heating to 350ºC + quenching. Au tube lower weld higher weld powdered quartz. Saline solution. Pre-fractured quartz pri
DESCRAMBLE: Drilling in dEep Super-CRitical AMBient of continentaL Europe
Post-drilling characterization of pressure-temperature conditions in the Venelle 2 well from petrographic studies and synthetic fluid inclusion analyses G. Ruggieri1, A. Dini2, A. Orlando1, L. Peruzzo3 1IGG-CNR,
UOS of Florence, Florence, Italy 2IGG-CNR, Headquarters, Pisa, Italy 3IGG-CNR, UOS of Padua, Padua, Italy
DESCRAMBLE Pressure - temperature characterization are essential for the evaluation of geothermal resources, however…. Pressure-temperature measurements in extreme conditions (i.e. temperature > 400°C, presence of aggressive fluids) such those encountered in the deepest parts of the Venelle 2 well, is almost impossible by using conventional logging methods. This problem was addressed by two methods: - Development of a new logging tool (SINTEF PT tool) during the DESCRAMBLE project. - A method developed during the IMAGE (FP7) project based on the production of synthetic fluid inclusions within geothermal well. Petrographic studies of deep core samples of the Venelle 2 well Information on the thermal regime of the deep part of the well 2
DESCRAMBLE
Information from petrographic data
The deepest core (2900 m) show tiny hydrothermal veins of biotite, tourmaline and possibly zinnwaldite. Fluids responsible for these veins exploited both extensional cracks and along-foliation weaknesses. Similar to those found at the bottom of the San Pompeo 2 well.
Zinwaldite (?)
tourmaline
biotite
3
DESCRAMBLE
Information from petrographic data
The effects of a supposed underneath pluton could be recognized in particular features such as: - static porphyroblasthesis of muscovite+biotite (T ≥ 400°C), - Ca-plagioclase+biotite enriched levels, - limited biotite+tourmaline infilling along the foliation - transversal veins filled by: o quartz+biotite+muscovite+Ca-plagioclase+epidote+tourmaline o quartz+biotite+tourmaline+zinwaldite. 4
DESCRAMBLE
Synthetic fluid inclusion method
Temperature logging by using synthetic fluid inclusions: based on the formation of fluid inclusions in cracked minerals.
What are fluid inclusions? They are small (usually microscopic) portions of fluid trapped within minerals during or after their growth. What are synthetic fluid inclusions? They are fluid inclusions formed artificially (for example through a batch autoclave) by trapping a fluid within fractures in minerals (usually quartz) that are subsequently healed. H2O
5
DESCRAMBLE
Synthetic fluid inclusion method cut quartz by low-speed saw Production of micro-fractures in quartz prisms by thermal shock: heating to 350ºC + quenching
gold capsule
higher weld
Pre-fractured quartz prism Saline solution powdered quartz
lower weld Au tube
• Fluid inclusions form in pre-fractured minerals (usually quartz) placed in sealed gold capsule together with the solution which will be trapped. • The solution is saturated with respect to that minerals (adding powdered quartz). • In laboratory experiments the capsule is placed within a batch autoclave at fixed P-T conditions for several days or weeks. 6
DESCRAMBLE Method 1
Gold capsules containing pre-fractured quartz and a saline-alkaline solutions placed within a micro-reactor which contain a volume of de-ionized water such that the density of water in the micro-reactor has the critical value. The micro-reactor is lowered in the geothermal well at the depth of the established depth of measurements. Trapping conditions are along the H2O liquid/vapor curve or the critical isochore of H2O. Trapping temperature can be calculated from the intersection of the isochore of the saline solution with the LV curve or the critical isochore of H2O. 7
DESCRAMBLE
Tests during IMAGE project of method 1
Krafla (Iceland)
Larderello (Italy)
Depth b.g.l.(m)
Depth=920 m T= 249°C
Depth 1770 T = 336°C
339-343°C
IN: February 17 OUT: February 24
Synthetic fluid inclusions T : 251°C 8
DESCRAMBLE
Method 2 (not previously tested)
Production of synthetic fluid inclusions in gold capsules containing saline-alkaline solutions and pre-fractured quartz placed in direct contact with the environment of the well.
