MARINE MT IN CHINA WITH PHOENIX EQUIPMENT

Issue 34 • December 2004 © PHOENIX GEOPHYSICS Published by Phoenix Geophysics Ltd.

The very first marine MT survey inChina was completed in summer2004 with Phoenix on-shore MT

equipment adapted for off-shore use. Zhejiang Petroleum Exploration (ZPX)

of Hangzhou, PRC, adapted their existingPhoenix System 2000 to conduct anextremely cost-effective shallow marineMT survey of the oil and gas producingGulf of Bohai in northeast China. SeveralChinese and multinational oil companiesare exploring the area.

Marine MT was used because somecostly offshore wells in Bohai (based onseismic images of the deep structure)were dry holes; feasibility studies (see p. 2) showed that MT could imagethe deep structure better than seismic.ZPX found that marine MT cost less thanmarine seismic, provided better resolu-tion for this problem, and providedfaster interpretation turnaround.

Since 1995, marine MT (originallydeveloped by oceanographers for mid-ocean deep crust studies) has beentested and successfully adapted fordeep-water oil and gas exploration. Dr.Steve Constable at Scripps Institute of

2 Marine MT in China, continued

3&4 Fluxgate and Induction Sensor Comparison

5 Phoenix World News

6 Hoping to See YouOn the RoadPresident’s Message

Oceanography in SanDiego, California,played a key role in theadaptation of oceano-graphic marine MT tohydrocarbon explo-ration.

The initial deep-water (1,000-2,000m)marine MT tests in theGulf of Mexico weresupported by multina-tional oil companies,whose use of marine MTis rapidly increasing.

Deep-water marineMT equipment is com-plex and costly, requiring large vesselsand attendant high costs. A single deep-water marine MT sounding point costsabout US $10,000 and takes several daysto acquire.

However, there are very large shallow-water hydrocarbon-prospective areas onthe continental shelves and in inlandseas (such as the northern Caspian Seaand much of the Gulf of Bohai) wherecostly deep-water MT equipment is

either not required orcannot be used.

ZPX’s first survey com-prised approximately 50MT sites, from 50-100 kmoffshore, in water about20m deep. Electrodeswere placed on the seafloor. Magnetic field wasmeasured onshore, andcombined with the off-shore electric field meas-urements. Data qualitywas good, and ZPX has

Above: The Chinese fishing trawler that served as the ZPX’s“mother ship”; survey equipment was deployed from a smallmotor boat. Below: The ZPX crew prepares MT survey equip-ment on the trawler’s deck. The banner reads, ZhejiangPetroleum Exploration Survey Team 713.

completed 150 sites, both in Bohai andin a new area, the South China Sea, inwater up to 50m deep. ZPX expects theshallow marine MT market to grow.

China plans to spend US $6 billion inBohai to build 50 offshore oil platformsand drill 1,100 wells. Chinese oil expertsbelieve Bohai could produce 600,000barrels per day.

C O N T E N T S

continued on page 2

from MT is shown in Figure 3. The base-ment is faulted into horst-and-grabenblocks. The well in Figure 1 was drilled tothe horst block on the left in Figure 3.CYU’s onshore / transition zone MT workshowed MT could be used to map deeptarget horizons in Bohai, and that MT isan economic and useful complement toseismic.

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MARINE MT IN CHINA … continued from page 1

Experience shows that seismic images ofBohai’s deep structure may not be reliable.Figure 1 shows a large 70 sq. km. antiformalstructure with 200m of relief, an excellentdrilling target determined from seismic.The first well drilled (blue circle) foundcommercial oil at 5,000m, but stepout wellsdrilled only a few hundred meters awaywere dry. The oil company concluded thatthe seismic image was not correct.

The oil company then contracted CYU totest MT’s ability to define the deep struc-ture and the target horizon, an ancient, per-meable, weathered limestone paleosurfacemore than 5,000m below the sea floor. Thislayer is a good MT target because it hasmuch lower resistivity than either the lay-ered younger sediments above or thebasement rocks below.

The MT feasibility study included a lineorthogonal to the coast (Figure 2) that wasextended into the transition zone duringlow tide.

