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Study On Shanxi Stage Sedimentary Facies And Seismic Reservoir Recognition In Yanchang Exploration Area Of Ordos Basin

Posted on:2011-11-18Degree:DoctorType:Dissertation
Country:ChinaCandidate:P B LiuFull Text:PDF
GTID:1100360305457983Subject:Mineral prospecting and exploration
Abstract/Summary:PDF Full Text Request
The yanchang exploration area locates in the mid-eastern of Ordos Basin, which is found high gas rate wells at the Shanxi formation of the upper paleozoic, showing a good exploration prospect in this area. Meanwhile, the indefinite distribution of reservoir sandstones and oil-gas abundance law restrict the following exploration.Aiming at the recent problems in the exploration, on the basis of previous studies and according to the available exploration data to find favorable exploration targets for the ultimate goal, this paper comprehensively used the principle and method of sequence stratigraphy, reservoir sedimentary, seismic sedimentology and petroleum geology etc. to do research in the stratigraphic classification, sedimentary facies analysis, seismic reservoir recognition and analysis of favorable exploration target, which provided scientific basis for later exploration and well spacing.The innovative points mainly embodies in:firstly, taking various seismic forward modeling techniques for means to analyze and explain seismic attributes; secondly, using geological and geophysical methods mutual feedback in sedimentary facies analysis and seismic reservoir identification, sedimentary model can guides seismic reservoir identification, the results of seismic reservoir identification can perfect sedimentary face understanding furtherly.The main results and understandings from the research are as follows:(1) In the base-level cyclic sequences method of Cross for major guiding ideology, using the method of stratum thickness, well-seismic cycling calibration method to assist, this paper divided shanxi formation of study area into two long-term, six middle-term datum plane cycles. The two long-term cycles correspond to the first and the second member of Shanxi Formation respectively; the six middle-term cycles grossly correspond to six sand sets of Shan23~Shan11.(2) Shanxi formation is a typical shallow slope delta depositional model, which mainly develop delta front.The features during Shanxi formation depositional period were shallow water, flat terrain, relatively weak reformation of lake waves. Underwater distributary channel and bay are the main sedimentary microfacies types of the delta front in which the typical mouth bar developed poorly. The energy of underwater distributary channel was strong, the bottom washout structures are very developed, and the river sandstone usually clip mud bricks. Sandstone sorts are mid-fine grained sandstone of quartz sandstone with good sorting and grinding which is less than 6m in thickness, big thick layer of sandstone is overlaied by multi-stages channels cutting. Sandstone had a poor horizontal continuity and lens shaped distribution in the section, and shaped distribution in lobes in the plane, which exhibited in certain direction effected by the river.The water gradually deepened during Shanxi formation depositional process, the shore-lacuatrine system and subsidence center both moved toward north, the northern delta system moved backward and southern delta system northward.(3) The forward modeling study shows that seismic amplitude, phase, multi-traces statistical coherent and waveform classification attributes cannot reflect the sandstone, which mainly due to the comprehensive effect of gas sandstone with AVO effect, coal and limestone shielding and shale silty sandstone (silty mudstones) have the similar speed with sandstone.The AVO forward modeling of actual containing gas wells with different pore fluid (original state, gas and water saturated state) illustrated:water saturation, gas saturation model and the original model AVO intercept are positive, the AVO gradient are negative. The higher the gas saturation was, the bigger the absolute value |G| of AVO was with offset increases.1D forward modeling study shows that, thickness variation of the coal can cause to significantly change of amplitude, but the sand can not. The thin-low velocity coal seam was the mainly contribution to seismic amplitude, almost completely submerged sandstone contribution.(4) According to the analysis of the seismic data, with all kinds of seismic inversion method, the principle and the applicability, in the 3D area author selected seismic character parameters inversion method subject with log data to invert GR, IMP, VEL and POR parameters etc., use the combination of GR and IMP to identify sandstone; sandstone reflection using IMP which were inverted by constrained sparse spike inversion were selected in the 2D area.The sandstone thickness calculated by the inversion results in 3D area changed significantly horizontally, which had a fine match with well statistical sand thickness. Meanwhile, north to south exhibition features reflect the delta front distributary channel of sedimentary characteristics and the source direction in 3D area.The impedance inversion in 2D area can not accurately reveal horizontal changes of sandstone reservoir, but can distinguish mudstone from sandstone roughly, wells had thick sandstone are located within the high impedance anomalous zone.(5) Seismic gas-bearing properties detection shows that gas bearing sandstone can effect the absorption of high frequency, the distribution of high frequency F3 can indicate strata gas bearing properties well.(6) Base-level cycle obviously controlled reservoir development characteristics, good connectivity, thick sandstone developed in early base-level cycle. At the same time, the thicker the sandstone were, the stronger the hydrodynamic conditions in depositional period were; the coarser the grain were, the stronger the anti-compaction in late diagenesis period were, which were better for forming the relatively high porosity and permeability reservoirs.(7) Local and regional seal bed and the channel sandstone clamped by source rock in Shanxi formation formed a reservoir combination of self generation and self preservation. Yanchang exploration area had a gentle structure and undeveloped fault, source rock provided gas source to reservoir neighboring, which belongs to typical lithologic reservoir. Reservoirs conditions were the main controlling factors of reservoir forming in the "wide covered type" hydrocarbon generation model, exploration well spacing should be preferred to the thick sandstone overlaied by multi-stages channels.
Keywords/Search Tags:Yanchang exploration area, Ordos Basin, AVO, forward modeling, shallow water delta, seismic character parameter inversion, constrained sparse spike inversion, lithologic gas reservoir
PDF Full Text Request
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