Energy Exploration International - EEI Inc

Seismic Technology

Exploration for oil and gas involves the evaluation of a variety of information. Well logs provide detailed information at specific locations, usually an area less than one meter surrounding the well bore. We use our knowledge of formation signatures to recognize depositional environments and try to project this information between wells.

Reflection seismic methods can be used to create images of the geologic changes between wells. These images can help complete a picture of the subsurface that should enhance the ability of the geologist to successfully select future well locations. Seismic is an effective tool as long as it provides meaningful and helpful images for the desired objectives.

Reflection seismic is a method that allows us to image changes in the subsurface geology by inducing an acoustic wave from near the surface of the earth and listening for the echoes from deeper stratigraphic boundaries (much like ultra-sound is used to create pictures of unborn babies in their mothers’ wombs).

2D seismic is recorded using straight lines of receivers crossing the surface of the earth. Acoustic energy is usually provided by the detonation of explosive charges or by large vibroseis trucks. The sound spreads out through the subsurface as a spherical wave front. Interfaces between different types of rocks will both reflect and transmit this wave front. The reflected signals return to the surface where they are observed by sensitive microphones known as geophones. The signals detected by these devices are recorded on magnetic tape and sent to data processors where they are adjusted and corrected for known distortions. The final processed data is displayed in a form known as "stacked" data.

In order to record data with sufficient density over large areas, we require a large number of recording channels. The operations of 3D are considerably more elaborate than 2D and the daily cost of crew is substantially increased. However, the rewards include fewer dry holes, more optimized well locations, guidance for horizontal drilling projects, more complete evaluation of mineral rights and better understanding of the nature of prospects.

3D seismic has become a common exploration and production tool. Although 3D does not remove all exploration risk, it generally improves success rates and productive wells will more often be on optimal locations and should deliver better production and exhibit slightly longer life.

Seismic Reprocessing

Using 3-D technology, seismic information is transformed from raw data into a unified analysis of potential reserves. Although it’s primary function is to clarify existing prospects, seismic reprocessing can also pinpoint high-quality locations previously unrecognized by older technologies. In prospects that have already been identified, 3-D technology serves as a sifting tool, separating the good from the bad. Our objective is to perfect the data in order to minimize the number of dry holes drilled and increase the number of productive wells.

Frequency Absorption Response (FAR)

This methodology detects anomalies that absorb high frequencies at a much faster rate than low frequencies. This greatly increases the reliability of the results and makes FAR an excellent tool to further high-grade AVO (Amplitude versus Offset) anomalies. The amplitude variations with offset (AVO) technology was introduced over 20 years ago. In the intervening years, the technique has evolved from a concept to a primary component of seismic exploration. AVO methods can add reliable constraints to quantitative reservoir characterization if the operator understands the underlying concepts and how to apply the technology.

Often called "Bright Spot Analysis," AVO reveals significant anomalies, or bright spots, when sound waves reflect off a gas-bearing formation. Properly imaged relative amplitudes are a key component of this process and are attained using fully pre-stack data. This detection technique is based on the principle that gas-saturated sands have a lower velocity than adjacent water-bearing sands. As seismic waves pass through gas zones a reflection of higher amplitude is readily seen when compared to the same stratum on either side of the gas zones. Beneath the high amplitude zone is a strong peak, followed by absorption (seismic lines appear stretched when compared to the adjacent area). Thus, on seismic a ‘Bright Spot’ is a strong trough followed by a strong peak, followed by absorption. It is considered a highly successful (state-of-the-art) gaseous hydrocarbon indicator. During the decade of the 1990’s wide spread use of 3D seismic, has dramatically improved the drilling success of most oil and gas companies worldwide. Bright Spot Analysis has been applied with great success along the Texas Gulf Coast.

Enhanced View

This state-of-the-art technology shows an enhanced image of both of the geologic formations, identified in the 3D analysis, occurring at the 2,250 foot Miocene and 4,150 foot Frio Sand anomalies. In this image, the enhancement of interest is shown as the yellow in the Miocene Sands and green in the Frio Sand bars. These gas charged sands appear in the Sklar prospect in both the targets. Spectral decomposition analysis of the Miocene and Frio Sands indicate these structural formations are being fed with gas.