AAPG/GSTT HEDBERG CONFERENCE

“Mobile Shale Basins – Genesis, Evolution and Hydrocarbon Systems”

June 4-7, 2006 – Port of Spain, Trinidad & Tobago

Mud volcanoes in the mobile shale basin of the Trinidad area with special focus on the spectacular eruption of the Piparo mud volcano

Fazal Hosein

Consultant Geologist, International Geological Services Ltd, Trinidad

The Trinidad – Eastern Venezuelan Basin has long been recognized as mobile shale basin with a complex tectonic and stratigraphic history. As the basin evolved ideal conditions developed for the genesis of mud volcanoes along its’ axis. Many of these mud volcanoes have gained recognition by virtue of their spectacular eruptions. This paper reviews the distribution of mud volcanoes in the Trinidad area and focuses on the causes of the dramatic eruption of the Piparo Mud volcano on February 22, 1997 in central onshore Trinidad.

In Trinidad, studies as early as 1813 by J.J. Dauxion Lavayssee recognized the presence of mud volcanoes where eruptions of mud, exotic boulders and oil were thought to be the result of igneous volcanism.

Subsequent classic work by Wall & Sawkins in 1960 set the tone for a better understanding of mud volcanoes when he studied in detail four (4) mud volcanoes in south Trinidad.

This was followed by an excellent report by Cunningham – Craig in 1902 which influenced prospectors into concentrating their exploration efforts in areas with oil seepages and gas shows with the hope that there was some connection between subsurface hydrocarbon accumulations and mud volcanoes.

In the following years, mud volcanoes have been mapped by many researchers including Anderson (1911), Weeks (1929), Maerky (1931), Kugler (1932 & 1968) and Wilson and Birchwood (1965).  A study by George Higgins and John Saunders (1967) outlined the distribution of the mud volcanoes in the Trinidad area.

The mud volcanoes of the Trinidad – Eastern Venezuela area were formed within a mobile shale basin which extends from Maturin in Venezuela to the deep water areas of eastern offshore Trinidad. This basin developed within the northeast – southwest trending foredeep formed as a result of the collision of the Caribbean plate with the South American plate. Foredeeps developed from Eocene to end Mid Miocene time. Shales were deposited rapidly as the Nariva shales of Oligocene, the Lengua -Lower Cruse and Karamat shales of late Miocene and the deep water Gros Morne / Cruse shales of Pliocene age in the eastern offshore area. The shales mobilized into mud diapirs in response to gravity loading from overburden and thrust imbricates and culminated in the surface expression of mud volcanoes when gases added to the shales increased the upward mobility. The volcanoes ejected mainly mud, water and gas on the surface but when these flows sealed the vents or fracture planes, pressure built up in the subsurface which resulted in later spectacular eruptions at surface as at Piparo.

Mud volcanoes have erupted in the marine environment forming small islands which were shortlived due to wave action. Onshore, the volcanoes are present in more than twenty seven (27)

sites which are all linked in some way to thrust fault and wrench fault systems which tap into the pressured mobile shales. These volcanoes are not generally associated with the presence of hydrocarbon accumulations although a few are present within the oil fields. A Mud diapir in the Forest Reserve Field is documented as an intrusive event. Similar situations are probably present in Main Field and Southwest Soldado and in Pedernales field.    In the eastern offshore deep water areas, studies by Bramii et all (2000) documented many mud volcanoes which formed on the sea floor bringing up parent matrix of Pliocene shales.

The seal at Piparo was removed by a landslide caused by abnormal excessive rainfall which caused down slope slippage of four (4) feet which was enough to shift the mud cap seal. The result was an eruption of mud and gas and water up to 100 feet in the air and deposition of mud over an area of 14 acres.

There was considerable damage to houses accompanied by loss of livestock and property. The road has since been abandoned and the area of the last mudflow is now inhabitable. The mud volcano at Piparo is now quiet with passive emissions of gas and water. We may not be able to accurately predict the next eruption but we know now what signs to look for. This eruption was a classic example of the movement of shale in a mobile basin.