Reservoir Seismic Response Characteristics Analysis And Reservoir Distribution Prediction Study: A Case Study Of Xujiahe Formation At AY Study Field, In Central Sichuan, China.

AY Study area lies at the southwest of Moxi-Longnusi structure belt whichbelongs to the ancient tectonic uplift in central Sichuan basin. The second member ofXujiahe Formation is a kind of typical tight sandstone reservoir in this research area,but reservoir with good physical properties could be found in speckled distributionamong this area, this distribution type is called sweet spot by field specialists. In severalyears’ research, many oil and gas seepages and the prolific gas wells indicate the gasexploration potential of Xujiahe Formation in AY. But exclude the affection from partsof old seismic data, some questions that need to be answered still exist in the research,which is underway in my research area, about Xujiahe Formation. For instance,although all the second and the first also the third member of Xujiahe formationlongitudinally constitute a well known superior source-reservoir-cap assemblage. Thedrilling success rate of gas and oil exploration that targeted Xujiahe Formation not onlydepends on the play assemblage, also not hinge on the structure factor. In generally thekey is the distribution of reservoir with good physical properties, which is so-calledsweet spot distribution mode, this is the reason why the Xujiahe2ed gas reservoir hasbeen categorized the lithologic reservoir, however the analysis material about this keydistribution monde is not much, so the Xujiahe2ed has been selected as the mainresearch object in this paper. During this paper, a research idea that geological andproduction test data closely combine geophysical methods is applied in the reservoirs,which possess good physical properties, prediction research. The main achievements inthis paper made known as show below: (1) Firstly, the reservoir in this research area is classified by production test data,subsequently these kinds of reservoir study through logging response characteristics toconfirm the logging identification parameter of multiple reservoir own, for example,through porosity and speed fitting formula, speed statistic histogram to confirmgeological logging identification parameters from reservoir of high yield well, reservoirof middle yield well, reservoir of low yield well. In this part, the result that reservoirand tight sandstone could be distinguished easily by using the velocity attributes,meanwhile the low speed material may be reservoir also could be mudstone.(2) According to the research original idea that geological and production test dataclosely combine geophysical methods, I applied several methods that one-dimensionalforward model and displace reservoir test and two-dimensional forward model toanalysis seismic response characteristics from all categories of reservoir in my studyarea, then establishing the seismic response model of mudstone and reservoir with goodphysical properties, also clearation and defination geological formation mechanism ofthe seismic response characteristics from mudstone and any kinds of reservoir.Summarizes the seismic response identification features of high quality reservoirs, andthere are differences exist in seismic reflection characteristics between mudstone andhigh quality reservoir. At the same time, during interpreting the seismic data, manysmall faults were found existing in the Xujiahe2ed, and part of the faults combinationis complex, also most of the faults only developed internal of the target layer. Up to thegeological formation mechanism, one could be certain is that the development of highquality reservoir related to the existence of small faults and micro cracks.(3) On the basis of reservoir logging response characteristics study, furtherclarified the floor level about reservoir porosity, which exist in my research area, alsothe upper limit of velocity and GR value. And carry out inversion study according to thefollowing ideas: Firstly, on the basis of the GR value which is the upper limit toimplement the gamma inversion for distinguishing the shale and sandstone, accordingthe upper limit velocity data to carry out the velocity inversion. Secondly, combine theboth gamma and velocity inversion results to eliminate the mudstone on the velocityinversion profile, only lifting velocity inversion of pure sandstone. Finally, employfitting formula of porosity and speed to obtain the porosity inversion data. Under theguidance of the inversion idea, carry out inversion method study and test, the testedmethod list as below: sparse pulse wave impedance inversion and inversion based onthe model constraint and inversion based on the log data, but the effect of all theseapplication result could be better. At last, adopt improved simulated annealing inversion method which obtain a better inversion result, for example, vertical andhorizontal resolution is much higher, fit the logging data, correspond seismic reflectionpattern of reservoir and mudstone.(4) Through selecting a suitable time window which fit with Xujiahe Formation topick up of the sampling points, what need to be explained is that we can get a traveltime by combination these sanmpling points. After that, apply time-depth conversionto get the reservoir thickness plane distribution map. Through the porosity inversionresult obtain reservoir porosity plane distribution map. Then according the thicknessand porosity plane distribution map to get reservoir energy storage coefficientdistribution.(5) Analysis and describe the high quality reservoirs distribution mode which isso-called sweet spot distribution mode, come to a conclusion that the geologicalmechanism of this distribution pattern is small faults and micro cracks related to thequality of reservoir, the high quality reservoir is result of the physical propertyreconstruction which caused by small faults and micro cracks development. With thinreservoir thickness and structure uplifting background in my study area, that the targetlayer possessed the development potential of small faults and micro cracks, so thereservoir which is in a certain thickness range and existing with small faults and microcracks should be the main target of petroleum and natural gas exploration in AY.With this study I found under the circumstances that the structure and reservoirgeologic material is insufficient, we still can gain wonderful research achievements byadopting the research idea that geological and production test data closely combinegeophysical methods. Also makes the whole study more in combination with theproduction practice, meet the needs from the production unit. Moreover, we could moreeasily to analysis and describe the geological formation mechanism of seismic responsecharacteristics which belongs to high quality reservoirs by applying theone-dimensional modeling analysis methods, for example, synthetic seismic recordsand displace reservoir test, etc. During this research the two-dimensional modelinganalysis method is used to validate the research result of geological formationmechanism analysis about seismic response characteristics from multiple reservoirs. Ingeneral, all the application effect of modeling analysis method is excellent.