ACG Field Geohazards Management: Unwinding the Past, Securing the Future

Abstract

The super-giant ACG field lies in the Azerbaijani sector of the south Caspian Sea. The significant complexity of the geohazards setting over the field was realized in 1993 when negotiations for the PSA to develop the field were still ongoing. This resulted in the need to understand geohazard risks being recognized in the Minimum Obligatory Work Program terms set out in the "Contract of the Century" in September 1994. Over the last twenty years work to define and refine understanding of the multiple geohazard issues has been ongoing. Work started in early 1995 with the completion of two deep geotechnical boreholes and a PSA contract area wide geophysical and geological geohazards campaign that delivered an early, first pass geohazards stop-light map and supported delivery of the Early Oil Project (1997). The results of these two initial pieces of work formed the basis of the first PSA contract area wide integrated geohazard study that addressed the threats of individual sources of geohazard to Full-Field Development planning. These included, amongst other issues: slope instability, mud volcano stand-offs and fault risks, all being included in the first integrated geohazards risk map of the PSA's contract area in 1999. Since this time, direct experience, in drilling and facilities installation, has driven the need for an ongoing update of data and improvement in geohazard understanding. New sources of hazard, such as the implications to riser-less drilling from super-saline soils, have had to be assessed and new data acquired to assist in mitigation of the risks identified. Most recently HR3D data has been acquired across the entire PSA which, tandemed with AUV seabed and shallow profiler imagery has been used to guide a further series of geotechnical campaigns. These results have been used to drive an update to the geohazards zonation addressing, in particular, slope instability in field areas previously considered too sensitive for development. This paper provides a timeline of geohazards activity on the ACG PSA over the past twenty years as a background to other papers being offered in the technical session that discuss how specific geohazard data acquisition and analysis issues have been addressed.

Seismic geomechanics of mud volcanoes

“…Mud volcanoes have been systematically studied worldwide to develop an understanding of (a) the structural controls on mud volcano development (Roberts et al 2011;Bonini 2013;Mazzini & Etiope 2017); (b) the factors influencing the severity of eruptions (Lerche & Bagirov 1999;Kopf et al 2009;Contet & Uterseh 2015); (c) the controls on their internal structure and geomorphology (Hovland et al 1997;Dimitrov 2002;Deville et al 2003;Evans et al 2007;); (c) fluid/sediment flow under mud volcano complexes (Planke et al 2003;Calvès et al 2008), and (e) controls on the geochemistry of the erupted fluids (Azzaro et al 1993;Bristow et al 2000;Mazzini et al 2009;Oppo et al 2014). To date numerous multiscale near-surface geological studies have been carried out in offshore areas for risk mitigation in seabed facilities linked with occurrence of mud volcano activity and associated hazardous phenomena, such as shallow gas, slope failure and pockmarks (Contet & Uterseh 2015;Hill et al 2015;. Nevertheless the extent to which drilling in such zones has to be avoided because of mud volcano related risks remains uncertain.…”

“…However the use of wave-form inversion created seismic velocity data together with reflection seismic data in offshore mud volcanoes have enabled understanding and evaluation of their potential in terms of geohazards (Tough et al 2010). This in turn has aided in better defining the hazard and reducing the associated risks to potential future production wells and allows a better understanding of the limitations on well planning and siting (Gray et al 2015;Hill et al 2015).…”

“…these mounds have been subject of recent studies as a result of the use of high resolution geophysical monitoring techniques, their distribution and nature of activity across the region are relatively less constrained.Mud volcanoes and associated fluid flow features have a variety of implications ranging from petroleum exploration and development to seafloor biology and environmental impact (e.g Hill et al 2015;Gulmammadov et al 2017)…”

“…;Evans et al 2007; Soto et al 2011), (b) the structural controls on mud volcano locations(Roberts et al 2011; Bonini 2013), (c) fluid/sediment flow under mud volcano complexes (Planke et al 2003; Calvès et al 2008), (d) the factors influencing the severity of mud volcano eruptions (Lerche & Bagirov 1999; Kopf et al 2009; Contet & Unterseh 2015; Hill et al 2015); and (e) controls on the geochemistry of the erupted fluids (Azzaro et al 1993; Bristow et al 2000; Guliyev et al 2001; Mazzini et al 2009; Feseker et al 2010; Feyzullayev & Movsumova 2010; Carragher et al 2013; Oppo et al2014). In offshore areas, numerous multi-scale near-surface geological studies have been performed to mitigate the risks to seabed facilities that are associated with mud volcano activity and its accompanying hazardous phenomena, such as the presence of shallow gas, slope failure and pockmarksHill et al 2015; …”

Application of the Shear Band Propagation Method to Slope Stability Analysis of a Palaeo-Landslide in the Caspian Sea

“…Successful development of the field has depended in part on the management of an extreme level of marine geohazard complexity over the last 20 years (Hill et al, 2015a). the Azeri and Chirag fields and the Deep Water Portion of the Gunashli field) lies in the Azerbaijani sector of the south Caspian Sea, 130km to the south-east of Baku in water depths of 95 to 435m.…”