Identification Of Carbonate Rock Lithology Of Changxing Formation In Yuanba Area

Carbonate reservoirs are typical unconventional oil and gas reservoirs.Carbonate lithology identification is a key step in the description of reservoir characteristics.Logging methods are an important means of identifying lithology.However,carbonate rock has various lithology,complex pore structure and strong heterogeneity,which makes conventional logging technology face major challenges in identifying lithology.The Yuanba area is located at the junction of the Sichuan North Depression in the Sichuan Basin and the low-lying tectonic belt in the Sichuan Basin.The Changxing Formation developed two types of reservoirs,the bioreef and the shoal,which have the characteristics of mesopores and medium-low permeability.The reservoir space types are irregular dissolved pores and caves,and a small number of micro-cracks.The pore throat sorting is poor.The structure is complex and the types of pores are diverse.The rock composition of the reservoir rocks is diverse due to different diagenesis.Such research areas increase the difficulty of identifying lithology of carbonate rocks.Based on the analysis of reservoir characteristics,well logging data and geological data,this paper carries out lithology identification of carbonate reservoirs,and conducts carbonate lithology through mineral component inversion method,Fisher discriminant method and random forest method.Qualitative and quantitative descriptions,and a systematic study of the Changxing Formation carbonate reservoirs in the Yuanba area,and achieved the following results:Inversion of mineral composition is one of the important means to identify the lithology of carbonate rocks.This paper determines the mineral composition of the formation by combining the observation of thin slices and core with the diagenetic type of the block,and finally selects dolomite,calcite,quartz,The four minerals of iron ore,the five-element volume model of dolomite,calcite,quartz,iron ore and pores are constructed.The five-element overdetermined equations are constructed based on the model,and solved by the least square method with constraints to calculate the carbon.The percentage of mineral component volume of the acid rock reservoir.Finally,according to the mineral content classification lithology and logging lithology profile comparison,the lithology comparison results are basically the same,which provides reference for the carbonate lithology identification logging method in similar research areas.Facing the complex lithology of carbonate reservoirs,conventional logging techniques are difficult to effectively classify carbonate lithology,and at the same time,to solve the mineral component inversion and identify lithology,due to the logging curve The continuous qualitative change of lithology is proposed by applying mathematical methods to identify lithology.According to the lithology characteristics of the Changxing Formation in the Yuanba area,four logging parameters,such as density,neutron compensation,acoustic time difference and deep resistivity,which are sensitive to lithology are selected,and the lithology is divided by the intersection diagram method,but for the dolomite The transitional lithology between the limestone and the limestone is poorly differentiated.In order to divide the lithology more finely,it is proposed to classify various lithologies into dolomites and limestones,and then classify the lithology of dolomites and limestones,and finally obtain them by Fisher discriminant method and random forest method.Realize and establish a lithology identification model,the discrimination result has a high accuracy rate and meet the accuracy requirements.