Improvement on Drilling Techniques Adopted for the Kuroko Green Tuff Region

Abstract

Drilling has been carried out extensively in the Hokuroku area of Akita Prefecture since 1910 with the purpose of locating Kuroko deposits. Traditional drilling methods could not yield satisfactory results in all aspects such as drilling depth, core recovery, and so on. The major reasons for this dissapointing performance were the altered green tuff formation and the equipment and techniques not suited to the lithology of the formation.
Akema Drilling company established in 1929, has carried out drilling extensively in this area and at the same time has expended.every effort to improve the performance of the operation. The major improvement and innovation were in equipment and the techniques of drilling, of which the important items are as follows.
1. Application of large drilling machines and tri-cone bits.
2. Use of diamond bits and the improvement of the matrix, bortz size, and water way.
3. Application of wire-line method.
4. Use of chrome-mud.
5. Manufacture and use of over-sized bits and rods.
6. Improvement and use of derricks.
Because of the above development, now, the company can drill to depth of more than 1000 m with almost 100 per cent core recovery in these altered geological units. This has contributed greatly to the prospecting for Kuroko deposits.