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Review of NQ Academy Webinar #2: MT vs Drilling

NQ News, Friday October 30, 2020

The Magneto-Telluric (MT) survey on geothermal exploration is mandatory like seismic in the oil and gas industry and MT method is mandatory in geothermal detailed survey in Indonesia.

In the exploration stage (even in the development stage), geophysics is the most important surface method used to image the subsurface physical parameters associated with a geothermal system. MT imaging is the most powerful technology to define the top of reservoir, delineate the geometry of reservoir and determine well target zones. Many wells have been drilled on the basis of the MT resistivity guidance to the target zones. Some of the target zones as indicated by MT data are confirmed by drilling, but some are not (i.e. there is disagreement between drilling result and MT resistivity). This such situation may generate critical questions directed to the MT technology.

When the exploration technologies have been applied properly, proper interpretation from experienced geothermal expert will be a key point for: Resource Evaluation and Assessment, Development of Conceptual Model, Best Drilling Targeting and Potential Estimation.

Among NewQuest Geotechnology commitments, as one of the geothermal industry stakeholders to be precise as a geothermal exploration service company, is conducting Research and Development (R&D) in exploration that focused in improving technology and increasing drilling success ratio.

The 2^nd NQ Academy webinar entitled MT vs Drilling discussed 3 case studies about successful/unsuccessful drilling and MT technology innovations as one of solutions to reduce drilling risks based on NQG experience and study.

Case 1: Unrealistic 3D Inversion result: thickening below fumarole while thinning away from the fumarole. 2 wells were drilled on the basis of the resistivity distribution and failed. The bottom hole (about 2000 m depth) shows only 100^oC and 150^oC.

The unrealistic 3D MT model may be the cause for the unsuccessful drilling. NQ study proves that New MT Model after conducting a reprocessing & remodeling has good agreement with drilling data.

Case 2: MT data is not clean and genuine may be the cause for the unsuccessful drilling. Noisy, with unclear and unrealistic trend, improper data processing or only “cut” or “blank” the noisy data and static shift effects.

Applying suitable data processing, time-series inspection. Different method in MT data processing may produce different trend curve and auto processing may generate uncorrected trend curve. NQ study proves that new MT model after reprocessing and remodeling, the result of new MT model has good agreement with drilling data

Case 3: Discovering hidden geothermal reservoir in Blawan Ijen Indonesia with unimpressive manifestations as Bicarbonate-Sulphate Hot Springs with T = 35 – 50^oC.

3 lessons learned from the NQ above in determining/reviewing well targeting using the MT method are expected to be considered by geothermal industries, especially in Indonesia, which in the near future will carry out a lot of exploration drilling where it’s success rate below 50%.

The 2^nd NQ Academy Webinar was attended by more than 200 participants who were quite enthusiastic about this topic, some of the questioners were lucky because their questions were answered directly by Dr. Yunus Daud during the Q&A session, while the rest were answered via email.

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NQ News, Friday October 30, 2020

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