Frictional stability of Longmaxi shale gouges and its implication for deep seismic potential in the southeastern Sichuan Basin

Abstract

Microearthquakes accompanying shale gas recovery highlight the importance of exploring the frictional and stability properties of shale gouges. Aiming to reveal the influencing factors on fault stability, this paper explores the impact of mineral compositions, effective stress and temperature on the frictional stability of Longmaxi shale gouges in deep reservoirs located in the Luzhou area, southeastern Sichuan Basin. Eleven shear experiments were conducted to define the frictional strength and stability of five shale gouges. The specific experimental conditions were as follows: temperatures: 90-270°C; a confining stress: 95 MPa; and pore fluid pressures: 25-55 MPa. The results show that all five shale gouges generally display high frictional strength with friction coefficients ranging from 0.60 to 0.70 at the aforementioned experiment condition of pressures, and temperatures. Frictional stability is significantly affected by temperature and mineral compositions, but is insensitive to variation in pore fluid pressures. Fault instability is enhanced at higher temperatures (especially at >200°C) and with higher tectosilicate/carbonate contents. The results demonstrate that the combined effect of mineral composition and temperature is particularly important for induced seismicity during hydraulic fracturing in deep shale reservoirs.

Deep Groundwater Flow Patterns Induced by Mine Water Injection Activity

“…Therefore, it was beneficial to the geological storage of mine water in the basin-scale for the Ordos basin, but the renaissance of induced seismicity should be avoided [ 73 ]. The high frequency of water injection often induced the seismic activities around wells and was analogous to faults re-activation seismic in the gas extraction [ 74 ].…”

Impact of Crossflow and Two-Phase Flow on Gas Production from Stacked Deposits

“…These three types of reservoirs alternate in the vertical direction and have multiple distribution forms. , A typical distribution of multilayer reservoirs in the coal measure is shown in Figure , in the order of shale, coalbed, and tight sandstone reservoir. The interlayer is generally a low-permeability layer, such as mudstones, and its permeability is much smaller than that of gas reservoirs.…”

Analytical Model of Wellbore Stability Analysis of Inclined Well Based on the Advantageous Synergy among the Five Strength Criteria

“…As shown in Figure 2(b), the radial stress (σ rr ) is always one of the principal stresses, owing to it being always perpendicular to the wall of the wellbore, and the other two principal stresses must be within the plane of wellbore (θ, z b ). Therefore, according to material mechanics, both normal and shear stress within the plane of wellbore (θ, z b ) can be expressed as σ = σ θθ cos 2 γ + 2τ θz cos γ sin γ + σ zz sin 2 3 Geofluids Take the first derivative of σ with respect to γ to be zero, so that the direction of the major and minor principal stresses can be determined, and applying the Biot effective stress law (σ ′ = σ − αp p ), the effective principal stresses (EPSs) can be written as [21]…”

“…In recent years, unconventional petroleum reservoirs are receiving increasing attentions [1], particularly, shale reservoir [2], tight-sand reservoir [3], and coalbed methane reservoir [4]. Owing to advances in directional drilling technologies, directional, horizontal, and extended-reach wells are widely employed to develop these unconventional petro-leum reservoirs [5,6].…”