Fluvial Facies Tight Sandstone Gas Reservoirs Characterization And Effective Sandstone Prediction In Sulige Gasfield

The reaseach object is tight gas reservoirs in Sulige on the paper, according to the difficulties on the characteristic with Paleozoic river facies sandstone reservoir, such as low porostiy, low permeability, deep burial, thin reservoir thickness, rapid space change, strong reservoir heterogeneity; the gas reservoir have strong concealment in mainly with lithology-stratigraphy trap; the reservoir feature of geophysical is complex, and low seismic datum.This study not only applies comprehensively well drilling, cores, analysis assay, testing, well logging, seismics data, but also adopts the latest theories and technique and methods of resolution of Sequence Stratigraphy, Sedimentology, Petrophysics, Reservoir Geology, Geophysics, etc. Exerting the predominance of many subjects jointly tackling key problem, developing the research on sequence stratigraphy, sedimentary micro-facies, diagenesis and the growth of effective reservoir, etc, apply with multi-seismic new technology and new method, based on geology (drilling) calibrate logging, integrating a tache with logging constrained seismic, geology, logging that carrying out comparative and analytic research on seismic datum of far&near and post-stack & pre stack, comprehensive utilization of kinds attribute information (including seismic reflection structure, waveform characteristic, retrieval information) do multi-attribute analysis, study on the connection of different sesimic attribute characteristic and gas reservoirs, found its multivariate mapping relationship, and then analyse spread rules of effective reservoir, predict comparative high enrichment area, optimization for drilling object, It formed a good recognition way aimed at tight sandstone gas reservoirs in Sulige area.Mainly sumarize cognitive on this paper:1.From Shanxi group to Shihezi group dispart 4 secular cycle and 10 medium cycle (equivalent toⅣ,Ⅴgrade cycle, subsequence) in study area;2.Major pay are He 8 and Shan 1 section in this block, and also distributing some gas pay in Shan 2section, the kind of depositional system is braided-rive under the swamp background in the He 8 lower, develop four kinds of microfacies:braided channel, mid-channel bar, flood plain and interchannel lake; Shan 1 and Shan 2 section mainly belong to meandering river depositional system. the effective reservoir are controlled by microfacies and its hydrodynamic condition which is main factor, the effective sandbody mostly develop in mid- channel bar, main channel and point bar microfacies, etc3.He 8 and Shan 1 section have typical characteristic on diagenesis of coal formation that mainly presented as strong compaction, low in carbonate cement, quartz secondary and Kaolinite developping generally, secondary pore formed with particles dissolution is the main pore type. primary reservoir space is dissolution pore, secondly is primary intergranular pore and kaolinite intergranular microporous.Throat is mostly bending flake and tube bunchiness, and also appearing flake throat.bad connectivity of hole and throat, give priority to the type of small hole-fine throat.4.The reservoir of He 8 section mainfest the feature of low porostiy, low permeability collectivity in the study area. The porostiy distribution is 1.4%-13.8%, the average value is 7.69%, the permeability distribution is 0.0073-1.1088×10-3μm2, the average value is 0.33×10-3μm2.He 8 lower is more favorable conditions in Sedimentary and diagenesis than He 8 upper, Obviously the physical properties of He 8 lower are better than He 8 upper;5.The reservoir is now in middle stage of diagenetic B in the study area.The diagenesis takes turns as follows:compaction→authigenic chlorite clay rim→quartz overgrowths→calcite cementation→kaolinite cementation→calcite dissolution→mixed layer clay→the second quartz overgrowths→hydrocarbon filling→Tuffaceous easy solution components later dissolution→calcite metasomatism.6.The primary porosity of sandstone is 37% in the study area, when experienced mechanical compaction and chemical pressure solution, the porosity lose 26.24%, later experienced the cement such as chlorite, calcite, siliceous filling, the porosity lose 7.76%, but dissolution resulted from the porosity increase 4.69%, their present average porosity is 7.69%.7.Main diagenetic facies in the study area:dissolution diagenetic facies, siliceous cementation diagenetic facies, alteration dense diagenetic facies, strong compaction dense diagenetic facies. dissolution diagenetic facies mostly distribute in the sandstone of drainage line that own coarse grain and thick genetic unit; siliceous cementation diagenetic facies mainly distribute in the miniature channel; alteration dense diagenetic facies distribute limitation relatively and little influence for reservoir, usually show the distribution of intermittent physical sandwich.strong compaction dense diagenetic facies more develop in fine grained sediments in the top of river or middle channel baras well as sand and mud interstratification in the overbank.8.High-efficient reservoirs in Su 20 block are controlled by particle size and mineral composition in petrology, particle size and mineral composition are interdependence, particle size plays a decisive role, only gritstone in sandstone form effective reservoir; particle size, size of genetic unit (sandbody) and Sedimentary Sequence character control the effective reservoir distribution, Finding the definition of high-efficient reservoirs that on the universal low permeability sandstone background must depend on sedimentary micro-facies.9.To obtain high quality seismic datum using reservoir predict, must work best in analysing frequency, signal to noise, energy, etc, in processing flows notice the disposal difference that amplitude, energy, time difference and frequence caused by dispelling excitation, receiving andnear-surface variety. By noise suppression basing on model, surface consistent amplitude and frequency correction technique, static correction technique, keep amplitude migration technology, decomposition deconvolution technology, this is a full series flow that keep amplitude process, can catch the basic data with effective reservoir seismic predict.10.The waveform characteristics of He8 and Shan 1 reservoir 1 section is divided into 4 categories in seismic general profile, just is A-type: strong amplitude, good continuity, and higher frequency; B categories:medium amplitude, medium-low frequency, poor continuous; C Class: wake-medium amplitude, low frequency and poor continuity; D category: He8 blank-weak amplitude, low frequency, poor continuity; Sh1 paragraphs blank reflex amplitude. B and C types of seismic facies separately on behalf of mid-channel bar (or point bar) and river sediment, is a favorable distribution of sandbody.11.Comparative analysis of He8 and Shanl reservoir waveform on the near & far seismic stack profile, think that could be divided into 4 types, type A resprent for increased amplitude from near to far seismic profile, just is "bright-type"; B category amplitude significantly decreased, just is"dark point"; Tpye C show that the co_rotating distorted obviously or continuity being poor, it is just co_rotating axis variational;D category changed little, that is changeless, A and B two types that can give better prediction results which reservoir of gas-bearing, can be used to provide the target block for the forecast;12.Analysis of seismic attribute show that, attribute such as time thickness, energy half time, arc length, RMS, etc can reflect the sandbody spread or enrich area generally.the classification figure of seismic predict reservoir througth integrating multi-attribute information with research results, consider that medium amplitude, medium-strong amplitude and dominant frequency ratio, low frequency, medium-high (P, G, poisson ratio, fluid factor), medium-lowλandμ, lowλ/μ, the favor accumulation area come great amplitude difference from near to far seismic profile, which reservoir development and good physical.13.According to the integration analysis of seismic sandbody predicting, reservoir sedimentary facies analysis, distribution of reservoir effective thickness and reservoir value class results, evaluate typeⅠ+Ⅱas effective reservoir and avail gas enrich area, determine the southwest and northern area of Su 20 block for further exploration object.