Study On The Dissolution Of Lacustrine Mudstone And Shale By Organic Acid In Dongying Sag

In recent years,with strong development of shale gas exploration and development and the progress of modern technology,the mud shale not only can be a cap rock,but also can be used as a reservoir to accumulate shale oil and shale gas.As a self-generating and self-preserving system,mud shale is dissolved by organic acid is an important part of the natural phenomena,and what degree of the influence of mud shale reservoir porosity by the organic acid and the influencing factors of organic acid dissolution is an important scientific problem,the solution of the problem has an important significance on the prediction of the shale oil and gas reservoir.Based on comprehensive analysis of logging data,formation data,minerals and other related data,we have done a series of experiment or test on the mudstone and shale samples from the lower member of Paleogene Shahejie Formation in Dongying sag.The methods include organic acid dissolution experiment,organic acid generation experiment,XRD and ICP,scanning electron microscopy,nitrogen adsorption,etc.According to the results of the dissolution experiments of organic acid on mud shale,mineral ions has released from mud shale,the mineral composition,the shale pore shape,pore size distribution and specific surface area also has changed in this corrosion process.Specifically,(1)the elevation of temperature can strengthen the dissolution of the mud shale.But different ion behave differently with the change of temperature.(2)Carbonate minerals such as calcite carbonate minerals are disappeared basicly,aluminum silicate minerals such as feldspar also presents the downward trend,quartz content is remained basicly in the corrosion progress of acetic acid and oxalic acid on the mud shale,At the same time,we can see the emergence of new minerals such as illite,kaolinite,clay mineral,etc.(3)Intragranular pore's diameter and amount increases,there is a small-scale dissolution in the contact part of intergranular pore,even net hole phenomenon happens.In addition,the width of the micro cracks increase.(4)The mud shale's pore volume increased significantly under the erosion of acetic acid or oxalic acid.The acetic acid influence on surface area mainly,but oxalic acid on the average pore diameter mainly.The organic acids can also change mud shale's pore structure,pore volume and specific surface area.The results of organic acid generation experiment show that the generation of organic acid is mainly controlled by temperature,PH,TOC,Among them,the TOC is the most important factor.According to the experiment's result,the amunt of organic acid has been calculated by the relation between it and TOC,and we have done the preliminary simulation prediction of organic acid in Dongying sag.Rock physical model and calibration logging method is then used to characterize reservoir space of the mud shale,after compared the organic acid generation with the distribution of reservoir pore space of mud shale,we found that the association of them is very good,thus shows the organic acids can control the reservoir space of mud shale to some extent.