World Geothermal Congress 2020+1
March - October, 2021

Mise A La Masse Exploration at Wayang Windu Geothermal Area, Indonesia

Prihadi SUMINTADIREJA and Asrizal MASRI

[Institut Teknologi Bandung, Indonesia]

A Mise A La Masse (MAM) field survey data acquisition have been conducted from October 11, 2012 to November 11, 2012. Survey area is in the Star Energy, Wayang Windu Geothermal Area and focus on three Star Energy well production, North Well, Central Well, and South Well (LAPI ITB, 2013). Each well has 192 electrodes potential surrounding central MAM (well). The main purpose of this survey is to map the apparent resistivity values and residual equipotensial be used to generate permeability zones based on the resistivity map. The MAM field data acquisition consists of two fixed current electrodes C1 and C2, which are located about 5 to 6 km apart and are assumed not to influence each other. The fixed potential electrode, P2, is located about 3 to 4 km distances away in the opposite direction of the current electrode C2. The potential electrode P1 distributed around the charged well C1. The MAM field survey is based on maximum coverage from the current electrode at the production well within the study area. Position of all MAM measurement station provided by the high precision GPS with adopting rapid static or real time kinematic method. The GPS base station consists of primary and second order base station. Meanwhile the primary order base station was determined using high precision method of GPS measurement. The points are CORS ITB1 (located at ITB campus). The coordinate has very good quality because it has taken after 2004 and well defined in national as well as international reference system and frame. Interpretations of the Wayang Windu MAM data have been made The main feature evident contour on the maps is a relatively confirm with geological structures identified by MNL through the interpretation of remote sensing images and aerial photography. The geologic structures shown are supported by strong geologic evidence, including drilling results. MAM average residual map shows the measurement results corresponding to the steam production (1996-1998) in Wayang-Windu geothermal area. Along with MAM survey, we conduct Vertical Electrical Sounding (VES) measurements between central well and south well, consist of 17 VES points along a 4 km profile. Each VES point spread + 2000 meters AB/2 distant with each VES interval of 200-300 m, and designed target depth of approximately 1000 m. The inversion used since the target cannot exceed 1000 meter depth. By considering the smoothness of the resulting inverse model for each VES data, all inversion results plotted and contoured to form a quasi 2-D resistivity section. The conductive cap rocks (100 Ohm.m) under the cap rock correspond to reservoir geothermal system (Pangalengan Formation). The Pangalengan Formation consists predominantly of intercalated lahars and tuffs. This unit is further distinguished by a basal conglomerate that is overlain by interbedded sandstones, siltstones, and minor lignite beds. This unit character is usually good and ideal for reservoir geothermal system. The discontinuity of resistivity distribution pattern associated and correlates with the geological structures. The structures clearly describe with discontinuities of resistivity distribution quasi 2D model inversion. Quasi 2D resistivity model indicated new structure not exposed in surface. The combination of the residual MAM with VES data results showed an interesting result. The shaded area at residual MAM associated with a thick cap rock at VES Model section (quasi 2 D model), otherwise unshaded associated with a thin cap rock. Thick cap rock enables the high pressure reservoir. Theoretically in the geothermal area, cap rock can be formed from alteration activities. Increasing alteration thickness correlate with the results of a large heat source underneath. Rather a thin cover layer resulting from a heat source which is not too big. Residual MAM , steam production well and VES data compilation can be concluded that the shaded area in residual MAM is possible a geothermal prospect with a good steam production and also can associated with good permeability zone.

        Topic: Exploration Paper Number: 11000

         Session 13A: Exploration 4 -- Asia, Americas [Tuesday 11th May 2021, 06:00 am] (UTC-8)
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