Development of a Novel Hybrid-Type Rotary Steerable System for Directional Drilling
Unlike conventional resources, unconventional resources, such as shale gas and coal bed methane, are situated horizontally under geological formations. To exploit these resources, directional drilling and hydraulic fracturing technologies are required. In directional drilling, the dog leg severity (DLS), which indicates how much the angle changes while drilling 100 ft, is a major issue with respect to the cost and time of drilling. In this paper, we briefly review different types of directional drilling methods and propose a new hybrid-type rotary steerable system (RSS). DLS calculations based on three-point geometry for these systems are suggested. This hybrid RSS combining two conventional types of RSSs: point-the-bit and push-the-bit systems, achieves better steerability. The hybrid mechanism is implemented using hybrid pads with hydraulic cylinders and a spherical joint. The advantages of the proposed system are demonstrated by performing small-scale prototype and cement block drilling tests.
New Directions in Rotary Steerable Drilling
nology (next page). Local geology might dictate a complicated well trajectory, such as drilling around salt domes, salt tablets or salt sheets. Reservoir drainage or production from a particular well might improve if a well penetrated multiple fault blocks or was constructed horizontally to intersect fractures or to maximize wellbore surface area within the reservoir. A multilateral typically drains several reservoir compartments. Small compartments in mature fields can also be produced economically if directional wells are located skillfully. Operators drill extended-reach wells to reservoirs that cannot be exploited otherwise without unacceptable cost or environmental risk, for instance to drill from a surface location onshore to a bottomhole location offshore rather than constructing an artificial island. Drilling multiple wells from one surface location has been standard practice offshore for years and is now common in restricted onshore locations, like rain forests, for environmental protection. There are also instances in which the operator wants to drill a vertical wellbore, notably the deep well of the KTB Program (German Continental Deep Drilling Program), and uses a steering system to keep the hole straight.
A critical evaluation of unconventional gas recovery from the marcellus shale, northeastern United States
The Marcellus tight gas shale represents a significant resource within the northeastern United States. It is both a large reserve, with an estimated 30 to 300 TCF of recoverable gas, and is close to some of the largest prospective markets in the country. However, production is fraught with technological obstacles, the most significant of which include prospecting, access by drilling, stimulation, and recovery. Prospecting is difficult because viability of the reservoir relies both on the original gas in place and in the ability to access that gas through pre-existing fractures that may be developed through stimulation. Drilling is a challenge since drilling costs typically comprise 50% of the cost of the wells and access to the reservoir is improved with horizontal drilling which may access a longer productive zone within the reservoir than cheaper vertical wells. Finally, stimulation methods are necessary to improve gas yields and to reduce the environmental impacts of both consumptive water use and the subsequent problems of safe disposal of fracwater waste. We discuss the challenges involved in the economic recovery of gas from tight gas shales in general and the Marcellus in particular.