Characterization And Distribution Evaluation Of Carbonate Cap Rock From The Ordovician Penglaiba Formation In Tahe Oilfield,Tarim Basin

The dense carbonate rocks have the potential to sever as cap rock,and can be significance to find effective cap rock for hydrocarbon reservoirs.Tahe block,however,suffered multi-stages tectonic movements,resulting in the strong heterogeneity of the Ordovician strata.Generally,Penglaiba Formation develop dolomitization and the lithology is mostly dolomite.Thus,there are signification differences between the study-layers and the overlap ones,and the carbonate cap rock in the Penglaiba Formation in this area needs further discussed.In this dissertation,based on the field outcrop and core sample description,rock-slice microscope interpretation,conventional logging and FMI imaging logging data recognition,we fit a combining log curve,which responding well to the dense layer identification,and establish the responding tight-carbon identification mark.Analyzed the single-well and cross well,we put out the tight-layer distribution regular within the crossline and inline direction.With the pore permeability test and the microporous structure test,and integrating.The identification standard of the dense layer established by the logging response,seismic attribute,dominated dominant lithology;we get the cap-rock evaluation parameters.Then,we predicated the ideal cap distribution.The carbonate cap rock in Tahe area can be identified through the logging response of cap rock,the seismic attribute and physical property.The conclusions are as follows:1?The dominant lithologic types of the carbonate cap rock is micrite,silty crystalline dolomite and fine crystalline dolomite,the secondary is arene micrite.The carbonate cap rock don't developed dissolution holes,with less structural cracks.The suture lines are not developed or weak.And the pore of the sand limestone is obviously larger than the muddy limestone.2?The values of RD/RS,GR,DEN and AC curves of dense section were selected for fitting.The fitting log curve A₁=0.55RD-0.15RS+0.35GR+0.1DEN+0.15AC.When A₁>0.4,the rock is dense,the image is bright yellow with less brown.There are no obvious cracks and dissolution cavities,matching with the dominant lithology of dense layer.3?There are a number of thin cap rock in Penglaiba Formation.Well S88,Well TS2 and Well TS1respective have 11,14 and 13 thin cap rock.From the well-tie,2 sets of regional cap rock can be identified in Penglaiba Formation,and 3 sets of regional cap rock can be identified in Penglaiba Formation.4?The criteria of physical properties evaluation of carbonate caprock are as follows:the breakthrough pressure value is more than 0.15Mpa,the porosity value is less than 0.5%,and the permeability is less than10^-2md,the pore throat is more than 60%.5?The fitting formula is AW=0.26A₁+0.52A₂+0.03A₃+0.19A_4.And it can be used to evaluate e and predict the covered layer.The result is Type I cap rock and Type II cap rock of the first member of Penglaiba Formation developed in the northwest and eastern regions of the study area.The Type I cap rock and Type II cap rock of the second member of Penglaiba Formation developed in the north-west and northeastern regions of the study area.