Time-space structures of reservoiring elements and process influence the level of hydrocarbon enrichment.In plays that are adjacent to the source rocks and regional cap rocks

when the reservoiring occurred close to the hydrocarbon-generating period

the reservoirs would have relatively high hydrocarbon enrichment.Most of the major reservoirs in a basin or petroleum system belong to this type of reservoirs.Vertically

if there is no large and prominent tectonic events or depositional breaks between the source and reservoir rocks

we call it near-source combination

and its specific time interval is preliminarily determined to be no longer than an "Age"(in Mesozoic and Cenozoic)or an "Epoch"(in Paleozoic);otherwise we call it far-source combination. Laterally

near-source and far-source areas can be defined according to their location to be within or outside the effective source rock area—hydrocarbon kitchen.The available exploration results indicate that most of the discovered large and medium oil and gas fields in Tarim basin

such as Hadson oilfield

Lungu-Tahe oil/gas field

Kela 2 gas field and Yaha oil/gas field

are(indigenous-or)near-source combinations.Over 95% of the proved oil reserves in Songliao basin is distributed in Saertu

Putaohua and Gaotaizi oil reservoirs between the major source and cap rocks.Therefore

"near-source exploration" is an important and practical principle for discovering prolific oil and gas enrichment areas.Exploration of near-source oil and gas fields is commonly very fruitful.However

most of the near-source oil and gas fields are distributed in structural zones with high exploration difficulties

in complex plays or in deep and ultra-deep horizons of the exploration area

thus they are commonly discovered behind the "far-source" oil and gas reservoirs.