Velocity or Checkshot Survey

Zero Offset Vertical Seismic Profile (ZVSP)

The unique geometry of a zero offset VSP allows for multiples, recorded above the depth of the deepest receiver, to be identified and removed. The end result is a zero-phase, primaries-only dataset. This dataset can be used to identify residual multiple reflections on the surface seismic data, as well as to phase and frequency match the surface seismic data to the zero-phase VSP.

Operation Highlights

• Improved time-depth relationship

• True wavelet corridor stack

• Multiple free corridor stack

• Identify surface seismic events as primary reflection or multiple reflections

• Identify depth at which seismic event intersects wellbore

• Depth prediction of seismic events ahead of the drill bit

• Improved vertical resolution compared to surface seismic data

• Wavelet extraction and wavelet shaping

• Phase determination and matching of surface seismic data

• Complex structure and wellbore deviation to allow for offset imaging with improved lateral resolution Attenuation studies (Q estimation)

• Extraction of parameters for enhanced surface seismic processing

Benefits

• Measured averaged and interval velocities and improved time-depth relationship

• Identify surface seismic events as primary reflections or multiple reflections

With a zero offset VSP, the energy source is placed a relatively short distance from the well. The downhole receiver spacing is usually denser than that used when recording a velocity survey. In addition to measuring the elapsed time for the surface-activated energy source pulse to travel to the geophone, as is done with a velocity survey, the VSP technique is used to record and interpret the seismic response that follows the first arrival pulse. The primary output from the zero offset VSP is a single stacked trace, which represents the acoustic response of the subsurface at the well location. This single trace, consisting of primary reflections called the corridor stack trace, is compared to the surface seismic data at the well location. The VSP receiver is placed downhole rather than on the surface to provide the following benefits:

Vertical Seismic Profile(VSP)

Down hole Seismic Surveys

• availability of special devices in receive modules for determining spatial orientation of geophones in the course of each recording cycle;

• the possibility to increase the number of acquisition module in the tool, interchangeability of modules;

• low level of intrinsic instrumental noise allowing measurement and recording weak seismic signals and utilize non-explosive low-energy seismic sources;

• availability in receive modules of controllable calibrators making it possible to monitor metrological characteristics of electronic measuring channels and parameters of geophones;

• small dimensions and weight of receive modules and availability in the modules of a powerful electromechanical clamping device minimizing the adverse effects of resonance of system “tool borehole wall” as well as of noise waves (mud wave, cable waves) on recored seismic vibrations;

• in order to reduce the time of clamping/freeing the modules, a possibility to simultaneously actuate up to 10 modules is provided;

• versatility of the hardware-software system providing for the opportunity of utilizing it various modifications of down hole seismic surveys, the possibility to test the entire complex, quality control of acquired data.

Equipment Specifications

The present-day level of development of seismic surveys is based on obtaining reliable information about structure and characteristics of the wave field. With this purpose, the company Asmary has conducted a big scope of research and development operations along with practical field acquisition operations for creation of equipment and instrumentation, methodological, algorithmic and software tools for best-quality performance of down hole seismic measurements. The Company has created the new multilevel multi-component tool for down hole seismic measurements. Operations are conducted in both onshore and offshore wells.

The main specific features of this tool

The available equipment capability makes it possible to arrange simultaneous operation of up to three crews working in different regions. For working in remote and had-to-reach areas, necessary equipment and personnel may be delivered on a helicopter. Depending on problems to solve and surface conditions, seismic signals may be excited by explosive or by down hole air guns. Down hole equipment makes it possible to conduct surveys in cased well and open hole with deviation up to 63. Surveys may be conducted in boreholes with diameter from 54 mm (thru-tubing operation) to 420 mm, a depths up to 7000 m, pressure up to 140 MPa and temperature up to 200C. The software used makes it possible to design optimal observation systems and perform quick-look data processing.

Down hole tool (VSP10*48)