Adel Sheshtawy and Marlin Howell
TRI-MAX Industries, Houston, Texas

ABSTRACT

Designing a well with reduced clearance between casing strings is a must for drilling deep offshore wells. The wider application of RCCP is hindered by the difficulties of drilling enlarged holes below the previous casing string, especially in directional and horizontal wells.

The EWD & ES tools are effective in reducing the cost of the RCCP well. They are the tools to encourage the wider application of RCCP in offshore and onshore wells.

The EWD shown in Figure 1 will drill cement inside the casing and continues to drill the required enlarged size hole immediately below the casing shoe. The ES will effectively stabilize the Bottom Hole Assembly (BHA) in vertical or directional enlarged hole as the Integral Blade Stabilizer (IBS) does in regular size hole.

This paper presents a recommended RCCP and describes the EWD and ES development and case histories of their application in RCCP and regular wells.

INTRODUCTION

The attempt to maximize production casing size in deep offshore wells while maintaining surface casing and BOP with sufficient pressure ratings, dictate the use of RCCP in these wells.

In today's oil & gas price/drilling cost challenging environments RCCP must be considered not only for deep water offshore wells, but also for other offshore and onshore wells.

John Barker in his paper "Wellbore Design with Reduced Clearance Between Casing Strings" presented detailed RCCP hole and casing sizes possible application. John Barker stated "The rules-of-thumb relied upon to determine the clearance between casing strings are often found to be conservative or out-of-date". We agree with his finding based on our study of ninety-eight RCCP and conventional wells. Our study shows, RCCP reduces well costs by ± 27 % compared to Conventional Casing Program (CCP) for 16,000ft wells. If all cost elements are considered such as casing weight, volumes of mud and cement, volume of cuttings (especially for wells drilled with oil base mud), BOP size and pressure rating, ROP, cost of downhole drilling and cementing tools, and rig size.

For RCCP, a pilot hole is drilled with a standard size bit, which passes through the drift diameter of the previous casing. The pilot hole is under-reamed to the required size. This procedure is the common approach especially for hole sizes 17 1/2" or larger. Bi-center tools (bi-center bit or RWD*) are commonly used for hole sizes smaller than 171/2".

The use of bi-center tools eliminates the disadvantages of the extra under-reaming time and the risk of lost arms or cones of the under-reamer in the hole.

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