immisciblity
Pressure-temperature conditions in the deepest part of the Venelle 2 well are such that fluid immiscibility is expected within the gold capsules, i.e. very high-salinity liquid coexists with a low-salinity vapor. Trapping temperature, in this case, is directly derived from the homogenization temperature of fluid inclusions
9
DESCRAMBLE
Measurements at Venelle 2
Solutions used Gold capsules in the micro-reactor: SF 17: H2O + 10 wt.% NaCl + 0.4 wt.% NaOH SF 19: H2O + 20 wt.% NaCl + 0.4 wt.% NaOH Gold capsules in direct contact with the well: SF 18: H2O + 10 wt.% NaCl + 0.4 wt.% NaOH SF 20: H2O + 20 wt.% NaCl + 0.4 wt.% NaOH.
Capsule weight before the test (g) Capsule weight after the test (g)
SF 17 1.1558
SF 18 1.0663
SF 19 1.2667
SF 20 1.3035
1.1542
1.0660
1.3263
1.3036
≈48 hours of permanence at 2900 m b.gl.
capsule opened
10
DESCRAMBLE
Results of method 1
19.8°C
L
478°C
L V
V
Number of measurements
25 20
SF 18
15 10
SF 18
5 0
Pressure
440
450
460
470
480
490
500
Th (°C)
liquid
Cp Ph
l+v
Number of measurements
iso ch ore
10
SF 20 8 6 4
SF 20
2
vapor 0
Th
Temperature
440
460
480
500
Th (°C)
520
540
11
DESCRAMBLE
Results of method 1
800
700
700
600
600 Pressure (bars)
Pressure (bars)
800
500
500
400
400
300
300
200
200
400
450
500 Temperature (°C)
550
600
400
450
500
Temperature (°C)
550
600
12
DESCRAMBLE
Results of method 2
Three-phase (liquid+vapor+halite) liquid-rich inclusions coexist with two-phase (liquid+vapor) vapor-rich inclusions → evidence of fluid immiscibility
vapor liquid halite
liquid
vapor
13
DESCRAMBLE
Results of method 2
34.4°C
vapor
450°C
halite
h
liquid
515°C
v l
v
Pressure
l
liquid liquid+halite
v l+
Ph
518.9°C
l
vapor
+h l+v
Temperature
Tmh Thtot
14
DESCRAMBLE
Results of method 2
15
Number of measurements
Number of measurements
15
SF 17 10
5
0
T: 510±10°C 10
SF 17
5
0 420
430
440
450
Tmh (°C)
460
470
440
460
480
500
520
540
Thtot (°C)
15
DESCRAMBLE
Results of method 2 Temperature (°C) 0
100
200
300
400
500
1000
Temperature extrapolations 1500
Depth (m)
Log with SINTEF tool
2000
2500
Mechanical Kuster log: > 504°C
Synthetic fluid inclusions 510±10°C 3000
16
DESCRAMBLE
Results of method 2 80
70
SF 17
Pressure (Mpa)
60
P: 42±3 MPa
50
40
V L+ + H halite + vapor
30
20
10
0 0
10
20
30
40
50
60
70
80
NaCl (wt.%)
17
§ The thermal effects of a supposed pluton occurring below the Venelle 2 well are recorded by core-samples recovered during the DESCRMABLE project. (Further analyses are needed to assess if high-temperature mineral assemblages are related to the recent granite emplacement or if they were inherited from previous thermal events). § Trapping temperature values of synthetic fluid produced by two different methods are relatively similar (510±10°C and 509±8°C) suggesting that such values are realistic estimates of the temperature occurring in the deepest part of the Venelle 2 well. § Synthetic fluid inclusions formed within gold capsules in contact with well environment indicate maximum pressure of about 42±3MPa.
THANK YOU! The research leading to these results has received funding from the European Union’s Horizon2020 Research and Innovation Program under grant agreement No 640573 (Project DESCRAMBLE)
18
