Abstract
Today, the drilling operators use the Colloidal Gas Aphron (CGA) fluids as a part of drilling fluids in their operations to reduce formation damages in low-pressure, mature or depleted reservoirs. In this paper, a Taguchi design of experiment (DOE) has been designed to analyse the effect of salinity, polymer and surfactant types and concentration on the stability of CGA fluids. Poly Anionic Cellulose (PacR) and Xanthan Gum (XG) polymers are employed as viscosifier; Hexadecyl Trimethyl Ammonium Bromide (HTAB) and Sodium Dodecyl Benzene Sulphonate (SDBS) have been also utilized as aphronizer. Moreover, bubble size distributions, rheological and filtration properties of aphronized fluids are investigated. According to the results, the polymer type has the highest effect, whereas the surfactant type has the lowest effect on the stability of CGA drilling fluid. It was also observed that increasing salinity in CGA fluid reduces the stability. Finally, it should be noted that the micro-bubbles generated with HTAB surfactant in an electrolyte system, are more stable than SDBS surfactant.
Highlights
Aphrons that are known as colloidal dispersed micro-bubbles, usually consist of a spherical core with an internal phase covered by a thin shell
As previously mentioned, L36 array Taguchi design of experiments (DOE) was adopted in this study to reduce the number of trials
36 samples were generated based on DOE and stability, density and initial volumetric fraction of micro-bubbles of the Colloidal Gas Aphron (CGA) drilling fluids were measured immediately after CGAs generation (Table 3)
Summary
Aphrons that are known as colloidal dispersed micro-bubbles (with size distribution between 10–100 microns), usually consist of a spherical core with an internal phase covered by a thin shell. The polymer is used to increase the viscosity of water and a surfactant is required to generate micro-bubbles by reducing surface tension of the base fluid. Save and Pangarkar [2] studied the effect of viscosity on CGA based fluids stability half-time and drain rate (the rate of drained liquid from CGA dispersion). Their study reported that, as the polymer and surfactant concentration increases, the yield point, plastic viscosity (which will be named in this paper as viscosity) and apparent viscosity of CGA based drilling fluids increase. The outputs of their research showed that a mixture of XG and SDS has a great performance in decreasing filtration loss and improvement of stability of CGAs. All the mentioned works have been performed on the water based CGAs, which is not proposed to be used in high temperature and shale formations. It should be mentioned that, the oil based Aphron is suitable for shale formation drilling because it does not cause shale instability; oil-based fluids are good lubricants, which reduces the drilling torque
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