The Application And Research About The Method Of The Prestack-time Migration Applied To Project Of Jidong Oilfield

Jidong Oilfield in the South Limburg region in recent years was found to containa fractured carbonate oil-bearing structure.In order to accurately predict thecharacteristics of the underground oil reservoir, pre-stack inversion requires commonreflection point gathers with high signal to noise ratio.Conventional post-stackmigration can not meet the requirements of pre-stack inversion; in addition, the SouthLimburg region with complicated fracture system, which has buried hill surface andthe unconformity structure, makes the conventional post-stack time migrationinaccurate. The purpose of this paper contains the following aspects:1) How to get the accurate seismic section with the diffraction homing、clearbreakpoints and the correct imaging of the high steep d ip layer. It is our purpose thatthe good body of data should be provided to the interpreter.2) How to get the accurate crp gathers with high signal to noise ratio.3) How to choose the parameters of the pre-stack time migration: the migrationaperture, migration angle and anti-aliasing factorconventional CMP stack will be able to meet the correct imaging of the formation,when the stratum is the horizontal layered media.But, when the local stratum containsthe stratum with the inclination, the conventional CMP gathers stacked section is notequal to zero offset stacked section, and post-stack time migration can not really meetthe correct imaging of the subsurface; pre-stack time migration can meet the commonreflection point stack and provide high signal-to-noise ratio data for pre-stackreservoir prediction.So we select the pre-stack time migration for this processing. Inall pre-stack time migration, Kirchhoff-type pre-stack time migration is able to adaptto changes in the observing system and the requirements of the subsurface velocityfield is also unlike the pre-stack depth migration.The migration travel time calculation of kirchhoff pre-stack time migrationcontains two types: straight ray and bending ray. The straight ray travel timecalculation is based on isotropic medium assumption and the bending ray travel timecalculation is based on layer structure assumption. The bending ray travel time calculation keeps high order aspects of offset and it is more accurate than the straightray travel time calculation. This paper theoretically analyse the choice of migrationaperture、migration angle and anti-aliased factor. This paper also gives some attentionabout the migration processing.This paper also gives the following conclusion:1) Pre-stack time migration can achieve the correct imaging of the reflected waveand diffracted wave, and the imaging is more accurate than the post-stack timemigration.2) The bending ray travel time calculation is more accurate than the straight raytravel time migration.3) Too large or too small migration aperture or migration angle affect migrationimaging. The anti-aliased factor should be chosen prudentially.