Slimhole Drilling and Coring - A New Approach

Abstract

fax 01-972.952-9435. AbstractOver the past years, slimhole drilling has proved to be a cost effective way of drilling certain exploration and exploitation wells. However, one of the major downsides to slimhole drilling are poor penetration rates as compared to conventional hole sizes. The paper presents the design and proof of a dual-body bit concept which gives the user the possibility to change the bit's characteristics (profile, cutting structure, hydraulics, etc.) and thus alter its performance significantly without the necessity of a round trip. Additionally, with this approach, the purpose of the drilling mode can be easily switched from coring to full hole drilling and vice versa, This is done, similar to the process of adjusting the bit, from the surface with the use of a conventional wireline assembly, which gives a reasonable potential for improvement for the overall drilling process.The idea for this new drilling approach emerged from a research project that initially had the aim of filling the gap of optimal slimhole PDC drill and core bit design. The studies confirmed that there is a limitation for the use of PDCS when drilling certain hard, heterogeneous multi-layered formations, no matter how sophisticated the bit design itself might be.' After exhausting all conventional slimhole PDC bit designs it became evident that an entire new paradigm was needed, The mining industry had experimented with the two body bit, but had never seriously exploited the concept for sedimentary drilling. Today the possibility of easily running the inner bit and retrieving it is standard technology. This project has taken the mining technology to a higher level by introducing the concept of dynamically changing the properties of the bit downhole (without tripping) to optimize penetration rate performance for all kind of sedimentary rocks.Results from an in-house laboratory testing series are included, documenting first dual body bit design efforts, and performances achieved.

An Experimental Investigation of Drilling Performance Improvement Using Reaming While Drilling

“…There are several RWD techniques, one of which is the dualbody bits as is discussed in this work. The RWD topic has been also considered for slim-hole wireline continuous core drilling [12][13][14]. Dual-body bits have several provided several advantages in improving the drilling performance including:…”

“…• Providing a sufficiently large borehole and more complex completion string access to reservoir has several advantages for exploration and production wells [15]. Despite the advantages, the deployment of two cutting tools (i.e., the pilot bit and reamer) in the bottomhole assembly (BHA) leads to additional drill-string vibrations because the weight and torque will be distributed between the pilot and reamer [10][11][12][13][14][15][16]. Therefore, hole enlargement generally suffers from downhole tool failures, shorter BHA life-time, lower drilling performance, poor borehole quality, and compromised directional efficiency [11].…”