Study On Seismic Reservoir Prediction And Hydrocarbon Detection Technology In Block 8 Of Sulige Gas Field

With abundant reserves and high production, the tight sand gas has played a noticeably increasing role in unconventional natural gas exploration and development. The research and exploration of tight gas is significant for the development of the furture gas industry. Owning the richest reserves and highest annual output in China, the Sulige gas field has become the largest gas field.59area is located in the west of Sulige gas field and the north of ordos basin. Its structure is simple distributing as broad and gentle monoclonal structure. The tight sandstone reservoirs in P1h8member of the Xiashihezi Formation belongs to lithologic trap. As the mainly sedimentary face of P1h8member is braided river, reservoir distribute widely. However, the thickness of a single sand body is relatively small; in transverse the reservoir changes quickly; in vertical the reservoir has multiple levels; thin layers is widespread; gas-water relationship is complex; the main frequence of seismic data is low; and the band width is relatively narrow. Therefore, the reservoir prediction has great difficulties.Combining the information of the seismic, logging, geology, and drilling of this region, the objective of this thesis is to show the potential of using three kinds of seismic methods to characterize the distribution and oritentation of Sulige P1h8member tight gas sand. First of all, based on the statistic of seismic response for the reservoir on the borehole, post-stack sensitive attributes was extracted along with horizon slice. Second, impedance inversion was used to predict the distribution of sandstone. Next, combining with the AVO forward modelling, the method of using the cross plot of intercept and gradient was adopted to interpret the gas sand area. Finally, through integrating these three methods, the comprehensive seismic reservoir prediction of Sulige P1h8member was obtained, which effectively improved the accuracy of prediction and achieved a good result.This article research mainly made the following progress:firstly, Statistics of seismic response of reservoir showed that reservoir of P1h8member usually exhibit in the form of two peak and a wave trough. What’s more, class Ⅰ and Ⅱ well commonly showed a strong wave trough, on the other hand, class Ⅲ well was middle wave trough. Based on this distinction, sensitive properties was extracted along with isochronous slice. Then using principal component analysis to remove the correlation between the attributes. And the ancient river sand was described. Secondly, constrained sparse spike inversion has advantage in oil and gas reservoir predication because it does not rely on the original model and is loyal to seismic data. Specifically, in study area, He83-He84gas reservoir is mainly distribute in the relatively low impedance about9150-10500g/cm3*m/s. Thirdly, AVO forward modeling of thick-layer showed that:overlying strata could influence the AVO type and overlying strata with high impedance is the major factor for research area AVO type is Ⅳ. What’s more, when gas saturation and cap rock condition is fixed, the smaller the intercept, the greater the porosity. In addition, when overlying strata is constant, in low porosity reservoir, the greater the absolute gradient, the higher the gas saturation; and on the other hand, in the reservoir with large porosity, the small absolute value of gradient and the large absolute value of intercept are relevant to reservoir of high gas saturation. Analysis of AVO numerical modeling for thin inter-layer reservoir indicated that compared with acoustic medium, elastic medium is more reasonable. Finally, in the guide of AVO forward modeling, P-G attribute could predict the gas sand with III and IV class accurately. The result is good matched with well, which is able to distinguish the gas well, water well or dry well.This study combined geology, drilling, seismic and etc with a comprehensive application of attribute analysis, inversion and AVO method, then a set of practical method to predict tight sand reservoir is summed up, providing a reference for the next well deployment, exploration and development.