In the past, a favored approach may have been used to treat most or all lost circulation incidents. However, improvements in understanding all aspects of lost circulation show that the “favored approach” method can be technically unwise today. The delineation of fracture geometry induced during drilling, based on rock properties, may point out significant differences in the length and width and severity of anticipated induced fractures. Major differences in permeability between shale, sandstone and vugular limestone also show immediately that “one-size-fits-all” solutions are not going to be effective or efficient. When possible, these types of information need to be incorporated into any plan for controlling lost circulation.
Lost circulation is a principal culprit in drilling non-productive time (NPT). Generally speaking, the drilling industry handles lost circulation much as it did many years ago, but new modeling and operational techniques are changing industry perceptions. The petroleum industry has invested a significant effort into understanding the mechanisms behind lost circulation, developing new tools to help locate the thief zone, and implementing new steps to minimize or eliminate this problem.
Controlling loss of circulation during well construction is more than just selecting the proper type of lost circulation material (LCM). A fully engineered wellbore stress management (WSM) approach is required. During the planning phase, this approach incorporates borehole stability analysis, equivalent circulating density (ECD) modeling, leak-off flow-path geometry modeling, plus drilling fluid and LCM material selection to help minimize effects on ECD.
During the execution phase, real-time hydraulics modeling, pressure-while-drilling (PWD) data, connection flow monitoring techniques, and timely application of LCM and treatments are proving to minimize and in some cases eliminate losses in high-risk areas.