Story and Photos by K. A. Leavitt, Western Geophysical, originally published in the 1974 Summer Western Profile; recounted by Scott Singleton.
The Doodlebugger Diary recounts the experiences of geophysicists during their working lives. I’ve published extensively on my own experiences and encourage those of you with experiences of your own to also contribute. Your fellow industry professionals would love to hear your stories.
I’ve been occasionally reprinting a series of early 1980’s articles from the GSI Shotpoints and GSI Grapevine that can be found at http://gsinet.us/. I also have reprinted various Western Geophysical Profile articles. These can be found at https://library.seg.org/page/western-profile. This month’s article reminds me very much of the series of articles I have recounted about Peru which I describe in my prolog below.
Prolog by Scott Singleton
In the past several years I’ve had a number of installments on early exploration of South America. In January through May, 2019, I ran a 5-part series on my time in coastal Peru. I followed this by a 3-part series (June, Sept, Oct, 2019) about ex-SEG president Nancy House’s early exploration of the Peruvian Amazon for Mobil. Then in June of this year I ran an article about Western Geophysical’s early surveys in the Peruvian Amazon. This month we get to jump across the Peru/Brazil border and take a journey with Western Geophysical Party 179 as they explore all along the mighty Amazon River and its plethora of tributaries.
Take note of the background storyline presented by this article from the early 1970’s. This was a remote, mostly pristine area that was seeing some exploration by major oil companies which was in turn bringing modern technology to areas that had scarcely seen it previously. Fast forward a half century and we are almost continuously bombarded by news reports of massive deforestation that was endorsed and promoted by (now ex-) Brazilian President Jair Bolsonaro, whose climate-denial proved disastrous to the entire Amazon basin (10 Amazon Rainforest Deforestation Facts to Know About | Earth.Org). As horrible as his tenure was, it was actually only the latest episode in the progressive destruction of this basin. In the 1990’s and early 2000’s deforestation was much worse. During that time, the rainforest was losing an average of 20,000 sq km/year, an area equal to the size of New Jersey (Tracking Amazon Deforestation from Above (nasa.gov)). However, in 2004 the Brazilian government adopted an aggressive policy plan that was responsible for vastly reducing the burning and razing of large tracts of forest. We can only hope that with the recent change of governments in Brazil the country once again realizes that this basin contains a resource that needs to be preserved in a sustainable manner.
Deep in the Amazon Basin, Brazil
IT'S BEEN A LITTLE MORE than a year since Party 179 last reported in the PROFILE, the entire structure and operation of the crew has changed drastically. As you may remember from our last article (Spring 1973 PROFILE), Party 179 had been working among the reefs off the Brazilian coast. Now, many streamer cables later, we are working the rivers and streams of the middle Amazon basin.
The M/V Cynthia Walker left the seaport of Fortaleza, Brazil (Figures, 1, 2, 3), in May 1973 to begin work out of our present base, Manaus, in the north-central interior of Brazil, late the next month (Figure 4). We were joined in Manaus by a floating "gypsy" camp from Colombia that called itself Party 44. This addition to our crew consisted of four barges (Figure 5) and a couple of hairy, odoriferous boat drivers who had just completed a 2,000-mile trip from the headwaters of the Putumayo River in Colombia to Manaus with stops only for fuel and an occasional cold beer – the latter very occasional as there were few villages along the way.
The rigging and general integration of equipment from the two crews was supervised by an old Western hand who had stayed with us as acting coordinator-instrument technician until his replacement arrived on the scene (Figure 6). This coordinator had joined Party 179 from Singapore earlier but had been on loan for a ‘two-week’ assignment to another crew; only after two months and many telexes were we able to get him back.
All instruments, streamers and guns had to be configured and tested (Figures 7, 8, 9, 10)). After this was completed the crew set out to try a new technique in river seismic shooting. We were towing a specially designed streamer cable using a transponder radiolocation system to maintain correct shot spacing. Position determination in the river was made using photos of the radar screen at selected intervals (emphasis added by editor). These data were then compiled to produce the post-plot map using satellite points as reference marks at 50-kilometer intervals. Whew! Sounds complicated. In the hands of Chief Computer Paul Robinson, however, the final product was a map with precisely located post-plotted points.
An independent part of our operation is our satellite crew (Figure 11). These hardy souls stay out in the boondocks by themselves on a barge, sometimes not getting into port for three to four weeks at a time. Crew rotation is maintained by supply boat. The "sat" crew establishes geographical coordinate positions along the rivers to be tied into the seismic lines. This survey will later serve as a base net for all horizontal control in the mid-Amazon region.
Concept of New Technique of River Surveys
The concept of this new technique that we are using to survey the system of smaller rivers in the Amazon basin is a takeoff from the basic continuous-tow approach. Inherent in any river survey are several problems that in the past have severely limited production and increased the cost per mile. These factors have been a deterrent to such surveys until the perfection of our present technique. Some of the problems incurred in river surveys are: ( 1 ) heavy timber cover limiting the range of radiolocation systems; (2) meandering river paths resulting in high noise level as the cable is pulled against the riverbank and low CDP multiplicity due to curvature in the cable; ( 3) difficult continuous-tow operation with 24 groups, due to excessive cable length; ( 4) high cost for "pickup-layout" operation with bay cables due to low production; and ( 5) difficult logistic support as small rivers such as the ones that we are working are usually distant from any supply point and navigation is generally slow against the current.
