Improving Well Productivity through Openhole Frac-Pack Completion Design

Abstract

Abstract Formation damage due to fines migration after the onset of water production presents a major technical challenge for many sandstone reservoirs around the globe. Oftentimes, significant productivity impairment is observed shortly after water breakthrough. This is particularly true for the Chad Doba basin lower "M" and "A" Sand reservoirs where studies have shown that a major contributor to this damage mechanism is the fluid velocity near the wellbore. As a result, exponential decline in productivity index is typically observed over very short periods. To arrest the productivity impairment, various completion techniques were evaluated for ways to reduce the velocity of the produced fluids near the borehole. Typical completion designs employed to date have been cased hole gravel packs (including frac-packs) which enhances the velocity profile of the well as produced fluids converge to the perforations. Maximizing the reservoir to the wellbore interface reduces the velocity profile and conceptually prolongs the onset of formation damage caused by fines migration. Based on that conceptual model, openhole completion techniques were evaluated for feasibility. Upon analyzing the geology of the selected candidate, it became apparent that fracturing the formation was possible as it was a relatively thin amalgamated sand package. As a result, the openhole frac-pack concept became a practical option as it results in the lowest velocity completion possible by maximizing the reservoir surface flow area. Openhole frac-pack completion activities were executed in mid-2009 and well productivity has been sustained even after water breakthrough. This paper reviews initial openhole frac-pack design concepts, execution lessons learned, and well productivity performance.