3D surface seismic processing.

Main items

  1. Critical situation when mature oil deposits are exhausted leads to the need for extraction of residual oil deposits from old reservoirs and development of new small reservoirs characterized by complicated geological structure.
  2. Solution of the specified problem requests for more detailed and accurate models of productive layers to be recovered from seismic exploration data.
  3. Both modern surface seismic exploration and VSP technologies feature a set of principal drawbacks constraining further increase in accuracy and resolution of processing results.
  4. Modern 3D acquisition geometries 2D+VSP and 3D+VSP provide for integration of the surface seismic and VSP surveys allowing to solve the identified problems.

Layer velocities map including a permafrost area

Drawbacks of Seismic Exploration on the Surface (SES)

  1. Lack of information about actual P and S waves velocity distribution
  2. Exact information about signature is not available
  3. Imaging procedures is based on sub-horizontal velocity model

Relation between SES, VSP and 3D+VSP

Conclusions
Two applications of combined surface and downhole acquisition geometries are described. They are called “2D+VSP” and “3D+VSP”. The advantages are based on the use of downhole arrival times and signatures to improve surface seismic data. The case stories approve the proclaimed features of proposed technology.

  1. Seismic prospecting on the surface solves main modern exploration problems, but contains fundamental limitations:
    • inaccurate velocity model
    • inaccurate signature determination
    • simplified model for migration.
  2. SP provides accurate solutions to tie surface reflections to logs and investigation of near borehole space for small offsets. But all modifications of VSP including 2D VSP and 3D VSP contain sufficient uncompensatable errors due to insymmetrical acquisition geometry..
  3. Combined acquisition geometries 2D+VSP and 3D+VSP provides more accurate solutions for next problems:
    • adjustment of velocity models
    • estimation of true signature
    • model-based vector migration.
  4. 3D acqusition systems and model-based processing may be recommended as one of leading developments for improvement of resolution and accuracy of seismic exploration to meet challenges of oil industry.
Compasition of processing results by means of 3D+VSP technique and ordinary 3D technique
Modern state of hydrocarbon resources and exploitation temps of oil deposits demand for significant increase in resolution and accuracy of seismic studies of productive layers to successfully deal with complicated reservoirs and residual deposits. The proposed concept of integrated three-dimensional acquisition geometries (2D/3D+VSP) allow to combine strong features of both surface seismic and VSP and extend informational value of seismic exploration

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