| Abstract |
Geological risk is the most difficult to be assessed and quantified among many exploration risks. This is because it consists of many risk factors with various level of uncertainty. Assessment of this risk needs geological understanding of the project area, the targeted geothermal system type, and the distribution and magnitude of thermal energy indicators defined by previous exploration (geology, geochemistry, and geophysics). Nevertheless, these key factors of assessment often unreliable, unrepeatable, and nonstandard, making the risk become difficult to identify or quantify. Therefore it is necessary to develop a standard assessment for quantifying geologic risk. The purpose of this paper is to give an example on how geologic risk can possibly be quantified from various exploration data during early exploration up to well defined prospect. Therefore the study area is chosen in in Galunggung as an example for green field prospect and Patuha as developed field but has not been produced yet. The idea of the assessment and quantifying the risk is adopted from the developed method in petroleum evaluation project. The Geologic risk is assessed by considering the probability that the three independent components of a large potential geothermal systems, in particular hydrothermal system, exist. They are heat source, reservoir rock and fluid (and to a lesser extent cap rock), and recharge area - discharge area with its surface manifestation. The probability of geologic success (low risk) is obtained by multiplying the probabilities of occurrence of each of the above three components. The probability of occurrence each component is the result of assessment of the elements of the risk factors, which are expressed as unfavorable, questionable, neutral, encouraging, and favorable. The element of risk factor is all critical aspects of geologic risk that must be considered for the assessment, for example the element of risk of reservoir consists of temperature, pressure, fluid chemistry, area thickness, etc. The final result of assessment is probability of geological success that determined by value from 0.01 to 0.99, which translates into very high risk to very low risk. The value of probability from Galunggung and Patuha will show how much risk that the operator facing. The challenge of this work is how to determine the element of risk and giving the value of each element so that the method can be standardize, reliable and repeatable. |