Recent Advances in Aphron Drilling Fluids

Abstract

TX 75083-3836, U.S.A., fax 1.972.952.9435. AbstractAphron drilling fluids are being used globally to drill through depleted reservoirs and other under-pressured zones. The primary features of these fluids are their unique low-shear rheology and aphrons (specially designed pressure-resistant microbubbles of air). However, how aphron drilling fluids work is not well understood, which limits acceptance of this technology, along with efforts to optimize the system's performance. Recently a study was undertaken under the auspices of the U.S. Department of Energy to gain some understanding of the workings of aphron drilling fluids. Those results are presented here.Various laboratory techniques were applied to determine the physicochemical properties of aphrons and other components in the fluid and how they affect flow through permeable and fractured media. These included wettability and surface tension, bubble stability, radial and dynamic flow visualization, and fluid displacement tests.One key discovery was that aphrons can survive compression to at least 4000 psig, whereas conventional bubbles do not survive long past a few hundred psig. When drilling fluid migrates into a loss zone under the drill bit, aphrons move faster than the surrounding liquid phase and quickly form a layer of bubbles at the fluid front. At the same time, the shear rate of the fluid continually decreases and the viscosity is rapidly rising. The combination of the bubble layer and the rapidly increasing viscosity of the liquid severely curtails fluid invasion. Another key finding of the study is that aphrons show little affinity for each other or for the mineral surfaces of the pore or fracture; consequently, the seal they form is soft and their lack of adhesion enables them to be flushed out easily during production.Depleted wells which are very expensive to drill underbalanced or with other remediation techniques can now be drilled overbalanced. This study has provided a sound technical basis for the success of aphron drilling fluids and is providing guidance on the way to run these fluids in the field to optimize their performance.

Effectiveness of Colloidal Gas Aphron Fluids Formulated with a Biosurfactant Enhanced by Silica Nanoparticles

“…The velocities of invading fluids tend to slow as a consequence of radial flow around the wellbore and the bridging action of the CGA bubbles. This causes their shear rates to decrease and viscosities to rise [73].…”

Herschel–Bulkley rheological parameters of lightweight colloidal gas aphron (CGA) based fluids

“…The potential of aphrons as components of drilling fluids rests in their ability to form a solid free, tough, and elastic internal bridge in pore networks or fractures to minimize deep invasion by means of air microbubbles (Belkin et al, 2005;Growcock et al, 2003). This microenvironment seal readily cleans up with reservoir flow-back as production is initiated, thereby reducing cost associated with stimulation processes (Growcock et al, 2006;Ivan et al, 2002). The use of CGAs as a drilling/completion fluid also presents several advantages.…”

“…The use of CGAs as a drilling/completion fluid also presents several advantages. The high carrying capacity, the minimum amount of fluid placed in the formation, and the excellent fluid recovery after treatment are some of the advantages that CGA based fluids present when used during operations (Brookey, 1998;Growcock et al, 2006). The major implementation of rheological parameters for evaluating drilling fluid behavior are in solving problems of hydraulic calculations, suspension of cuttings and hole cleaning (Arabloo et al, 2012b).…”

Pore-Scale Studies on the Stability of Microfoam and the Effect of Parameters on Its Bubble Size

“…Microfoam has a drainage half-life up to 24 hours, which shows good dynamic stability and coagulation stability [4] . Microfoam has strong toughness and deformability and it can match different sizes of pore channels, thus an effective plugging can be obtained [5] . It has been observed that microfoam fluid showed more stable frontal displacement and lower injection pressure as compared to polymer solutions [6] .…”