Distribution laws of intensively weathering and leached zones in deep-water buried hills of the Pearl River Mouth Basin and their controlling factors
The prediction of favorable reservoirs and the progress of natural gas exploration in the deep-water buried hills of the Pearl River Mouth Basin are seriously restricted due to scarce well drilling data.Taking the buried hill in the east of Baiyun sag as an example,this paper mainly dissects the distribution laws of its intensively weathering and leached zones by making comprehensive use of well data and high-accuracy 3D seismic data.Then,the microscopic and logging response characteristics of the intensively weathering and leached zones are clarified.Based on this,the distribution laws of the intensively weathering and leached zones are revealed by means of well-seismic calibration,combined with high-accuracy 3D seismic data.Finally,the factors controlling the distribution laws of the intensively weathering and leached zones are discussed.And the following research results are obtained.First,the intensively weathering and leached zones in the buried hill show low-density logging response characteristics.The plagioclase and mica in these zones suffer severe alteration,and the fractures in the plagioclase get wide and bend in different degrees under the action of intensive dissolution reworking.Second,these are characterized by blank seismic reflections and significant vertical heterogeneity.They are distributed in the current western geomorphologic high and the eastern slope of the buried hill.Third,before and during the Early Eocene,the buried hills in this area were all located at the palaeogeomorphologic high,where the prolonged weathering-leaching process effectively promoted the formation of intensively weathering and leached zones.During the Middle to Late Eocene,the intensively weathering and leached zones in the west were still at the palaeogeomorphologic high due to the differential extension which was strong in the east but weak in the west,while the eastern area was transformed into the current slope due to the uplift caused by fault block rotation and magma underplating.In conclusion,the differential seepage of atmospheric precipitation along the faults and fractures inside the buried hill leads to differential weathering,resulting in vertical heterogeneity of the intensively weathering and leached zones.What's more,palaeogeomorphology is the main factor controlling the differential distribution of intensively weathering and leached zones of buried hill in the west and the east.
Pearl River Mouth BasinBaiyun sagIntensively weathering and leached zoneBuried hillPalaeogeomorphologyReservoir heterogeneity