Abstract

The geohazard assessment for Block 1 identified multiple geohazards in the field development area. The most significant of these hazards are active faulting, mud volcanoes, shallow gas and earthquakes. Less dramatic but equally important features identified were seabed ridges and channels at or just below seabed.

In many cases, such hazards would seriously jeopardise a successful and safe development of a hydrocarbon field. However, for the Block 1 development, these hazards were identified in a timely manner such that their accompanying risks could be incorporated in the field layout design without major cost implications. Initial field layout was such that mud volcanoes and shallow gas occurrences were avoided, and well planning incorporated the location of the active faults.

In the Block 1 field development, an early understanding of the geological setting combined with good interaction between the structural engineers, drilling engineers and geohazard specialists resulted in a cost-effective field design minimising the uncertainty and financial as well as environmental risks.

This paper illustrates that geohazards need not always have a major impact on hydrocarbon field development. It shows that, with the right approach and timely recognition, successful hydrocarbon development is possible in one of the world's most geohazard prone and complex areas.

Introduction

The Block 1 area, in which Petronas Carigali intends to develop the Livanov, Barinov and Gubkin field, is located on the eastern part of the Apsheron Ridge, approximately 65 km to 95 km offshore Turkmenistan (Figure 1). The area covers about 2000 km2 and the water depth ranges from 40 m in the east to 100 m in the west of the area.

Figure 1. Location of Block 1 on the Turkmenistan Shelf, Caspian Sea. (Available in full paper)

Virtually no detailed information has been published on the geology of the Turkmenistan shelf. However, previous experience along the Apsheron Ridge suggested that geohazards might well pose serious problems for field development in the Block 1 area. This is indicated by, for instance, the presence of many collapsed platforms and wells, which form relicts of the attempted development of the fields during Soviet times.

To deal with the geological challenges, an extensive site characterisation study based on 3D exploration seismic data and regional 2DHR seismic data was performed during an early phase of field development. The resulting 3D site model to a depth of 1000 m sub-seabed was subsequently used to prepare a conceptual field development plan and to perform a realistic conceptual engineering study.

Geological Setting

The Block 1 area in the Caspian Sea lies on the Apsheron Ridge, which forms the boundary between the South and Central Caspian Basins.

The South Caspian Basin is thought to be a remnant of oceanic crust from the late Mesozoic or early Tertiary Tethys Sea, and is being subducted beneath the Eurasian plate in the north and the Arabian plate in the south.

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