Abstract

Multiple-stage fracturing is a very common practice, especially in reservoirs with microDarcy permeability. The process of perforating, fracturing, and setting plugs has been performed for many years and has both advantages and disadvantages. Coiled tubing (CT) completion methods have increased completion efficiencies but can have limitations as well. Though multistage tools placed in the casing string have become a standard completion practice in horizontal completions, little has been done in vertical, cemented wellbores. As multiple wells drilled on single pads become more common, increased economic completion efficiencies are necessary.

To address the increasing need for completion efficiency, an alternate method of multiple completions was tested in several vertical wellbores. The casing strings were conventionally cemented in place and ball-activated sliding sleeves were placed across target completion intervals. Failures in similar techniques can have catastrophic effects if the initial tool does not open. To address this issue, a new hydraulic-actuated sleeve was developed. It was successfully tested in multiple wellbores and performed as designed. Multiple fractures were completed in a continuous operation with excellent production results.

This completion process can provide an efficient method for multistage fracturing in conventional and unconventional reservoirs in either vertical or horizontal wellbores. It can be used on single-well completions or on multiwellpads.

This process provides an efficient, low-cost alternative to conventional multistage fracturing for vertical and horizontal wells.

Introduction

For decades, the standard method of multistage fracturing has been to perforate, frac, and set an isolation plug. Advances in CT fracturing have increased the efficiency for multiple completions that allow for deeper completions (Peak et al. 2007); however, eliminating perforating, wireline intervention, and problematic means of isolation from the completion process is still desired. The installation of sliding sleeves in casing strings, specifically ball-activated versions that enable the interventionless completion methods, is not new and has been common practice in openhole, horizontal applications (Vargus et al. 2008). However, there has been concern regarding if this type of system could be deployed in vertical, cemented wellbores. A new set of problems was identified with this completion method when cement was used as the method of zonal isolation. One specific challenge identified was how the interventionless process would be initiated. In past cemented applications, the cement was overdisplaced so that a wet shoe would be present, providing a flow path that enabled the initiation of the interventionless process. This was not an acceptable solution in many cases because of the downfalls of having a wet shoe (i.e., possible leak paths, lack of isolation, and no pressure integrity of the casing, etc). To address these issues, the development of a specialized hydraulic sliding sleeve, minor modifications to the remaining ball-activated sliding sleeves, and adjustments to the processes and procedures were required to enable an interventionless completion method for cemented applications.

Development of the specialized hydraulic sliding sleeve, changes to the existing ball-activated sliding sleeves, and all process and procedure changes were completed within six months. The system was installed and field tested with excellent results. Challenges included development of a new hydraulic sliding-sleeve design that allowed for proper tool operation with cement contamination and setting up the remaining equipment, process, and procedures to help ensure the sliding sleeve was not unintentionally opened. Four field trails were conducted to determine the operational accuracy of the sliding sleeves as well as the production results after the fracture treatments.

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