Gas Potential Detection Of Shallow Reservoirs By Three-dimensional In Jiannan Area

As Chinese major petroleum exploration of onshore basin entered the high maturity period, the direction and object of exploration is also transferred from looking for large oil-gas field to the small, from shallow gas reservoir to the deep, from oil-gas reservoir mainly about structure to the non-structural lithologic hydrocarbon reservoir, and strengthen the exploration of poor reservoir and oil-gas layer. The increasing complexity of exploration target lead to difficulty of oil-gas exploration and development.In order to break through these complex exploration targets and meet the transitional demand of direction and targets of exploration we should put forward higher requirements to the seismic technology. As pre-stack seismic data contained lots of useful information, and AVO technology just can get wealthy information about formation lithology and petroleum from the pre-stack seismic data. So the technology is adaptive to exploration and development needs.AVO (Amplitude versus offset) is a technique of processing and interpreting seismic data, through analysising the characteristics and laws of pre-stack seismic data amplitude changing versus offset, and thus making prediction and judgments on the nature、reservoir lithology of reservoir fluids.On pre-stack seismic reservoir prediction is concerned, AVO application can be grouped into two parts:One is to study the gas-bearing reservoir in response to the unusual characteristics of the AVO based on log data on seismic reflection through the AVO forward modeling. And using it as the basis for guidance inversion AVO anomalies to explain the properties based on the pre-stack seismic data; Secondly, proceeding AVO inversion based on pre-stack seismic data, and Extracting AVO abnormal attribute parameters, based on knowledge representation and AVO forward modeling to predict distribution of reservoir and gas-bearing status. The former is a study of AVO, the latter is the application of AVO. The two interdependent with each other, that is, it embodys that AVO is independent of the seismic data identifying objectively the reservoir based on knowledge expression,and embodys the affirmative of AVO forward modeling study on AVO anomaly in response to the reservoir.AVO technology basic principle is the theoretical basis, on the premise of pre-stack common reflection gathering and layer speed model came from fine pre-stack data process, in order to use AVO technology and seismic inversion means to extract meaningful parameters about lithology and fluid information from pre-stack seismic data, the paper made detailed description about AVO inversion basic principles, methods and process, and do AVO inversion of various attributes parameters for practical information. First of all, the paper systematically discussed the basic AVO analysis methodology of forward modeling and inversion, and took the western block of JianNan field as the example for AVO forward modeling to study AVO response characteristics of sand with different percentage of gas bearing, in order to understand the effect of lithology, petrophisical properties and hydrocarbon bearing on AVO response characteristics, so have total and systematic grasp for inversion problem. Then use AVO forward model performancing gas-bearing reservoir’s AVO anomaly responsing characteristics as a guide, through prestack fine process and AVO goal process on the works area’s CMP gathers, obtained a series of AVO attribute data object using AVO inversion simulation, and from the various AVO attribute data object, presented their relationship with the gas-bearing reservoir by comparison with the known well using the attribute profiles pass Well. At last, on the base of evaluation and optimization of attributes parameters out of Inversion, the paper discussed the method of using various attribute to do AVO analysis, using the method based on Baysian classification, according to logging explanation results of seismic interpretation abnormal position and well point to build study samples, using information from the wells of the CMP gather performance against the AVO attributes and corresponding attributes gained from inversion of practical information beside well to make a comparative for analysis each property, on the basis of seismic attribute parameters optimized to select8-10seismic attribute abnormal parameters to make pattern recognition for the single reservoir parameters. On the promise of available parameters come from AVO inversion and attributes evaluation, the paper use attribution slice analysis, AVO attributes intersection Analysis and AVO attribute profile analysis to identify and explain the abnormal AVO which can grasp the overall abnormal location and distribution characteristics. Then use AVO attributes intersection analysis and kinds of AVO attributes profile analysis to confirm and explain the AVO anomaly.Jiannan gas field located in from western Hubei to eastern Chongqing areas. The Xujiahe group of target layer is the main reservoirs of this area. We passed on the synthetical analysis of the Poisson’s ratio slice, Fluid Factor slice and reservoir predicted parameters, from forecast results can see:the distribution of the favorable gas block in region is controlled by the factors of lithologic character and physical property (include fissure), local anomaly zones show obviously, but anomaly does not distribute continuously. The AVO abnormal response belongs to the third kind when the reservoir has high gas saturation. By the application of AVO technology in deep layer of Jiannan field, we can see that AVO anomaly identification and explanation method based on various attributes data came from AVO inversion is a ratively severity, and there is verification among each step which has a positive meaning for the AVO study of complex area.