Research Of Reservoir's Quantitative Characterization Method And High-quality Reservoir's Formation Mechanism On Tight Sandstone Reservoirs

Reservoirs within the Chang 4+5 member of the west Jiyuan oilfield are really some of the tight sandstone.A large amount of the related oil test and production data have revealed that much oil and gas resources are still enriched in those reservoirs although part of resources have been explored and utilized.Thus in order to increase the petroleum production in the future,it's important to do some more exploration work within the Chang 4+5 member.The aim of doing the progressive exploration is to have a comprehensive and clear understanding on sedimentary distribution,physical characteristics,diagenetic characteristics,oiliness and other content of the target reservoirs,and it is suggested to solve the problems turned out in such work in a semi-quantitative or quantitative way.However,most of research findings regarding those reservoirs are qualitative,unreliable,and simple.Here listing some reasons:the lithology and lithofacies are universally recognized based on personal experience or the usage of some oldest and inefficient methods that cannot provide the recognized results with satisfactory accuracy,thus the conclusions derived from the single-well facies,the multi-wells facies and the plane facies analysis becoming unreliable;the models applied for calculating porosity,permeability and other physical parameters generally need to use some statistical parameters in their data process,and naturally the accuracy of those parameters depends on the amount and the kind of raw statistical data,so that the validity of the results obtained from those models remains to be discussed;results acquired from the pore evolution method that uses to reveal the reservoir's densification process often show large errors in order that the corresponding speculative conclusions handled in present are not reliable enough;some explanations related to the formation mechanism of high-quality reservoirs seem to be one-sided.As such,in order to solve the problems above and then capture more oil and gas resources from the Chang 4+5member,some researches on reservoir characteristics,prediction of favorable zones and other work will be done in this dissertation.In this dissertation,based on both theories of geology and information processing,some research ideas and methods will be specially used to get a new understanding on reservoirs characteristics,oil reservoirs distribution and other things of the Chang 4+5member.The details of those ideas and methods are:firstly,the isochronal stratigraphic framework will be established after stratigraphic division which should be completed in accordance with the analysis of the logging response characteristics of some important formations;secondly,lithology,lithofacies and other sedimentary characteristics will be known on the basis of core observation,and then with the analysis of the logging data,some neural networks will be used to recognize the lithology and the lithofacies of the non-core wells,thus the reasonable conclusions of the laws of sedimentary distribution can being deduced from the single-well facies,the multi-wells facies and the plane facies analysis;thirdly,a small part of reservoirs will be classified according to the comprehensive understanding on their sedimentary,physical,diagenetic and other characteristics,and then based on the defined classification standard the rest reservoirs will be evaluated by the fuzzy method,so that the distribution of the reservoirs can be revealed;in this step,porosity,permeability and other physical parameters will be calculated by a compound neural network in order to avoid the application of some kind of statistical parameters,and some image processing techniques will be used to analyze and evaluate the pores and the throats from thin sections,therefore without the effects of subjective factors,the obtained pore and throat data can being more reliable;fourthly,a kind of neural network will be adopted to correct the results acquired from the pore evaluation method so as to build up a more reliable densification process of the reservoirs,and then with the comprehensive analysis on the densification process of reservoirs,the hydrocarbon generating history of source rock and other data,the understanding on the relationship between reservoir's densification process and hydrocarbon accumulation and the formation mechanism of high-quality reservoirs can be got;finally,under the deep analysis of the reservoirs in the aspects of their sedimentary,physical,diagenetic,oiliness and other characteristics,the favorable and the recommended development zones will be predicted,which will be used to guide the following work of oil and gas exploitation.The achieved important research findings are:the Chang 4+5 member can be direction of sediment provenance is from NE to SW;the main type of sedimentary microfacies includes subsea distributary channel,subsea natural barrier and subsea interdistributary bar;the average thickness of sand bodies shows a large-small-large permeability of the Chang 4+5 member are respectively about 10.89%and 0.65m D;according to the porosity and permeability,the overall storage capacity of the reservoirs main type of pores includes intergranular pore,intergranular dissolved pore and intercrystalline pore,and the main types of throats are flake throat and arciform throat;the permeability capacity of reservoir largely depends on the average radius of throat;the calcite-cemented and the caly-cemented reservoirs are respectively suited to acidized with hydrochloric acid and mud acid;the main type of diagenesis includes mechanical compaction,dissolution and cementation;the main type of diagenetic facies includes film-shaped chlorite cementation-intergranular pore facies,illite with chlorite cementation-dissolution facies,illite cementation facies and carbonate cementation;the main stage of the diagenetic evolution of reservoirs has reached in the mid-stage A;the reservoirs can be divided into 4 types,including the low permeability,the extra-low permeability,the ultra-low permeability and the tight,or 6 subtypes,including the ?,the ?,the ?_a,the ?_b,the ?_c and the ?;the overall quality of the reservoirs shows a densification limitation standards of the radius of throat,the porosity and the permeability are respectively about 0.539?m,10.5%and 0.95m D;the densification evolution of the reservoirs is comprised of 4 stages,all of which are the mechanical compaction,the compaction with the early cementation,the dissolution and the late cementation;from the late Triassic to the early stage of the early Cretaceous,the oil and gas progressively accumulated in the reservoirs after the reservoirs had being tight,but from the early stage to the late stage of the early Cretaceous,the densification of reservoirs and the accumulation of hydrocarbon proceeded at the same time;the formation of high-quality reservoirs can be explained by the pore preservation and the pore extension mechanism;the overall distribution range of oil formations shows a thickness of the oil formations unexpectedly shows a large-small-large changing rule;the numbers of predictive favorable zones and recommended development zones within the Chang 4+5 member are respectively about 30 and 25,and the distribution areas are respectively about 115.5km² and 57.1 km²,and the estimated hydrocarbon reserves is 4+5₂²¹ have the more numbers,the larger distribution areas and the more hydrocarbon reserves in the aspects of predictive favorable zones and recommended development zones.The important research findings indicate that the sedimentary process of reservoirs mainly experienced a early transgression and a late regression from the Chang 4+5₂²² to the Chang 4+5₁¹¹;the overall quality of reservoirs shows a high-low-?high-medium? and gas progressively accumulated in the reservoirs after those reservoirs had being tight,but in the late period,the densification of reservoirs and the accumulation of hydrocarbon proceeded simultaneously;pore preservation and pore extension are the two main mechanisms that controls the formation of high-quality reservoirs;under the comparisons of 8 formations in the aspect of the number,the distribution area and the hydrocarbon reserves of predictive favorable zones and recommended development zones,the best formation for the exploitation is the Chang 4+5₂²²,and the second choice is the Chang 4+5₂²¹.