theory of Geomechanics. Then using the combined Mohr-Coulomb criterion and Griffith’s criterion and considering the effect of filling degree in fractures, we continued to modify and deduce the mechanical models of fracture parameters under complex stress states. Finally, all the geomechanical equations were loaded into the finite element (FE) platform to quantitatively simulate the present-day 3-D distributions of fracture density, aperture, porosity, permeability and occurrence based on paleostructure restoration of the Keshen anticline. Its predictions agreed well with in-situ core observations and formation micro-imaging (FMI) interpretations. The prediction results of permeability were basically consistent with the unobstructed flow distributions before and after the reservoir reformation.

Numerical investigation of the influence of discontinuity orientations on fault permeability evolution and slip displacement

“…From reports (e.g. Shrivastava and Lawatia 2011;Xue et al 2014;Wang et al 2016;Feng et al 2018;Eyinla et al 2021), tight reservoirs have specific variations from the conventional reservoirs because of certain factors which include high heterogeneity, their deeper depth of burial, diagenetic properties, low porosities, very low permeability, poorly developed fracture system and abnormal pressure with. While rocks contain different forms of discontinuities which play an inevitable role in the overall mechanical and elastoplastic behaviour, the most significant types of discontinuities in rocks include faults, fractures, weak planes/joints, shear zones, planes of foliation, bedding planes and planes of cleavage (Eshiet and Sheng 2017).…”

“…An essential factor which also determines the quality and yield of tight reservoirs is the distribution of fracture-controlled permeability resulting from fluid injection, which could be attributed to several factors such as the pattern of joints. Nonetheless, one way of characterizing these fractures is by the application of numerical forward modeling (Parker 2013) and laboratory experiments (Asahina et al 2018;Feng et al 2018). The combination of both would give a more detailed study and allows adequate scientific correlation.…”

Rock physics and geomechanical application in the interpretation of rock property trends for overpressure detection

“…From previous studies (e.g. Streit and Hillis 2004; Archer and Rasouli 2012; Oladunjoye 2014, 2018;Eshkalak et al 2014;Vilarrasa et al 2016;Abijah and Tse 2016;Kumar et al 2017;Turner et al 2017;Feng et al 2018), these applications often include the predictions of overpressure and sand production, modeling of rock's fracability during hydraulic fracturing, and in the estimation of injection-induced seismicity during fluid injection. Thus, the ability to safely plan hydraulic fracturing program and drill through abnormal pressure intervals require a multiple approach to understand the dynamics of the overpressure mechanisms (Zhang 2019).…”

“…Formation fracturing pressure is one of the key parameters used in hydraulic fracturing design, and the magnitude of this parameter depends on formation depth and the material properties (Guo et al 2007). Generally, the unconventional (tight) reservoirs differ greatly from conventional reservoirs as a result of their deeper depth of burial, strong diagenetic properties, huge heterogeneity, reduced porosity, abnormal pressure with low permeability, and poorly developed natural fractures (Xue et al 2014;Wang et al 2016;Feng et al 2018). Therefore, the nature of fracture propagation and hydraulic fracture initiation in a naturally fractured reservoir is influenced by the properties of the natural fractures, pore pressure and in situ stresses.…”

“…The production from low permeable or unconventional reservoirs like tight sands, shale gas and carbonates, has become possible and more successful primarily because of various injection and hydraulic fracturing processes which have greatly improved the fault permeability, creating room for more recovery. As formation pressure in rocks changes due to the varying tectonic history and burial conditions, the resulting effect is often seen in the response of the reservoir to fluid injection and artificial fracturing (Feng et al 2018;Eshkalak et al 2014;Fan et al 2016;Abijah and Tse 2016;Eyinla and Oladunjoye 2018). Nevertheless, the inherent strength of rocks has a direct correlation with the elastic properties, which has been observed to be a good source of information regarding the pressure state and sanding rate during production (Dresser Atlas 1982; Eyinla and Oladunjoye 2014).…”