Stability of Microbubble-Based Drilling Fluids Under Downhole Conditions

Abstract

Colloidal gas aphrons (CGA) have the unique ability to form a bridge in the pores of reservoirs, which stops fluid invasion. Sizing microbubbles in accordance with the rock pore size distribution is imperative for effective sealing during drilling. The effects of time, temperature and pressure on the stability and size of the microbubbles needs to be better understood in order to design a fluid that will sufficiently block the pores of the formation for extended periods. In this study, the effects of time, pressure and temperature on the size of microbubbles and the stability of microbubble (CGA)-based drilling fluids were investigated. The change in the CGA diameter with time was determined by using a microscopic imaging technique. Effects of base fluid viscosity and surfactant concentration on the size and stability of the microbubbles were also investigated. Introduction CGA-based drilling fluids have been successfully used in high-angle and horizontal well drilling in highly depleted reservoirs(1). Microbubbles in CGA-based drilling fluids form a bridge in front of the pores of the rock. This bridge is believed to stabilize the rock while sustaining minimal damage to the formation. Stability of the microbubbles and how bubble size changes as a function of downhole conditions (i.e. temperature and pressure) are some of the major concerns associated with the application of CGA-based drilling fluids. A stable CGA structure requires maintaining an ideal film wall thickness of 4 to 10 microns(2). Another factor affecting CGA stability is the rate of transfer of the surfactant molecules between the viscous water shell and the bulk phase due to gravity drainage or temperature gradients. This leads to a surface tension gradient at the surface of the shell. As a result, the Marangoni Effect will counteract this deformation(3–4). Increasing the viscosity of the shell can help to minimize the transfer of surfactant molecules. Usually a biopolymer is added to adjust the shell viscosity(3). The third property that the CGA structure must have is low diffusivity, which is the ability of the air that is in the core to transfer to the aqueous shell. CGA bubble size and stability have been the subject of earlier studies(5–12). Longe(6) analyzed the bubble size distribution of CGAs for soil and groundwater decontamination applications. Longe's analyses included effects of surfactant concentration, surfactant type and electrolytes on the stability of the CGAs over the time. Jauregi et al.(7) also investigated the stability of CGAs as a function of surfactant concentration. Results from both studies indicated that the stability of CGAs increase with increasing surfactant concentration. Chaphalkar et al.(8) measured the size distribution of CGAs using a particle size analyzer. The CGAs were virtually non-existent after 20 minutes for three different types of surfactant. Roy et al.(9) reported similar results. Amiri and Woodburn(10) studied the rate of drainage, as well as the CGA bubble size, by recording the images of the CGAs over time. They reported that after 10 minutes, the bubble shape had changed from spheres to polyhedral structures.

Mathematical modeling of the Colloidal Gas Aphron transport through porous medium using the filtration theory

“…Recently, Aphron fluids have been successfully employed in drilling depleted reservoirs or formations which had previously experienced huge fluid losses (Brookey, 1998) (Ivan et al, 2001) (Ramirez et al, 2002) (Bjorndalen and Kuru, 2008). Brookey was the first one who introduced Aphrons for horizontal well drilling.…”

“…From the other hand, the costs which must paid for compressors and equipment employed in foam drilling operation eliminated in case of Aphron fluid drilling operation (White et al, 2003)There is no corrosion issues of drill string and related equipment in case of using Aphron drilling fluids, since most of air in the system is trapped in Aphron shell (Bjorndalen and Kuru, 2008).…”

“…In this type of drilling operation, fluid pressure must be maintained at a higher level than the formation pressure, but the pressure difference must not be so high to avoid fluid invasion into the formation rock (Belkin et al, 2005). Although more experimental investigation is carried out on Aphron fluid filtration and its related parameters (Sebba, 1987) (Brookey, 1998) (Ivan et al, 2001) (Ramirez et al, 2002) (Bjorndalen and Kuru, 2008), a few modeling works were carried out in the literature (Belkin et al, 2005), recently Alizadeh and Khamehch have published some works on the Aphron modeling and flow through porous medium (Alizadeh and Khamehchi, 2015a) (Alizadeh and Khamehchi, 2015b) (Alizadeh and Khamehchi, 2016a) (Alizadeh and Khamehchi, 2016b) (Alizadeh and Khamehchi, 2016c) When a solid free fluid is created due to environmental issues, the use of Aphron drilling fluids is considered. Bridging in the front of the porous media in near wellbore zone, in fractured or depleted reservoirs, reduces the formation damage and fluid depth of invasion into the formation.…”

Rheology, stability and filtration characteristics of Colloidal Gas Aphron fluids: Role of surfactant and polymer type

“…In dispersed micro bubbles, stability is defined as the rate of liquid separation from foam because there is no appreciable breakdown of the microbubbles until after a large volume of the liquid has drained from the CGA based fluids (Yan et al, 2005). Bjorndalen and Kuru (2008a) investigated the aphron drilling fluids stability under different conditions and parameters. They expressed that the base fluid viscosity has a significant effect on the stability, and an increase in base fluid viscosity will lead to greater stability.…”

“…Therefore, special additives should be added to the drilling fluids to create a filter cake around the well bore, thus filter loss into the formation is reduced and delayed (Kosynkin et al 2011). Srivatsa and Ziaja (2011) Although various characteristics of CGA based fluids have been reported by some researchers during the past decades (Bjorndalen and Kuru, 2008a;Arabloo et al, 2012a and2012b;Arabloo and Pordel Shahri, 2014;Ziaee et al, 2015), a comprehensive investigation on the stability, filtration and interpretation of the rheological model of CGA based fluids has not been fully studied. Highlighting the contribution of the article, in this study various surfactants and polymers are used to prepare the aphron-laden fluids.…”