I. BORUGA1, ST. AIRINEI2
1Intreprinderea de Prospectiuni Geologice si Geofizice pentru Hidrocarburi,
Bucuresti
2Universitatea Bucuresti
OBSERVATIONS ON THE DRILLING FLUID TEMPERATURE IN A GROUP OF WELLS PERFORMED
IN THE AREA OF A COMPLEX STRUCTURE FROM THE NORTH-EAST BANAT
(Abstract)
The authors present some preliminary and qualitative data on the measurement
and processing of the drilling fluid temperature in a group of 16 drilling
wells situated on a complex seismic structure that is assumed to have an economic
potential (Fig. 1). Temperatures were measured for each 30 m-section, beginning
with the depth of 500 m down to an average of 1200 m (the bottom of the wells).
The systematization of relative temperature values for each well is shown in
Fig. 2. Temperature gradient variations for three stratigraphic periods (on
the boundaries of the Pliocene, Miocene and at the bottom of the wells), as
well as the loss rate of the drilling fluid temperature, calculated on the
ascending branch (Table 1), are of 1.5°C/100 m, on average. The morphology
of thermodiagrams (Fig. 2), the values of thermal gradient variation for the
stratigraphic periods on the boundaries of the Pliocene and Miocene, as well
as the map of geothermal gradient variation down to the well bottom (Fig. 3)
are dominated by thermal anomalies of a striking maximum and minimum caused
by the thermal conditions specific to each case discussed in the paper. The
processing and interpretation of thermometric and drilling data has led to
a substantial improvement of the seismic structure map, completing it in the
geological section opened by the wells, with a location of the permeable levels
loaded with natural gas, or CO2 under pressure, ground-water etc. The thermodiagram
of well 7 (Fig. 4 and Table 2) reveals that the drilling fluid (mud) column,
when stationed, is a good heat conductor due to its thermal conductivity which
is by far greater than that of the rocks in the borehole wells.
The authors recommend the described mechanisms as an efficient and easily feasible
procedure at any drilling well, the data obtained being readily processed and
plotted on thermodiagrams thus affording a better reading and earlier detection
of major events in the drilling process than geophysical coring does.