Comprehensive Study Of High-resolution Sequence Stratigraphy And Storage Sandbody Of The Second Member Of Shanxi Formation In Ordos Basin

Ordos basin is one of the most potential gas reservoir region in China and the Upper Paleozoic is the important exploration target. Changbei gas field is a river lothology-stratigraphic trap gas pool on the west trend monocline background, it is located in the east of the basin, it has thin bed, low-porosity, low-permeability, low-pressure, low-deliverability character and develop difficulty(HeGuang-huai, 2002), especially to develop this thin bed and unhomogeneity seriously river sandbody gas pool is much difficulty. Along with horizon development well to implement, some problem became more and more gravity, such as sandbody'scale and sandbody'boundary was uncertainty and layer pressure was uneqilibrium for different well area development degree is not community. These taked a few difficulty of comprehensive evaluaterating, deploying horizon development well, adjusting well trackway for the gas field, and it might take any geologic risk.Aimed at these problem, this paper taked 63 well drilling's rock mineral document and logging document as main analysis object, combined reservoir sedimentology, sequence stratigraphy, logging geology together to research sedimentary system, sequence stratigraphy, lithofacies paleographic, sandbody distribution three dimensional visualization, reservoir character and reservoir sandbody comprehensive evaluation, it offers reference and criterion for Changbei gas field gas reservoir's exploration and development.Based on the above researching, this paper has been gained some progesses and innovations:1. We have taked sedimentary facies research on the second member of Shanxi formation of Changbei gas field, this area pertained to marine facies braid river delta sedimentary system, we have gived a detailed discriiption on different subfacies, microfacies, sandbody's sedimentary character and distribution for the braid river delta sedimentary system. Based on it, we have been constructed fluvial dominated delta sedimentary model from north to south.2. Using high-resolution sequence stratigraphy theory and technique method to analyse sequence on Changbei gas field, we divided it to one long-term, two middle-term, four short-term, nine super short-term basal level cycle sequence and discrpited its structure model, sedimentary series, distribution model, discussed the relation between middle-term, short-term, super-term basal level cycle structure and resevoir growth. And then based on the high-resolution sequence stratigraphy equitime comparison, constructed high-resolution of accuracy degree's equitime stratigraphy framework, choped and equitime traced on sand layer, small sandbody, single sandbody, putted forward a Stratigraphy dividing scheme to sand layer(big scale), small sandbody(middle scale), single sandbody(small scale).3. Based on high-resolution sequence analysis and stratigraphy equitime trace comparison, taked sequence-lithofacies palaeogeographical technique, choosed middle-term and short-term hemiscycle which equivalented to sand layer and small sandbody as stratigraphy unit, compiled a few short time scale sediment microfacies picture. And then taked phase control construction model as direction, combined sequential indication mathematics method, choosed middle-term and short-term hemiscycle which equivalented to sand layer and small sandbody as equitime stratigraphy unit, constructed short time scale's sandbody three dimensional model. Based on the middle-time and short-time hemicycle sediment microfacies distribution foundation, sumed sandbody's genetic type, geometric shape, flat distribution and evolution character, analyzed the relations between reservoir quality and base level cycle, this offers to futher forecast and evaluate for high permeability zone.4. After researched on the reservoir character of changbei gas field, based on the sand stone reservoir pore structure and physical property, we have certained accumulation space was remainder primary pore and secondary intergranular dissolved pore, break seam and grain boundary seam forms fragmental rock accumulation space. Accumulation type is mained as low pore and low permeability reservoir.5 Based on the basic geology condition foundation, choosed sandbody total thickness, sand stone density, drilling encounter rate, physical property, reservoir growing situtation and sandbody space distribution character as ration evaluation indicator, we have constructed small layer sandbody and single sandbody comprensive indication system and have taked quantitative evaluation to small layer sandbody and single sandbody's beneficial growth layer and high permeability zone of the two member of Shanxi formation. From these evaluation, we have got five best beneficial single sandbody layer and four relative beneficial single sandbody layer and have forecasted nine high permeability zone of advantageous litho stratigraphic trap condition and two sandbody continuous overriding beneficial prediction zone..