Abstract

Modern drilling techniques now have capabilities to drill tortuous well paths so that reserves previously considered inaccessible can be recovered. Often, however, the wellbores will require specialized drilling tools and considerable planning in order to drill through depleted sands or problematic formations. In many of these cases, the liner cannot be run to bottom. When this situation occurs, therequired remedial work along with the resulting delays to first production can cost millions of dollars.

This paper will discuss an expandable liner hanger system that has been developed to address these problems by allowing drill-in of the liner through tight or collapsed formations in previously drilled holes, and in some cases, can be drilled in to make a new hole. The considerations for drilling with the liner hanger system include:

  1. ROP (rate of penetration)

  2. Torque (surface, at bit and through hanger system)

  3. WOB (weight on bit)

  4. Circulation rate

  5. Design of drill bit.

These factors must be considered to anticipate how the forces will act on the liner hanger system. In addition to the liner drill-in application, the paper will discuss the planning involved to successfully drill a new hole with the liner as an integral part of the drilling assembly.

The above applications are planned, but another drill-in application can result when running a liner through a weak or problem formation. Although the installation had not been planned originally as a drill-in, the liner hanger still must withstand similar forces.

The drill in liner hanger was developed using Finite Element Analysis (FEA) to predict the failure mode of the hanger system. Prototype testing was conducted to confirm the FEA model, and finally, field use of the system was conducted to verify the model capabilities. A case history will illustrate the different types of formation problems in which the drill-in expandable liner hanger was used as well as the results that were gained.

Introduction

Advances in drill-in liner technology have provided operators with the ability to drill in casing and liners through depleted zones and other problem formations. To fully make use of the capabilities of this technology for liner installations, the liner hanger and its running tool must be designed to allow for high torque transmission, compressive and tensile loading, and high circulation rates. While conventional liner hangers have been upgraded to allow them to be used in drill-in applications, there have been reliability issues, many of which have been caused by the complex design of the liner hanger. Conventional hangers use slips and cone technology, which disturbs the flow path around the hanger and can cause cuttings to build up. This can restrict flow, which then can lead to increased equivalent circulating density (ECD). In the worst case scenarios, increased ECD can cause lost circulation, and there is also the possibility that this condition can preset the hanger or packer mechanically.

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