A Study And Assessment Of Geometry Based On Wave Field Theory

With the development and progress of oil-gas exploration, the challenge of increasingly complicated target points and increasingly high precision demands is faced in modern oil-gas exploration. Seismic data acquisition includes exploding, receiving and acquisition geometry. The level of the optimum designing 3D acquisition geometry can directly affect the imaging quality of subsurface structure, especially, in some complicated regions. It is an important theme how to sieve an optimal acquisition geometry.Professor Berkhout has developed an approach for estimating acquisition geometry that is guided by prestack imaging quality of target points based on the double focusing theory of the WRW model. According to the theory of the WRW model, the process of seismic wave propagation can be divided into 5 independent procedures: 1) sources explode, which can be signified by operator S; 2) seismic wave propagates downward, which can be signified by operator Ws ; 3) seismic wave is reflected at the subsurface, which can be signified by operator R ; 4) seismic wave propagates upward, which can be signified by operator Wd ; 5) receivers acquire the seismic wave, which can be signified by operator D . The product of the 5 operators is the WRW model. We define two focusing operators: focal source operator Fs and focal detector operator Fd . The two operators separately implement focusing on sources and detectors. Focused the seismic wave field by Fs , and then downward continue the wave field to image subsurface, thus get focal detector beam. Likewise, Focused the seismic wave field by Fd , and then downward continue the wave field to image subsurface, thus get focal shot beam. They separately indicate imaging resolution of detectors and sources to target points. The resolution of a single spread is the product of focal detector beam and focal source beam. The total resolution of the whole acquisition geometry is the summation of resolutions of all the single spreads. Extrapolating wave field is most important in the whole process.Based on Berkhout's theory of double focusing of the WRW model, in order to adapt to the calculating ability of current computers and actual needs of production, this dissertation has made some simplifications and improvements. The software of"assessment system of 2D acquisition geometry's resolution"can be adapted to an arbitrarily complicated geology model. The software of"assessment system of 3D acquisition geometry's resolution"can be adapted to a relatively simple geology model. Calculation of theoretic and actual models indicates feasibility and practicality of the simplified approach.