What's happening in exploration

November 1999 Vol. 220 No. 11  Exploration

Perry A. Fischer,  Engineering Editor

Radar love

Back in March 1999, this column mentioned Relucent technologies, along with the words "this editor does not endorse, nor has a clue as to the validity of, this technology, but nevertheless found it interesting." The "Relucent effect" was claimed to be an interaction between hydrocarbon micro-seepage, telluric fields and microwaves. Solar-lunar tides also had something to do with the effect.

Following a discussion on the topic with Deet Schumacher at an AAPG conference, Deet was kind enough to mail this editor the paper, A review of radar for the detection of gas seepage associated with underground oil and gas deposits, by M. Skolnik and T. Baily. Dr. Skolnik has 30 years’ experience in radar work and held the position of Superintendent of the Radar Division at the Naval Research Lab. Bailey worked 24 years at Amoco where he chaired the company’s Surface Prospecting Task Force. A summary of their paper and its conclusions follow.

The use of short EM waves to locate gas seepage was first patented in 1939 by L.W. Blau and W.B. Lewis. Their apparatus, comprising a separate transmitter and receiver, would today be called forward-scatter radar. The technique was further advanced by the late Robert Owen, who patented a method for using conventional radar to locate gas seepage (Owen and Busby, 1972).

The 1972 patent describes receiving a reflected signal at a frequency different than transmitted. The belief was that since UV light shifts wavelengths when illuminating oil-bearing rock, i.e., it fluoresces, the same thing might happen at radar frequencies. Unfortunately, no such effect is known at radar wavelengths, other than a Doppler shift via reflection. In fact, a sound theoretical framework to explain how radar can be used to detect gas seepage is crucial to further the technique.

In 1978, the DOE conducted a radar survey of a small area in Kansas. Of the ten anomalies detected, a major anomaly was an existing field, five moderates were never drilled, and of four minor anomalies (don’t drill indicators), two were subsequently drilled — and came up dry. Owen’s company, Hydrocarbon Gas Surveys, offered literature that claimed a 75% wildcat success rate based on their radar surveys of 25 wildcat sites. The literature further stated a 100% success rate in predicting dry holes, based on 23 drill sites that showed no echoes.

A survey by Sun Exploration & Production in 1984 involved a large number of wells. Sun gave radar a 43% success rate. A 1990 proprietary survey, flown by Airborne Petroleum Surveys in the Hardeman basin in North Texas, gave radar a 42% positive correlation over 64 active fields. Other surveys put the success rate in the 40-50% range, but correct "don’t drill" decisions score higher.

The type of radar that is typically used is unaltered, off-the-shelf marine radar. However, without a sound theoretical framework that establishes cause-and-effect relationships, there is no way to know how to alter or optimize the acquisition equipment.

The authors conclude: "This is an effect that has not received the attention it should, considering what it has been able to do thus far and what little we know about its physics. We believe there is much more that can be done to enhance the use of radar as an important exploration tool. One can go quite far with experimental trial and error. However, one can go much farther with controlled experimentation and development of a theory that can lead to better radar design."

An interesting play has been developing in Tennessee. Tengasco has just completed its 17th successful well in the company’s Swan Creek field, which is located in the Eastern Overthrust Belt in Hancock County, Tennessee. The Paul Reed-5 was drilled to 3,210 ft, encountering 28 ft of fractured porosity in the Stones River formation. The well tested 360 bopd of high-gravity crude, which is a lot by Tennessee standards; it also proved up additional reserves of 702,500 barrels of oil, based on 40-acre spacing.

This is the third successful oil well in Swan Creek field, bringing proven oil reserves to 1.5 million bbl. Based on engineering data, Swan Creek’s proven gas reserves to date stand at 62.3 Bcf, and probable undeveloped reserves are 253.8 Bcf, based on 3-D seismic and geological data. John Clendening, a former senior geologist of Amoco, said that this could be the largest gas and oil area in the Appalachian basin, with potential reserves of 2 to 3 Tcf of natural gas and 100 million bbl of oil.

Tengasco’s plan is to accelerate its drilling program, with a goal of adding 50 additional wells. To that end, the company has signed an agreement with Miller Petroleum to allow Miller to acquire up to 20 drill sites on a farmout basis.

Offshore Australia discovery. Chevron announced a noteworthy gas discovery with its Geryon-1 wildcat, operated by the West Australian Petroleum Pty. Ltd. (WAPET) JV. Geyron-1 was spudded in August in 4,000 ft of water and reached 11,460 ft subsea. Initial results indicate three high-quality reservoirs zones with net gas pay of 368 ft. This was the first exploration well in permit area WA-267-P, which was awarded in 1997.

Drilled by the deepwater drilling rig Marine 500, the rig will return to WA-267-P in early 2000 to further explore the area’s potential. WAPET JV partners in WA-267-P are Chevron, Texaco and Mobil (with a 25% stake each); and Shell and BP Amoco (with 12.5% each).

The discovery adds to Chevron’s position as the largest single holder of gas reserves offshore Western Australia. Within the WAPET-operated permits, proven plus probable and possible gas reserves add to 21 Tcf. These levels of reserves will allow for long-term LNG supply to overseas buyers.

Comments? Write: fischerp@gulfpub.com

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