A relationship between abnormally high pressure in Enping Formation and hydrocarbon accumulation in Wenchang A sag

By comprehensively using several kinds of data,such as geology,seism ic,geochem istry and w ellbore rock-electricity, and applying the approach of hydrocarbon accum ulation dynam ics,the distribution, origin of abnorm ally high pressure in E nping Form ation and its relationship w ith hydrocarbon accum ulation in W enchang A sag,Zhu III depression,w ere system atically studied.The results are as follow s: Abnorm ally high pressure generally develops in E nping form ation w ithin the center of the sag,and its m ain origin m ay be the undercom paction resulted from rapid subsidence of Low er Oligocene m udstone and the late hydrocarbon generation; The episodic hydrocarbon expulsion and m igration under high pressure in E nping Form ation have resulted in favorable plays in Zhuhai and Zhujiang Form ation, w ith ZH-Ⅱ and ZH-Ⅲ M em bers and Zhujiang Form ation respectively being a play w ith low porosity and perm eability in norm al-transition pressure zone and an oil play in norm al pressure zone.These tw o plays are different in m igration pattern and accum ulation periods,w hich has led to a hydrocarbon distribution of "gas in the deep sag,oil and gas on the slope and oil on the uplift". From these new concepts, tw o m odes of hydrocarbon accum ulation are presented, i. e. a vertical m igration-accum ulation m ode on the steep slope and a vertical-lateral m igration-accum ulation m ode on the gentle slope,and the north gentle slope in the sag and the dow nthrow n side of Zhu III south fault are considered as the im portant targets in the next hydrocarbon exploration.