The Reformation Of Shallow Fluid For Granite Reservoir Of Buried Hill In Penglai 9-1

Penglai 9-1 structure is the first large Mesozoic granite buried-hill oilfield in the Bohai Sea and its reservoir spaces mainly are fractures and porosities.It is composed of large-scale semi-anticline structure,which is attached to eastern boundary large fault in Miaoxibei uplift.The buried hill has a double structure,which consist of intrusions jointly by Proterozoic metamorphic rocks and Mesozoic granite.There are two independent culminations in south and north.The granitoid weathering crust is developed at invaded zone,which is an ideal reservoir space for oil and gas.Above the weathering crust mainly is the meandering stream-shallow water delta deposition.The development of Penglai 9-1 oil reservoir and the ideal combination of storage and cover constitute excellent reservoir forming conditions.The reservoir space of the granite buried hill shows a regular change,porosity-fracture-porosity-porosity-fracture.The properties of the fluid provide a condition for the formation of quality reservoir.This paper researched Penglai 9-1 buried-hill granite,simulated the interaction between three different fluids and granite,and eventually unveiled the control mechanism of different fluids to granite reservoir.The three fluids were atmospheric water,organic acid(formation water),atmospheric water + organic acid(formation water).Experimental study was carried out to measure the interaction between three different fluids and granite samples at 60 ?,90 ?,120 ?,150 and 180 ? ?.The results showed that:(1)the minerals were corroded and dissolved: when the granite samples were influenced by the three fluids at various temperatures,plagioclase and alkali feldspar were corroded and dissolved along the fractures and cleavage fissure and on the surface,the degree of dissolution increased with rising temperature,and corrosion process proceeded as pit-shallow slot-band-trench;quartz wasnot corroded obviously.(2)Secondary minerals were formed: after the granite samples underwent the experiments with three fluids at various temperatures,different forms of secondary kaolinite were generated on the mineral surface and pore,schistose chlorite was found in the experiment of atmospheric water,and with rising reaction temperature,crystal form of secondary kaolinite changed from flake to plate.(3)The pore radius and surface porosity increased: through experiment,it was found that with the rising reaction temperature,the mineral cleavage fissures and fractures of the three experimental samples expanded,which enlarged the pore space and improved the surface porosity.(1)In the experiment of reaction between atmospheric water and granite,the surface porosity was 4.76% prior to the experiment and up to 11.89% at 180 ?as the temperature increased,with surface porosity increasing by 7.13% averagely;(2)In the experiment of reaction between organic acid and granite,surface porosity of sample was 4.76% prior to the experiment and gradually up to 17.01% at 180 ?,with surface porosity increasing by 12.25% averagely.(3)In the experiment of reaction between atmospheric water + organic acid and granite,surface porosity of sample was 4.76% prior to the experiment and gradually up to 13.61% at 180 ?,with surface porosity increasing by 8.85% averagely.(4)Under the condition of organic acid,the sample wascorroded more severely: compared with the experimental results of the three groups,it was found that the sample was corroded more severely under the condition of organic acid;the higher the temperature,the stronger the physical change by fluid to the sample.The change results of solution containing organic acid to the sample's physical properties showed that: surface porosity of experimental sample increased by 12.25%,and the pore expanded by 5.35?m averagely at 180 compared with those prior to the experiment,and thus the physical properties of ?granite reservoir were significantly improved.Different fluids have different effects on reservoir physical properties under different temperature conditions.Through the experiment,it is found that the change by organic acid to the sample is the most obvious,which provides direct evidence for the formation of good reservoir physical properties.The reservoir physical properties have important influence on the distribution and enrichment of oil and gas.Therefore,from the perspective of oil and gas bearing reservoir,it is of significance to study the effect of fluid on change to the reservoir.To find out the mechanism of change brought by shallow fluid to Penglai 9-1 buried-hill granite reservoir holds the key to further optimize the reservoir space.The experimental study on the change brought by the shallow fluid to Penglai 9-1 buried-hill granite reservoir is conducive to further investigating the stability and geochemical characteristics of granite in different media conditions and to unfolding the change caused by fluid to reservoir physical properties,which provides direct evidence for the mechanism of granite reservoir formation in this area and has practical significance for fluid alternation of later stage in the sandstone reservoir of other areas.