Bandung
Feb. 20–24
Welcome to Bandung Geo-EM
From the outset, taking the DISC to Bandung promised to be a new experience. The First International Geo-EM conference was scheduled for Feb. 22–23 and we presented the DISC course on the Monday (Feb. 20). This provided participants at the conference with fundamentals about EM that proved to be useful throughout the conference. The goals of Geo-EM Conference were overlap substantially with our DISC and hence merging the two events was a good strategy.
We arrived in Bandung and were warmly and enthusiastically met by Lutfi and Nano who are undergraduates in geophysics. Nano is the Vice President of the SEG-ITB (Institute of Technology Bandung) student chapter and will be president next year. Indonesia is more chaotic than Malaysia. It took some time to get to our villa but this is definitely a superb place to stay for a week. The owner is also a fantastic cook!
After a welcomed sleep, we met our host Widodo and walked to ITB. Banners announcing the DISC and Geo-EM were on many streets and in front of buildings. It was apparent that the event was well advertised and that this was going to be successful.
DISC day
We had thought that 8:00am would be an early start for the DISC but we later found out that classes start at 7:00am. As a Muslim country with morning prayers at 5am, students and faculty were ready to go by the time we arrived. After getting over a few technology hurdles with computers and projectors, we were launched. About 90 people were in attendance including undergrads, grads, faculty, and industry professionals. By polling the audience, it quickly became apparent that the major topics of interest were: geothermal energy, hydrocarbons, geotechnical problems (particularly landslides), minerals and some water issues. Geothermal energy was the front-runner. Indonesia is the world’s third largest producer of geothermal energy (US being #1) and they have exploited only about 4% of their resources. With a growing economy, they are using more energy than they can produce and currently have to import oil, so they are also actively trying to find further hydrocarbon resources, particularly in marine environments.
The wide range of EM backgrounds for participants made presentation of EM material a challenge. We were gratified by the positive comments on our feedback form:
Really inspiring, [the course] enlightening me that electromagnetics [as a] subject is increasingly demanded and favoured in the geoscience world. Connecting EM geoscientists via Geosci is a totally brilliant idea.
[At the courses at ITB] we were mainly focused on the practical aspects and if we discuss / teach the concept at all, it is with something that we have (experience, equipment, project) in hand, i.e. MT only. Through this DISC, we have the opportunity to learn EM concepts as a whole
I learned new things about EM, but there are some parts that I don’t really understand. This is because I’m still new in EM Geophysics, so that doesn’t really matter. The point is, DISC increases my curiosity, so that I want to explore more of this kind of knowledge by myself in the future.
An extended noon break gave people time to eat a traditional Indonesian box lunch and play with some apps. It also provided opportunities to talk with attendees. Students were especially enthusiastic about learning about EM and how it can be applied. For the use of app, we encouraged participants to think first based upon your physical intuition, then press button to check your thought process. The EM apps are great tools, but without questions, and motivation for understanding the fundamentals, they are just tools providing pretty images.
The highlight of the afternoon was magnetotellurics (MT). As pointed before, geothermal exploration is active in Indonesia, and as a country, they still have huge potential for further exploration. MT is the most important geophysical method since it can see deep conductivity structure. Participants were excited about the Hengil geothermal case history, and how conductivity models from a 3D MT inversion result could help geothermal exploration. Questions and discussion concerned during the MT section were:
- Static shifts and whether inductive TEM surveys are affected as much as galvanic surveys
- Remote reference location; where to put the remote and how to evaluate the noise characteristics of the station.
The DISC day wrapped with discussions about the Future of EM geophysics, and also photo-time for students who wanted to take pictures with us.
DISC Lab
Bandung was a different venue for us since there was no formal DISC Lab day. Instead of meeting in a room to capture problems that people were working on, we attended talks and poster sessions at Geo-EM. A diverse suite of geoscience problems exist and snapshots of the posters are available (Link). The problems include geothermal and hydrocarbon resources, natural hazards, and near surface studies for structure and agriculture.
Several completed case histories are captured from individual communications from presenters:
Yunus Daud (presentation, 7 steps) :MT for Geothermal Energy
A successful case history in geothermal exploration at Blawan-Ijen (a volcano) area was presented, and the conductivity model produced from a 3D MT inversion played an important role in the decision of where to drill. The challenge for this volcano was the existence of highly acidic fluids near the rim of the volcano. These acidic fluids can be hugely damaging from the development point of view because they will erode drilling facilities. The MT results suggested a site towards the center of the caldera and fortunately, the fluids there were quite neutral. Differentiating between acidic and neutral fluids is a remaining challenge for geothermal exploration in Indonesia and likely elsewhere. This topic lead to discussions about the potential use of the induced polarization (IP) technique to distinguish between them.
Kurt Strack (presentation) (Hydrocarbon: Imaging Sediments below Basalt using LOTem)
We had previously contacted Kurt and initiated connection with him to capture a Long Offset TEM (LOTEM) case history in India. However, meeting in person is a much better way for communication. Kurt was our villa mate, so we got together on the bench of our villa. An important question for this case history was the imaging of the Mesozoic sediment below the basalt layer in India. This mesozoic sediment potentially contains hydrocarbons and its existence, depth and thickness are important parameters to quantify. Imaging the sub-basalt mesozoic sediment is a challenging target for a seismic reflection survey due to the significant fractures in basalt layer. LOTEM surveys and interpretation showed that EM could see the conductive Mesozoic sediment, and estimate variation in its thickness over the survey area.
