Study Of Logging And Evaluation Methods For Physical Parameters Of Complex Lithologically Altered Reservoirs In The Bohai Subduction Mountains

Buried-hill oil and gas reservoirs have been a key national exploration type in recent years,especially in the Bohai Bay Basin submerged tectonic zone gas exploration has made significant breakthroughs,and the discovery of these submerged tectonic zones is of great significance to promote the exploration and development of the Bohai Bay Basin.However,the complex lithology of buried hill reservoirs has brought great difficulties to logging interpretation and research,making it difficult to accurately predict and evaluate key physical property parameters of the reservoir.In this paper,under the guidance of petrology,rock mechanics and logging,we systematically analyze the lithological characteristics of the reservoir and the alteration of the rocks in the Buriedhill metamorphic reservoir in the Bohai A area,carry out lithological identification and classification of the alteration degree of the formation on the analysis results,and finally establish a multi-mineral optimal inverse volume model and a permeability model based on mineral components to predict the porosity and permeability.The method provides an important basis and technical support for the quantitative evaluation of Archean buried hill reservoir logging interpretation.Through rock slice identification,experimental core analysis,logging response characteristics,combined with existing geological data,detailed analysis is carried out from the aspects of rock type,mineral composition and rock alteration metasomatism.Reservoir rocks are found to contain two major rock types: metamorphic rock and igneous rock.Metamorphic rocks are common in gneiss,shallow granule,and metamorphic granite;igneous rocks are common in andesite,porphyry,basalt,granite,and some mixed rocks.The mineral composition is common quartz,feldspar,biotite,sericite,chlorite,iron dolomite,siderite and other minerals.Metamorphic rocks and igneous rocks have undergone different degrees of clay alteration and carbonate alteration at the same time,and along with the generation of new minerals,the rock structure and physical properties have changed.The logging response in the study area is complex and the regularity is weak.This resulted in complex lithology and strong heterogeneity of the Archean buried hill reservoir.The mathematical model and identification chart of rock alteration degree were established by combining rock mechanical parameters and conventional logging curves.The altered strata can be divided to accurately predict the physical properties of the reservoir.According to the degree of rock alteration,metamorphic rocks are the smallest,intrusive rocks are the second,and volcanic rocks are the highest;the buried hill stratum is divided into type I(non-altered),type II(altered)and type III(strong alteration).The study of the alteration degree model provides technical support for the evaluation of altered formations containing metamorphic and igneous rocks,and at the same time better solves the problem of evaluating the physical properties of reservoirs with different lithologies and alteration degrees.The optimal multi-mineral component inversion method is used to apply the heavy mineral double indication curve and alteration stratigraphic delineation results in the inversion model to improve the inversion accuracy,and then use the multi-mineral inversion porosity and mineral volume content,combined with the alteration degree model on the stratigraphic delineation results,to accurately predict and evaluate the permeability.The final predicted porosity and permeability are in good agreement with the core.The multi-mineral component inversion method better reduces the influence on the physical properties due to the complex mineral composition in the Bohai A area.