Document Type : Article
Authors
1
School of Civil Engineering And Architecture, Henan University, Henan, 475004, Peoples Republic of China
2
- School of Civil Engineering And Architecture, Hen1 School of Civil Engineering And Architecture, Henan University, Henan, 475004, Peoples Republic of China - Engineering Research Center of Geothermal Resources Development Technology and Equipment, Ministry of Education, Jilin University, Changchun, 130026, China
3
School of Engineering and Technology, China University of Geosciences (Beijing), Beijing, 100083, P.R. China
Abstract
The Colloidal Gas Aphron (CGA) drilling fluid successfully solved the problems of serious lost circulation and reservoir damage that are faced by drilling in depleted oil/gas reservoirs and low-pressure areas. However, the lack of high-temperature resistance, salt and calcium resistance are the key problems that restrict its application in complex formations. This study provides an environmentally friendly and non-toxic CGA formula based on self-developed reagents. Microscopic tests showed that stable aphrons were successfully generated in 36%NaCl-CGA or 7.5%CaCl2-CGA aged at 150℃, with stabilization of ＞2 hours. The Herschel-Bulkely model accurately describes the rheological behavior of CGA fluids containing NaCl/CaCl2. The addition of NaCl increases CGA fluid viscosity, while CaCl2 is the opposite. However, CGA fluid maintains appropriate rheological parameters and shear thinning behavior, which means good cutting carrying capacity. With the addition of NaCl/CaCl2, CGA has low filtration volumes, which meets API requirements. NaCl/CaCl2 reduces the lubrication coefficient and increases the adhesion of the mud cake. Moreover, the anti-cuttings pollution ability of 150℃ aged CGA can reach 10%. CGA, 36%NaCl-CGA, and 7.5%CaCl2-CGA all have low linear expansion rates (<28%) and high rolling recovery rates (>84%). Therefore, the CGA system has good inhibitory performance and is compatible with easily hydrated formations.
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