Quantitative comparison of two 3-D resistivity models of the Montelago geothermal prospect

5th ITB International Geothermal Workshop

Van Leeuwen, W.A.^1 ; Suryantini^2 ; Hersir, G.P.^3

IF Technology, Velperweg 37, Arnhem

6813DP, Netherlands^1

Institut Teknologi Bandung, Jl. Ganesha 10, Bandung

40132, Indonesia^2

Iceland GeoSurvey (ÍSOR), Grensásvegur 9, Reykjavík

108, Iceland^3

关键词: Geothermal reservoir;    High temperature minerals;    Initial formation temperature;    Model interpretations;    Quantitative comparison;    Resistivity modeling;    Resistivity response;    Resistivity structure;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/42/1/012029/pdf
DOI  :  10.1088/1755-1315/42/1/012029

来源: IOP

【 摘 要 】

A combined TEM-MT survey was carried out in the Montelago geothermal prospect, situated on Mindoro Island, the Philippines, with the aim to obtain the dimensions and depth of the geothermal reservoir as well as to formulate the prospects' conceptual model. The acquired MT data are static shift corrected using the TEM measurements. Two different 3D inversion codes are used to create subsurface resistivity models of the corrected MT data set. The similarities and differences between the two resistivity models are quantitatively assessed using a set of structural metrics. Both resistivity models can be generalized by a three-layered model. The model consists of a thin heterogeneous, conductive layer overlying a thick resistive layer, while the basement has a decreased resistivity. Although this is a common characteristic resistivity response for the alteration mineralogy of a volcanic geothermal system, the temperatures at depth are lower than would be expected when interpreting the modelled resistivity model accordingly. Since the last volcanic activity in the area was about one million years ago, it is anticipated that the resolved resistivity structure is a remnant of a hydrothermal system associated with a volcanic heat source. This model interpretation is validated by the alteration minerals present in the exploration wells, where high temperature minerals such as epidote are present at depths with a lower temperature than epidote's initial formation temperature. This generalized description of the resistivity model is confirmed by both resistivity models. In this paper the two inversion models are not only compared by assessing the inversion models, but also by reviewing a set of gradient based structural metrics. An attempt is made to improve the interpretation of the conceptual model by analyzing these structural metrics. Based on these analyses it is concluded that both inversions resolve similar resistivity structures and that the location of the two slim holes drilled are well chosen.