Measurements completed in connection with drilling, geological mapping of drill cores and drill cuttings, and down‑hole logging

Investigations performed between data freeze 1.2 and 2.3

During and after drilling, the different categories of boreholes produced were the subject of standard-ised investigation programmes by geological, geophysical, hydrogeological and hydrogeochemical methods. In addition to different SKB method documents, these programmes are described in detail in /SKB 2005a/, and the descriptions are not repeated here.

In the following text, a summary of the investigations performed after data freeze 1.2 and onwards is given. The investigations are presented and grouped according to geoscientific discipline and, within each discipline, roughly in chronological order, although investigations to some extent have been conducted simultaneously. Data and/or P-reports not available until after data freeze 2.3 are presented separately.

The results from standard geological and geophysical borehole investigations and single-hole interpretations became successively available from the new cored and percussion-drilled boreholes as they were completed, cf. the drilling succession in the previous section. However, the only investigations carried out in the shallow boreholes KFM90A–E were BIPS-logging, drill-core mapping and deviation measurements. More information on these standard investigations is presented in section 5.2.2.

Vertical seismic profiling measurements were undertaken in the two deep, almost vertical telescopic boreholes KFM01A and KFM02A in order to improve the resolution in the identification of seismic reflectors and to provide some constraints on the extension of geological structures. The surveys were conducted to a borehole length of 775 m in each borehole. Major seismic features were identi-fied to depths exceeding 1.5 km and to a lateral distance of 2–3 km from the borehole collars.

Measurements of ground currents generated by the Fennoskan high-voltage cable were performed in boreholes KFM04A, 07A and 08A. Ground self-potential measurements were also conducted between drill sites 4 and 1.

An in situ thermal experiment was performed in the short cored boreholes KFM90A–E close to drill site 7. The main purpose was to explore the degree of anisotropy of thermal properties in the type of metamorphosed granite prevailing in rock domain RFM029. The results from this large-scale field experiment were compared with results from a small scale in situ experiment as well as with laboratory tests.

Overcoring rock stress measurements were conducted successively during drilling of boreholes KFM07B, 07C and 02B. Furthermore, hydraulic fracturing (HF) and hydraulic tests on pre-existing fractures (HTPF) were carried out in boreholes KFM07C, 08A, 09A and 09B.

A pilot study of borehole breakouts based on acoustic televiewer data from KFM01A and KFM01B was made, demonstrating that borehole breakouts and other fallout structures in the borehole wall, mainly micro-fallouts, exist in the deep boreholes at Forsmark. With these results in mind, this study was followed by an extended mapping (subdivided into two activities) in boreholes KFM01A, 01B, 02A, 03A, 03B, 04A, 05A, 06A, 07C, 08A, 08C, 09A, 09B and 90B. A re-logging with the acoustic televiewer was performed in KFM08A approximately two years after the first logging, in order to disclose if any time dependence could be observed regarding development of borehole breakouts and other fallout structures.

Single-hole hydraulic tests comprised both difference flow logging and double-packer injection tests in boreholes KFM06A, 07A, 08A, 08C and 11A. Furthermore, difference flow logging was carried out in KFM01D, 07C, 02B and 08D, whereas double-packer measurements were conducted in KFM04A, 05A, part of KFM02A (after hydraulic fracturing), KFM06B, 08B, 06C, 09A, 07B, 09B, 01C, 10A and 12A. All new percussion-drilled boreholes were flow logged with the HTHB-equipment (open hole pumping test). However, although attempts were made, flow logging was not possible in HFM25, 28, 29 and 31 due to very limited water yield.

A number of multiple-hole interference tests were performed with different purposes. Firstly, three short-term cross-hole tests between percussion-drilled and cored boreholes as well as between various percussion boreholes were carried out. The purpose of these tests was to investigate/verify hydraulic connections between boreholes at drill sites 1, 2, 3 and 4.

Groundwater flow was determined during both undisturbed and stressed conditions, the latter caused by pumping in HFM14. The aim was to further increase the understanding of the hydraulic conditions in the area and to assess the possibilities to later perform a large-scale, multiple-hole tracer test.

Hydrogeochemical logging and hydrogeochemical characterisation as well as microbial investigations were conducted in the telescopic boreholes KFM05A, 06A, 07A, 08A and 01D as well as in the con-ventional cored borehole KFM09A. Hydrogeochemical characterisation was also carried out in the telescopic boreholes KFM10A and KFM11A.

Results and a P-report from a study of uranium oxidation states in groundwater with high uranium concentrations were supplied immediately prior to data freeze 2.3.

In percussion-drilled holes, chemical characterisation is accomplished mainly by monitoring, i.e. recurrent sampling and analysis, in those boreholes which are supplied with monitoring equip-ment, see section 2.4. However, groundwater sampling in connection with other activities, mainly during HTHB-logging or interference tests, or sampling from boreholes serving as flushing water wells, has also contributed to the understanding of the hydrogeochemical conditions. Prior to data freeze 1.2, this kind of sampling/analysis was performed in percussion boreholes HFM03, 05, 06, 08, 09, 10, 11, 12, 14, 17 and 18. Between data freezes 1.2 and 2.3 boreholes HFM20, 22, 23, 24, 25, 26, 28, 29, 30, 33, 34, 35, 36, 37 and 38 were also included.

