Petroleum Geochemometric Differentiation Of Crude Oils

There are many variables and parameters in petroleum geochemistry,and they are interacted and interconnected.It is difficult to consider all parameters for traditional data analysis methods,while petroleum geochemometrics has a unique advantage in comprehensive consideration of multiple parameters.Chemometrics can extract the efficacious information from dada sets,reveal the geochemical significance it contains and provide a reliable basis for oil-oil and oil-source correlation.It is important to select the appropriate chemometrics method based on the geological background and the characteristic of crude oils in the study of geochemistry.The Jiyang Depression is characterized by multiple sources and multistage hydrocarbon generation.The Dongying Depression and Zhanhua Depression are the most important petroliferous structural units in the Jiyang Depression.In this study,crude oil samples recovered from the Dongying Depression and Zhanhua Depression were investigated to gain the geochemical characteristic,and geochemometrics was employed for oil-oil and oil-source correlation.The upper Es4 and lower Es3 intervals are the main source rocks in the Dongying Depression.The upper Es4 was deposited in a saline lacustrine environment that contained a stratified water column,which was beneficial to organic preservation.It has experienced several periods of hydrocarbon expulsion,and generated low-mature to mature oil.The lower Es3 was deposited in a slightly oxidized and brackish to freshwater lacustrine setting.It displays a single-stage hydrocarbon generation process that produced only mature oil.A total of 57 crude oil samples from the Dongying Depression were selected for geochemical analysis.HCA and PCA identified four distinct oil families.Oils in family I were mainly from the Ed formation of the Wangjiagang Oilfield(located in the south gentle slope),their source rocks should be deposited in a reducing,stratified saline environment,and contains microalgal material that could produce lots of wax,can't match any source rocks known up to now.Family II oils were mainly from the Niuzhuang sag and the south gentle slope,and the maturity is low.The source rocks were deposited in strongly reduced stratified saline environment,and have more algae input than bacteria,which is consistent with the upper Es4 interval.The source rock of Family III(mainly collected in the southwest of the Dongying Depression)was inferred to be the lower Es3 interval,which was deposited under freshwater depositional conditions with algae and prokaryotic or microbially reworked terrigenous organic matter input.The source-and depositional-related parameters of Family IV exhibit variation,the source rocks are the upper Es4 and lower Es3 intervals.Three endmembers were identified by ALS,they are stand for a lower thermal maturity upper Es4,a mature upper Es4 and the lower Es3 source rocks,respectively.Their contribution was 11%,46%,43%,respectively.The Zhanhua Depression is located in the northeast of the Jiyang Depression.The source rocks are mainly distributed in the Bonan,Gubei and Bonan sag.65 crude oil samples were collected from the Zhanhua Depression for organic geochemistry study.ALS was employed to unmixing the oils.The contribution of the upper Es4 and the lower Es3 source rocks for oils in the center of the Bonan Sag and the Yihezhuang Arch is close to 1:1.Oils in the south and west of the Bonan Sag,Gubei Sag were mainly from the lower Es3 source rock.The contribution of the upper Es4 and the lower Es3 source rocks for the Gudao High change greatly.Oils in the Luojia and Chenjiazhuang High stored in shallow formation and are at low-mature stage,the major source rock is the upper Es4 interval.The Gudong oilfield is in the eastern margin of the Zhanhua Depression,and charged by multiple source rocks.31 crude oil samples were obtained from the Gudong Oilfield for oil-oil correlation.The oils were classified into four families by HCA and PCA.Family I is at mature stage,the source rock was deposited in fresh to brackish water,microalgae were the dominant organic matter input,which is consistent with the lower Es3 source rocks in the Gunan Sag.The source rock of Family II was deposited in weak oxidative environment,the terrigenous plants had a greater contribution for the original organic matter,thus corresponding to the Ed₃formation in the Huanghekou Sag.Oils in Family III are widely distributed,their source rock was inferred as the lower Es3 in the Huanghekou Sag.It was deposited in an oxic environment with low salinity.Family IV is low-mature oil,the source rock was deposited in stratified saline and weak oxide environment.The inferred source rock is the Es1 interval in the Huanghekou Sag.This study is designed to better understand the geochemical characteristic of oils in the Dongying and Zhanhua Depression,and chemometrics was employed for the classification of crude oils and deconvolute the mixed oils.This study can provide more information for the oil exploration in the Jiyang Depression,which is meaningful for oil exploration.