Logging Evaluation Of Lower Youshashan Formation In 102 Area Of YD Oilfield

The study area is located at the southern edge of the Yingxiongling thrust uplift belt in the Qaidam Basin.It is adjacent to the Youshashan Oilfield,the Gaskule Oilfield,and the Wunan Oilfield,and is rich in oil and natural gas resources.There are many vertical layers,long intervals of oil and gas sections in YD oilfield.The faults are well-developed,and the physical properties greatly vary from different reservoirs.There exist major difficulties in the research of four-property relations,the calculation of reservoir parameters,as well as the identification of fluid types.Furthermore,there are still deficiencies in the understanding of hydrocarbon distribution and gas reservoir types.In view of the current problems,data of well logging,geological logging,coring,oil testing,and production dynamics were comprehensively used to the research of reservoir four-property relationship,fine interpretation of reservoir parameters,fluid type identification,and three-dimensional geology modeling,etc.,and the main achievements are as follows:Based on the characteristics of core lithology and logging curves,a model of lithology identification by neural network was established,and the coincidence rate was 90.4%after testing.And on the basis of lithology identification of individual wells,logging lithology was corrected,which has laid the foundation of reservoir division.Through the study of four-property relations,it could be concluded that the reservoir lithology is mainly dominated by siltstone,with an average porosity of 16.3%and an average permeability of 58.8×10^-3?m²,which belongs to medium porosity and medium permeability reservoirs.Porosity and permeability of the effective reservoir lower limit standard are respectively 12.2%and 0.57×10^-3?m² determined by using of the loss method,test method as well as minimum flow pore throat radius method.The calculation models of porosity and permeability are established by neural network,and the correlation coefficient R is greater than 0.91,which has been greatly improved compared to the conventional reservoir parameter calculation model.A number of intersection maps and neural network fluid identification models were established based on the decision tree ideas by comprehensive using of well logging,geological logging,oil testing,liquid production profiles and other data,and the methods included amplitude value method,the ratio method and the difference value method,etc.The coincidence rate of the models was lager than 90%.Through the work of single-well fluid identification,reservoir profile comparison and oil-gas distribution,it was concluded that the sand group VII in the study area was dominated by the development of oil and gas layers,and the gas zone was mainly controlled by well L22 and L12,which is located at the high part of the structure.The oil rim is distributed at the lower part and the reservoir type belongs to the gas gap gas reservoir.The three-dimensional geological model of the study area was established by using the calculation results of reservoir parameters,formation lithology identification,and geological stratification.The study area was characterized by high elevation in the east and reduced elevation in the direction of the north-west and south-east.The distribution of sandstone lithofacies in the northeast direction is relatively continuous,and the higher porosity is mainly distributed in the well L31-L27 in the northeast direction.The distribution areas of high permeability and high oil saturation are consistent with the distribution areas of high porosity.The quantitative classification criteria for reservoir types in the study area were established by using the grey correlation method.Based on the established criteria,the reservoirs can be divided into three types,of which type I is a high quality reservoir with an evaluation score of?0.65;type II is a medium reservoir,with an evaluation score of 0.35 to 0.65;type III is a poor reservoir,with an evaluation score of?0.35.The individual wells in the study area mainly contain type II reservoirs.The distribution of layer 3 and layer 8 sand bodies is relatively continuous,and the favorable areas of layer 3 are mainly distributed in the middle of study area next to well L32,L26,L28 and next to well L1 and L16;the favorable reservoirs of layer 8are mainly located next to well L9,L34 and next to well L1,L12,L16,and L39.