Oil and Gas Exploration

Oil and gas exploration come under the group of petroleum geology, this is their scientific designation.  The search for hydrocarbon deposits under the earth’s surface is hydrocarbon exploration or the hunt for gas and oil.

Different forms of petroleum have been found and used by various civilizations for thousands of years. They found oil seeps and other visible surface features like natural gas seeps and pockmarks. Pockmarks are underwater craters caused by escaping gas. These are evidences of hydrocarbon generation, which may be shallow or deep in the earth.

Today the need is much greater and sophisticated methods are employed to find and estimate the amount of the deposits. There are several geologic elements that are required to make deposits large enough for exploration.

There must be an organic-rich source rock which generates the oil or gas.

Rock porous enough to be the reservoir rock that stores the petroleum

A trap that stops the petroleum from leaking off

There are certain places where traps are normally formed.

·   The tops of anticlines

·   By faults

·   The updip of pinchouts of sandstone beds

·   Beneath unconformities

When petrophysicists think an area contains oil or natural gas they subject it to a text like a gravity survey or a magnetic survey. This helps them to detect larger features of the sub-surface geology. These are features that are interesting in terms of exploration.

Today they use large vibrator truck to create the shock waves; historically they exploded small dynamite packages in shallow holes. There are environmental laws these days that prevent using explosions to collect seismic data.

Seismic surveys are taken of leads. They send shock waves into the ground. Seismic surveys measure by calculating the time it takes reflected sound waves to go through rock and be reflected back to the surface. The time it takes is related to how dense the rock is. With this information they use the process of depth conversion to create a profile of the substructure.

They detect the returning sound waves with geophones.  They then process the geophone data with computers converting it into seismic lines. These are two-dimensional displays that look like cross-sections. They used to be two-dimensional lines. They create them by laying the geophones out in a single line. Now they use 3-D seismic volume. Which they use to make 3-D computer models of the subsurface geometries of the rocks.

So petrophysicists are hunting for rich oil fields. They are looking for a reservoir shaped to trap hydrocarbons that is covered by a sealing rock. Besides oil and natural gas there are forms of petroleum called asphalt and tar. These are solid and semi-solid forms respectively. The name for dark, viscous liquid petroleum is crude oil and the clear and volatile called condensate.

But even with all of this sophisticated equipment they don’t always find an economically viable oil deposit.

The development or extension has the best chance for success. Wildcat wells have a lot less success at finding a good oil well.