Research On Characteristics And Control Function Of Reservoir Forming Of Hydrocarbon Pathway System In Petroliferous Basins

Hydrocarbon pathway system is the “bridge” for oil and gas transporting from hydrocarbongeneration center to traps. To determine conduit system in detail is not only to confirmmigration pathways, but also find reservoirs, which indicates directions for exploration andproduction deploy. The conduit system is divided into four types: fault, sandstone transportinglayer, unconformity and multiple conduit systems. To determine characteristics and control onreservoir forming of conduit system in petroliferous basin, researches has been done to studyconduition forms, influence factors, favorable pathways and trace evidences of fault,sandstone transporting layer and unconformity respectively. Taking the typical areas in BohaiBay Basin, Songliao Basin and Tuha Basin as examples, the analysis on conduit ablility andcontrol on reservoir forming of three kinds of conduit systems illustrated transportcharacteristics and reservoir forming control modes of each kind of conduit system. And onthis basis, controling reservoir characteristics of four kinds of multiple conduit systemscontaining fault-carrier bed, fault-unconformity, carrier bed-unconformity and fault-carrierbed-unconformity were concluded.First of all, on the basis of previous study, research on characteristics and control onreservoir forming of fault transporting hydrocarbon has been done according to fieldobservation,3D seismic data, logging, test and biomarker. The results showed asfollowing(1)There are three stages during fault episodic activity. They are active stage,active-intermittent stage and intermittent stage. During active stage, migration dynamicscontains each or both of tectonic stress and overpressure. The passages are associated cracks.It is mainly episodic migration mechanism with high migration rate. Duringactive-intermittent stage, residual pressure and buoyancy are dynamics and induced cracks arepassages. The migration rate is high. During intermittent stage, it is a slow seepagemechanism controlled by buoyancy with interconnected pores as passages.(2)There are fourtypes of fault conduit forms, which are transport upward along faults, transport along faultstrike, transport downward along fault and transport across fault plane. The transport of threeprevious forms becomes more difficult one by one. However, the ability of transport acrossfault plane is determined by migration force and match of ratio of reservoir permeability.(3)There are differences in controling reservoir characteristics of different fault conduit forms.In transport upward along fault, transport passage of numbers of faults delivers morehydrocarbon than linear conduit by single fault. In transport along fault strike, there was morehydrocarbon accumulation at the two sides of fault strike. In downward transport form,hydrocarbon mainly gathered at the footwall of oil source fault.(4) The effective fault ridge ofoil source fault of the No.1structure of Nanpu sag in Bohai Bay Basin is dominant transportpassage. The analysis on biomarker trace indicated that fault is characterized by “F” type migration. The threshold value of residual effective thickness of NgⅢ volcanic cap rocksdetermined whether oil and gas can pass through cap rock to migrate upward. If the thicknessis less than threshold value, the hydrocarbon can migrate upward after pass through caprock.Instead, they accumulated under cap rocks.Secondly, with the application of seismic data, logging, test, side-wall coring and highpressure physical properties parameter of formation oil, analysis on transporting ability ofsandstone conduit layer indicated that the ability is influenced by sedimentation (sandbodymorphology, thickness and configuration relationships), diagenetic evolution, anisotropy,migration heterogeneity and configuration relationships of conduit layer and accumulationelements(source rock, cap rock and match of fault and sandbody). In Fuyu reservoir ofXingbei area of Daqing placanticline at Songliao Basin, the connectivity probability is higherif sandstone ratio is greater than1.6and there exists three kinds of conduit ridges as passage.They respectively are fault-lithology conduit ridge, anticline-lithology conduit ridge andlithology conduit ridge. Hydrocarbon primarily gathered and accumulated near anticline axisand conduit ridge of west abrupt slope belt. Instead, there was no show of hydrocarbon at eastgentle slope belt as a result of no dominant conduit passage.Besides, by using3D seismic data, logging, core, scanning electron microscope andgeochemistry trace element, comprehensive research on structure and conduit characteristicsof two periods of unconformity of the bottom of Qiketai formation and Jurassic in Tainan saghas been done. With the trace analysis of fluid inclusion and nitrogen-containing compound,the result indicated that (1) There are five types of unconformity which contains overlapunconformity, truncation unconformity, fault-fold unconformity, fold unconformity andparallel unconformity. Overlap and truncation unconformity developed widely whilefault-fold and fold unconformity only in local area.(2) At the bottom of Jurassic, theunconformity scale was big.At the bottom of Qiketai formation, it was only in local area ofLudong area., Semi-weathering rock thickness of unconformity three layer construction androck thickness at the top of unconformity(basal conglomerate and water-transgressionsandstone) tended to be consist, which instead had an negative correlation with weatheringclay bed.(3) The two periods of unconformity had double conduit passageways, among whichthe upper semi-weathering rock passageway was dominant. Hydrocarbon mainly accumulatedin semi-weathering rock of the bottom of Qiketai formation, which was less than10metersaway from the unconformity.In the bottom of Jurassic, the top of oil layer was less than60meters away from unconformity.(4) Unconformity structure controlled accumulation ofhydrocarbon. In Jurassic, more than95%of reservoirs accumulated at the unconformity uppersemi-weathering rock of the bottom of Qiketai formation and wells with much oil potentialdistributed in the area whose weathering clay bed thickness was more than3.3meter. In upper Karamay formation,90%of reservoirs distributed at the unconformity upper semi-weatheringrock of the bottom of Jurassic, and wells with much oil potential distributed in the area whoseweathering clay bed thickness was more than3meter.Finally, on the basis of three kinds of conduit systems above, analysis on characteristicsand control on reservoir forming of multiple conduit systems indicated that(1) Fault-carrierbed had two types. The first type was “first vertical then lateral”, which included antitheticfault, synthetic fault,“roof” type fault and “anti-roof” type fault. Oil and gas preferred toaccumulate at hanging wall of antithetic fault, footwall of consequent fault and both hangingand footwall of anti-weir fault. The second was “first lateral and then vertical” type.Consequent fault was helpful for vertical adjust. Instead, antithetic fault was in favor of lateralshelter with a great number of reservoirs in the footwall.(2)Fault-unconformity can bedivided into four modes. They were consequent fault-unconformity in the same bed conduit,consequent fault-unconformity across bed conduit,“weir” fault-unconformity conduit andanti-weir fault-unconformity conduit. Among them, consequent fault-unconformity type wasconducive to lateral echelonment transport and anti-weir fault-unconformity was benefical foroil and gas to accumulate.