Research On The Fluid Distribution And Accumulation Mechanism Of Ordovician Reservoirs In Tazhong Area

Because of multi-phase hydrocarbon charging and multicycle tectonic movements, the Ordovician reservoir distribution and fluid characteristics of Tarim basin are both complex,including condensate reservoir, volatile oil reservoir and normal oil reservoir.Multiple-phase reservoir formation mechanism and the east-west condensate reservoir mechanism differences haven’t reached a consensus. Therefore, finding out the controlling factors of fluid distribution, modeling the formation mechanism of multiple-phase reservoir and establishing the condensate gas reservoir genetic mechanism models are significant not only for guiding the carbonate hydrocarbon exploration & exploitation but also for developing condensate gas reservoir geological theory.Based on mass single wells’ production performances as well as testing data and data of seismic, drilling and so on, analyzing the fluid distribution, fault developing characteristics,reservoir differences and gas invasion strength, the fluids distribution regularity and controlling factors are revealed. Tazhong Ordovician carbonate reservoirs appear to be large scale quasi-layered on the whole, and the different type reservoirs with complex and obvious heterogeneous fluids characteristics distribute alternatively without clear boundaries. The weathered crust unconformities developing on the top of O1 y and O3 l controlled the hydrocarbon output location, the reservoir depth and reservoir thickness vertically. The reservoir inhomogeneity horizontally is an important reason for the fluids differential distribution. As hydrocarbon migration pathway, strike-slip fault is important for controlling the fluids and reservoir distribution, deciding the late gas invasion strength of different areas and the different type oil reservoirs’ distribution. Height difference caused by strike-slip fault has apparently affection on fluid accumulation so that structural high in the upside is more apt to oil/gas accumulation. The late gas invasion strength effecting on the ancient oil reservoirs is the direct reason for the hydrocarbon phase and fluids characteristics’ differences.On the basis of the fluid distribution characteristics, the Ordovician formation water characteristics are studied in detail. Affected by the strike-slip faults connecting the upper and the lower, the Ordovician formation water characteristics are closely related to the deeper high sanity fluids. The formation water characteristics can be an evaluation index for gas invasion strength and conducting strike-slip fault. Water distribution and watering types is complex in Tazhong area. By mass well drilling data and performance curve of producing test water ratio, watering style in Tazhong can be classified four kinds, and different watering models are established, which is positive to predict water distribution,watering strength and watering types.Hydrocarbon source mixing is universal in Ordovician of Tazhong area and the hydrocarbon sources are different in different area. For oil, condensate of western Tazhong mainly came from Cambrian, while oil reservoir of western Tazhong and reservoirs of eastern Tazhong mainly came from middle-upper Ordovician. The late natural gas is mainly oil cracking gas and there may be any kerogen cracking gas. Combining with fluids distribution controlling factors, hydrocarbon accumulation evolution process is recovered and at the same time three accumulation models are established: condensate reservoir,volatile oil reservoir and normal oil reservoir. Two condensate reservoir mechanism modes are established respectively for the western part and the eastern part. The western are mainly migration secondary condensate gas reservoir while the eastern are mainly residual secondary condensate gas reservoir.