The Research On Palaeokarst Characteristics And Development Model In Nanpu Sag And Surrounding Uplift

In recent years,the carbonate buried hill reservoirs has become a hot spot of exploration in Nanpu sag and its sourrounding.Karstification is one of the key factors that affect carbonate reservoir properties and distribution.Base on the research of classification of karst,supergene karst and buried karst were be identified in lower Paleozoic of Nanpu sag and its sourrounding.Supergene karst developed in the carbonate buried-hill an within 50 m to the unconformity,while buried karst always occurs in the Fujunshan formation,Maozhuang formation and Zhangxia formation within the carbonate buried-Hill.Systematically summarize the characteristic of these two type karst.There are four main characteristics of supergene karst.Frist of all,supergene karst is always harbor like,filling weathering clay at its surface and always developed karst collapse.Secondly,the dissolved pores are well developed,but the properties of matrix is not well;Thirdly,the drilling fluid was missing when drilling.Fourthly,the cathodoluminescence and C-O isotope indicate the influence of meteoric water.Buried karst has three major characteristic.In the frist place,buried karst dissolved holes developed,well crystal of calcite was found in karst cracks,quartz and vestigial clay after dissolved was filling in these holes.Secondly,buried karst dissolved holes are always matrix type and associated with high-temperature mineral and stitching lines.Thirdly,buried karst dissolved holes always filled with hydrocarbon fluid,and cathodoluminescence images shows the fluid quenching calcite.There are two period of supergene karst in Nanpu sag.They developed before the Mesozoic deposited and before the Paleogene deposited.The reserving space of supergene karst are dissolved holes and structure&corrosion fractures.The porosity and permeability are low and the mercury penetration show the holes were poor sorting.The buried karst also has two period in Nanpu sag.They developed before the Guantao formation deposited and before the Minghuazhen formation deposited.The reserving space of buried karst are matrix pores and solution fissure.The porosity and permeability are low and the mercury penetration show the holes were well sorting.The karst solution experimental results show that : In the supergene condition,calcite easily dissolved than dolomite.When the dolomite of carbonate content is less than 13%,because of “salt-soluble effect”,the increase of the content of dolomite dissolution of carbonate rocks gradually strengthened.More than the limit,along with the increase of the content of dolomite denudation gradually weakened.In the buried condition,dolomite is more easily dissolved than calcite.Calcite dissolution mainly occurred in the particle surface,produce the ladder-like dissolve scar.Dolomite grains internal corrosion more in-depth development solution hole and solution pores.with the increase of temperature and pressure,the dissolution of carbonate rocks gradually strengthened.After the temperature over 125~150 ?,the dissolution rate significantly increased.Tectonic evolution process of buried hill carbonate rocks played a key role in control of supergene karst development.It dominated the supergene karst issue and karst landform unit.Wild,core and test data show that limestone are more likely to happen supergene karst.The karst highland and slope is advantage geomorphic units of supergene karst.The karst consequent slope is more conducive to karst than the reverse slope.Under the buried condition of high temperature and high pressure,dolomite are more likely to happen dissolution.Dissolution of fluid migrates along the fault and fracture.The fracture development zone near the large fault is the advantage of the buried karst development zone.More evidence shows that buried karst is closely related with hydrocarbon filling.Buried karst development is controlled by strata properties,including “Baffle” effect and strata thickness.Based on the analysis of karst control factors,we set up a comprehensive karst development pattern in Nanpu sag,and determine the advantageous area of two kinds of karst.The follow is the required condition of supergene karst development.The supergene karst occurs in the carbonate buried hill surface under 50 m range.And it develops in the limestone area of the second supergene consequent slope.The follow is the required condition of buried karst development.The buried karst always occurs in the Fujunshan formation,Maozhuang formation and Zhangxia formation,which are under the dense rock formation.And they develop in the dolomite area of the fracture development zone near large fault.Under the guidance of karst model,we use the neural network prediction technology,based on the seismic multi-attribute,to predict the high quality reservoirs in the studied area.The supergene karst belt mainly develop limestone face,dolomite face and marl face.Five kinds of seismic attributes are selected to conduct the FCM cluster analysis,namely,skew-amplitude,average-peak-amplitude,min-amplitude,RMS-amplitude and average-instantaneous-frequency.And we estimate the lithofacies distribution.Through the analysis of ancient landform and slope orientation,the central area of Nanpu No.1 buried hill is advantage supergene karst area.Useing Move fracture prediction technology,we predict the fracture of Fujunshan formation,Maozhuang formation and the Zhangxia formation.On this basis,we forecast the supergene and buried karst reservoir.