Genetic Types and Accumulation Model of the Deep Cracked Gas Pools of Minfeng Area in Dongying depression

Liu Hua; Jiang You-lu; Song Guo-qi

According to hydrocarbon generation history of gas source rock, reservoir thermal history and reservoir bitumen of Minfeng area in Dongying depression, comprehended the gas accumulation geological background, the genetic types and characteristics of middle-deep gas pools are analyzed, and the gas accumulation model is set up.

Research shows that the middle-deep gas of Minfeng area in Dongying depression having been discovered is mainly cracked gas and comes from the lower Es4 source rock. During Es2 depositional period, the Es4 source rock began to generate oil and entered the associated gas generation stage at the end of Dongying formation depositional period. Affected by the structural movement of the end of Dongying, depositional period, the Minfeng area was uplifted overall and the temperature of formation decreased, hydrocarbon generation ceased. During Guantao depositional period, formation temperature is rising along with the deposition, source rock reached the threshold of petroleum generation again, and now the source rock in the central of Minfeng sag has entered the stage of cracking-gas generation and the source rock in slope zone has entered the associated gas generation stage. In addition, controlled by the evolution of the source rock, there are three genetic types of the gas reservoir and gas accumulation models:
（1）Paleo-reservoir oil cracking formed gas pool. The pre-produced crude oil entered suitable traps formed the oil pool, and with the increasing of the buried depth and formation temperature, the paleo-reservoir oil was subjected to high temperatures and gradually cracked to form gas. These cracked gas entered original traps or adjacent reservoirs formed gas pool.
（2）Kerogen-cracking gas infilling paleo-reservoir formed gas invasion enrichment gas pool. When latter part of kerogen and dispersed oil cracking, the kerogen-cracking gas can migrate along the early oil migration pathways and accumulate in the early oil reservoir, then the reservoir gas invasion effect occurs, with the amount of gas increasing, the gas invasion enrichment gas pool is formed.
（3）Kerogen-cracking gas directly entered traps formed gas pool. Latter part of kerogen and dispersed oil crack to gas, and the gas migrate and accumulate in the suitable new traps to form gas reservoirs.

The three genetic types of the gas reservoir have a certain distribution rule. The central of Minfeng sag is mainly accumulated with pure gas reservoir composed by cracked gas coming directly from kreogen, and some cracked gas reservoir generated from ancient oil reservoir. Slope zone is accumulated with gas invasion enrichment gas pool and only oil pools charged at late stage on the relatively shallow slope edge. So, from the central of sag to the high slope area, the distribution of gas, oil gas mixed phase and oil are coming in turn.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013