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Petroleum is one of the major energy resources in the world.
Reserves estimation is an important work during exploration or
development of an oil/gas field. The purpose of this study is
to estimate reserves by probabilistic concept, taking the
uncertainties of each parameter into consideration. It is called
probabilistic volumetric method. In the process of reserves
estimation, a probability distribution with the ranges of every
parameter is collected or given. And then, Monte Carlo
Simulation is run to generate a probability distribution of
reserves. This study uses the probabilistic volumetric method
to evaluate the reserves of X-gas filed (in Taiwan area) which
structurally divided into three blocks(namely, x1, x2 and x3) by
faults. The reserves for these three blocks are estimated
separately and then added these reserves together. The results
of reserves estimation are: proved reserves is 152 BCF; probable
reserves(including proved reserves) is 207 BCF; and possible
reserves(including probable reserves) is 278 BCF; and the most
likely value of the reserve of this field is 195 BCF. The
sensitivity analyses are also conducted. The most sensitive
parameters for x1, x2, and x3 blocks are porosity, net pay, and
water saturation, respectively. The estimated reserves are
affected mostly by the most sensitive parameter. The other
case study is the BA oil field in the United States. The
estimated proved reserve is 502 MMbbl; probable reserves(
including proved reserves) is 587 MMbbl; possible reserves(
including probable reserves) is 698 MMbbl; and the most likely
value of the reserve of this field is 555 MMbbl. The most
sensitive parameter in this case study is porosity.
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