Abstract: The deep cracked gas pool in Dongying sag is characterized by condensate gas reservoir and net gas reservoir. The gas source originates from high matured source rock of the lower sub-section of Es4. The factors controlling the cracked gas accumulation are studied by lab experiment, well log and seismic data analyses. Study shows that the hydrocarbon generation, hydrocarbon phase state and gas reservoir distribution are all controlled by in-situ geotemperature; the main reservoirs for the cracked gas accumulation are the mid-fan braided channel microfacies and front microfacies in nearshore submerged fan facies, and the reservoirs' conditions are improved by solution process, hence rising the gas-bearing property in them; the hydrocarbon migration and accumulation are controlled by the fluid potentials, allowing hydrocarbons to migrate from high potential zone in sag center to low potential zone at verges, finally to accumulate in the glutenites of favorable facies zones in faulted abrupt slope belt. It is concluded that the faulted abrupt slope belt in northern Dongying sag is an area for the deep cracked gas enrichment and distribution, thus it is also as a target for deep natural gas prospecting in the near future.

Key words: Dongying sag, gas pool, cracking, geotemperature, sedimentary facies