| Low resistivity reservoirs have become an important source of increasing reserves and production in domestic oilfields.However,with deeply exploration,low resistivity reservoirs containing conductive pyrite minerals have been found in the sandy conglomerate reservoirs of Qigu Formation in Che 60 well area of Junggar Basin and in A-4 fomation of Ba I and Ba II structures in Bayindulan Sag of Erlian Basin.Because pyrite is a metal mineral and depends on electronic conduction,the conductive mechanism of hydrocarbon and pyrite bearing low resistivity reservoirs has changed and the conductive law becomes complex compared with conventional hydrocarbon bearing reservoirs.Especially,when dispersed clay,laminated shale,conductive minerals exist in the same hydrocarbon bearing reservoir,the conductivity law of the hydrocarbon bearing reservoir becomes more complicated.The resistivity models in current use cannot be used to describe the conductive law of low resistivity hydrocarbon reservoir with conductive pyrite minerals.Therefore,it is of great significance to study the conductivity law of low resistivity reservoirs with conductive pyrite minerals from experiments and conductivity theory comprehensively and systematically,and establish a resistivity model suitable for interpretation of low resistivity reservoirs with conductive pyrite mineralsAiming at the difficulty of obtaining natural cores with different shale distribution forms and different shale and pyrite contents,the matrix-conducting artificial rock samples with different pyrite,shale content and distribution forms are manufactured,and the resistivity measurement and related other experimental measurements of the artificial rock samples are carried out to study the conductive law of artificial rock samples with matrix-conducting.On the basis of further study of conductive mechanism of matrix-conducting low resistivity reservoir,three general resistivity models of matrix-conducting low resistivity reservoir are established by using symmetrical effective medium conductive theory,connectivity conduction equation combined with HB equation or general Archie equation.Then the models are theoretically analyzed and experimentally verified,and the applicability and universality of them are evaluated.In this thesis,matrix grains covered with adhesive film are made firstly by mixing pyrite grains with quartz grains of different sizes in a certain proportion.Then illite clay grains are added to them,and rectangular pyrite-bearing dispersed clayey cores are compacted under the conditions of high temperature and high pressure.Finally,a layer of illite clay grains is compacted on them to make out rectangular rock cores containing pyrite,dispersed clay and laminated shale.After drilling and encapsulation,117 artificial matrix-conducting samples with different pyrite and shale contents and shale distribution are prepared.By adopting the experimental measurement scheme of classified and sequential items,the porosity-permeability measurement,resistivity measurement,whole rock analysis,particle size analysis,nuclear magnetic resonance analysis,mercury injection experiment and cation exchange capacity measurement of artificial rock samples are carried out,and the acquisition of a whole set of experimental data of "the same" rock sample has come true.The contents of dispersed clay and pyrite are determined by using the whole rock analysis data,and the laminated shale content is calculated by area ratio method.The conductivity of dispersed clay and pyrite is determined by using the resistivity data of dispersed clayey sand and pure pyrite samples,and the conductivity of laminated shale is also determined by using the experimental data of pyrite-bearing dispersed clayey and laminated shaly samples with different laminated shale contents.The ranges of porosity,permeability,pyrite content,dispersed clay content and laminated shale content of the artificial samples are 14.6%?33.1%,4.49 m D?138.84 m D,0%?74.1%,0%?13.7%,0%?28.9%,respectively.The conductivities of dispersed clay and pyrite are about 0.011S/m,0.0132S/m at room temperature,respectively.While they are about 0.027S/m and 0.041S/m at high temperature,respectively.The experimental data analysis shows that the artificial samples not only meet the experimental design requirements,but also meet the needs of conductive law research of matrix-conducting low resistivity reservoirs.Based on the measured experimental data of pyrite-bearing artificial rock samples with dispersed clay and laminated shale,the effects of pyrite content,dispersed clay content,laminated shale content,shale distribution and temperature on the conductivity of samples are studied.The conductivity of water-saturated artificial pyrite-bearing dispersed clayey and laminated shaly rocks increases as laminated shale,dispersed clay and pyrite contents increase.While the conductivity of hydrocarbon-bearing artificial pyrite-bearing dispersed clayey and laminated shaly rocks increases,and the resistivity index decreases as laminated shale,dispersed clay and pyrite contents increase,which follows the non-Archie law.Even if the sum of dispersed clay content and laminated shale content is constant,the conductivity of samples varies with dispersed clay content or laminated shale content.Therefore,the influence of shale distribution on the conductive law of rocks cannot be ignored.Based on the research results of conductive law of pyrite-bearing artificial rock samples with dispersed clay and laminated shale,and analysis of the conductive mechanism of matrixconducting low resistivity reservoir,the matrix-conducting dispersed clayey and laminated shaly sands are divided into seven components: laminated shale,dispersed clay,irreducible water,movable water,hydrocarbon,conductive matrix grains and non-conductive matrix grains.Then three general resistivity models for low resistivity reservoirs of five genetic types are established by using effective medium conductivity theory,connectivity conduction equation combined with HB equation or general Archie equation,The theoretical analysis shows that all three models satisfy the theoretical boundary conditions,and the conductivity laws described by the models agree well with theoretical understandings as contents and conductivities of pyrite,dispersed clay,laminated shale increase.The influence of the parameters of the model on conductive laws of matrix-conducting shaly rocks predicted by the model is studied by single factor analysis method.The rock resistivity for matrix-conducting low resistivity reservoirs predicted by the symmetrical effective medium resistivity model increases as percolation rates of dispersed clay and pyrite increase,and decreases as the percolation exponents of dispersed clay and pyrite increase.The rock resistivity for low resistivity reservoirs predicted by the resistivity model with connectivity conduction equation combined with HB equation or general Archie equation increases as the cementation exponent of conductive matrix grain and exponent of conductive clay phase increase.Based on resistivity data of pyrite-bearing dispersed clayey samples,the parameter values and parameter formulas of each model are established with the optimization method.Then parameter values and formulas are substituted into the model to calculate the conductivity and water saturation of pyrite-bearing dispersed clayey and laminated shaly rock samples.The comparison with the experimental data shows that the three general resistivity models proposed in the thesis can describe the conductive law of matrix-conducting dispersed clayey and laminated shaly rock samples.Theories and experiments show that all three models can describe the conductive laws of low resistivity reservoirs caused by conductive matrix grains,plentiful clay,high irreducible water saturation,interbedded sandshale and high formation water salinity.Among them,the effective medium resistivity model is more applicable and versatile.In the thesis,the proposed manufacture technology and experimental measurement scheme for artificial matrix-conducting dispersed clayey and laminated shaly rock samples have guiding significance for manufacture and experiment of artificial samples.Three general resistivity models proposed for low resistivity reservoirs with the coexistence of five genetic types can improve accuracy of saturation of low resistivity reservoirs.The research results in the paper are of great practical value. |
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