In petroleum exploration and production, mapping radial variations of formation velocities is of great significance in drilling induced fracture and determining rock mechanic properties, which are valuable for engineering measures, such as fracturing, wellbore stability evaluation, and optimal well completion.
The inversion methodologies are the main methods to determine radial wave velocity profiles employing dipole and multipole acoustic data. For monopole acoustic well logging, the calculation on arrival time of the waves is required in profiling the P-wave velocity, which is unstable and inaccurate in processing field data with noise to the most extent.
Recently, researchers from the Institute of Acoustics of the Chinese Academy of Sciences (IACAS) proposed a stepwise inversion method based on monopole acoustic well logging data to radially profile the near-borehole formation velocities. The inversion method did not require calculation on the arrival time of waves, thus mitigating the inaccuracy in processing field data with noises. In addition to profiling formation P-wave velocity, the proposed methodology also had an encouraging application in mapping formation S-wave velocity.
Instead of inverting the formation velocity variation and its corresponding radial position simultaneously as traditional methods do, researchers divided the inversion procedure into two steps: extracting the velocity array by semblance processing of contiguous receiver pairs of acoustic array data, and then getting the thickness of the layer (radial position) based on ray theory. The inversion results from Step 1 could be used to guide the operation and decide whether Step 2 was necessary.
Figure 1. The flow chart of the stepwise inversion method. (Image by IACAS)
The modelling-based inversion results and the application to field data (Figure 2) indicated the efficiency and accuracy of the stepwise inversion method. With its fast speed and stability in calculation, this work could provide real-time data processing results in the oilfield, which would be useful for engineering measures.
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Figure 2. Inversion results of P-and S-wave velocity variations from field data. (a) Radial profile of P-wave velocity variation (P-wave velocity ranges from 4000m/s to 6000m/s); (b) Radial profile of S-wave velocity variation (S-wave velocity ranges from 2400m/s to 3500m/s). (Image by IACAS)
The research, published in the Journal of Petroleum Science and Engineering, was supported by the National Natural Science Foundation of China (No.91630309, No.11574347, No.11774373, No.11734017).
Reference:
LIU Ying, CHEN Hao, LI Chao, HE Xiao, WANG Xiuming, Daryoush Habibi, Douglas Chai. Radial profiling of near-borehole formation velocities by a stepwise inversion of acoustic well logging data. Journal of Petroleum Science and Engineering, 2020: p. 107648. DOI: 10.1016/j.petrol.2020.107648.
Contact:
ZHOU Wenjia
Institute of Acoustics, Chinese Academy of Sciences, 100190 Beijing, China
E-mail: media@mail.ioa.ac.cn