Energy Exploration International - EEI Inc

Drilling Exploration - The Search for Petroleum

Earth scientists in the petroleum industry - including geologists, geophysicists, geochemists and paleontologists - study what has happened to rocks that may be buried thousands of feet below the surface, how those rocks were formed and affected by events stretching back millions of years, and how to identify traps where oil and gas have accumulated within rock formations.

Common Oil and Gas Traps

A trap requires three elements:

• A porous reservoir rock to accumulate the oil and gas - typically sandstones, limestones and dolomites
• An overlying impermeable rock to prevent the oil and gas from escaping
• A source for the oil and gas, typically black waxy shales

Seismic Surveys

In a seismic survey, the geophysical contractor's crew lays out a line or several lines of sensitive receivers, called geophones or jugs, on the ground. Then explosions or mechanical vibrations are created on the surface. The geophones record the energy reflected back as seismic waves from rock layers at various depths.

To reduce environmental impact, many contractors today use the mechanical virosesis method to send energy waves from a heavy, vibrating vehicle into the earth.

Like the rest of the petroleum industry, explorationists have adopted ever-higher environmental standards for seismic surveys. For example, improved methods for clearing and using narrower cutlines have reduced the impacts on soil, water, plants and wildlife in forested areas. In other sensitive areas such as mountainous terrain, seismic crews use helicopters or even packhorses to limit surface disturbance.

In offshore exploration, "air guns" using compressed air have replaced dynamite as a better, safer energy source which also minimizes the impact on marine life. A marine vessel records the reflected energy from a towed array of hydrophones. In shallow waters, the hydrophones may be laid out on the sea bed.

Drilling - The Moment of Truth

Drillers turn theory into hard economic reality. Even when a development well is located right between two producing wells, there is still a risk that nothing will be found - and also the possibility of greater-than-expected success. The stakes are much higher when the well is a wildcat in unexplored territory.

The basic drilling process is simple. A revolving steel bit at the bottom of a string of pipe grinds a hole through the rock layers.

There are many different types of rigs. The smallest are service rigs mounted on trucks, while the largest are installed on ships or offshore platforms. Some are specially equipped for sour gas exploration, Arctic operations, slanted holes, or horizontal drilling. As a general rule, the bigger the rig, the deeper it can drill.

About 75 workers are directly employed in the drilling of one well, although only four to seven may be on duty at the rig at any given time. The actual number can vary considerably, depending on the type of well being drilled.

The most common drilling technique is the rotary drilling system - a highly efficient mechanical system used on land and sea. When seismic surveys and other data indicate that oil and/or gas could be present, an exploration well is drilled.

A rotary drilling rig is made up of:

• Hoisting equipment
• Drilling bit
• Drill pipe
• Rotary equipment
• Mud circulating treating equipment
• Blowout prevention system
• Power source
• Drilling is a round-the-clock operation.

A drilling supervisor leads a team of experts who work in shifts. Wells are usually drilled vertically but can be drilled at an angle also. This technique, called directional drilling, is used for a variety of reasons.

A major advancement in oil and gas discovery is horizontal drilling, which drills along a reservoir and increases production. As the drill nears its final depth, engineers, geologists and management have to decide if there is enough oil and gas for the well to be completed.

 

Exploration Home | Formation & Location | Exploration & Drilling | Production & Transportation