Amir Haroon (7 steps) Water: Marine CSEM for Imaging Salt Water Boundary in an Aquifer
A time domain marine CSEM survey has been carried out to find an aquifer in a coastal area near Israel. Given that most marine CSEM surveys have been conducted to find deep hydrocarbon reservoirs, this was a different application, but similar in that we are looking for a resistive layer in a conductive background. Moreover, a time domain system was used, which is not common for a typical marine CSEM surveys. To focus the vertical current flow, two grounded sources were simultaneously used, which provided a greater depth penetration. A fresh aquifer, ~200 m below the seafloor, was clearly imaged through a 1D inversion. Although one objective, to image the fresh aquifer layer, was satisfied, there were still several scientific questions were raised from both Amir and us. From Amir:
Is our 1D assumption, used for interpretation, valid? Especially at the edge of the aquifer, we know it is not, but what are the consequences?
From us:
Which data do we need to invert?
- On-time data (Amir’s choice)
- Off-time data, and Frequency domain data (we can transform to frequency domain, since he has full waveform data)
We have some intuition about the answer to these questions, but we still need to experiment to solidify our understanding. Further collaboration between our GIF group and Amir has been started to answer these questions.
Bülent Tezkan (presentation) Environmental: Radio Frequency MT for Landfills
The Radio frequency magnetotelluric (RMT) method is used to map a land fill region. Compared to conventional MT, from an RMT survey, higher frequency data can be obtained 1kHz-100kHz. Transmitters are a vertical electric bipole tower that generate horizontal magnetic fields; this is similar to the VLF tower designed for submarine communication. Measurement locations are far enough away that we can use a plane wave assumption for the source. The data are tipper measurements, which is are transfer functions between vertical and horizontal magnetic field. A 2D grid of tipper data are measured and then inverted to recover a 3D conductivity model.
Yuguo Li (presentation) Hydrocarbon: Marine CSEM
An overview of the marine CSEM survey, and its interpretation were illustrated. The Ocean University of China has developed a marine CSEM system. For a test survey, they have deployed 10 ocean bottom EM (OBEM) receivers and successfully measured inline electric field data over a known hydrocarbon reservoir.
Although there were exceptions, it was apparent that knowledge and fundamental understanding about many of the important details regarding inversion and how it is applied in practice is not widespread. We held an afternoon session in which we walked through the DC resistivity app. Students were engaged and wanted more material, but there was not sufficient time to show how the equations could be solved numerically and how to formulate and solve the inverse problem. This has motivated us to put together more material on these subjects so that impromptu tutorials can be presented when they are needed.
Geosci-Indonesia: Group for Advancing Electromagnetics in Indonesia
Despite the enthusiasm from students for enhancing their technical backgrounds our big challenge was how to sustain that momentum and enthusiasm after we left. In subsequent discussions with students, we formulated a strategy whereby the SEG-ITB Student Chapter could play a major role in helping to develop computational capabilities in forward modelling and inversion of data sets related to geoscience problems. The important elements we identified were:
- Existence of a variety of geoscience problems in Indonesia
- Enthusiastic and bright students at ITB (this is the highest ranking geoscience university in Indonesia and they have ~70 students in each year of their program. They publish a high-quality Journal: La Terre)
- Availability of external resources (SimPEG software and tutorials, Geosci.xyz)
- Students at UBC and at other institutions who want to assist in applications.
We are working with a selected group of students and faculty to develop Geosci-Indonesia. If this can be accomplished, it has potential to make ITB students more employable, increase the sophistication of problems that can be solved at ITB, and overall be of benefit to students and industry in Indonesia. As Nano said when we were leaving: “Let’s just Do It” .
Thanks
There are many people who made our visit to Indonesia successful. We especially thank Widodo and the Geo-EM Committee for hosting us, advertising the DISC, and ensuring we had an audience. We benefited hugely from discussions and materials from the invited international speakers: (Kurt, Amir, Weerachai, Bülent, and Yuguo) and from discussions with Yunus regarding development of geothermal resources. But most importantly, we thank the students with whom we interacted (Nano, Sevi, Lutfi, Yogi, Nadia, …). Your desire to enhance your knowledge and computational abilities, and your enthusiasm for applying electromagnetics for geoscience problems, were an inspiration for us. We’re looking forward to Geosci-Indonesia being a success.
Appendix: Posters at Geo-EM
Geothermal applications:
Delineation of DOLOK MARWA geothermal prospct area / Joni et al.
Hydrothermal system of the Papandayan volcano from temperature / Byrdina et al.
Asymmetrical Hydrothermal system below Merapi volcano / Byrdina et al.
Geohazards
Slope monitoring by using 2D resistivity method at Sunga Batu, Malaysia / Mubarak et al.
Quality investigation of building structure using GPR method / Nugroho et al.
Detection of underground voids in Tahura Japan Cave Bandung / Azimmah and Widodo
Identification and monitoring of subsurface structure of tunnel using EM method / Amalia et al.
Landfill
Assessment of leachate infiltration from Piyungan landfill / Parhusip et al.
Distribution pattern of magnetic susceptibility and heavy metals in sediments from lake Liboto / Yunginger et al.
Other applications:
Deep electromagnetic sounding for minieral exploration / Morebe et al
Identification of near surface fault structure using Radomagnetotelluric (RMT) / Saputra and Widodo
Interpretation of VLF-EM and VLF-R data using tipper and impendace analyses / Prastyani and Nisari
Investigation of buried palechannel in Rumpet village eastern Banda Aceh using EM induction method / Yanis et al
Innovation of floating TEM method in the case of environmental geophysics / Nurjanah and Widodo
