RTM surface offset gathers (SOG) contain subsalt events spanning the entire offset range (i.e., longer usable curvatures for tomography). RTM SOGs also have more reliable residual curvatures because each offset and azimuth group is migrated independently and does not interfere with the neighboring ones. RTM SOGs are more beneficial for full azimuth (FAZ) and ultra-long offset data.
We designed and implemented a practical and comprehensive workflow to mitigate missing source wavelet information and waveforms with vast spatial variation for land dynamite surveys and addressed the common challenges of acoustic-FWI application on land surveys during field data preparation.
The prediction of porosity is essential for the identification of productive hydrocarbon reservoirs in oil and gas exploration. Numerous useful technologies have been developed for porosity prediction in the subsurface, such as multiple attribute analysis, kriging, and cokriging. Kriging allows us to create spatial maps from point information such as well log measurements of porosity. Cokriging combines well log measurements of porosity with seismic attributes recorded between the wells to improve the estimation accuracy of the overall map. However, the traditional cokriging for porosity estimation is limited to only one seismic attribute. To introduce more geological information and improve the accuracy of prediction, we develop a new cokriging system that extends traditional cokriging to two secondary variables. In this study, our new cokriging system is applied to the Blackfoot seismic data from Alberta, and the final estimated map is shown to be an improvement over kriging and traditional single attribute cokriging. To show this improvement, "leave-one-out" cross-validation is employed to evaluate the accuracy of porosity prediction with kriging, traditional cokriging, and our new approach. Compared to kriging and traditional cokriging, an improved porosity map, with higher lateral geological resolution and smaller variance of estimation error, was achieved using the new cokriging system. We believe that the new approach can be considered for porosity prediction in any area of sparse well control.
In 4D land and especially for Permanent Reservoir Monitoring (PRM), changes of the subsurface induce unwanted signal variations that interfere with the 4D signal recorded from the reservoir. A three-month PRM pilot was carried out for Shell on the Peace River heavy oil field in Alberta, Canada in 2009. During this period, reservoir production was monitored using active buried sources and buried receivers. We took advantage of this continuous seismic recording to extract surface waves from recorded ambient noise using cross-correlation techniques. Surface wave tomography is then applied to produce daily time-lapse surface wave velocity maps that monitor velocity variations within the shallow subsurface. We provide an image of the shallow subsurface velocities showing generally higher values in the southern part of the area. This pattern correlates fairly well with the known presence of swamp (muskeg) in the area and the wells pad location. Calendar observation of velocity maps shows stronger variation at low frequencies with good spatial coherence. In the case of PRM and continuous seismic monitoring, these findings could help to discriminate, at least qualitatively, contributions due to shallow subsurface variations from actual reservoir 4D variations.
In 4D seismic, the velocity model used for imaging and reservoir characterization can change over calendar time as the reservoir is produced. This is particularly true for heavy-oil reservoir produced by steam simulation (EOR). We propose an automatic 4D update of the 3D velocity model using an efficient technique based on 4D pre-stack time migration (4D-PSTM) that describes the pre-stack differential kinematic effects by matching the 4D dataset. On real continuous 4D seismic data, the 4D-PSTM allows us to quantify interval velocity variations that can be used to map temperature changes in the reservoir in agreement with petro-elastic model expectations.
A flexible Radon modelling algorithm using time-frequency sparseness weights is introduced. The method may be used for a number of applications and combines the dealiasing and time resolution benefits of existing methods. Compared with a frequency domain sparseness approach, the proposed method results in improved attenuation of low moveout multiples and better primary preservation. Demultiple results using a North Sea dataset are shown.
The paper gives an overview of a full 4C deblending process and its results up to migration in the case of a real 2D 4C dataset acquired offshore Malaysia. Special emphasis is put on the deblending QCs and the specificities of the deblending flow for the PP and PS datasets.
Analysis of time-lapse data is performed on migrated seismic images, which represent the spatial and time-lapse variability of the medium’s reflectivity. The process of migration effectively rotates the wavelet so that it is normal to the imaged reflectors. Processes used in 4D reservoir analysis such as deconvolution, inversion and warping need to follow the structure of the data. The traditional 1D convolutional approach does not honour this directivity. For this reason, we introduce a wave equation based approach which provides an effective platform for structurally consistent reservoir analysis. This includes applications such as wavelet extraction, warping and 4D time-strain inversion.
A new methodology is presented for building near-surface static corrections models consisting on multi-physics measurements integration. The methodology was applied in two geological contexts: presence of a complex, multi-layered sandy overburden on Kahlouche area, and important weathered zone fluctuations due to shallow complex geology on Reggane. Electric and electromagnetic methods were chosen to characterize near-surface geology and improve the existing up-holes velocity models. Seismic/resistivity cross-correlations provide detailed transit time maps fully integrable in the seismic static corrections processing workflow.