Effects Of Different Gas Charging On The Formation Of Diagenetic Differences-a Case Study On The Reservoirs In The Huangliu Formation Of The D13 Block,Yinggehai Basin

The Yinggehai Basin is famous for its strong thermal fluid activity and high temperature overpressure.Since the systematic exploration of this basin in the 1970s,many scholars have systematically studied its hydrocarbon accumulation mechanism.Especially in the mechanism of hydrocarbon accumulation related to overpressure fluid flow,outstanding achievements have been made.However,the quantitative study on the water-rock-hydrocarbon interaction under the high temperature and overpressure conditions and its influence on the diagenetic evolution of the reservoir in this basin is not clearly known.There are two types of natural gas reservoirs in the Huangliu Formation in the D13 block of the Yinggehai Basin.Specifically,the D13-1 block developed a CO₂-rich gas reservoir,and the D13-2 block formed a hydrocarbon-rich gas reservoir.This difference provides a natural laboratory for studying water-rock-hydrocarbon interactions in a high temperature and overpressure environment.In this study,based on synthetic analysis,including optical microscopy,scanning electron microscopy,cathode luminescence,X-ray diffraction,stable isotope analyses,and fluid inclusion determination,effects of CO₂-rich and hydrocarbon-rich gas charging on the formation of diagenesis from Huangliu Formation were studied on the D13 block in the Yinggehai Basin.Results showed that:(1)Due to the diapir activities,the D13-1 block near the diapir zone formed multi-stage reformed natural gas reservoirs with high maturity and CO₂ contents.The D13-2block far from the diapir zone mostly enriched in alkane.(2)The late-stage charging of CO₂-rich thermal fluid occurred in the D13-1 block which are close to the diapir zone and this region experienced strong dissolution(the secondary porosity contributes 39.9?58.4%for the total areal porosity in the thin section).However,due to the semi-open closed diagenetic system,a large amount of metal cations such as Ca²⁺,Mg²⁺,Fe²⁺formed during the dissolution process were not discharged in time.They re-precipitated to form abundant late carbonate cement,resulting in an increase of carbonate cement content(4.5?13.5%)and types,which in turn destroyed the pore throat and formed low-permeability reservoirs.(3)The D13-2 block which are far from the diapir zone were mainly charged by the early-stage hydrocarbon-rich fluid.This region experienced weak dissolution(the secondary porosity contributes 7.2?27.7%for the total areal porosity).At the same time,the diagenetic system was relatively open with acid hydrothermal system.Thus,middle porosity–middle permeability reservoir were formed with low-content carbonate cements(1.0?6.0%).(4)Comparing with the reservoir in the D13-2 block,the reservoir in the D13-1block was affected by the charging of the CO₂-rich thermal fluid in the late stage,which promotes the dissolution,but hardly affects the compaction during the diagenesis.