The Seismic Facies Analysis Of Reservoirs With Organic Reef And Bank In Northeastern Sichuan Basin

The carbonate reef and bank were perfect reservoirs for oil and gas. They are a kind of the special carbonate mass from the organic build-up and the oily sedimentation type in the carbonate. They have widely hydrocarbon potentiality. However, because the reef and bank strata were inhomogeneous, heterogeneous and differential, quantity of seismic data were usually poor, it is very difficult to identificate and forecast reef and bank reservoir, they belong to the subtle hydrocarbon reservoir which are more difficult for the exploration.In recent year, along with object complex degree of oil-gas exploratory development increasing and seismic interpretation technology being more and more mature day by day, seismic oil-gas forecasting technology develops toward fine and the practical direction. In order to enhance the rate of accuracy of the oil-gas forecasting , the seismic facies division is especially one important step, accuracy of the seismic facies division influences the reliability of result of oil-gas exploration. First of all, the paper analyze systematically the geologic characteristic, seismic response characteristic, log response characteristic of the reservoir of reef and bank facies. Second, we formulate the fundamental principle of the facies plane method, waveform classification and Principal component analysis(PCA). At the same time, we formulate the algorithm of waveform classification and PCA, and they were applied in the seismic data with orientation analysis of various parameters selection, we generalized a method of parameters selection which was fit for practical application and the problem of necessary notice which applied in seismic data. Finally, we applied multiple methods of seismic facies analysis in organic reef and bank reservoir of Changxing formation in SYB area and Feixianguan formation in HCL area in the northeastern Sichuan basin, then we divided the sedimentary facies and discriminated the reef and bank facies with some seismic attributes, inversion result and seismic facies analysis result. Main results of that topic involve below:â‘ We analysed the basic concept, main classification, regular pattern of growth and development and sedimentary environment of the carbonate reef and bank. we concluded some basic characteristic of seismic reflection and log (GR, Diplog and Image logging) response characteristic. They were the base of discriminating the reef and bank facies.â‘¡Because of the conventional method of seismic facies analysis(facies plane method) which divided the sedimentary facies by observing and finding the abnormal information on the seismic profile with eyes, and there must have many limitations. In order to resolve the problem, we take advantage of the distinguishing feature which the alteration of sedimentary formation physical property parameters reflect on the alteration of seismic trace waveform, then we interpreted the geologic characteristic of seismic information with technique of seismic data processing, computer technique and some mathematics method. We divided the seismic facies with one or more data volumes by self-organizing feature mapping of waveform classification and generated illustrative plain figure of seismic facies. The PCA can divide the seismic facies with multi-attribute seismic data volumes, when it finds the common tendency of multi-attribute data, then applying the most representative data to take part in classification of seismic facies, it can make the classification results more accurate and enhance the work efficiency of interpretation people.â‘¢In view of the problem of the interval selection, classification data, iteration times and component times. They were applied in testing and analyzing with seismic data , and we generalized a method of parameters selection which was fit for practical application and the problem of necessary notice which applied in seismic data. It will be the concrete base of the future research work and can enhance the future work efficiency.â‘£By means of seismic facies analysis we know that the Changxing formation of SYB area can divide four facies belts: open platform facies, platform edge reef and bank facies, carbonate slope facies and shelf facies. And we thought that the reef and bank facies distributed in the middle of the region of interest. However, the Feixianguang formation of HCL area can divide three facies belts: shelf facies, platform edge facies, platform internal facies. And it can divide some microfacies, such as platform edge shallow facies, platform internal shallow facies, restricted platform and so on. In view of the situation of the second and the third of Feixianguang formation, we know that the reservoir of bank facies distributed between ma2 well and hc1 well. Finally, we applied some seismic attributes and inversion results in verifying the division of sedimentary facies and the discrimination of reef and bank facies, and proved that the seismic facies results were comparatively dependable. But the seismic facies analysis had definite ambiguity sometimes, it must be used with some seismic attributes and geologic information, so the last result of geologic interpretation will be more dependable.