Study On Reservoir Prediction And Fluid Identification Of Reef Beach

Reef flat reservoir is the characteristics with good reservoir properties, large abundance,excellent oil and gas, high productivity, associated with great oil and gas potential. However,reef flat reservoir belongs to a lithological oil-gas reservoir, so it is difficult for exploration.The reservoir prediction and fluid identification of reef flat has long been a problem for oiland gas exploration.In this study, Taking reef flat reservoir of Changxing formation in SLG area as an example,the author studied drilling, well logging, testing, geological and seismic data, then developedthe targeted seismic technical series based on the characteristics of log and seismic responses ofreef flat reservoir in this area. The main research contents and key results of this paper are asfollows: Firstly, the author introduced the classification and definition of reef flat in details,then summarized not only the seismic and logging response characteristics, sedimentary faciespatterns, sedimentary environments and features, but also reef flat reservoir characteristic.Secondly, some seismic numerical simulation methods of reef flat reservoir were also studied,including MIVMAS seismic forward adapted to non-uniform media, viscosity acoustic waveequation seismic forward in fluid medium, and AVO seismic forward based on Gassmann andwave equations. By model test and simulation of actual data in SLG area, seismic reflectioncharacteristics of the reef flat reservoir and the fluid was acquired, such as seismic reflectionenergy gradually weakening, frequency attenuation and phase dispersion (waveformdrop-down or time delays) in and under the reef fluid reservoir, providing basis for reservoirprediction and fluid identification. Thirdly，the techniques of paleogeomorphology analysisbased on horizon flattening, three-dimensional visualization, and waveform classificationbased on neural network were studied and applied in the paper, which can effectively describethe distribution of reef flat in SLG area; Fourthly, The paper put forward the ideas and methodsof the reef reservoir prediction based on formation slice, seismic attribute analysis,time-frequency analysis and wave impedance inversion of post-stack data. The results showed that the reef flat reservoir in SLG area was characterized by medium-high amplitude, lowfrequency, low impedance, large frequency attenuation gradient (after the gas-bearing). Thereservoir is mainly distributed in the bio-buildups and foreslope. Fifthly, specific methodsbeing fit for oil and gas detection in reef flat reservoirs of SLG region was studied, includingthe seismic signals fractional domain Gabor transform, pre-stack elastic parameter inversion,fluid identification factor analysis and the analysis of two-parameter intersection etc. Bynumerical simulation tests and the actual seismic data analysis, it was showed that thefractional Gabor transform of optimal order obtained high-resolution signal time-frequencydistribution with minimum time-frequency bandwidth. Low-frequency-shadow oil and gasdetection technology made full use of the low frequency information of seismic waves. Thetechnique of time-frequency absorption properties analysis took advantage of thehigh-frequency attenuation. To calculate reservoir elastic parameters such as Poisson’s ratioand Lame coefficient using the P-and S-wave velocities and density gained from pre-stackinversion can be effective in predicting oil and gas reservoir. Fluid identification factorHSFIF was the most sensitive to fluid, and highly consistent with wells. Finally, the authorpointed out the favorable fluid distribution range in reef flat reservoir of Changxing formationof SLG region based on dual-parameter intersection analysis.In summary, Through the application of these methods, the distribution area of reef flatand reservoir can be effective predicted, as well as the favorable reservoir and fluid area,accordingly, to provide evidence for well deployment and reduce drilling errors.