Technology Research On Tertiary Reservoir Prediction In Jiyang Depression

The Tertiary stratum in Jiyang Depression is the chief series of exploration and development strata for Shengli Oilfield. The subtle oil & gas reservoirs have become the chief objects of exploration and development currently after the exploration and development of 40 years, and the reservoir prediction is the key of exploration and development for subtle reservoirs. According to statistical analysis in recent years, more than 40% drilling wells failed in Shengli Oilfield have resulted from reservoir prediction problems (reservoir not developed or ascertained), therefore the original seismic prediction of reservoir has failed to meet the actual needs.For this reason, the seismic prediction techniques of reservoir need deepening urgently in order to reduce the blindness in reservoir prediction effectively and the risk of exploration and development to improve prediction accuracy of reservoir and drilling success rate.In this study, based on a series of targeted seismic forward models by using a large number of seismic and geological data that combined with the development characteristics of Tertiary reservoir in Jiyang Depression, the seismic response characteristics of the Tertiary reservoirs were analysed by studying the relationship between the seismic forward models and seismic response. By ways of combining further analysis and study for the conditions of seismic prediction and the adaptability of prediction techniques with the four typical category reservoirs in Jiyang Depression, an effective series of technologies of exploration and development is optimized and integrated, which got the following four major innovations through the research:(1) In the basic research of reservoir prediction, the regulation of seismic response for the main reservoir in Jiyang Depressions summarized and the three-degree seismic model based on the results of test in laboratory and mathematical simulation is established. â‘ For the thick reservoir which is greater than 1/4 wavelength, its amplitude response has no relationship with the thickness of interlayer as well as reservoir itself and the reservoir structure. While the changes of petrophysical property and lithological characteristic are the main factors for the responses, which are the foundation of petrophyiscal property and fluid prediction for the reservoir using seismic attributes;â‘¡For the transitionary reservoir whose thickness is between 1/8 and 1/4 wavelength, the thickness of interlayer also have some influence except the petrophyiscal property and lithological characteristic;â‘¢For the complex thin sand-shale interbed, the key factors of seismic responses are the tuned thickness of reservoir, assembled structure of reservoir (the thickness of reservoir, interlayer and its structure) and the regulation for change of reservoir acoustic impedance etc;â‘£Established the three-degree seismic response model of reservoir which includes the brightness, scale and purity. The "brightness" means the relative acoustic impedance, the "scale" means the relative thickness of reservoir and the "purity" means lithological combination structure in certain thickness of reservoir. Directed by this model, combined with the practical characteristic of the Tertiary reservoir in Jiyang Depression, four reservoir based on the seismic responses were divided so as to settle the theoretical basic for studying the seismic prediction of reservoir.(2) In the feasibility research of reservoir prediction with the seismic data, the requirement of reservoir prediction for seismic data is made definitely.â‘ The noise immunity of seismic attributes rise while the thickness of sand body and acoustic impedance are great and the accuracy of reservoir prediction is correspondingly high; conversely, the reservoir prediction has higher requirement for the quality of seismic data.â‘¡The noise immunity of seismic attributes rise while the resolution of seismic data is greater, and the results of reservoir prediction are better; conversely, the reservoir prediction has higher requirement for the quality of seismic data.â‘¢The seismic cubes whose signal-noise ratios less than 2 are not suited for the research of reservoir prediction, that is to say, the signal-noise ratio should be larger than 2 for studying the geological problems(strata thickness, lithological characteristic and petroliferous property) using the seismic attributes.(3) In the adaptability research of the key technology for reservoir prediction, the applicable conditions of the three key techniques for reservoir prediction are made definitely.â‘ For the seismic inversion technology, we emphasized the ambiguity and integrity of inversion results, meanwhile, presented the evaluation discipline of "primality" and "average" for seismic inversion. The discipline of "primality" means the results of seismic inversion may approach the highest resolution of field acquisition in some content, because the inversion results may not be reliable by only improving the seismic resolution while neglecting the accuracy and scale restriction of seismic data. The "average" means that seismic inversion results are the average value of practical geological model which the average function is set as the window as the average value, for any seismic inversion has some average effect.â‘¡Made full analysis of the adaptability of spectral decomposition, summarized the applicable conditions and suitable range, presented the basic conditions of analysis the sedimentary cycle with seismic time-frequency characteristics and the "limit principle" in the application of spectral decomposition technology so as to settle the foundation for the further application of time-frequency analysis.â‘¢Carried out the optimization for the seismic attributes and pre-stack attributes, and used seismic attributes to optimize the sensitive parameter and made prediction to the complex beach bar sandbody and got good results.(4) As for the typical Tertiary reservoir of Jiyang Depression in Shengli Oilfield, the seismic prediction techniques are optimized and integrated, which present a series of suitable seismic prediction techniques for the four typical sand body of channel, turbidite, beach bar and glutenite.This study results has been applied to various lithological reservoir exploration such as Kendong, Laohekou and Chepaizi areas, and have given great guidance to the exploration. Contrasting with the known drilling wells, the prediction error of reservoir depth is less than 5%, reservoir thickness is less than 10%, and the success rate of prediction is greater than 70%. This study results has got obvious geological effects and economic benefits so as to verify the instructive significance of the research.