Development of the hybrid rotary steerable system and embedded drilling system for the shallow depth drilling

Abstract

Recently, the portion of unconventional resources in natural-gas is constantly increasing compared to conventional resources. To exploit unconventional resources such as shale gas and coal bed methane (CBM), directional drilling and hydraulic fracturing technologies are required. For directional drilling, the steering angle per 100ft is one of the major issues due to the drilling period and its costs. In this thesis, I briefly review different types of directional drilling methods and propose a new hybrid-type rotary steerable system (RSS). The hybrid RSS mechanism shows better performance in steerability by virtue of hybridizing two different conventional RSS types. This is made possible by designing the hybrid pad using hydraulic cylinders. The advantages of the designed system are demonstrated by a prototype test and a geo-block drilling test. In addition, existing drilling equipment has a limit in that large equipment such as the rig or mud circulation system must be accompanied, making it difficult to apply in space environment or polar region where large equipment can not accompanied. With focus on mobility, we have developed a drilling system which can be drilled by itself without any additional mud circulation system, rig, or pipelines. The system was constructed by mimicking the digging pattern of African mole-rat, and a neck mechanism for direction control and a leg mechanism for walking and removing soil particles were proposed. The drilling performance is demonstrated on Autoclaved Lightweight Concrete (ALC) blocks with compressive strength of 4 MPa. In addition, the system is partially fixed in the borehole during excavation, and a friction model for the system is proposed to obtain the force and requirements for the locking mechanism.