Study On The Evolution Of Carbonate Reservoir Type Reservoirs In

Carbonate rocks are widely distributed in the different geological ages, which contain abundant oil and gas resources. In the recent years, the reservoirs of carbonate rocks have been become one of the focuses of the petroleum exploration and development around the world. From the early1970’s to the present, the large carbonate oil field was first discovered in Ren Qiu which locates in the eastern of China, and then, the oil and gas explorations in the western of China (such as Chang qin, Sichuan, Tarim etc.) have also shown as new progresses. However, the prediction of carbonate fractured-vuggy type reservoirs with different size, morphological diversity, and complex distribution has strong heterogeneities as well as their complex geological origins. So, it has very important meaning that using seismic method in the light of local conditions effectively identifies the carbonate fractured-vuggy type reservoirs.In the Sichuan basin, Mao Kou carbonate formation of the lower Permian is one of main natural gas exploration and development stratum. But, in the Shu Nan area of this basin, the reservoirs of Mao Kou formation have a typical character of the carbonate fractured-vuggy growth. They are not completely controlled by the structures in this area. At the same time, it is more difficult to predict these reservoirs because of the characters about low porosity, low permeability, and strong heterogeneity. Therefore, by taking the carbonate fractured-vuggy type reservoirs in the He Bao Chang structure of Shu Nan area as an example and studying carefully for the geological features in this area, the reservoir prediction method based on the forward modeling research and fusing analysis of the multi-parameter was proposed. That is: first of all, according to the forward modeling analysis of the wave equation, the geological responses about the palaeokarst reservoir were acquired:and then, using these responses selected the seismic parameters to respectively describe the palaeokarst development zone and fracture development zone; finally, to take the method of fusing analysis of the multi-parameter comprehensively predicted the distribution of favorable carbonate fractured-vuggy type reservoirs. Through above processes, the favorable drilling areas of Mao Kou formation were found in the outside areas of the structural main portion and main faults. This research not only proposed an effective reservoir prediction method for the Mao Kou formation but also contributed the advanced way of thinking for the exploration and development in the He Bao Chang area.In this thesis, the following results were mainly achieved:1. According to the configuration relationship between the cave system and fractures, the important critical thinking of the reservoir prediction was obtained:that is to comprehensively predict favorable reservoirs based on the respective descriptions for the palaeokarst zone and fracture development zone.2. By the forward modeling of the wave equation, the rulers were found:When palaeokarst reservoirs were growth, seismic waveform will be changed. It means that the obvious abnormal features of strong wave trough and frequency will appear on the seismic section and the seismic reflection energy absorption attenuation as well as frequency dispersion phenomenon will be found. In fact, these changes mainly deal with the amplitude and frequency. Thus, the rulers of extracting sensitive parameters of seismic data can be found and these parameters will be used to predict the reservoirs.3. For the carbonate palaeokarst reservoir with the strong heterogeneity, the method of the waveform classification can well depict the palaeokarst features of Mao Kou formation and has an important role for predicting the palaeokarst distribution on the plan.4. The fusion analysis method of multi-parameter can be better to depict the distribution range of the fractured-vuggy type reservoirs. To wipe off the correlation among various properties by using the principal component analysis and to perform the weighted fusion of the seismic attribute by adopting maximum eigenvalue of new covariance properties which were reduced the dimensions can improve the precision of the prediction results.5. When there are the development reservoirs of Mao Kou formation in the area, in the range that the top of Mao Kou formation goes down40ms, the seismic responses which are the obvious lateral changes of the amplitudes, polarity reversal, bifurcate&merge of the seismic phases, like "eye" reflection, the small upheaval in the local places, and increasing time difference often appear on the seismic section.6. Through spatial connectivity analysis and characterization of the fractured-vuggy system, low velocity abnormal zones in the area were divided into10relatively independent zones. Where the low velocity abnormal zones Have relative development is located in the hanging wall of the Bao④fault and the heading wall of the Bao③fault of the nasal structure axis in the He Bao Chang area; the sporadic low velocity abnormal zones also exist on the heading wall of the Bao④fault in the western area of He Bao Chang area. Especially, in the east-west fault area near the main faults, low velocity abnormal zones have more developments due to effect from two direction’s faults.