The MT and seismic images are shown inFigure 2. The lines are approx. 30km long;inland is to the right, and seaward, to theleft. The resistive basement (orange, red,yellow) dips steeply towards the sea. Thetarget horizon is the conductive band justabove the resistive basement. The MTimage is clear and continuous. The seismicimage (the lower part) lacks definition ofthe deep structure.

The geological interpretation derivedFigure 3: Geological Interpretation Based on MT Profile

Figure 1

Figure 2: Comparison of 2D Inverted MT Resistivity Section (top) with Seismic Section (bottom)

China Yangtze University (CYU) — MT Feasibility Study in Bohai

Professor Wenbao Hu of CYU participated inthe Bohai feasibility study.

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INDUCTION COILS USED FOR ULTRA-LONG PERIOD MEASUREMENTS

Studies in 2003 and 2004 in Alberta, Canada, and in Japan show that“ b roadband” MTU-5A equipment (with MTC-50 induction sensors) cana c q u i re long-period data equivalent to a specialized long-period systemwith a fl uxgate magnetic sensor.

23 Day comparison (MTU vs. fluxgate) Oct-Nov, 2004The experiment was conducted mainly by the University of Alberta attheir long-period test site. Fluxgate-system data processing was doneby the university.

Two separate Phoenix systems were used (900m apart), togetherwith one fluxgate system. The second Phoenix system permitted theparallel sensor noise test (shown below). Results of this experiment

tenance visits of the field truck anrelevant operator motions andcould be easily eliminated using aslightly different layout configura-tion and maintenance procedure.The noise floor of the sensorsremains below the signal ampli-tude even at the lowest frequen-cies. In Figure B (lower) thecoherency remains close to 1except at the highest periods –again due to the above-mentionemaintenance visits.

are summarized in the plots described below.Figure A shows the transfer functions for fluxgate system

(left hand side) and those of the MTU-5A / MTC-50 inductiosensor system (right hand side.)

The spectra are very similar within the overlapping bandwidth, although the fluxgate system shows somewhat highephases at the longest periods. The Phoenix system plots 14f requencies per decade.

Figure B (upper) shows the S/N ratio spectra of the induction sensors across the whole available bandwidth, usingthe well-known parallel sensor noise test procedure. Themoderate noise at the highest frequencies was due to main

Figure B

Figure A

Background: Long-period MT (2,000sec to 100,000 sec) is used for deepcrustal studies such as diamond explo-ration (see Issue 15). Most long-periodsystems use a “fluxgate” magnetic sen-sor because fluxgate low-frequency per-formance was thought to be superior tothat of induction sensors.

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19 Day Study: Sawauchi Monitoring Station in Japan

Phoenix operates a 24/7/365 fully automated, solar-powered, internet-linkedMTU-5 monitoring site at Sawauchi, Honshu, Japan (see Issue 31). The plot belowshows the results of processing 19 days of continuous Sawauchi data.

The magnetic amplitude spectra extend smoothly and continuously to approx.100,000 seconds.

Summary The normal wideband inductionsensor provides long-period mag-netic field data equivalent to thespecialized fluxgate sensor used inspecialized long-period systems

Both types of sensor can obtaindata to periods of ca. 50,000 sec-onds or more

With either type of sensor, thedata are often quite noisy at peri-ods longer than 20,000 sec.

The long-period scatter is not dueto electrode instability, sincePhoenix long-period electrodeswere proven to be extremely stableby Japanese scientists in 1999.

Prof. Martyn Unsworth and Dr. Wolfgang Soyer of the University of Alberta, Edmonton, compared fluxgate vs.Induction Sensor in a 5.7 day side-by-side test of Phoenixequipment vs. the Geological Survey of Canada’s Long PeriodMT System (LIMS). Results are shown in the plots below.

Dr. Soyer concluded that: (1) the integrated dB/dt timeseries from the induction sensors agrees well with themagnetic field time series from the fluxgate sensor (2) the transfer functions from the two different systemsare equivalent.

