Dammam Dome to Get 3-D Seismic

Soon residents will see a new type of vehicle rolling around the streets of Dhahran. The vehicles are vibrators, the core of a seismic survey that is planned to start in mid-November.

Saudi Aramco plans to use the latest technology to get the best possible picture of the Dammam Field before beginning to put it into production again.

The first oil discovery in Saudi Arabia was made decades ago in the Dammam Dome. The dome is, in effect, an underground hill buried deep beneath Dhahran.

Dammam Field, which is 1,370 meters deep and covers 155 square kilometers, produced oil for dozens of years and then was capped. Now Saudi Aramco plans to develop it again. Acquiring a 3-D seismic survey over Dhahran and parts of the surrounding area is integral to the development plan.

Providing geological and geophysical support to petroleum engineering is a key factor in the success of any field development plan, said Abdulla A. Al-Naim, vice president of Exploration. Geoscientists use the seismic data they acquire from vibrator trucks to build 3-D geological models that accurately detail reservoir properties such as porosity, permeability and water saturation. Those models tell the company where to drill.

Ideally, the model represents a synthesis of the available engineering knowledge of the reservoir in an integrated multi-disciplinary effort, Al-Naim said.

Seismic data acquisition in Saudi Arabia dates back to 1938. In the late 1970s, the company conducted its first 3-D surveys. The word seismic is derived from a Greek word "seismos," meaning "shock." The method uses shock waves generated by the trucks' vibrating plates to probe the earth's interior. It is analogous to such medical imaging technologies as X-ray, ultra-sound and magnetic resonance.

As the seismic survey proceeds, residents will see two main parts. The first is an active part, in which the vibrators produce energy that penetrates the ground all the way to the field and is reflected back to the surface. The second part is passive. In it, receivers spread out on the ground, called geophones, pick up those reflections. Residents will see thousands of these receivers. They are connected by cables and send the signals to a central recording station.

Dhahran residents will see 3-D seismic workers in action as they lay out their receiver cables and record waves reflected to the surface.

You might be asking, "If the Dammam Field was discovered 70 years ago, why use cutting-edge 3-D seismic technology on it now?" The answer: The Dammam Dome still holds huge oil reserves. To efficiently extract the oil, a detailed model made from state-of-the-art technology is needed.

Geophysicists will interpret the seismic data to map the topography and other characteristics of the oil reservoirs inside this underground hill.

The current geological understanding of the Dammam Dome is based on widely spaced 2-D seismic lines. That old data is of little use now. In order to obtain a more accurate image of the oil reservoirs and maintain production, new 3-D seismic data is needed.

Multidisciplinary teamwork is essential to a successful survey. The process begins when reservoir engineers and geoscientists define the objectives of the seismic data acquisition. They include specifying the exact locations to be studied, determining the amount of seismic energy necessary and defining the arrangement of energy sources and receivers.

So when you see the seismic crew working around your neighborhood, you know how far down in the ground they are looking.


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