Elastic characteristics of overpressure due to smectite-to-illite transition based on micromechanism analysis

Qin, Xuan1,2; Han, De-Hua2; Zhao, Luanxiao3

2019-07-01

10.1190/GEO2018-0338.1

GEOPHYSICS   影响因子和分区

0016-8033

1942-2156

Characterizing the elastic signatures of overpressure of shale caused by the smectite-to-illite transition relies on a good understanding of this mechanism and is also necessary for pore-pressure prediction. Methods of pore-pressure prediction in shales that have undergone smectite-to-illite transition are mostly based on empirical fitting without a quantitative interpretation based on a micromechanism analysis. With upscaled wireline-logging data, two trends of smectite-to-illite transition are categorized by using the crossplot of sonic traveltime and density. Trend I associated with a fluid-expansion scenario exhibits a decrease of sonic velocity with little change in the bulk density, whereas trend II induced by a fluid-loss scenario contains an increase of density with little change in the sonic velocity. The fluid expansion typically gives rise to high-magnitude overpressure and tends to happen when the overlying formations have more shaly contents and low permeability. The fluid loss case tends to have relatively deeper overpressure onsets, and its overlying formations tend to have more sandy contents with relatively high permeability. We develop a modeling framework to capture the elastic and pore-pressure evolution characteristics in shale during the smectite-to-illite transition. With proper bulk volume models, the velocity, density, and pore pressure increase of shale can be computed in the fluid expansion, fluid loss, and a mixture of these two scenarios. After calibration with logging data, rock-physics modeling can quantitatively interpret the rock-property evolution characteristics within the smectite-to-illite transition zone.

SCI ; EI

英语

第一 ; 通讯

National Natural Science Foundation of China[41874124]

Geochemistry & Geophysics

Geochemistry & Geophysics

WOS:000480678900028

SOC EXPLORATION GEOPHYSICISTS

20191406741353

Acoustic logging ; Models ; Pore pressure ; Shale

Minerals:482.2 ; Soils and Soil Mechanics:483.1 ; Acoustic Properties of Materials:751.2

GEOSCIENCES

Web of Science

1.Southern Univ Sci & Technol, Dept Earth & Space Sci, Shenzhen 518055, Peoples R China
2.Univ Houston, Dept Earth & Atmospher Sci, Houston, TX 77004 USA
3.Tongji Univ, State Key Lab Marine Geol, Shanghai 200092, Peoples R China

Qin, Xuan,Han, De-Hua,Zhao, Luanxiao. Elastic characteristics of overpressure due to smectite-to-illite transition based on micromechanism analysis[J]. GEOPHYSICS,2019,84(4):WA23-WA42.

Qin, Xuan,Han, De-Hua,&Zhao, Luanxiao.(2019).Elastic characteristics of overpressure due to smectite-to-illite transition based on micromechanism analysis.GEOPHYSICS,84(4),WA23-WA42.

Qin, Xuan,et al."Elastic characteristics of overpressure due to smectite-to-illite transition based on micromechanism analysis".GEOPHYSICS 84.4(2019):WA23-WA42.