New method eliminates lost returns
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abstract
This article describes a fluid system developed to build integrity continuously to prevent lost returns while drilling. The primary attributes of the fluid that enable this are high solids content and extremely high filtration rates, as reflected in API fluid loss tests. It is referred to here as a Drill and Stress Fluid (DSF). In field applications, DSF water-based systems appear to be effective over a wide range of conditions. Circulating pressures have been sustained that exceed integrity by 1.0 to 3.0 ppg without detectable losses in depleted formations with permeability ranging from 1 to 1,000 mD and pay zones of 50-700 ft (15-250 m) in length. The mechanism through which the DSF is believed to arrest the growth of lost returns fractures and build near-wellbore stress is described. Generalized design criteria for a DSF system are presented, and the assumed relationship between the design parameters and fluid performance is discussed. The results of the application of DSF are presented for eight wells, including post-treatment evaluation logs of the drilling-induced fractures created while building stress. Operational practices that facilitate the safe use of an extremely high-fluid-loss system with overbalance exceeding 2,000 psi are also discussed.
