Local stress perturbations associated with the 2008 Wenchuan M 8.0 earthquake near the Longmenshan fault zone in the eastern margin of the Tibetan Plateau

Nat. Hazards Earth Syst. Sci.

Gao

Zhang

et al. 2022

Self Cite

Abstract. The Tangshan region is one of the most seismically active areas in the North China, and the 1976 M 7.8 earthquake occurred on 28 July near the Tangshan fault zone. The Matouying enhanced geothermal system (EGS) field is located ∼90 km away from the city of Tangshan. Since late 2020, preliminary hydraulic stimulation tests have been conducted at depths of ∼3965–4000 m. Fluid injection into geothermal reservoir facilitates a heat exchanger system. However, fluid injection may also induce earthquakes. In anticipation of the EGS operation at the Matouying uplift, it is essential to assess how the fault slip potential of the nearby active and quiescent faults will change in the presence of fluid injection. In this study, we first characterize the ambient stress field in the Tangshan region by performing stress tensor inversions using 98 focal-mechanism data (ML≥2.5). Then, we estimate the principal stress magnitudes near the Matouying EGS field by analyzing in situ stress measurements at shallow depths (∼600–1000 m). According to these data, we perform a quantitative risk assessment using the Mohr–Coulomb framework in order to evaluate how the main active faults might respond to hypothetical injected-related pore pressure increases due to the upcoming EGS production. Our results mainly show that most earthquakes in the Tangshan seismic region have occurred on the faults that have relatively high fault slip potential in the present ambient stress field. At well distances of less than 15 km, the probabilistic fault slip potential on most of the boundary faults increases with continuing fluid injection over time, especially on the faults with well distances of ∼6–10 km. The probabilistic fault slip potential (fsp) increases linearly with the fluid injection rate. However, the fsp values decrease exponentially with increased unit permeability. The case study of the Matouying EGS field has important implications for deep geothermal exploitation in China, especially for Gonghe EGS (in Qinghai Province) and Xiong'an New Area (in Hebei Province) geothermal reservoirs that are close to the Quaternary active faults. Ongoing injection operations in the regions should be conducted with these understandings in mind.

“…stress tensors to Eq. ( 6) from Feng et al (2020). As shown in Table 3, the predominant σ H orientations are 86 E) (Fig.…”

Section: Hydraulic Fracturing Measurements In the Mty Egs Fieldmentioning

confidence: 73%

Section: Hydraulic Fracturing Measurements In the Mty Egs Fieldmentioning

confidence: 99%

Fault slip potential induced by fluid injection in the Matouying enhanced geothermal system (EGS) field, Tangshan seismic region, North China

Nat. Hazards Earth Syst. Sci.

Gao

Zhang

et al. 2022

Self Cite

“…Furthermore, the orientations of σ H and σ h always have dips, not absolutely horizontal, and the orientation of σ v also has a dip, not absolutely vertical. Based on the research results from Feng et al [94], the assumptions of the orientations of the three principal stresses can be accepted in Qinghai-Tibet Plateau and its adjacent region.…”

Section: Discussionmentioning

confidence: 99%

The Influence Mechanism of In Situ Stress State on the Stability of Deep‐Buried‐Curved Tunnel in Qinghai‐Tibet Plateau and Its Adjacent Region

Wang

Tan

et al. 2021

Shock and Vibration

Self Cite

In China, rockburst disaster occurs mostly in construction of underground engineering in Qinghai-Tibet Plateau and its adjacent region. Previous research on deep-buried tunnels has indicated that tunnels stability is related to in situ stress state. To quantify these relationships, three-dimensional finite element modeling was done to analyze the influences that the angle φ between the maximum horizontal principal stress orientation and tunnel axis, and the lateral pressure coefficient KH, had on the tangential stress σ θ in a deep-buried-curved tunnel. Based on the in situ stress condition in Qinghai-Tibet Plateau and its adjacent region, 50 different simulation conditions were used to analyze the relationship that φ and KH had on σ θ for the rock mass surrounding the tunnel. With the simulation data produced, predictive equations were generated for σ θ as a function of φ and KH using multivariate regression analysis. These equations help estimate σ θ at various key positons along the tunnel boundary at Qinghai-Tibet plateau and its adjacent region. The equations were then proved by a set of typical tunnels to ensure validity. The results concluded that the change in φ has a significant impact on σ θ , and thus, the stability of the tunnel, when 30° < φ < 60°, with the most obvious influence being when φ is about 45°. With the equations, the rockburst potential at a certain location within a curved tunnel can be quickly estimated by calculating φ and KH on σ θ , without need of geo-stress background knowledge and heavy simulation, allowing for the practical value in engineering at design phase for the projects in Qinghai-Tibet Plateau and its adjacent region.

“…Finally, we estimate the predominant orientation of the maximum horizontal principal stress in different boreholes by applying the mean stress tensors to Eq. ( 6) from Feng et al (2020). As shown in Table 3,…”

Section: Hydraulic Fracturing Measurements In the Mty Egs Fieldmentioning

confidence: 91%

“…Using Eq. (A2) from Feng et al (2020) and our in situ stress data (Table 2), we first calculate the two-dimensional stress tensors at similar depths in the x (east) -o -y (north) coordinate system and then determine the tensorial mean of these stress states (Table 3). Finally, we estimate the predominant orientation of the maximum horizontal principal stress in different boreholes by applying the mean stress tensors to Eq.…”

Section: Hydraulic Fracturing Measurements In the Mty Egs Fieldmentioning

confidence: 99%

Fault slip potential induced by fluid injection in the Matouying EGS field, Tangshan seismic region, North China

Gao

Zhang

et al. 2022

Preprint

Self Cite

Abstract. The Tangshan region is one of the most seismically active areas in the North China, and the 1976 M 7.8 earthquake occurred on July 28th near the Tangshan fault zone. The Matouying Enhanced Geothermal Systems (EGS) field is located ~90 km away from Tangshan City. Since the late 2020, preliminary hydraulic stimulation tests have been conducted at depths of ~3965–4000 m. Fluid injection into geothermal reservoir facilitates heat exchanger system. However, fluid injection may also induce earthquakes. In anticipation of the EGS operation at the Matouying uplift, it is essential to assess how the fault slip potential of the nearby active and quiescent faults will change in the presence of fluid injection. In this study, we first characterize the ambient stress field in the Tangshan region by performing stress tensor inversions using 98 focal mechanism data (ML ≥ 2.5). Then, we estimate the principal stress magnitudes near the Matouying EGS field by analyzing in situ stress measurements at shallow depths (~600–1000 m). According to these data, we perform a quantitative risk assessment using the Mohr-Coulomb framework in order to evaluate how the main active faults might respond to hypothetical injected-related pore pressure increases due to the upcoming EGS production. Our results mainly show that most earthquakes in the Tangshan seismic region have occurred on the faults that have relatively high fault slip potential in the present ambient stress field. At well distances of less than 15 km, the probabilistic fault slip potential on most of the boundary faults increase with continuing fluid injection over time, especially on these faults with well distances of ~6–10 km. The probabilistic fault slip potential increases linearly with the fluid injection rate. However, the FSP values decrease exponentially with increased unit permeability. The case study of the Matouying EGS field has important implications for the deep geothermal exploitation in China, especially for Gonghe EGS (in Qinghai province) and Xiong’an New Area (in Hebei province) geothermal reservoirs that are close to the Quaternary active faults. Ongoing injection operations in the regions should be conducted with these understandings in mind.