Evaluation Method Of Low Resistivity Reservoir Based On Logging While Drilling Research

As a kind of oil and gas reservoir with low contrast between oil and water resistivity and strong concealment,low resistivity oil and gas reservoir has abundant reserves in the middle and shallow reservoirs of Bohai Basin and great exploration and development potential.Due to the complex reservoir conditions of low resistivity reservoir,it is difficult to identify and evaluate it effectively by conventional logging methods.The conventional evaluation method based on wireline logging technology is difficult to achieve the ideal effect.Therefore,it is necessary to study the evaluation method of low resistance reservoir based on logging while drilling according to the characteristics of low resistance reservoir.In view of the difficulties existing in the evaluation of low resistivity oil reservoir,this paper combined with the data of rock physics experiment and the logging response characteristics of typical low resistivity oil reservoir in the study area,analyzed the formation mechanism of low resistivity oil reservoir from two aspects of macro geological and micro petrophysical causes,and made it clear that the main micro causes are high immobile water saturation and strong clay additional conductivity.The main controlling factors of different low resistivity reservoirs are different.The complex pore structure and high content of clay minerals are the main reasons leading to high motionless water saturation.The main reason for the additional conductivity of strong clay is the high content of montmorillonite clay minerals with strong cation exchange ability.Combining with the characteristics and genetic types of low resistivity reservoirs,an evaluation method based on the main control causes of low resistivity reservoirs is proposed,and corresponding logging interpretation models are proposed for different types of low resistivity reservoirs.The specific research contents are as follows: ○1NMR logging while drilling is not affected by electrical properties and can reflect the pore structure and fluid properties of reservoir.By establishing high immobile water action indicator(HB)and strong clay additional electrical action indicator(SC),a new method for identifying low resistivity oil layers and classifying their genetic types is constructed.○2 Based on the advantages of logging while drilling and gas logging,the parameters ΔR and C1 x,which can indicate oil and gas display,are extracted by analyzing the response characteristics of low resistivity reservoir,and a set of low resistivity reservoir identification chart combined with logging and logging is established.○3 The influences of pore structure,clay minerals and other factors on the permeability of the reservoir were clarified,and the effects of reservoir heterogeneity were reduced by classifying the reservoirs according to the genetic type.A permeability evaluation model based on the genetic classification of low resistivity reservoirs was constructed.○4Combined with the lithology characteristics of low resistivity oil reservoir,the Simon degree model suitable for argillaceous sandstone reservoir is selected for saturation evaluation.Moreover,the clay additional conductivity is corrected to reduce the influence of cation exchange in the reservoir.○5 The relationship between the output capacity of low resistivity reservoir and the movable pore volume and pore structure is clarified.On the one hand,the T2 cutoff value was determined to evaluate the movable porosity of the reservoir.Combined with the production well data,a set of production capacity prediction model based on the movable porosity of the reservoir was constructed.On the other hand,combining with the advantages of NMR logging technology to evaluate reservoir pore structure,a set of NMR structure partitioning method based on NMR data extracted from T2 spectrum was established after principal component analysis and Gaussian mixture model clustering,and the pore structure type and lithofacies characteristics were connected to realize effective prediction of reservoir productivity.The above research results have achieved good application effect in the evaluation process of Guantao Formation low resistivity reservoir in Bohai Basin,and provide a new idea and method for evaluating low resistivity reservoir by using logging data while drilling.