Deterministic Slope Stability Analyses of the Sigsbee Escarpment

Abstract

The paper describes the slope stability analyses carried out for BP's planned developments of the Mad Dog and Atlantis prospects. Both prospects are located along the Sigsbee Escarpment in areas where extensive slumping has taken place. The approach was based on combining geological, geophysical and geotechnical data from field and laboratory testing to develop models for slope stability evaluation. Examples of results are presented, including a brief discussion on how sensitive the results are to the variables in the analytical models.The examples demonstrate how an interdisciplinary approach to the geological and geotechnical modeling renders possible extrapolation and interpolation of geotechnical soil data, and that slopes of heights up to 150 -230 m and slope angles of more than 22° have safety factors in the range 1.1 to 1.5 based on best estimate of soil parameters.

Geologic Setting of the Mad Dog Mooring System

“…Slope stability was previously investigated for the steepest part of the major slump labeled as Slump 8 and reported by Nadim et al (2003), Nowacki et al (2003), and Niedoroda et al (2003).…”

Bottom currents, submarine mass failures and halokinesis at the toe of the Sigsbee Escarpment (Gulf of Mexico): Contrasting regimes during lowstand and highstand conditions?

“…1, 2). Since the discovery of the Atlantis field, several studies have been dedicated to the understanding of geotechnical properties, pore pressure regime and sedimentation history of this portion of the Sigsbee Escarpment, in order to evaluate the stability of the slope and to quantify the recurrence time of potential hazardous events, such as landslides, debris flows and turbidity currents (Al-Khafaji et al, 2003;Nadim et al, 2003;Niedoroda et al, 2003a and b;Nowacki et al, 2003;Orange et al, 2003a and b;Slowey et al, 2003;Young et al, 2003;Prieto et al, 2014;Prieto et al, 2016). The development of the escarpment has reflected the dynamic evolution of the salt under the effect of cyclic loading due to sedimentation and eustasy (Swierz, 1992).…”

A numerical simulation of underwater slope failures generated by salt diapirism combined with active sedimentation

“…Poulos, 1988). A fundamental limitation of such approaches is their inability to capture the progressive failure processes that are known to develop in sensitive clays (Nowacki et al, 2003;Kvalstad et al, 2005), and in brittle soils whose shear strengths can degrade from peak to residual values as a result of clay particle reorientation (Skempton, 1977). The authors' approach is rooted in Potts et al's (1997) treatment of delayed failures in cuts formed in stiff plastic overconsolidated clays, which have been widely reported in highway and railway engineering (Parsons & Perry, 1985).…”

“…The Sigsbee escarpment in the Gulf of Mexico presents one example where long escarpments have been created by locally uplifting salt diapirs accompanied by large-scale sediment deposition. Nowacki et al (2003), Orange et al (2003) and Young et al (2003), among others, describe the interplay between geology, tectonics and large underwater slope failures in this region. These features are critical to assessments of potential present-day geohazards.…”