While-Drilling ‘Shield’ Stabilizes Eagle Ford Wells, Eliminates Casing String
Many Eagle Ford wells, particularly assets in the deeper northeast portion of the play, require mud densities higher than the fracture gradient of the overlying Wilcox sandstone. Accordingly, three-string casing designs have been required to isolate the fragile Wilcox. However, as illustrated in one two-string well design, significant gas influx encountered while drilling the lateral production section required higher-than programmed (13.2-13.5 lb/gal) mud weight. Consequently, the operator encountered total lost circulation in the Wilcox while attempting to place a high-density mud cap to assist in the overpressured Eagle Ford. The subsequent wellbore instability caused by the lost circulation event resulted in significant nonproductive time (NPT) and uncontrolled mud losses.
This paper discusses the application of a proactive wellbore shielding technology that enabled the operator to eliminate lost circulation and the NPT associated with whole mud losses and influxes, and allowed for the elimination of an intermediate casing string on subsequent wells (over 45 wells to date). The core of the technology is an ultra-low invasive additive that forms a low-permeability barrier over the pores and microfractures in mechanically weak, highly depleted formations.
The authors will explain how the technology has allowed Eagle Ford wells to be drilled total depth (TD) with mud weights greater than the maximum density predicted without the need of intermediate casing. Direct offset data analysis, including comparative NPT events, mud weights, lost volumes and tripping times, will be discussed to rationalize the average estimated savings of $500,000/well.