Application of a Synthetic Smectite to the Ultradeep Scientific Drilling Operations Makoto KOGA Nitchitsu Co., Ltd. Resources Development Devision, Powder Technological Laboratory 351-1 Kamitano, Arakawa-mura, Chichibu-gun, Saitama 369-18 Abstract The outlook of ultradeep scientific drilling operations are summarized. This review was conducted to infer the reason why the synthetic hectorite has been applied to the drilling muds. The results obtained are summarized as follows: 1. The viscosity of synthetic smectite-nacl suspensions showed the maximum value called viscosy hump at the NaCl concentration of 20meq/l approximately. 2. In a hydrothermal condition, Na-montmorillonite was easy to change, however, Ca-montmorillonite showed no significant changes. 3. Synthetic saponites showed a crystal growth with increasing hydrothermal duration at 300 Ž, and they also kept to have physicochemical and rheological properties. The observed differences of the synthetic and natural smectites were discussed in relation to rheological behaviors and hydrothermal stabilities. Key Words: hectorite, saponite, montmorillonite, drilling muds, hydrothermal stability.
Fig.1 A location map for the continental ultradeep scientific drilling operations.
Shear rate (s-1) Fig.3 Reological behaviour of 1.5% suspension of Dehydril HT and 4% one of Namontmorillonite at room temperature(av means apparent viscosity). Fig.2 X-ray powder diffraction patterns and TGA- DTA curves of Therma-Vis and Laponite XLG.
NoCl (meq/l) NaCl (x103 mg/1) Fig.4 Effect of NaCl concentration on apparent viscosity(av) of 2% suspension of Therma- Vis at room temperature. Fig.5 Effect of NaCl concentration on apparent viscosity(av) of 2% suspension of a synthetic saponite at room temperature. (Synthetic temperature; 280 Ž, Duration; treatment with various temperatures 2ƒ (degree)cukƒ Fig.6 X-ray powder diffraction patterns of Na-,Camontmorillonite after hydrothermal (Temperature; 250-350 Ž, Duration; 25-100hrs, Concentration; 1.5%). Basal reflection patterns are shown in case of Na-Mt.
Table 1. Mud properties of the water-synthetic hectorite system in the KTB pilot hole at different depths. Fig.7 X-ray powder diffraction patterns of saponites synthesized at various durations. (Synthetic temperature; 300 Ž).
Table 2. Chemical and physical data on saponites synthesized at various durations. (Synthetic temperature, 300 Ž). Fig.8 Schematic representations of two octahedral crystal fields and modes of particle association of a synthetic trioctahedral smectite.
Table 3. Characteristics of synthetic trioctahedral smectites. (a)16),(b)17); These are typical values.
Bottom hole temperature( Ž) Fig.9 Estimated bottom hole temperature versus depth for the proposed sites for the scientific drilling operations in Japan (It is impossible to illustrate the Hidaka Mountains). Zone A: Possible to drill with usual techniques, Zone B: Possible to drill with improved techniques, Zone C: Possible to drill with epoch-making techniques.