Interconnected porewater was successfully extracted by laboratory out-diffusion methods from about 20 drill core samples from KFM06A. The objective was to characterise these waters chemically and isotopically. In addition, the method of extraction, together with interfaced measurements of inter-connected porosity, provides the opportunity to derive diffusion coefficient values. Subsequently, drill core samples from KFM01D, 02B, 08C and 09B were also collected for determination of rock matrix porewater composition.

In situ formation factor logging was performed in boreholes KFM03A, 04A, 01D and 08C and the results compared with formation factors obtained in the laboratory by electrical methods.

The results from the previously performed in situ groundwater flow measurements with dilution technique and single-hole tracer tests in KFM04A became available. Groundwater flow measure-ments were also conducted in KFM01A, 01D, 02A, 03A, 03B, 04A and 08A and single-hole tracer tests in KFM02A, 03A, 04A and 08A. The objectives of the activities were to achieve information about groundwater flow under in situ (i.e. undisturbed) hydraulic gradients and to determine transport properties of groundwater flow paths in fractures/fracture zones.

Data and/or P-reports available after data freeze 2.3

As far as standard geological and geophysical investigations are concerned, predominantly P-reports from the following boreholes were not available until after data freeze 2.3:

• KFM02B, 08D, 11A, 90B and 12A (geophysical logging).

• KFM07C, 02B, 08D, 11A and 12A as well as HFM36 and HFM37 (interpretation of geophysical borehole measurements).

• KFM02B, 08D and 12A (RAMAC and BIPS-logging).

• KFM02B, 12A and 08D as well as HFM33, 34, 35, 36 and 37 (Boremap mapping).

As far as single-hole interpretations are concerned, both data and P-reports from the following boreholes emerged after the data freeze 2.3:

• KFM11A, 08D, 02B and 12A as well as HFM33, 34, 35, 36 and 37.

The activities within the field of thermal properties and rock mechanics that were delayed are listed below.

• Evaluation of the in situ thermal experiment in the five short cored boreholes KFM90A–E, close to drill site 7. The results were not available until spring 2008.

• Data and P-reports from overcoring rock stress measurements in KFM07B, KFM07C and KFM02B. The major part of the field work was performed prior to data freeze 2.3, but became available during autumn 2007 and spring 2008.

• A draft report from the major campaign of hydraulic fracturing (HF) and hydraulic tests on pre-existing fractures (HTPF) comprising 13 tests in KFM07A, 15 tests in KFM07C, 23 tests in KFM08A, 16 tests in KFM09A and 18 tests in KFM09B was finished by late 2006, but the final P-report was delayed until the end of 2007, due to the major revision of borehole deviation measurements and fracture orientations performed by SKB.

• The pilot study of the existence of borehole breakouts and other types of fallouts from the borehole wall was completed early in 2005, but the report was not printed until after data freeze 2.3. However, the study did not generate data to Sicada.

• The mapping of borehole breakouts (and other fallout structures) from televiewer logging in boreholes KFM01A, 01B, 02A, 03A, 03B, 04A, 05A, 06A and 07C as well as from KFM08A, 08C, 09A, 09B and KFM90B provided data and two P-reports first after data freeze 2.3.

• A review was made of rock stress measurements conducted within the site investigation pro-gramme at Forsmark up to and including 2004. The study, which did not generate data to Sicada, was completed in April 2006, although the report was not printed until after data freeze 2.3. The stress data included in the analysis involved overcoring stress data from borehole KFM01B and the cored boreholes DBT-1 and DBT-3 situated at the Forsmark power plant III and drilled long before the Forsmark site investigations, as well as hydraulic stress data from boreholes KFM01A, KFM01B, KFM02A, and KFM04A.

The following hydrogeological investigations (single-hole tests and multiple-hole interference tests) were not fully completed until after data freeze 2.3.

• Difference flow logging in boreholes KFM02B, 08D and 11A. In KFM11A, flow logging was performed until an obstacle was encountered at 498 metres borehole length. Below this depth, double-packer injection tests were made instead.

• Two large-scale interference/tracer tests that used the percussion-drilled boreholes HFM14 at drill site 5 and HFM33 at drill site 11 as pumping boreholes were carried out during the summer and early autumn 2007, in order to verify previous assessments of the hydrogeological conditions in the north-western part of the Forsmark candidate area.

The following hydrogeochemical investigations were not fully completed until after data freeze 2.3.

• Hydrogeochemical characterisation in the telescopic boreholes KFM08D and KFM12A. In KFM12A, a simplified measurements approach was applied by employing SKB’s double-packer injection test equipment. This equipment was also used in KFM11A for part of the hydrogeochemical sampling.

Hydrogeochemical data and reports from these boreholes as well as from KFM10A, HFM36, HFM37 and HFM38 were not available until after data freeze 2.3. The investigations in KFM10A, 11A and 08D included the study of number, viability, and methabolic diversity of microrganisms, and in KFM11A also colloids.

• Results of the rock matrix porewater composition in drill core samples from KFM01D, 02B, 08C and 09B were not available until after data freeze 2.3. Part II of this project, chloride diffusion coefficient modelling, which needed to be evaluated on the basis of the tracer experiment performed in KFM02B, will not be reported until after the summer of 2008.

Some investigations regarding transport properties were also late.

• A tracer test between the nearby telescopic boreholes KFM02A and KFM02B was initiated prior to data freeze 2.3 and continued afterwards. Data and report were not available until spring 2008.

• In situ formation factor logging by electrical methods in KFM01D and KFM08C.

2.3.3 Sampling and analysis of intact rock material for laboratory