As the oil and natural gas industry explores ever-deeper targets, particularly in the Gulf of Mexico (GOM), the Department of Energy (DOE) used a cost-shared project managed by the Office of Fossil Energy’s National Energy Technology Laboratory (NETL) to develop groundbreaking pre-drill seismic technology.
Deep oil and gas resources are defined as those located in reservoirs at depths of 15,000 feet or more. Although less than 1% of all the wells in the United States have penetrated below 15,000 feet, these wells account for a significant portion of domestic gas production, the DOE noted. However, because of the high costs to not only find but drill these deep wells, only the most promising seismic targets are drilled.
In a venture with Houston-based Rock Solid Images, the NETL helped to develop pre-drill seismic imaging technology to improve oil and gas detection in the reservoir and reduce the risks — and costs — associated with drilling deep wells. The modeling software so far has been successfully tested in the GOM, Norway and offshore West Africa.
Conventional seismic imaging and attribute analysis becomes less reliable the deeper the target because the acoustic energy attenuates and loses strength as it travels through successively deeper layers of rock, which results in poor image resolution and less reliable hydrocarbon detection for deep oil and gas prospects. In the case of deep natural gas prospects, the imprecise seismic data can incorrectly indicate the presence of a productive gas reservoir when in fact the reservoir contains only traces of gas, or no gas at all.
However, the new seismic processing technology uses a set of independent indicators known as seismic attenuation attributes, which confirm the presence of oil or gas in deep reservoirs where conventional techniques prove unreliable. Essentially, the degree of attenuation is used to track the amount of gas or oil in the reservoir, and combined with conventional seismic analysis techniques, these attenuation attributes may effectively confirm or disprove the presence of reserves at certain depths, avoiding the risk and expense of drilling an unconfirmed well.
In a test offshore Norway, where conventional analysis indicated possible hydrocarbons beneath a well drilled to 14,000 feet, Rock Solid applied the new technology and found that the anomaly was caused by a marked change in rock type rather than oil or gas in the reservoir. The DOE estimated that the operator saved millions of dollars because of the test.
For more information, visit www.fossil.energy.gov/.
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