Comprehensive Evaluation Method Of Logging For Buried Hill Reservoir In The Northern South China Sea

In recent years,we have drilled Mesozoic bedrock buried hill natural oil and gas reservoirs in Yongle,Huizhou,Weizhou,and other areas in the northern South China Sea.Previous exploration results have revealed the huge potential of buried hill reservoirs in the northern South China Sea.However,buried hill reservoirs in various regions are characterized by complex and variable lithology,diverse reservoir space types,and strong heterogeneity.Compared to clastic rock reservoirs,the formation mechanism of buried hill fractured reservoirs has greater diversity and uncertainty.Currently,there is no logging comprehensive evaluation technology for complex lithology bedrock buried hill reservoirs.Based on logging data,this paper conducts in-depth research on the two key and difficult issues of lithologic identification and reservoir effectiveness evaluation for buried hill reservoirs in the north of the South China Sea,providing technical support for the exploration and development of oil and gas fields in the buried hill in the north of the South China Sea.(1)The lithology of buried hill reservoirs in the northern South China Sea is complex and variable,including carbonate,igneous,and metamorphic rocks.In terms of lithology identification,igneous rocks are the most representative.Their main lithology includes granite,dacite,andesite,diorite,and diabase.The mineral composition is complex,mainly including quartz,orthoclase,plagioclase,and dark minerals.It is difficult to identify lithology,and the accuracy of mineral content and porosity calculation is questioned.On the basis of fully understanding the lithological characteristics of the study area,taking into account logging data,this paper establishes a lithological qualitative identification chart from both qualitative identification of lithology and quantitative calculation of mineral content,and innovatively proposes a method for inversion of formation mineral content by logging.(1)In terms of qualitative identification of lithology,this paper has established a series of qualitative identification charts using conventional logging and element logging data,including three porosity lithology identification charts,natural gamma-three porosity lithology identification charts,and X-ray fluorescence element logging lithology identification charts,providing theoretical ideas for qualitative identification of buried hill reservoirs in the northern South China Sea.(2)In terms of quantitative calculation of mineral content,based on the multi-mineral and multi-component optimization logging interpretation model,this paper deduces the response equation of X-ray diffraction logging in principle,innovatively introducing Xray diffraction logging analysis data as effective information into the target function of logging optimization interpretation,comprehensively considering the joint inversion of mineral component content of the formation from logging and logging data,The calculation accuracy of mineral component content in complex lithology is effectively improved.(2)Based on comprehensive logging and experimental analysis data,we find that the development of bedrock buried hill reservoirs in the north of the South China Sea is controlled by various geological factors.The weathering,denudation,and leaching corrosion that ancient buried hills undergo when exposed to the surface have a significant improvement effect on the reservoir.When buried underground,they undergo further transformation such as tectonic movement,formation water dissolution,and metamorphism,The superposition of these factors results in a significant vertical zonation in the distribution of buried hill reservoirs at the macro level,and a randomness at the micro level.At the macro level,the reservoir gradually changes from pore type to fracture type from top to bottom,forming a complex porous medium reservoir with multiple pore space structures,including matrix pores,fractures,and corrosion expansion.At the micro level,the development of fractures and corrosion is characterized by randomness and uncertainty,which together lead to difficulties in evaluating the effectiveness of buried hill reservoirs in the northern South China Sea.In this paper,based on conventional logging,imaging logging,and array acoustic logging,we first proposed sensitive parameters for effectiveness evaluation,and analyzed the sensitivity differences between different evaluation parameters on reservoir effectiveness and permeability effectiveness.On this basis,based on the principles of acoustic,radiological,and electrical multi-source logging methods,we analyzed their differences in detection depth and established buried hill reservoir effectiveness evaluation methods with different detection depths and different effectiveness evaluation angles.(1)In terms of conventional logging,based on the buried hill porous media reservoir model,we have derived a theoretical model of rock conductivity efficiency that includes three reservoir spaces: matrix porosity,fractures,and dissolution expansion.Through numerical simulation,we have explored the relationship between the development of matrix porosity,fractures,and dissolution expansion of the reservoir and the value of rock conductivity efficiency,Finally,we propose a method to evaluate the effectiveness of buried hill reservoirs in the northern South China Sea using rock conductivity efficiency based on the reservoir spatial characteristics of buried hill reservoirs in the northern South China Sea.(2)In terms of electrical imaging logging,this paper extracts parameters such as mean value,variance,peak value,and right width of spectral peak from the porosity spectrum of electrical imaging logging.Through comparative analysis with resistivity logging curves and imaging logging charts,it is found that the mean value and variance of porosity spectrum can effectively describe the reservoir effectiveness of buried hill reservoirs in the northern South China Sea,and the right width of spectral peak can effectively describe the fracture development and permeability effectiveness of reservoirs.(3)In array acoustic logging,we use Fourier transform to convert the full wave train information of array acoustic logging into a frequency spectrum,which can effectively avoid the time difference problem caused by different source distances of array acoustic logging.Comparing the spectral information of far and near acoustic waves,it is extracted that the spectral energy difference and spectral correlation coefficient of far and near acoustic waves have a good correlation with reservoir effectiveness,that is,the reservoir with good effectiveness has a large spectral energy difference and a small spectral correlation coefficient.(4)To address the issue of comprehensive logging evaluation of the effectiveness of buried hill reservoirs,we have proposed comprehensive imaging logging,conventional logging,and array acoustic logging evaluation methods.That is,a comprehensive evaluation method for the effectiveness of bedrock buried hill reservoirs in the north of the South China Sea has been developed based on the imaging log porosity spectral variance and spectral peak right width as shallow scales,conventional log porosity and conductivity efficiency as medium scales,and array acoustic logging far and near acoustic spectrum differences as deep scales from both reservoir and permeability perspectives.In general,this study proposes an innovative comprehensive interpretation method for logging integration aimed at solving the difficult issues of complex lithology identification,fracture hole identification,and reservoir effectiveness evaluation of buried hill reservoirs in the north of the South China Sea,providing technical support for the exploration and development of oil and gas fields in the buried hill in the north of the South China Sea.