Development of a Multi-disk type Borehole Seismic Source

摘要

In 1991, OYO corporation developed the borehole seismic source (OWS: OYO Wappa Source) with a spring accelerated, mass impact, single stage, fluid filled, and multi-disk design for the civil engineering field surveys. Testing showed that this seismic source has several advantages such as good repeatability, easy operation, and low electric power requirements.Japan National Oil Corporation (JNOC) and OYO Corporation have made modifications to the OWS that will assure its practicability for borehole surveys in oil fields. The source has been modified with four points: (1) output improvements on the kinetic energy excitation, (2) output improvements on the energy conversion efficiency, (3) improvements on the source durability, and (4) improvements on the operation depth. The tests show that the multi-stage and multi-disk design effectively increases the source energy output. The new source (JOWS: JNOC-OYO Wappa Source) has 7 stages and 10 disks per stage. The redesign also includes a unique mechanism of transmitting the energy from hammer to anvil, simultaneously impacting all seven stages.We carried out a field experiment at JNOC's Kashiwazaki Test Field in 1994 to understand the basic characteristics of JOWS. As JOWS worked without trouble through the 4-day experiment, we performed a field test at a carbonate-reservoir oil field of West Texas in 1995. The distance between the source and receiver boreholes was about 372 m (about 1,200 ft). Though the lengths of ray paths were over 600 m (straight-ray path assumption), the JOWS could generate sharp P-wave first break which is required for the accurate tomography result.Finally, source characteristics such as a radiation pattern and energy conversion efficiency were evaluated. We concluded the JOWS is one of the most practicable borehole seismic source for oil field survey with following features.(1) Seismic wave generation is quite repeatable and stable. The generated seismic wave can penetrate more than 600 m in the carbonate rocks.(2) The source tool is durable enough for 10,000 times shots.(3) The operation depth and temperature limits are more than 3,000 m and 150 deg C, respectively.(4) The electric requirement is very low. A commercial electric source of 100 V AC (700 W) is sufficient for operation.