Compaction Resistant Wellbore for Sand-Producing Wells
Authors: Shute D.M. , Kaiser T.M.V. , Munoz H. 
Published: March 2010

A common production strategy from heavy oil sands is to produce the sand with the oil to maintain, or even increase, the deliverability of the well. Where very high sand production is realized, the cumulative sand volume 'mined' from the reservoir can be very large. This can result in large vertical deformations relative to the elastic strain limit of steel and associated deformation of the liner through the producing interval. A new completion system has been developed to address the deformation associated with very high sand production wells. The Compaction Resistant Wellbore (CRW) was designed to absorb the axial compaction strain and improve structural capacity. Strain-absorbing tools accommodate axial deformation and preserve the elastic characteristics of the pipe. A new type of completion tool through the producing interval provides substantially increased compression strength and buckling resistance to distribute deformation to the strain-absorbing tools. Although the system is novel, it can be run with only slight modifications to conventional procedures.

Introduction

Cold heavy oil production with sand (CHOPS) has proven to be an effective strategy for increasing recovery rates to levels significantly beyond conventional practice. However, experience with this strategy also demonstrates that where the strategy is most successful, well life is often reduced by deformations due to sand production. Bent and buckled casing often compromises the pump and prevents well access to facilitate repair. Tension failures in the cap rock above the reservoir compromise pressure integrity, resulting in higher abandonment costs. While the improved productivity generally offsets the cost of such problems, there is substantial opportunity for improving the economic performance of the sand-producing strategy if the problems associated with reservoir compaction can be reduced or eliminated.

Much attention has been focused on compaction-induced problems over the past 20 years in the oil industry. Many issues have been characterized, and a variety of solutions have been proposed. In this paper, deformation mechanisms are reviewed, considered in the context of a high sand production strategy, and a solution for extending the life of such wells is presented. A case study of a high sand-producing field is reviewed, showing a history of well operation and the implementation of this approach for increasing the well life.

Background

Many modern production strategies in the oil industry achieve very high recovery rates in reservoirs where the void space containing the oil can be reduced by production. Examples include North Sea chalk reservoirs, like Valhall(1) and Ekofisk(2, 3), where compaction drive produces superior recovery rates. While production associated with compaction is a significant benefit, the cost associated with compaction is also high. Subsidence and casing deformation problems arising from compaction can be difficult and costly to characterize and mitigate(3–6). Completion performance is also a challenge because of the high compaction strain relative to the completion limits, often exceeding ten times the yield limit of steel.

One solution that has been proposed to solve this problem is to use slip joints in the casing or liner to absorb compaction strains so the well structure can accommodate axial deformation without exceeding tensile or compressive limits(7).