VSP Processing and Interpretation

The VSP data processing technique and interpretation of the results include the following steps:

1. Pretreatment

• Entering static corrections for OM in the initial VSP data and control device;
• Entering static corrections calculated from the records of the control device;
• Correction of the waveform of the control device;
• Minimum-phase high-pass filtering to eliminate zero bias;
• Definition of the hodograph of the first arrivals;
• Suppression of harmonic noise and peak emissions;
• Determination of polarization parameters;
• The orientation of the three-component record is conversion to the PRT coordinate system.

The result of these procedures is a three-component wave field prepared for selection.

2. Kinematic processing

• Determination of the boundaries of the reservoirs by analyzing the interval velocity curve calculated from the hodographs of the adjacent reservoirs and using a priori information (including well logging data);
• Determination of reservoir velocities by optimizing model parameters using near-field traveltime curves;
• Correction of the obtained velocity model taking into account the absorbing characteristics of the medium and optimization according to the hodographs of the first arrivals of all points of excitation;
• Calculation of the vertical travel time curve of average speeds.

The result of kinematic processing is a reservoir model of the medium taking into account the anisotropy parameters, a vertical hodograph, and also curves of interval and average speeds.

3. Dynamic processing

• Wave selection - separation of the VSP wave field into regular waves and the field of residues (an iterative combined technique is used to improve the quality of the generated waves, including FK filtering and the POLICOR wave extraction method based on summing the traces with weights estimated by calculating multiple correlations);
• Deconvolution according to the shape of the incident wave (the calculated filters are then applied to all selected wave fields of the reflected longitudinal and converted waves);
• Entering kinematic corrections and obtaining the field of reflected waves brought to the vertical;
• Corridor summation and acquisition of a path of single reflections (LLP) on a time scale and depth scale;
• Obtaining acoustic impedance at a depth scale and comparing it and the LLP with GIS and CDP data.

4. Treatment of distant shots

• The construction of deep and temporary sections of the VSP-OGT on the reflected longitudinal waves.

The reflected waves migrate according to the model of the medium with anisotropy taking into account inclinometry, angles of exit to the point of reception, divergence, passage and angles of incidence at the boundary.

5. Interpretation of processing results

• Kinematic characteristics of the environment;
• Study of the absorbing characteristics of the section;
• Lithological and stratigraphic linking of GIS, OGT and VSP data;
• Evaluation of the signal shape of a section of an OGT section and deconvolution of a VSP-OGT section (reduction of a signal to a zero-phase form and an increase in the information content of an OGT section);
• Estimation of shear wave velocity anisotropy;
• Structural interpretation of VSP-OGT images of the near-wellbore space.