A laboratory investigation of the factors controlling the filtration loss when drilling with colloidal gas aphron (CGA) fluids H.N. Bjorndalen a , W.E. Jossy a , J.M. Alvarez a , E. Kuru b,n a Alberta Research Council 1 , 250 Karl Clark Road, Edmonton, AB, Canada T6N 1E4 b School of Mining and Petroleum Engineering, Markin-CNRL Natural Resources Engineering Facility, University of Alberta, 3-133, Edmonton, AB, Canada T6G 2W2 article info Article history: Received 4 June 2010 Accepted 4 March 2014 Available online 24 March 2014 Keywords: colloidal gas aphrons drilling fluid filtration loss abstract The colloidal gas aphron (CGA) drilling fluids are designed to minimize formation damage by blocking pores of the rock with microbubbles and reducing the filtration loss. In order to gain a better understanding of the factors controlling the pore blocking mechanisms of microbubbles, a set of core flooding experiments was conducted by using various CGA drilling fluid formulations. The differential pressure drop along the sand-pack was measured. Effects of CGA fluid composition, flow rates, type of reservoir saturating fluids, permeability and wettability on the resistance to CGA drilling fluid flow through porous media (i.e., pressure drop due to CGA fluid flow) have been investigated. An increasing resistance to flow of CGA drilling fluids through porous media was observed as more CGA fluid was injected. Results confirmed that CGA microbubble build-up across the pore structure could establish an effective seal for controlling filtration loss. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Like regular foams, colloidal gas aphrons (CGAs) are typically composed of a gaseous core but unlike foams, CGA's have a thin aqueous protective shell. CGA's are composed of an inner shell as well as an outer shell. Fig. 1 illustrates the structure of the aphron on a molecular level. The two shells are separated by a viscous water phase. The inner shell consists of surfactant molecules that are hydrophobic inwards. This layer supports and separates the air core from the viscous layer. The outer shell which also supports the viscous layer is hydrophobic outwards. Since this bubble is in contact with the bulk water it is only natural to believe that there is another layer in which the surfactant molecules are hydrophobic inwards. This indicates that there is a region in between the aphron outer shell and the bulk phase layer where a hydrophobic globule will be comfortable and adhere to the gas aphron (Sebba, 1987). CGA flow and blockage in porous media has not been studied extensively. Rather extensive literature, however, can be found on the on the flow of conventional foams in porous media (Smith et al., 1969; Albrecht and Marsden, 1970; Aarra and Skauge, 1994; Khalil and Asghari, 2006). Although CGA's and foams show structural differences, some of the results from foam flow in porous media studies can be helpful to understand the CGA's behavior. Therefore, a brief discussion of the literature on the use foam in porous media is presented here. Much of the conventional foam research has focused on foam applications for enhancing oil recovery. As well, there is a large focus on the creation of foams in the porous media itself (Yang and Reed, 1989; Sanchez and Hazlett, 1992). Bernard and Holm (1964) studied the effect of foam on the reduction of gas permeability while Bernard et al. (1965) studied the effect of foam of the reduction of water permeability. They found that foam effectively plugged the gas flow in the reservoir. Albrecht and Marsden (1970) studied foam blocking and found that with an increase in surfactant concentration, the blocking effect was greater. Manlowe and Radke (1990) investigated the effect of oil on foam stability in porous media using an etched glass model. They found that the lack of stability of the foam when in contact with oil is determined by the strength of the film in between the bubble and the oil. Foam gel combinations have also been studied to enhance blocking (Wassmuth et al., 2000; Romero and Kantzas, 2004; Asghari et al., 2005; Romero-Zeron and Kantzas, 2006). Wassmuth et al. (2000) investigated the blocking ability of polymer enhanced foam and foam gels. They found that with an increase in the polymer viscosity, the blocking ability increased. Dalland and Hanssen (1997) also compared foams, polymer enhanced foams and foam gels. They found that the polymer enhanced foams Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/petrol Journal of Petroleum Science and Engineering http://dx.doi.org/10.1016/j.petrol.2014.03.003 0920-4105/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. 1 Now Alberta Innovates. Journal of Petroleum Science and Engineering 117 (2014) 1–7