Improving Well Productivity through Openhole Frac-Pack Completion Design

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. Doba

Treatment of Oil Production Data under Fines Migration and Productivity Decline

“…To account for the velocity and connate water saturation dependencies, we introduce two critical pore radii, r c (U) and r c (S wi ), defined in Equations ( 3) and (4).…”

“…The model exhibits stabilisation of the Figure 11 shows the growth of the skin factor against the total produced oil, presented as pore volumes (PV). For this data, oil is produced from six Upper Cretaceous fields in the Doba Basin in Chad, Central Africa [4]. The rock is an extremely unconsolidated sandstone consisting of 4% fine content, of which more than 90% have been identified as kaolinite.…”

“…Fines migration has been shown to be a significant factor in various areas of petroleum, water, and environmental engineering. Field studies have demonstrated the impact of fines migration on both the injectivity [1][2][3] and productivity [4,5] of wells during the extraction of oil and gas. Other situations in which fines migration has been shown to be important include during fluid leak-off when drilling oil and gas wells [6], during the storage of fresh water in shallow aquifers [7], during CO 2 geo-sequestration [8], with methane production from coal beds [9], or as a contributing factor to contaminant transport in shallow water aquifers [10,11].…”

First Installation of Alternate Path Openhole Packer Providing True Zonal Isolation in Openhole Gravel Packs

“…Although the formation grain sizes are typically large, mobile fines tend to plug the cased hole gravel packs once water cut increases. There has been recent success with OHGP and openhole FP (Kamps 2010) completions preventing fines migration and plugging problems, resulting in the highest productivity wells in the field.…”