Effects of hydration on the microstructure and physical properties of shale

Wang

Acta Geologica Sinica (Eng)

et al. 2020

The sedimentary, paleogeomorphological and reservoir characteristics of the Jurassic Yan'an Formation in the southwestern Ordos Basin, northwestern China, were studied by means of casting thin sections, scanning electron microscopy, inclusion analysis and identification of low-amplitude structures. A model for reservoir formation is established, and the controlling effects of sedimentary facies, paleotopography, low-amplitude structures and formation water on oil reservoirs are revealed. There are significant differences in the sedimentary characteristics, structural morphology and paleowater characteristics between the reservoirs above the Yan 10 Member and those in the Yan 9 to Yan 7 Members. The Yan 10 Member contains fluvial sediments, whereas the Yan 9 to Yan 7 members contain delta-plain anastomosing-river deposits. The distribution of high-permeability reservoir is controlled by pre-Jurassic paleogeomorphology and sedimentary facies. Some of these facies exhibit high porosity and high permeability in a lowpermeability background. The main hydrocarbon accumulation period was the late Early Cretaceous, filling was continuous, and the charging strength altered from weak to strong and then from strong to weak. The Yan 10 reservoir is mainly controlled by the paleogeomorphology: hydrocarbons migrated upward at a high speed through the unconformity surface, and accumulated in the favorable traps formed by paleogeomorphic structural units, such as gentle slopes or channel island. Furthermore, groundwater alternation in these areas was relatively stagnant, providing good reservoir preservation conditions. The reservoirs in the Yan 9 and higher members are controlled by the sedimentary facies, lowamplitude structure and paleowater characteristics. Hydrocarbons migrated through the three-dimensional delivery system, influenced by favorable sedimentary facies and high-salinity groundwater, then accumulated in the favorable low-amplitude structural traps that formed during the hydrocarbon production period.

“…seawater salinity; Fig. 21), indicating that the high-salinity region of the study area is a favorable zone for oil or gas preservation (Xue et al, 2018).…”

Section: Factors Controlling Oil Accumulation In the Yan 9 And Highermentioning

confidence: 98%

Factors Controlling Hydrocarbon Accumulation in Jurassic Reservoirs in the Southwest Ordos Basin, NW China

Wang

Acta Geologica Sinica (Eng)

et al. 2020

“…The increase of the water content could lead to mineral particle dissolution and the increase of clay minerals. As a result, the shale structure becomes loose, the mic-cracks gradually increase, and finally, the rock degrades and softens (Feng and Ding, 2005;Cornelius et al, 2011;Zhu et al, 2015;Ling et al, 2016;Liu et al, 2016;Xue et al, 2018;Li et al, 2019). Moreover, a filed investigation found that the primary porosity of shale in the landslide area was well developed, and three sets of the superior fractures caused the loosening of the rock.…”

Section: Failure Mechanism Of the Zhongbao Landslidementioning

confidence: 99%

Emergency Survey and Stability Analysis of a Rainfall-Induced Soil-Rock Mixture Landslide at Chongqing City, China

Zhou

Ai²,

Huang³

et al. 2021

Front. Earth Sci.

The stability analysis of damaged landslides and unstable debris is important for rescue work and emergency operations. This paper investigates a predisposed geological emergence, inducing the factors and deformation processes of the Zhongbao landslide, which happened on July 25, 2020. The stability of the landslide debris was evaluated by an integrated monitoring system consisting of ground-based radar, unmanned aerial vehicles, airborne Lidar, thermal infrared temperature monitoring, GNSS displacement monitoring, deep displacement monitoring, and rainfall monitoring. The strata and weak layer controlled the landslide failure, and topography defined the boundary of the failed rock mass. A continually intensive rainfall caused the deformation and accelerated failure of the landslide. The shallow and steep deposit (Part I) firstly slid at a high velocity, and then pushed the rear part of the landslide (Part II) to deform, forming numerous cracks, which accelerated the rainfall infiltrating into the rock mass. The moisture content increase could decrease the strength of the shale rock within the bedding planes. Finally, with the rock and soil mass sliding along the weak layer, a barrier dam and a barrier lake were formed. The monitoring and numerical simulation results showed that after the landslide failure, there was still local collapse and deformation occurrences which threatened rescue work and barrier lake excavation, and the stability of the accumulation area gradually decreased as the rainfall increased. Therefore, the barrier dam was not excavated until the accumulation rate gradually stabilized on July 28. Moreover, most of the reactivated deposits still accumulated in the transportation and source areas. Thus, in August, the displacement of the landslide debris gradually accelerated in a stepwise manner, and responded strongly to rainfall, especially in the accumulation area, so that it was inferred that the damaged landslide could slide again and cause a more threatening and severe failure. The analysis results of the study area can provide references for the failure mechanism of a rainfall-induced landslide and the stability evaluation of a damaged landslide.

“…The increase of the water content could lead to the mineral particle dissolution and the increase of the clay mineral. As results, the shale structure become loose, the mic-cracks gradually increase, and nally, the rock degrades and softens (Zhu et al, 2015;Feng et al, 2005;Cornelius et al, 2011;Ling et al, 2016;Liu et al, 2016;Xue et al, 2018Li et al, 2019. Moreover, led investigation found that the primary porosity of shale in the landslide area was well developed, and three sets of the superior fractures caused the loose of the rock.…”

Section: Stability Of the Failure Landslide (1) Visual Observation Ofmentioning

confidence: 99%

Monitoring and Stability Evaluation of the Damaged Landslide Based on Multiple Monitoring Technologies

Huang

Zhou

Xu³

et al. 2021

Preprint

The stability evaluation of the damaged landslide is important for rescue work and emergency operation. This paper investigated a predisposing geological emergence, inducing the factors and deformation processes of the Zhongbao landslide, which happened on 25 July 2020. The stability of the damaged landslide was evaluated by an integrated monitoring system consisting of ground-based radar, unmanned aerial vehicles, airborne Lidar, thermal infrared temperature monitoring, GNSS displacement monitoring, deep displacement monitoring and rainfall monitoring. The strata and weak layer controlled the landslide failure, and topography defined the boundary of the failed rock mass. A continually intensive rainfall caused the deformation and accelerated failure of the landslide. The shallow and steep deposit (Part I) firstly slid at a high velocity, and then pushed the rear part of the landslide (Part II) to deform, forming numerous cracks, and the rainfall infiltrated into the rock mass. Finally, the rock and soil mass sliding along the weak layer, a barrier dam and a barrier lake were formed. The monitoring results showed that after the landslide failure, there were still local collapse and deformation occurrence which threatened rescue work and barrier lake excavation. Therefore, the barrier dam wasn’t excavated until the accumulation rate gradually stabilized on July 28. Moreover, most of the reactivated deposits still accumulated in the transportation and source areas. Thus, in August, the displacement of the damaged landslide gradually accelerated in a stepwise manner, and responded strongly to rainfall, especially in the accumulation area, so that it was inferred that the damaged landslide could slide again and caused a more threatening and severe failure. The analysis results of the study area can provide references for the failure mechanism of a rainfall-induced landslide and the stability evaluation of a damaged landslide.