| Sequence stratigraphy has been widely used in the exploration and development of oil and gas fields.Strengthening the research methods of sequence stratigraphy is conducive to improving the success rate of oil and gas field drilling.This paper mainly studies sequence stratigraphy by using attribute analysis method of maximum entropy spectrum of logging data.When applying INPEFA technology to sequence stratigraphy analysis,in order to establish sequence stratigraphic framework,it is necessary to analyze the maximum entropy spectrum attribute of well logging data in order to identify low-frequency sequence first,then to analyze the maximum entropy spectrum attribute of target interval logging data in order to identify high-frequency sequence,and finally to delineate reservoir sand body according to sequence stratigraphic framework control.The connectivity of sand body can be distinguished by comparison and division.By analyzing the maximum entropy spectrum attributes of different logging curves,it can be concluded that sequence boundaries,stratigraphic sedimentary cycles,flooding surfaces and high quality reservoirs can be identified by using INPEFA curve characteristics.Sequence stratigraphy of Xu 5 member of Xujiahe Formation in West Sichuan Depression is studied in detail by this method.The results obtained by seismic,drilling and logging data are mutually verified with the research results in this paper,and have good application effect.Through this study,the following conclusions can be drawn:(1)INPEFA analysis technology has the technical characteristics of extracting spectrum characteristics of signals from complex and changeable original logging signals,and establishing corresponding sequence cycle patterns according to different spectrum characteristics.It has the function of quickly identifying sequence boundary,flooding surface,sedimentary cycle and sequence order in sequence stratigraphy.(2)Using the positive and negative trend of INPEFA curve to represent a process of water influx and regression and the positive inflection point to represent the sequence boundary,the sequence of Xujiahe Formation in West Sichuan Depression is identified and divided into three to five stages.The Xujiahe Formation is divided into three stages,namely,upper,middle and lower Xujiahe Formation.One step is subdivided into nine five-level sequences: TX5-1,TX5-2,TX5-3,TX5-4,TX5-5,TX5-6,TX5-7,TX5-8 and TX5-9.(3)The trend characteristics of INPEFA curve can be used to identify different sedimentary cycles of different stages.The positive trend represents a process of water inflow,including the change of climate from dry to wet,and the change of sediment particles from coarse to fine;the negative trend represents a process of water recession,the change of climate from wet to dry,and the change of sediment particles from fine to coarse.Natural gamma-ray logging curves have the distinguishing characteristics for the changed sedimentary environment.Therefore,three medium-term cycles(fourth-order sequence)and nine short-term cycles(fifth-order sequence)are identified by using the trend of GR-INPEFA curves in Xujiahe Formation,West Sichuan Depression,respectively.Eighteen half-cycles are identified as nine,and six half-cycles are identified as three positive cycles and three reverse cycles respectively.Positive cycles and 9 reverse cycles.(4)Using the characteristics of INPEFA curve to identify high-quality reservoirs,the positive inflection point of INPEFA curve corresponds to sequence interface,and the upper and lower interface corresponds to low-level system tract and high-level system tract.It is the development site of high-quality reservoirs,which is in good agreement with the high-energy sand of grain size median analysis.Therefore,57 wells in Xu 5 member of Xujiahe Formation in West Sichuan Depression are studied and analyzed by using INPEFA curve characteristics.Three sets of high quality reservoirs are identified and developed in the three sequences of TX5-7,TX5-8 and TX5-9,respectively. |
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