Simultaneous Drilling and Reaming with Fixed Blade Reamers

Abstract

Abstract Deep well drilling programs often require the use of multiple casings or liners. Designing these wells require compromises between using the smallest surface hole possible to minimize tubular costs and maintaining the largest hole possible to allow for contingencies and for the optimum completion design. The conflict between these two considerations can be resolved somewhat by nesting the casing strings with the minimum clearance between them. Unfortunately this often requires that the section drilled below a casing string be reamed to a larger diameter than the casing ID. The reaming process is often fraught with many inefficiencies. This paper describes a technique for simultaneously drilling and reaming with a bi-center reamer run on a stabilized assembly above a pilot bit. The successful use of the technique in three field wells is reported. Introduction The geological environment of many deep wells may dictate that as many as six or more strings of casing be set to reach TD. The most economical way to accommodate these casing strings is to start with the smallest acceptable production casing and nest the other strings as closely as possible. Often a tighter nesting can be achieved if the open hole below some strings is enlarged to a diameter greater than the previous casing ID. For example, the largest bit that can be run through 13–3/8" casing is 12–1/4". This limits the next casing string to 9–5/8". but by enlarging the hole below the 13–3/8" casing to 13–3/4" the next casing can be an 11–3/4" liner. Similarly enlarging the hole below the 11–3/4" liner to 12–1/4" allows a 9–5/8" liner to be run and cemented without difficulty. Three different techniques are used to drill and enlarge the open hole sections. The first technique is simply to drill a pilot hole to the next casing setting depth and then open the hole with an expandable arm underreamer. This technique often takes as long or longer to ream the hole to its final diameter as it took to drill the pilot hole. The second technique combines the drilling and underreaming into a single operation, but there have been difficulties with downhole tool failures (particularly the loss of underreamer arms), drillstring and MWD tool failures. and slow penetration rates. The third technique uses a bi-center bit to drill a hole larger than the casing ID. This technique seems to be the most cost effective, but it is not trouble free either. Bicenter bits run on rotary drilling assemblies are weight limited because of deviation tendencies and rotary speed limited because of the inability to stabilize them properly. There are still drillstring failures, slow penetration rates, cases where the reamed interval is not as large as expected, and occurrences of abnormal tool wear (particularly on MWD tools). This paper presents the results of combining the simultaneous drilling and reaming concept with the bi-center bit concept to provide a more efficient drilling procedure. It is a continuation and extension of the work presented by Kalloo. First, bi-center bit design concepts are reviewed, then the technical considerations for the proposed procedure are presented, and finally the results of applying the technology in three field wells are reviewed. P. 251