Main Controlling Factors Of High-Quality Reservoir In Pinghu Group In The Ramp Region Of Xihu Depression

Xihu depression is a Cenozoic continental margin rift basin and the location of it is in the East China Sea shelf basin.Study and the practice of exploration and development show us that there are some better reservoir belts which porosity and permeability is good relatively under the circumstance of reservoir is generally relatively poor in the medium-deep strata of Xihu depression.However,we don't have a clear realization about the distribution and main controling factors of the kind of high quality reservoir.On the basis of researches and knowledge in the past,by observation of drill cores and taking rock samples,and using some analytic testing technologies.Such as identification of casting slice,scanning electron microscope,cathodolumin escence,inclusion thermometry the author analyze and research Petrography,diag enesis and diagenetic evolution sequence,pore type and structure,physical characteristics of the reservoir of Pinghu group in the ramp region of Xihu depress ion.Finally,the author use these results of the analysis and study to do comprehensive evaluation of controlling factors of reservoir of stuy area.The main lithology of Sandstone are feldspathic lithic sandstone,feldspat hic lithic sandstone,quartz lithic sandstone,feldspar quartz sandstone,secondly are lithic quartz sandstone,feldspar quartz sandstone,and the interstitial material are mainly carbonate cement,kaolinite and siliceous in stuy area.In addition,the reare some lithic sandstone and feldspathic sandstone in stuy area,generally,san dstone maturity decrease from south to north.The main types of diagenesis are mechanical compaction and pressure solution,cementation and dissolution.Mecha nical compaction and pressure solution are medium and decrease from south to north.The influence of compaction is greater in the early diagenesis.And in the late diagenesis the pressure solution is more is main.The content of carbonate cements is the highest in the study area.And they are disadvantageous to the porosity and permeability of reservoir.However,Carbonate cements have the effect of the compaction resistance in the early.The existence of kaolinite indicates the relative growth of dissolution pore and dissolution pores are widespread in the study area.Mostly,the siliceous exists in the form of overgrowth edge and it can cause the blockage of intergranular pore.Dissolution can be divide into two phases in the study area,in the early dissolution is caused mainly by at mospheric corrosion of freshwater and In the late it is caused mainly by Organic acid,carbonic acid and deep hydrothermal fluid.According to X-ray diffraction of clay minerals,vitrinite reflectivity and some other elementswe can confirm the rock of study area is in the stage A of middle diagenesis.And based on it,we establish a sequence of diagenetic evolution of rock of the study area.The pore types are numerous in deep reservoir,they include residual intergranular pore,intergranular dissolution pore,mold hole and so on.These pores usually constitute the pore combined modes of coarse roared-large pore throats and medium roared-medium pore that is disadvantageous to the development of good reservoir and these pore combined modes are widespread in the study area.There are two reasons for the development of these pore types:firstly,high pressure which undercompaction caused by rapid bury and the organic matter hydrocarbon generation produce can preserve a part of primary pores in sandstone;secondly,ingredients low maturity of deep sandstone that make a lot of Cuttings and feldspar be dissolved,especislly,in the south dissolution become more strong because of magma intrusion.Early meteoric water dissolution,carbonic,acids and deep hydrothermal fluid makes dissolution is very common.The reservoir porosity and permeability of Pinghu group is good relatively,linear relationship between porosity and permeability is also very good and secondary pore is widespread in the western slope zone of Xihu depression.In general,the reservoir in this area belongs to medium porosity,permeability reservoir.The circumstance of high porosity and the second highest porosity's development of upper and middle section of Pinghu group significantly better than low section of Pinghu group.According to the analysis and research of deep reservoir,we propose the standard low limit of the reservoir delineation program:the low limit of porosity is 10%and the low limit of permeability is 1×10^-3?m².Based on the program,we divide the reservoir into the?,?,?,?four classes and make classification and evaluation of reservoir types of individual well in the study area.The good sedimentary facies belt is the basis of the reservoir development,diagenesis is the key controlling factor of the reservoir development,and the abnormal high-pressure is the important factor affecting the reservoir physical properties.Those structures belong to the Central section of Slope belt such as P structure,W structure,B structure,K structure of Slope belt are all good reservoir development belts.