The unparalleled spread and variety of completions in use by the industry have clouded the selection of suitable completion and best fracturing strategies for optimizing productivity of hydraulically fractured horizontal wells. There also exists a gap in our understanding of the mechanics of fracture initiation and extension in horizontal wells. This has resulted in uncertainty in our response to large variations observed within and between different fracturing stages in the same horizontal well, and in fact within the reservoir.
This paper is based on review of many horizontal well hydraulic fractures. It includes a discussion of multiple completion options for both open and cased holes. It shows that in open hole completions there is strong tendency for fractures to initially grow axially (longitudinally) before re-orienting to become perpendicular to the least in-situ principal stress. This can cause fracture extension across open-hole packers and possibility of randomly located transverse fractures (well orientation permitting). Infrequent screen-outs usually occur within the open hole section itself. There is evidence indicating that the sealing balls used for separating different fracturing stages may sometimes break during the treatment. This may prohibit fracturing all well segments, and may also interfere with production. In cases of open hole fractures created by hydrajetting techniques one of the issues is propensity to proppant flowback.
In cased hole completions the tendency for axial initiation and early growth still exists. One of the popular techniques is creation of multiple closely-spaced limited entry fractures within each isolated wellbore interval. Treatment data shows that many of these fractures soon join and coalesce towards a single fracture. Furthermore, proppant and fluid have different distributions between various perforations. The issues with techniques based on hydra-jetting include inadequate perforations, hardware problems, and tendency for proppant flowback.