New Advancement Of The Wsm Project On The Stress Perturbation In Sedimentary Basins

Abstract

Crustal stresses are of extreme importance for understanding both natural processes (e.g. neotectonics, earthquake cycle and seismic hazard assessment) and anthropogenic activities of underground usage (e.g. petroleum exploration and production, geothermal energy extraction, CO2 sequestration, mine stability and design of radioactive waste repositories). The World Stress Map (WSM) is the only public-domain project that compiles since 1986, global information on the crustal stress state. It has had three major phases so far to mainly compile the orientation of maximum horizontal stress (SHmax). The first phase of the project (1986-1992) with ~7,700 data records revealed that plate-scale stress fields are controlled by forces exerted at plate boundaries (e.g. mid-ocean ridges, continental collision zones), commonly resulting in regional stress orientations sub-parallel to absolute plate motion. Further studies by the WSM team during the second phase (1995-2008) of the project provided 21,750 data records across the world and highlighted that “the large plate boundary forces are not enough” to explain the stress pattern of smaller scales such as sedimentary basins. Last year marked the end of the third phase of the WSM project, and also the 30th anniversary of the project. The new release of the WSM project contains approximately double the information of the 2008 release, with 42,870 data records from various sources of information and across the world. In particular the new database contain more than 4,000 new data records from sedimentary basins in Australia, New Zealand, China, Canada as well as new stress information from places that previously had limited data such as Eastern South America, Africa and Iceland. This compilation increased the in-situ stress data density significantly and allows revisiting the analysis of stress pattern across spatial scales ranging from plate-wide to basin. Detailed analysis of present-day stresses from over 100 sedimentary basins reveals that significant and complex variations in the present-day stress orientation are commonly observed at both basin (10-200 km) and field (0.1-10 km) scales. Such localised stress rotations have significant petroleum implications, as the stability of wells, direction of induced hydraulic fractures and reactivation potential of faults may vary greatly, even within a single field or well.

Herein, we present the details of the new release of the WSM and the results of a global comparison between absolute plate motion and the mean orientation of maximum horizontal stress on a global regular grid. We also show the newly compiled Australian Stress Map project that contains in-situ stress information in 20 Australian sedimentary basins. In particular we show that in-situ stress orientation is controlled by the superposition of plate boundary forces, major intra-plate stress sources, basin geometry, mechanical stratigraphy and geological features. Finally, we demonstrate this relative contribution of the crustal stress sources with an example from Eastern Australia where the stress pattern changes due to different sources. This variability can be used as a proxy to identify and quantify local and regional stress sources and to constrain geomechanical-numerical models of the 3D stress tensor that describe the distance to a critical stress state.

AAPG Datapages/Search and Discovery Article #90324 © 2018 AAPG Asia Pacific Region GTW, Pore Pressure & Geomechanics: From Exploration to Abandonment, Perth, Australia, June 6-7, 2018