Environmental Engineering Reference
In-Depth Information
This chapter describes application of homogenization temperature to estimate current
reservoir fluid temperature in liquid-dominated and vapor- dominated geothermal fields, Japan.
This chapter presents moreover two gas analytical methods (individual and bulk gas analyses)
of fluid inclusions using a quadrupole mass spectrometer (QMS), and its application on fluid
inclusions in anhydrite and quartz collected during drilling of production wells in Japanese
geothermal fields. The location of this study fields in this chapter is shown in figure 1.
2. Microthermometry
2.1. Estimation of Reservoir Temperature
It is significantly important to know exactly temperature of reservoir around a production
well on evaluating the potential of a geothermal field. The reservoir temperature is usually
estimated by the temperature build-up test. To be concrete, a developer measures usually a
static borehole temperature (Tb) several times after the end of drilling of a production well
because of cooling down by circulation of mud on drilling, afterward estimates the recovery
temperature (RT) using Horner plots (e.g. Hanano and Matsuo, 1990). The validity of the
method is discussed below.
Since 1980, the New Energy and Industrial Technology Development Organization
(NEDO) had taken the initiative in surveying the promising Japanese geothermal energy
fields where development survey has not been conducted because of the risk of exploration.
This survey aims to verify the presence of geothermal reservoir in a regional field of 50 to 70
km
2
for the promotion of the development of geothermal power generation by private
enterprises. Figure 2a illustrates the relation of Tb values between after a short standing time
of 120 hours and a long standing time of 30 days to two years for many wells drilled on all
over Japan from 1980 to 1988 by the “Geothermal Development Promotion Survey (GDPS)”
project. The latter Tb value reflects a true pre-drilling reservoir temperature because of the
data obtained after a long period of thermal recovery. The Tb value is 30 to 80 ºC lower after
a standing time of 120 hours than after a long standing time of 30 days to two years in
reservoir temperature over 150 ºC. The former Tb thus shows a value on the recovering way
of the reservoir temperature. Figure 2b illustrates the relation between the Tb value after a
long standing time of 30 days to two years and the RT value. The RT values estimated from
data of the temperature logging sets (Standing times of 8, 16, 32, 48, 96 and 120 hours) using
Horner plots are in good agreement with the static borehole temperatures, suggesting that the
RT value is nearly equal to the reservoir temperature.
The estimation method of the reservoir temperature using the temperature build-up test is
unfortunately defective in high cost as consequence of long standing times and so on. By
contrast, microthermometry of fluid inclusion is useful method to resolve the problem. From
the reason, fluid inclusion has been widely used to determine reservoir temperature during
drilling of a well with real time at a development site. When we measure homogenization
temperature (Th) of many fluid inclusions in mineral at a depth of a well using a heating
stage, we can usually obtain Th values with various ranges (figures 3, 4). To solve how Th
data reflects the reservoir temperature, it is necessary to clarify the relation between Th and
RT in a geothermal field. The relationship between the Th and the RT in each well of
geothermal field is divided into four patterns as follows:
Search WWH ::
Custom Search