This paper presents a holistic model describing the relationship between the state of the hoop stress in a given well and the selection of lost circulation treatments. While some losses are vugular, the majority of lost returns events are due to the propagation of a fracture that develops when the borehole pressure overcomes the total hoop stress, which is the stress holding the hole closed. Although methods such as casing drilling, lost circulation pills or continuous fracture sealing fluids appear dissimilar, each stops losses by modifying the hoop stress. If a treatment does not modify the stress holding the hole closed, it does not change the pressure at which the borehole will open. This unifying concept is not always apparent to engineers and operations personnel since treatments are described to act in ways as diverse and seemingly unrelated as tip plugging, sealing, smearing, etc. Consequently, those who develop and execute new treatments may not be asking important questions that could further improve treatment performance and operational practices. In the proposed model, the potential state of the hoop stress is placed on a single pathway that is divided into four distinct regimes. At one end of the spectrum are those treatments that prevent losses by simply ensuring that the ideal hoop stress predicted by Kirsch is preserved. At the other end of the spectrum are severely depleted wells where treatments must achieve very large increases in hoop stress. Common industry treatments are categorized by the hoop stress regime in which they are applicable, and the conceptual limit to which each might enhance integrity is discussed. The authors?purpose in describing these concepts and treatments within a holistic hoop stress continuum is to improve treatment selection, facilitate field diagnostics, and highlight the need for further research in some areas.
展开▼
