ABSTRACT
Aiming at the problems of high brittleness, low tensile strength, poor impact resistance and fracture resistance of oil well cement stone, three kinds of inorganic fibers with high modulus, high strength and good dispersibility were selected to toughen the cement stone according to the toughening mechanism of the fiber and the demand of practical engineering application. The optimum ratio of three kinds of fibers was determined by orthogonal test, and the multiscale fiber toughener BCE-230S was invented. Effects of different additions and different ages on mechanical properties of oil well cement were investigated. The experimental results show that the BCE-230S has good toughening effect on oil well cement stone. When the fiber content is 5%, under the condition of 80 °C curing 7 days, compared with blank control, the tensile strength increased by 23.17%, the compressive strength increased by 2.42%, the elastic modulus decreased by 16.54% and the impact power increased by 22.57%.This toughener has been applied in low permeability wells a dozen times in Jidong Oilfield, with high cementing quality and smooth fracturing.
The long-term effective interlayer isolation capability of the cement sheath in the wellbore is not only the premise for developing and increasing production in oil and gas fields, but also for guaranteeing the long-term production life of oil and gas wells( Liu, RG, Zhou, SM, Tao, Q Yan, PY, Ding, SD, 2015). However, set cement is a brittle material with inherent microscopic defects, such as, poor deformation capacity, low tensile strength, poor impact resistance, and poor fracture resistance (Li, M, Yang, YJ, Guo, XY, 2015; Cheng, RC, Bu, YH, Wang, Rh, 2006).In the processes associated with subsequent construction, such as pressure testing, perforation, fracturing and mining, due to the influence of temperature and pressure changes, impact, vibration, etc., the cement sheath is prone to rupture, resulting in a loss of mechanical integrity. It will result in annulus pressure, annular gas migration, and the well may even be abandoned (Zou, S, Zou, JL, Zhao, BH, Shi, LL, Yang, KP, Liu, AP, 2017;Zou, S, Zou, JL, Zhao, BH, Shi, LL, Yang, KP, Liu, AP, 2017; Hua, SD, Yao, X, 2007). Therefore, it is particularly important to improve the mechanical properties of oil well cement.