We could not hope to solve all of the problems in all areas, but we were successful in designing a type of operation that could cope with most of them in most situations. Taken in order, our solutions to the problems were:
Conventional radiolocation systems depend on a minimum of two known points in order to position base stations and pre-determine positions along a given line. We deviated from that method and decided that if we knew where we had had been and could maintain a constant pop interval, we would accomplish the same thing. We could determine our position in reference to the riverbank by use of radar photos. This got us in the ball park. We then used the transponder stations to carry control from one visual reference (or satellite position) to another. There are many villages, islands, points of land, and the like that are easily identifiable on a map. These were used as "tie points" within which we distributed any accumulated error on the final post-plot map. The result was a map with a high degree of accuracy, the only errors in location being contained between any two known visual (or satellite-determined) points.
Cable noise is the perennial problem of the doodlebugger. It is especially bad when a cable is being dragged over a floating log or being scraped against a riverbank when going around a corner. We were almost able to eliminate cable noise on corners entirely by merely stopping and taking several pops in one place. In order to keep the position against the current, it was necessary to reduce multiplicity in some cases. With the reduced noise level, however, the result was better data – and that is what it is all about!
To solve the problem of excessive cable length, that vast body of thinkers in Houston called ‘research and development’ was called in. They, in collaboration with the Houston instrument lab, came up with a proprietary cable design that incorporated: (a) short length; (b) long enough group length for adequate long wavelength noise attenuation; (c) full 24-trace recording; (d) small diameter for easy handling on the barges; (e) acceleration-canceling phones for low noise level in river currents; and (f) neutral buoyancy for continuous-tow operations. How did they do all of this in the same cable? That is a secret! Suffice it to say, however, that it is a fact; and it works just great in river shooting.
The high cost of the "pickup-layout" operation was solved by the "miracle cable" described in #3. Now, we do not advocate that continuous-tow operations be employed in all rivers. In fact, on our return to the Amazon we have quite a bit of bay cable work ahead of us; but the cable that we have been using has opened up a vast amount of river work that was previously thought either impossible or too costly using standard, everyday methods.
Logistic support is where the mother ship Cynthia Walker came into play. By having her placed strategically in the prospect area, she could serve as supply, quarters, transport, and sometimes even as recording ship.
Dream Assignment
An assignment on Party 179 is truly what every marine doodlebugger dreams about. We have a beautiful tropical paradise, no rocking and pitching of the ship, pretty girls, excellent weather, excellent fishing and hunting, just the right amount of work, and some unusual pastimes such as alligator hunting. Observer Hector Burgess and Mechanic Tom Hickman are our alligator experts. At night, with a bright light in their eyes to blind them, it is possible to catch alligators barehanded, a great sport among the crew. Of course, they throw them back as it is prohibited by law to kill the 'gators. And talk about fishing! How many of you have laid a lip over a tasty piranha steak, or broiled tambaqui, or piraruru, or tucunare! Wild duck hunting is a favorite pastime of the transponder station operators.
Our field office is located in Manaus (Figures 12, 13, 14). With a population of approximately 320,000, Manaus is the largest city in the region. lt was founded in 1850 and rapidly grew to be the largest inland port during the rubber boom days. It once boasted of having the finest opera house in South America, attracting singers from all over the world. With the development of synthetic rubber, however, Manaus fell into decadence in the late 1940's and remained in a state of stagnation until recently.
In an effort to stimulate the local economy, the Brazilian government declared Manaus to be a duty-free zone in 1967, bringing about an economic boom in the area. Today the city swarms with tourists and doodlebuggers, who are anxious to part with their cruzeiros in exchange for a tape recorder or a camera. In addition to our Western seismic crew working out of Manaus, other contractors are presently operating three land crews, two drilling crews, and one aeromag crew.
New buildings and hotels are growing like mushrooms, and even the old opera house is undergoing restoration as part of a government project to preserve the old culture. New industry is moving in, attracted by favorable tax benefits and the ability to ship products out via water or the new Trans-Amazon Highway. The Trans-Amazon, which begins at Belem on the northern coast, is almost totally paved to Porto Velho, a distance of about 2,000 miles through virgin jungle. It is quite a sight to fly over.
From Jungle to Coast
Flash! Our client, dynamic in its search for oil as are all of our clients, has just ordered the crew back to Fortaleza as a respite from our jungle work. Talk about hustling! Dietmar Jakobs was just seen crying over a gallon of beer about the large amount of money that he lost in selling his dune buggy on short notice. Derek Hough returned from vacation to find that his girlfriend had left him for someone with longer roots who would remain planted in Manaus. Last-minute purchases at the duty-free stores of Manaus (the rest of Brazil is subject to extremely high taxes on luxury items) added an estimated eight tons to the gross weight of the Cynthia Walker. She looked like a floating audiophile center. But do not worry, ladies, because our crew will be gone only for an estimated three months, after which the men will return to resume old friendships, apartment leases, and the like. We have all heard that old song and dance before, however. To quote Western Vice President Vic Boyd, "You will be gone only three weeks . . . ; and two years later we are still here!".
Inasmuch as we have been awarded an addition of some 12 to 14 months of work, we shall likely appear again on the pages of the PROFILE. Until then, Ate logo from the middle Amazon and its rivers Abacaxis, Apoquiauamirim, Nhamunda, ltapacurazinho, and the others that we have traveled, including, of course, the mighty Amazonas.
コメント