Log Evaluation Method Study Of Calcareous Sandstone Reservoir Based On Effective Medium HB Resistivity Model

In western region of Daqing placanticline,Saertu and Putaohua oil-bearing formation contain calcium widely which include dispersed calcium particle and ostracoda fossils.Ostracoda fossils exist in sand matrix and have less impact on well logging interpretation evaluation.Dispersed calcium particle cemented in pore leads to low-porosity,complex pore structure with smaller pore throats and smaller electrical conduction area,thus higher value in resistivity log response,which makes it difficult to distinguish oil-gas formation from calciferous sandstone formation.Therefore the coincidence rate of well logging interpretation of calciferous sandstone formation is low in the region.Aiming at calciferous sandstone formation,the research of former scholars focus on using statistical regression method to calculate calcium content,and build the function relation between calcium content and resistivity value.Then,the deep lateral resistivity is corrected to eliminate calcareous effect through resistivity index correction method based on the function relation.Resistivity index correction method is a qualitative analysis,which does not analyze the effect of calcium on rock resistivity quantitatively from conductive mechanism and saturation model.In this paper,based on characteristic of calciferous sandstone conductivity,effective medium HB resistivity model is applied to analyze the effect of calcium on rock resistivity quantitatively.The function relation between cementation exponent and calcium content,shale content is built by controlling variable using artificial core technology.Finally,calciferous sandstone formation quantitative analysis method is established based on effective medium HB resistivity model.First,lithology can be divided into calcareous cementation sandstone,ostracoda sandstone,calcareous intercalation and sandstone through thin section data,porosity-permeability data and carbonate analysis data.According to log characteristics of different lithology,calcareous cementation sandstone,ostracoda sandstone,calcareous intercalation and sandstone are identified by the hierarchical analytical process of crossplot technique.Calcareous cementation sandstone has a significant impact on resistivity log response,so calcareous cementation sandstone is identified mainly in this paper.The identification result shows coincidence rate of calcareous cementation sandstone in Saertu oil-bearing formation is 82.4%.And the coincidence rate in Putaohua oil-bearing formation is 85.7%.After lithology identification,based on effective medium HB resistivity model,clay-water resistivity computational formula is improved through dual-water model analysis results.Meanwhile,in order to conduct a resistivity quantitative research of the effect of shale content and calcium content on the resistivity of rock,the artificial cores are obtained using artificial core technology to eliminate the uncontrollable parameters disadvantages of nature cores.The artificial cores have the same size distribution of grain as the size of the formation rock grain.And then the resistivity experiment measurement is achieved after the artificial cores are saturated with different salinity water.Based on improved Berg model,the relation of cementation exponent m with shale content and calcium content is established through the resistivity experimental data.Dispersed calcium particles is added to improved Berg model as dispersed phase,and the effective medium HB resistivity model of calciferous argillaceous sandstone is established.Interpretation parameters calculation is necessary when saturation model is applied to the formations of the region.So well logging calculation methods of porosity,shale content,calcium content,clay content are achieved by core scale logging method.Thus,well logging evaluation method suitable to calcareous cementation sandstone formation is obtained in this area.Finally,the effective medium HB resistivity model of calciferous argillaceous sandstone is applied to the log evaluation of nine calcareous cementation formations from two wells in this region.Comparison of the interpretation result with oil testing shows eight formations are correct,and the coincidence rate is 88.9%.Improved Berg model is also applied in this area where cementation exponent is calculated by volume-weighted method,and the comparison of interpretation result with oil testing shows six formations are correct and the coincidence rate is 66.7%.It can be seen that the coincidence rate of the effective medium HB resistivity model of calciferous argillaceous sandstone is higher than improved Berg calculation method.This result shows that the effect of clay and calcium on the conductivity of the rock is fully considered in the effective medium HB resistivity model of calciferous argillaceous sandstone,and this model is suitable for well logging quantitative evaluation of Saertu and Putaohua oil-bearing formation in the western region of Daqing placanticline.