As more operators wish to stimulate horizontal wells with liners, they also find some of the difficulties. This paper discusses a new system that helps prevent a mechanically-operated packer from setting prematurely above a deviated or horizontal liner without interfering with packer operation in the liner. This system makes liner completions in horizontal wells more desirable and economical by helping eliminate a common mechanical problem. Preliminary testing and North Sea field case histories illustrate the role and success of this new system.
Many operators are discovering the flexibility and control offered by horizontal liner completions. Even though horizontal liner completions offer better stimulation possibilities than other types of horizontal well completions, liners have posed some difficulties for running in tools needed to isolate and treat zones (Figure 1). For example I Stagg and Reiley note I "While the rate benefits of horizontal completions are being confirmed around the globe, there is also universal concern over both the mechanics and the requirements of horizontal well completions."1Another author explains, "Stimulation of horizontal wells has not been widely applied for a variety of reasons: lack of zone isolation, little or unreliable skin information or a lack of a mechanical means to do the treatment."2
As more operators recognize the need to stimulate horizontal wells to realize the full potential of the reservoir, the need to modify tools and technology to address the special needs of horizontal wells becomes apparent. This paper addresses the concerns of the operator wishing for a safe, mechanical means of stimulating a horizontal well completed with a liner. This presentation reviews some of the concerns that led to the development of a new locking system for a retrievable packer, and explains the system operation and benefits. Reviews of the testing and case histories illustrate the capabilities of the system.
This section outlines some of the difficulties experienced in the field before the development of the locking system. Difficulties with workstring drag and torque or the liner itself hinder some stimulation treatments in horizontal wells with liners.
Workstring Drag. As extended reach and horizontal drilling push farther from the vertical borehole, liner completions move farther down the deviated section (radius) of the well. In these deep liner completions, workstring drag in the radius above the liner may cause mechanically-set packers to operate prematurely. For example, some jobs take 100,000 lb to push the workstring through the horizontal section. Such a great load can cause a packer designed to work in a 7 in. liner to move accidentally to the set position while going around the radius bend in 9 5/B in. casing, for example.
Greenip explains, "Casing loads in an extended reach well or a horizontal well are no different than those developed in a conventional oil or gas well. There is, however, a distinct difference in the magnitude of those loads. Because of this difference, casing string design for these applications frequently requires structural considerations such as bending and torque.