Logging Evaluation Of The Ultra-deep Tight Sandstone Reservoir Of Cretaceous In Kuqa Region

The typical ultra-deep tight sandstone reservoir of cretaceous in Kuqa foreland basin have complex characteristics of deep burial,large thickness,poor physical properties,strong crustal stress and so on,which lead to the difficulty of exploration and development.It have put forward higher request to log data acquisition,because of ultra high temperature and high pressure condition of hole.The high density oil-based mud have been used widely to protect the hole,and also take challenges to log interpretation evaluation;Due to the dual influence of the fault structure and the sedimentary environment,the water salinity of the local strata is changed violently,and the resistivity of the formation water is very unstable.The complex sedimentary evolution and tectonic compression lead to strong geostress and general development of fractures,which have great influence on reservoir resistivity.The characteristics of the poor physical properties make difficulties of reservoir parameter calculation,reservoir space evaluation and fluid identification.In view of the above problems and difficulties,this paper comprehensively utilizes datas such as core,geology,logging,logging and production test,and researches on reservoir logging evaluation method in the research area.This paper select the cretaceous sandstone reservoir of bashijiqike formation as the main research object.Firstly,the comprehensive analysis of the reservoir geology,petrology,reservoir space,physical property,electric property,crustal stress characteristics and their mutual relationship reaserch have been take;The distribution characteristics of reservoir water salinity in keshen,dabei and shenmu area have been cleared.The shale method and spontaneous potential method have been applied to calculate the formation water resistivity in oil-based and water-based mud;Based on the idea of core calibration logging,the reservoir parameters,which include the shale content,porosity,permeability and bound water saturation,are modeled in detail.The pore structure of the reservoir was classified by using mercury injection experiment data,nuclear magnetic experiment data,conventional and nuclear magnetic logging and FMI data.The influence factors of rock electrical parameters and their selection methods are studied and analyzed in this paper,and a variety of methods are used to calculate the water saturation of the reservoir.The reservoir fluid type and gas layers of the tight sandstone reservoirs are effectively identified by the method of cross-section and conventional logging.The results showed that the lithology of the study area was mainly composed of fine sandstone and medium sandstone.The reservoir space type was mainly composed of primary granular pore,inter-grain pore and intragranular dissolved pore,and partially reservoir developed microfractures.The porosity of the reservoir with microfractures have little increased,but the permeability is raised one order of magnitude.Reservoir resistivity anomaly increased,which be mainly influenced by the reservoir physical property,lithology,reservoir space types,fracture and crustal stress,and the fracture caused by tectonic stress is one of the dominating factors for the formation resistivity increase.The formation water salinity increased slightly with the burial depth in dabei and keshen area,while it decreased obviously with the burial depth in shenmu area.The mudstone property of keshen area is less affected by strong tectonic stress,and the mudstone is stable,dense and has a large cementation index.With the increase of formation water salinity,the cementation index of reservoir is obviously increased,but it has little influence on the saturation index.The formation resistivity increases with the abnormal increase of the difference of horizontal principal stress as a power exponent relationship.In a certain range,the cementation index increases with the abnormal increase of the difference of the horizontal principal stress as a quadratic power function relationship,whereas the increasing trend gradually slows down.