May, 2003 5.7 Day Comparison study by University of Alberta, Canada

INDUCTION COILS USED FOR ULTRA-LONG PERIOD MEASUREMENTS

NEWS FROM AROUND THE WORLD

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CANADA

Phoenix conducted asurvey in Rainy River,Ontario, for Nuinscoin November.Right: Billy Faragher,Oleks Hlazyrin, andMitchell Lackie

IRELAND/INDIA

Dr. Alan Jones of DIAS (Dublin) and Dr. Rao of IIG (Mum-bai) are both expanding their systems. Dr. Rao is a visitingscientist at DIAS.

RUSSIA

Nordwest Co. of Moscow was extremely active in 2004,measuring almost 3,500 MT sites. Nordwest worked all overRussia; international work included a job in Armenia and a600-site 3D MT survey in Bulgaria.

Right: Nordwest’sPhoenix equipment atMutnovskaya geother-mal power plant on theKamchatka Peninsulain the Russian Far East.

Below: Nordwestused horses for accessto MT survey sites inChukotka, a remoteregion in Arctic Siberia.

CHINA

Clients in China have now ordered ten V8 systems with vari-ous functions. Deliveries have been made to BGP-5th Divi-sion, Xinjiang Geology and Geochemistry, and Beijing Geo-science University.

LIBYA

BGP International in Tripoli,Libya, rented ten MTU-5Asystems for a 400-site 3DMT survey for an oil com-pany client in central Libyaduring summer 2004. Herethe field crew prepares tocalibrate the equipment in the Libyan desert.

USA

Montason (USA) is developing new EMtechniques for oil and gas exploration.See www.montason.com for details.

Right: Montason President Vic Grabianin Phoenix booth, SEG in October

Above: Montason field crew with Phoenix truck-mounted T-30 transmitter and MG-30 motor generator

RUSSIA (continued): SPMI completed more large-scale MT sur-veys in Russia in 2004. Below, an SPMI crew works near an oildrilling rig. Temperatures were as low as -55º C.

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ON THE ROAD HOPING TO SEE YOU IN…

USA: Carlos Guerrero,Yann Avram and Leo Foxrepresented Phoenix atthe 74th Annual Meetingof SEG in Denver, Col-orado, October 10-15.New SEG presidentCraig Beasley, left and outgoing presi-dent Peter Duncan, right

India: Phoenix presi-dent Leo Fox attendedthe 17th Electromag-netic Induction Work-shop held at theNational GeophysicalResearch Institute(NGRI) in Hyderabad,India, Oct. 18-23. Theworkshop is the premiervenue for EM researchers to exchange research results and newdevelopments. Special thanks to Dr. Harinarayana (head of thelocal organizing committee) and to Prof. Baldev Arora. Above: opening ceremony with George Jiracek, (USA memberof the working group), left, and His Excellency, Shri Surjit SinghBarnala, centre, Governor of the state of Andhra Pradesh.

Japan: Leo Fox and Mits Yamashita attended the SEGJ, inSendai, Japan, November 2004.

Canada: The Prospectors and Developers Association ofCanada will hold their 73rd annual convention March 6-9,2005, at the Metro Toronto Convention Centre. Please visit our booth to learn more about our 30th anniver-sary celebration.

Russia: Contact our office for further information about the3rd International Seminar on Research and Applied Geo-physics in St. Petersburg in April, 2005 and the 5th Annualworkshop and field camp in May, 2005 near Moscow.

The old and famous Sendai sparrow dance was performed at theSEGJ reception.

Left to right: Mr K.Matsuo (NMC), LeoFox, Prof. K. Ushijima,President of SEGJ, andMits Yamashita

Phoenix will be 30 years old in May, 2005. Althoughmany geophysical companies have disappeared inrecent years, Phoenix is thriving, growing and develop-ing new products such as the V8 wireless data acquisi-tion system. Visit our booth at the PDAC in Toronto(March, 2005) for details about our 30th birthday party!

The October 2004 issue ofThe Phoenix marked the 10thyear of its publication. Westarted in black and white in1994, moving to full color in2003. We’ve stopped wonderingwhat to write about and nowworry how to find space for allthe news and pictures.

Feedback from our readers around the world is grat-ifying. Thank you to all who have submitted great pho-tographs, information from their surveys and storyideas. Please keep them coming. ~Leo Fox

MESSAGE FROM THE PRESIDENT