January 2011

JOIN EVENT: UI SC AAPG & HMGF

GEOPHYSICAL SURVEY

FIELD CAMP 2011

 

On 5th – 11th January 2011, University of Indonesia – Student Chapter of American Association of Petro­leum Geologists was held Geophysical Survey – Field Camp West Java 2011 in Mount Pancar, West Java. This is an advance field trip which related to credits on Geophysics Field Camp Class that taught by Mr. Yunus Daud. This field camp leads by Mr. Yunus Daud himself and Mr. Syamsu Rosid; along with guest lec­turer Mr. Yanto (BPPT) and Mr. Jatmiko (BPPT); also co-assisted by 5 BMKG Operators and 3 field assistants.

This is a closed event which could attend only by students who registered on Geophysics Field Camp Class with Mr. Yunus Daud. Our main survey area is Mount Pancar and its surroundings. There were 43 students who participated to this event; consists of 5 upper-class seniors (5th year students), 33 seniors (4th year students), and 5 parallel program students.

This activity focused on identifying geothermal resources in Mount Pancar and its surrounding by doing both Geology and Geophysics Acquisition; those are Gravity Survey, Magnetic Survey, and Re­sistivity Survey. Because of large amount of partici­pants while there were limited instrument, assistant, and time; participants split into 2 main groups, each group consists of 4 teams. Group 1 was doing survey during 5th – 8th January 2011, and Group 2 was doing survey during 8th – 11th January 2011. Those groups and teams basically doing the same acquisi­tion rundown but different survey point.

GEOLOGY SURVEY

Group 1 (All Team): 5th January 2011

Group 2 (All Team): 8th January 2011

First survey that did in this activity is Geology Survey, because hopefully understanding its geological settings could help participants in doing Geophysics Survey later. This survey leads by Mr. Yanto (Group 1) and Mr. Jatmiko (Group 2). In this survey, all partic pants saw and studied geological settings of Mount Pancar environments by studying its outcrops and surface manifestation. We need to know the out­crops in order to understand Mount Pancar main structure. And understanding its surface manifesta­tion could help all participants to understand which geothermal system that might be occur in Mount Pancar and also help participants to know where the reservoir might lies.

After doing Geology Survey, all participants know that main structure of Mount Pancar is a strike slip fault that lies from East to West; it was marked by hot-spring distribution that lies from North to South. This is very important information, based on this information we change the direction of resistivity survey line in order to get the better data. Partic pants also saw some surface manifestation besides hot-springs; those are silica sinter an also many and varied clay alteration. Another interesting object is Milonitic Zone which indicated the contact area be­tween Jatiluhur Formation and Andesitic-intrusion rocks (Mount Pancar itself ), it might be the bound­ary of high gravity and magnetic anomaly.

GRAVITY ACQUISITION

Group 1: Team 3 (6th January 2011) – Team 1 (7th January 2011)

Group 2: Team8 (9th January 2011) – Team 6 (10th January 2011)

Limited survey license time, instrument, assistant, and relatively difficult area causing not every team could did this survey. For this survey, we were using Lacoste-Romberg Gravimeter, the old version of gravimeter. The operational of this instrument is a bit more difficult than CG5 – the instrument we are usually used. This is manual and analog operational instrument, not digital one. That is why every mea­surement took approximately 15 minutes; it was not included time for instrument settings and finding the relatively flat place – because gravimeter must be placed in relatively flat land.

Difficult survey area made all team could not reach the target on previously survey design; we could only reach 48 survey points of total 64 survey points with interval 250 meters.

 

 

MAGNETIC ACQUISITION

Group 1: Team 4 (6th January 2011) – Team 2 (7th January 2011)

Group 2: Team 7 (9th January 2011) – Team 5 (10th January 2011)

There were not too many differences between Grav­ity and Magnetic Acquisition, because we did the measurements in the same points with gravity did. We were using Proton-Precession Magnetometer, the instrument we are usually used, so that we did not find difficulties in operating this Magnetometer.

At least 2 persons need to be stay in base camp to monitor base magnetometer and predict its diurnal variation based on that day’s condition; whether raining or some other noise appearance, it was im­portant in order to do the right correction in mag­netic processing later.

All team could only reach 54 survey points of total 64 survey points with interval 250 meters, again it caused by difficult survey area.

 

 

RESISTIVITY ACQUISITION

Group 1: Team 1 & 2 (6th January 2011) – Team 3 & 4 (7th January 2011)

Group 2: Team 5 & 6 (9th January 2011) – Team 7 & 8 (10th January 2011)

Resistivity Acquisition needs more people in doing this survey, so that 2 teams were doing 1 survey line together. One participant along with an assistant become an operator who ran the instrument – mul­tichannel resistivity meter, they are also giving an instruction when the induction and measurements did and giving information if there were an error electrode. Other team members are always moving in order to put the electrode on the ground and link it with ARES cables and also always stand by to move every error electrode to the new place that might not in problem anymore. One member also needs to mark the coordinate where the electrodes were placed to know its elevation.

Our resistivity survey design consists of 4 lines, but because we only have 32 electrodes, so that we need to do this survey measurements 4 times

First measurement (set 1 – 4), second measure­ment (set 2 – 5), third measurement (set 3 – 6), and fourth measurement (set 4 – 7). When move from first to second measurement, we had to move the electrodes from set 1 to set 5. Then we did the same thing until the acquisition is done.

One measurement has 155 meters length, so that we hopefully could reach approximately 40 meters depth.

Most of Gravity and Magnetic Acquisition done un­til late afternoon and must arrived at base camp on late night because of difficult survey area, but there were still unfinished survey. Although we could not doing acquisition in all grid survey design for gravity and magnetic, but we could finished all line survey for resistivity.

In every night, participants were came together to evaluate, sharing, and discuss about what we had been doing during the day, and also made strate­gies for the better acquisition for tomorrow. It is very helpful section, because participants need the better preparation.

Participants also input the acquisition data that had been done that day and made slight analyzes. We could not do processing during field camp, but will do the processing when the survey has been done and back to Jakarta. Lecturers gave us 2 weeks to process and interpret all data and doing presenta­tion after that.

This activity is such a priceless experience for Geo­physics UI Students. By doing this activity, students would be able to do such data acquisition also know how to respect those data, so that someday students could anticipating poor acquisition data and know how to process such data without put their blame on acquisition team. This activity also helps students to try to create survey design according to regional geology data, not only based on trial and error.

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