| The exploration of the Paleogene middle-deep reservoir in southwestern Huizhou Sag and southern Lufeng Sag in ZhuⅠ Depression of Pearl River Mouth Basin has encountered a bottleneck due to the constraints of reservoir conditions.According to the observation of core and thin section,combining logging data,and based on the technique such as scanning electron microscopy,cathodoluminescence,grain size analysis and X-ray diffraction,the data in the study area of Enping Formation and Wenchang Formation were analyzed.The petrologic features,diagenesis and reserving space characteristics of the sandstone reservoirs were studied,and then the main controlling factors and mechanism of reservoir quality difference were discussed,which provided the basis for the classification evaluation of reservoir and the prediction of favorable areas.The rock type of Paleogene reservoir in Huizhou and Lufeng areas are mainly litharenite and feldspathic litharenite with lower mineral maturity.The content of clay matrix in reservoir changes greatly and the heterogeneity is obvious.The content of cement is low,which mainly composed of kaolinite and carbonate minerals.Kaolinite strongly metasomatized clastic particles.The rock maturity in southern Lufeng area is slightly higher than that in southwestern Huizhou area,and the maturity of Enping Formation is higher than that in the same facies belt of Wenchang Formation,which is mainly affected by the type of sedimentary facies and transportation distance.The diagenetic characteristics of southwestern Huizhou are ‘strong compaction,weak cementation and medium dissolution’,and that of southern Lufeng is ‘medium-strong compaction,weak cementation and medium dissolution’.The diagenetic characteristics of the two regions are highly similar.Due to the different burial depth and sandstone composition,the intensity of compaction in southwestern Huizhou area is higher than that in southern Lufeng area,and the compaction of Wenchang Formation is stronger than that of Enping Formation.The reservoir space types in the study area are divided into residual primary intergranular pores,secondary dissolved pores,intergranular pores,matrix micropores and fractures.The pore types of southern Lufeng reservoir are primary intergranular pores,and the mixed pores of residual primary intergranular pores and intragranular dissolved pores are mainly developed in southwestern Huizhou.Under the condition of the same porosity,the reservoir permeability of southwestern Huizhou area is lower,which is due to the difference of matrix content and burial depth.The quality of the reservoir in the study area is controlled by rock maturity,sand body thickness,the intensity of compaction,fluid transformation,and tuffaceous filling.But rock maturity and the intensity of compaction have a greater impact on reservoir.Sedimentary facies and parent rock composition determine rock maturity,which in turn determines initial porosity.The feldspar-containing rigid grains and the burial process determine the intensity of compaction and control the loss rate of primary pores.The dissolution of feldspar in thick sandstone forms secondary pores,which significantly improves the reservoir.The outer front reservoir has high structural maturity and strong organic acid dissolution,which can reduce the influence of tuffaceous filling.The reservoir is divided into four types,which are braided river delta branch channel proximal sand body,braided river delta branch channel distal sand body,fan delta sand body and beach dam sand body.The reservoir characteristics and controlling factors of nine zones in the study area are compared.Based on the favorable reservoir evaluation criteria,the reservoir evaluation plane prediction maps of the target layers in the study area are drawn.The favorable reservoirs in southwestern Huizhou are mainly located in Huizhou 26 and Huizhou 25 area,and which in southern Lufeng are located in Lufeng14-4 and Lufeng 13-8 area. |
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