| Due to the influences of paleo karst geomorphology,sedimentary environment,and dissolution,the Ordovician carbonate reservoirs in the Sulige gas field are characterized by low porosity,low permeability and strong heterogeneity.The drilling gas well test data show that the member 5 of the Lower Ordovician Majiagou formation is an important gas-bearing layer,which has a better exploration prospect.On the basis of previous research,the data,including geology,well logging,seismic data et al,are used to develop and improve the research of evaluation technology and gas-bearing prediction technology within the carbonate reservoirs,which will further provide an important guide role for the exploration of oil and gas.Taking the carbonate reservoir of Sudong 41-33 in Sulige gas field as the study target in this paper,the general idea of the paper is realized by the way of qualitative and quantitative analysis combined with multi-discipline data,which provides a set of possible solution for the evaluation and study of carbonate reservoirs.Firstly,based on the decompaction correction of the strata and well logging data,collaborative iterative optimization methods of combining residual thickness method and impression method was adopted to restore the paleogeomorphology.Secondly,the SFLA-SVM method was used to identify the types of lithology and fluids with the information of well log characteristics for different types of lithology and fluids.We also analyze the petrological characteristics,sedimentary facies,and properties of the reservoir using the core observation data and test data.Seismic forward modeling method is used to carry out the research on the seismic response characteristics of different fluids and then GA-BP method was used to carry the prediction of gas-bearing of member 5 of Majiagou formation with the multi-seismic attributes.And the prediction results based on GA-BP method are also verified by AVO forward modeling method.Finally,the evaluation factors of carbonate reservoirs were determined through the research results and then the comprehensive evaluation of carbonate reservoirs was carried out.Through the research,the following conclusions have been obtained.The rock types of the member 5 of Majiagou formation are mainly limestone,dolomite and transitional types.The overall reservoir properties of this area are poor,which is represented by low porosity and low permeability.The pore types mainly consist of dissolved pores,intercrystalline pores and micro-fracture pores,which belong to fine and fine throats.The paleogeomorphology restoration results show that the proposed method can better maintain the consistency between the residual thickness and the thickness of the impression.And the the study area has mainly developed three geomorphic units,including paleo-groove,paleo-monadnock and paleo-slope lands.Based on the analysis of sensitivity parameters,SFLA-SVM method are used in the recognition of lithology type and fluids type and the recognition accuracy is over 85%.The forward simulation results based on logging data and petrophysical analysis show that different reservoirs thicknesses and different gas-bearing reservoirs show obviously anomalous seismic response characteristics and the AVO type are mainly type III.The gas-bearing prediction of multi-seismic attribute method is developed based on the GA-BP method.The results have a higher prediction accuracy and also are consistent with AVO prestack seismic information.Based on the research results above,rock types,sedimentary facies,reservoir properties,lithology types and paleo-geomorphology were used as evaluation factores of reservoirs,and 2 types of favorable areas were divided according to the predicted result of gas-bearing.The study shows that the research idea of the paper has achieved obvious results in the reservoir characteristics and evaluation process in the Sudong area,which serves as a reference for reservoir evaluation in similar regions and has a certain practical value in the production process. |
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