Application of acoustic emission, anisotropy of acoustic velocity and palaeomagnetie technology to determine in-situ stress in tight sands

Abstract

In-situ stress is an important basic parameter for well path optimization, hydraulic fracturing design, sand control and safe drilling mud window design. Tradition in-situ stress determination methods include lab and field tests. laboratory in-situ stress experiments became more and more sophisticated by incorporating methods known from disciplines like seismology, acoustic emission and non-destructive testing. However, most of lab in-situ stress experiments such as differential strain analysis, and acoustic emission et al., only can only judge in-situ stress magnitude or orientation. Moreover, it’s expensive and time-consuming for core samples preparation, processing and conduct in-situ stress experiments. Therefore, improve experimental accuracy and speed with low cost is highly desirable. In this paper, the combination of acoustic emission, anisotropy of acoustic velocity and palaeomagnetie technology to determine in-situ stress magnitude and orientation is proposed. Anisotropy of acoustic velocity method is applied to determine the direction of the maximum principle stress with respect to the master orientation line. The geographic orientation of cores is calibrated by using viscous remanent magnetization component. Then, the geographic orientations of the maximum and minor principal in-situ stresses are determined, which can guide the direction of drilled cores in following acoustic emission experiments. The in-situ stress measurement using Kaiser effect in maximum and minimum principal in-situ stress direction under confining pressures with the same depth was performed, which can simulate the original in-situ stress condition of rock samples and decrease the number of drilled cores. Eight in-situ stress test points at different depth in tight sands of Changqing oilfield, Ordos Basin, China are examined to validate the accuracy of this approach. The results demonstrate that the calculated results based on the experiments are in good accordance with mini-frac measurements, which provide a good tool for drilling and hydraulic fracturing stimulation design. © 2017 by Korean Society for Rock Mechanics