Task 1: Logging activities

Start: July 1996 (month 5)
End: December 1997 (month 22)
Responsible partner: GFZ.DR.DBL

As described in the previous reports, three logging campaigns took place in 1996. During these campaigns, repeated measurements were performed in well LL-03 (Nefsholt). In cooperation with Orkustofnun, logging was done in 5 other boreholes, of which at least the borehole-televiewer measurements in well LJ-08 are relevant for this project.

The recent activities within this subproject comprise two logging campaigns in 1997, one in September, the second in December. The first was exclusively concerned with repeated logging in borehole LL-03 (Nefsholt) inside the SISZ. During the second campaign, additional logs were run with the borehole-televiewer in Bödmódsstadir (located at the northern edge of the SISZ, close to Laugarvatn) and in Thykkvibær (slightly south of the SISZ, near the south coast). The latter borehole was drilled very recently. The locations are shown in Figure 22.

  

Figure 22: Map of the south-western part of Iceland showing the location of the site of repeated logging (Nefsholt) and of the other two boreholes where borehole-televiewer measurements have been performed during 1997.

Table 1 shows the logs performed during the first and second year of this project.

These five campaigns have thus attributed to the two aims of this subproject:

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Observation of changes in physical parameters of the rock and of changes in degree of fracturing and orientation of principal stresses with respect to seismic activity.

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Indirect measurement of tectonic stress orientation to evaluate the tectonic stress field in the area of the SISZ.

 

Table: As borehole NG-01 partly collapsed between log runs, the hole was abandoned and well LL-03 was chosen for repeated logging. GR indicates Gamma-Ray-log, SP stands for Spontaneous Potential. FED means Four-Arm-Dipmeter which includes an oriented four-arm-caliper. BHTV means ultrasonic Borehole-Televiewer. BCS is Borehole-Compensated-Sonic; DIL is Dual-Induction/Latero log. For technical reasons, no FED run was possible in LL-03, no BHTV run was possible in LJ-08 below 1330 m depth, no BHTV run was possible in BS-11 above 703 m depth. Due to the limited availability of a crane, no BHTV or FED run were possible in TN-02. The deepest parts of wells LJ-08, LL-03, THB-13 and BS-11 were not accessible anymore.

Name:	Location:	Max.	Logged	Tools used:	Date:
		depth:	interval:
NG-01	Ólafsvellir	1070 m	180-1070 m	FED, GR, SP,	July 1996
	(inside SISZ)			3-arm-caliper,
				16"- and 64"-
				resistivity
HS-36	Reykjavík	980 m	330-980 m	BHTV, BCS-GR	July 1996
LPN-10	Laugaland	890 m	80-880 m	BHTV,	July 1996
	near Akureyri,			BCS-DIL-GR
	North Iceland
LJ-08	Sydra Laugaland	2740 m	120-1890 m	FED, BHTV,	July 1996
	near Akureyri		120-1330 m	BCS-DIL-GR
TN-02	Ytri-Tjarnir	1370 m	260-1370 m	BCS, GR	July 1996
	near Akureyri
LL-03	Nefsholt	1309 m	80-1100 m	BHTV, BCS-DIL-GR,	July 1996
	(inside SISZ,			neutron-neutron,	October 1996
	site of repeated			X-Y-caliper,	September 1997
	logging)			16"- and 64"-	December 1997
				resistivity, SP
THB-13	Thykkvibær	1254 m	466-1225 m	BHTV	December 1997
	south-west of Hella
	near the south coast
BS-11	Bödmódsstadir	1193 m	703-1090 m	BHTV	December 1997
	near Laugarvatn