Petroleum in the Jurassic Reservoirs within the Eastern Fukang Sub-depression,Junggar Basin,NW China:Correlation and Source Rock

The origin and source of the petroleum in the Jurassic reservoirs within the eastern Fukang sub-depression were geochemically investigated.They show thermal maturities matching the peak generation stage,while the condensates are at the early stage of intense cracking.Oils and condensates may have experienced mild evaporative fractionation,while mixing of severely biodegraded with non-biodegraded oils has occurred.Using biomarkers and isotopes,petroleums were classified into GroupⅠ,ⅡandⅢgenetic groups,with GroupⅢfurther divided intoⅢa andⅢb subgroups.GroupⅠpetroleum displays heavy carbon isotopes,a strong predominance of pristine over phytane,high C_(19)and C_(20)tricyclic and C_(24)tetracyclic terpanes,low gammacerane,and dominant C_(29)steranes,while GroupⅡshows light carbon isotopes,a predominance of phytane over pristine,high C_(21)and C_(23)tricyclic with low C_(24)tetracyclic terpanes,high gammacerane and dominant C_(27)steranes.GroupⅢa petroleum shows mixing compositions of GroupⅠandⅡ,while GroupⅢb displays similar compositions to Group I,but with significantly higher Ts,C_(29)Ts and C_(30)diahopane proportions.Oil-source rock correlation suggests GroupⅠandⅡpetroleums originate from Jurassic and Permian source rocks,respectively,while GroupⅢa are mixtures sourced from these rocks andⅢb are mixtures from Jurassic and Triassic source rocks.

Equilibrium modeling of water-gas systems in Jurassic–Cretaceous reservoirs of the Arctic petroleum province, northern West Siberia

To reveal the equilibrium state of oil and gas and water in a petroliferous basin with a high content of saline water, calculations of water-gas equilibrium were carried out, using a new simulation method, for the Arctic territories of the West Siberian oil and gas bearing province. The water-bearing layers in this area vary widely in gas saturation and have gas saturation coefficients(C;) from 0.2 to 1.0. The gas saturation coefficient increases with depth and total gas saturation of the formation water. All the water layers with gas saturation bigger than 1.8 L/L have the critical gas saturation coefficient value of 1.0, which creates favorable conditions for the accumulation of hydrocarbons;and unsaturated formation water can dissolve gas in the existent pool. The gas saturation coefficient of formation water is related to the type of fluid in the reservoir. Condensate gas fields have gas saturation coefficients from 0.8 to 1.0, while oil reservoirs have lower gas saturation coefficient. Complex gas-water exchange patterns indicate that gas in the Jurassic–Cretaceous reservoirs of the study area is complex in origin.

Restoration of the pre-Jurassic paleogeomorphology and its control on hydrocarbon distribution in western Ordos Basin

In recent years,the discovery of the Jurassic oil reservoirs in the Western Thrust Belt of the Ordos Basin reveals that the Jurassic formation in this area has huge oil and gas potential.The pre-Jurassic paleo-geomorphology plays a vital role in the formation of the Jurassic oil reservoirs.In this paper,the impression method is applied to restore the pre-Jurassic paleogeomorphology of the Hongde area in the western Ordos Basin,using a large number of drilling,logging,well testing and the latest 3D seismic data.The pre-Jurassic paleogeomorphological units in the study area can be categorized into five groups,including ancient channel valley,ancient terrace,slope,interchannel mound,and low residual mound facies.The oil reservoirs are mainly distributed in highland areas such as slope belts and low residual mounds,the main areas where hydrocarbons accumulate.In addition,the branch ditches in the study area are developed to the southeast and merged into the Ganshan ancient channel.The sandstone in the confluence area of the branch gully is well sorted and connected under frequent scouring by the river.The sand bodies of good connectivity therefore form a drainage system for long-term hydrocarbon migration.The formation of the Jurassic reservoirs in the study area is mainly affected by sedimentary facies,deposition location,and hydrocarbon migration pathway(or fault)of pre-Jurassic paleo-morphology.The results from this study can be useful for the prediction of the Jurassic sweet spots in the western margin of the Ordos Basin.

The effect of physical property change on the water flooding development in Changqing oilfield Jurassic low permeability reservoir

Changqing old oilfield Jurassic reservoir's average calibration recovery is 24.7%,with geological reserves recovery of 16.6%,water cut of 65.2%.And most of Jurassic reservoirs are in the middle and later field life,part of them has entered the high water cut and high recovery stage.Traditional water flooding way for improving oil recovery becomes more difficult,and new method has to be considered.Maling oilfield BS district is a typical representative,with high water cut of 90.8%,high recovery percent of 26.1%and low oil recovery rate of 0.25%.To explore the new way to improve oil recovery,the polymer and surfactant(SP for short)important pilot test has been developed.The low permeability reservoir indoor core data in high water cut stage and inspection well results indicate that the reservoir permeability,pore combination characteristics and pore type changed greatly after long-term water flooding development.These changes bring more difficulties to the continue development,especially the high injection pressure,which can cause other problems for well pattern infilling and EOR.This paper takes the high injection pressure problem of Maling BS district Jurassic reservoir for example,analyzes the physical property change law on the following aspects:the development mode in the past,core analysis,formation sensitivity,interstitial matter,well test interpretation results,in order to help to further effective development and provide important parameters for tertiary oil recovery technique for similar reservoirs and others.