As openhole completions become increasingly more complex, the need to create annular zone isolation within the borehole becomes critical for effective production or injection. Intelligent completions using gravel packs and stand-alone screens across the payzone are becoming a reality, with positive zone isolation a necessity. Historically, creating zone isolation within openhole completions has required a relatively complicated process, utilizing External Casing Packers (ECPs) that must be inflated during the completion installation. As long-term applications require cement inflation to minimize adverse effects on the packer, the installation process is further complicated, especially in highly deviated and horizontal wellbores.
Utilizing the latest packer construction and materials technology, a non-inflatable openhole packer system has been developed which simplifies the installation operation and creates a positive annular seal, even in non-circular wellbores, while reducing overall risk to the operator. Composite material fabrication allows the mechanical packing element of the packer to expand and seal in irregular-shaped holes (washouts), which have proven difficult to effectively seal using conventional technology. The packer has been designed with a hydrostatic pressure driven setting mechanism, allowing one-trip installations utilizing a shifting tool run on the bottom of the inner workstring. Used in conjunction with other emerging technologies, this new zonal isolation system is compatible with horizontal gravel packing operations, allowing the packers to be expanded against the borehole wall after the gravel pack is displaced.
This paper will describe the collaborative effort between a key North Sea operator and major service company in developing a simplified and reliable method to create openhole zone isolation. The packer and system design process will be reviewed along with a discussion of the verification-testing program used to validate the design. A summary of actual field applications employing this new system will also be presented, along with technical and operational comparisons to traditional isolation methods.
Introduction
Modern, advanced openhole completions generally have requirements for zonal isolation in the liner/openhole annulus. Annular isolation is critical to allow certain sections of the openhole completion to be closed off to production in the event of future gas or water encroachment, or to mitigate annular flow in stand-alone screen or slotted-liner applications. Most wells start to produce water/gas after some time of production and internal and external shut off options are important to maximize production of hydrocarbons. Injection profile modification may also be possible if there is effective zone isolation. Internal shut off in the liner is normally done with mechanical plugs or cement, while external liner shut off is traditionally done with cement or ECPs. Openhole completions utilizing stand-alone screens or screens installed with gravel packs combined with external zone isolation have large potential if the zone isolation method is effective. This is especially applicable for layered reservoirs with different reservoir properties.
In late 1999 a joint development project was initiated between Statoil and Baker Oil Tools to investigate a simplified, low risk method of obtaining openhole zone isolation. Openhole horizontal completions using conventional means for isolation are a growing trend1. Past means to isolate against the borehole have been limited to ECPs, as no other viable form of sealing mechanism was available. Cemented casing strings in horizontal applications have not been widely viewed as an option in long, horizontal wells due to difficulty in efficient mud displacement.
