Study On Methods Of Evaluating Igneous Reservoir By Logging

At the moment, with the increase of the world demand on hydrocarbon resources, and the difficulty advancement of exploration and development, it is difficult for the clastic rock and carbonate rock to meet the demand on the energy in the future. It is very important to find reservoir of new type, and this is a general trend. The exploration in home and abroad indicates that igneous rock can become good reservoir. Under suitable conditions, igneous rock can become good reservoir if it combines well with hydrocarbon mother rock and capping formation.With the development of oil exploration, more and more igneous rock reservoirs are found. Igneous rock reservoirs are found in Cuba, Japan, Argentina, America and former Soviet Union during the end of 19 century and the early of 20 century. Igneous reservoirs are also found in many areas of China.As a particular reservoir type, igneous reservoir is attracting more and more concern. The study on evaluating igneous reservoir is another important field in reservoir evaluation by logging after sandstone and carbonate reservoir evaluation. As nonhomogeneity reservoir, the relationship between the rock and the electric property of igneous reservoir is more complicated than that of sandstone and carbonate reservoir, which arises difficulty in reservoir evaluation by logging. The complicate lithology and pore type, and the poor physical property are the bottleneck problem of logging evaluation. How to establish the evaluation model of igneous rock is the important task in the future.There are three main difficulties when evaluating the igneous rock by logging. First, due to the anisotropism of the reservoir, it is difficult to evaluate quantitatively using the methods based on the isotrope. Second, igneous rock reservoirs are controlled by structure, hydrocarbon mother rock and phase belt, so they have more gas and water system, and different volcanic edifice or the different well of the same volcanic edifice each have its gas and water system. Third, it is very difficult to define the pore configuration, fracture width and development degree.The exsiting methods on evaluating igneous rock are mainly about summing up the log response feature, identifying the lithology and simply computing the parameters. There are not many references which specially deal with the theory and method on evaluating igneous rock by logging. It can be seen that the log features of igneous rock have zonality, the lithology of different area have big difference which are arised by the complex of igneous rock. The interpretation models are established on analytical data of special area, and many equations are defined according to experience, they are different in different area. The exsiting models mainly are two-mineral model ,rock mineral or multi-mineral model when igneous rock are interpreted .It is dependant on Archie's equations to derive water saturation. In order to well evaluating igneous rock, this thesis aims at establishing appropriate mixed matrix model and porosity model,then defining the water saturation , forming the theory and method, finally applying to reality by systematically researching the method and theory of evaluating igneous rock. The main research contents include: ①summing up the log response featuresReferred to the log response features in the references home and abroad, and combined the log response features of igneous rock in north Songliao basin, the log response features of different lithology are summing up and log response laws are understood.②research on the methods of identifying igneous rock lithologyThe relationships between lithology and log curves are studied and the close or distant relationships between different lithology are evaluated by using factor analysis method, and the favorable curves which are used to identify lithology are selected .The main methods used to identify lithology are:R-factor analysis method, fuzzy clustering method, nerve network method, TAS method and linear dimension-reducing mapping method.③Identify fracture and quantitatively evaluate the extent of fracture developmentThis paper studies the extent of fracture development and computes the fracture porosity, fracture openness and fracture permeability by using the conventional logging data. In view of the complexity of igneous rock, this paper analyzes the effectiveness from the two resources by comparing the fracture porosity computed with the fracture parameter derived from FMI.④Mixed matrix model and porosity model which are appropriate for evaluating igneous rock are established.⑤The water saturation equation is defined.⑥The methods of qualitatively identifying the fluid property in igneous rock are researched.⑦Optimization algorithm which is used to compute reservoir relevant parameter are dealt with.⑧The methods of quantitatively identifying the fluid property in igneous rock are researched.Referring to the characteristic of igneous rock, this paper tries to resolve the problems in evaluating igneous rock. On the basis of summing up the log response of igneous rock in various areas and the existing research outcomes of predecessors, this paper proposed some new ideas and processing methods which have innovation. The innovations include:①Linear dimension-reducing mapping method is used to identify igneous rock lithology.②Mixed matrix model is established to evaluate igneous reservoir;③Triple porosity model is used to evaluate igneous reservoir first;④Self adaptive genetic optimization algorithm is used to compute total porosity, mixed mineral and shale content.⑤The methods of qualitatively identifying the fluid property in igneous rock are researched.⑥The water saturation equation is defined.⑦The methods of quantitatively identifying the fluid property in igneous rock are researched.After finishing above research, the following awarenesses are achieved:①on identifying lithology of igneous rockThe relationships between the development extent of igneous reservoir and rock type are not very obvious. Basic basalt, mediosilicic andesite, acidic rhyolite and volcaniclastic rock all can become reservoir rock. The first work of evaluating igneous rock is to identify lithology. Identifying the lithology accurately is the foundation of accurately computing porosity and water saturation.The methods of identifying lithology include: the method of crossplot, the method of facotr analysis, the method of fuzzy clustering , the method of nerve network, the method of TAS. This paper newly proposed the method of linear dimension-reducing mapping.②on mixed mineral modelAccording to mixed mineral model, the rock volume can simplify into porosity, shale and mixed matrix, big differences of physical property are existed among them. Therefore, the discriminability of the model is advanced, and it is easy to accurately compute the entire parameters, which raised the accuracy of the reservoir parameters. Moreover, under the restrictions of matrix content, the relative contents of the minerals which make up of the igneous rock can be computed, so the geology lithological profile like ELAN can be achieved .In short, the mixed mineral model protruded the main contradiction, dissolved less important contradiction.③on triple porosity modelIgneous reservoir is classified into fractured reservoir, and its pore space has many types, including: pore, fracture, dissolved pore (vug) and fracture-pore, fracture-dissolved pore (vug), dissolved cavern-fracture due to their coupling. The pore space of fractured reservoir is far more complex than that of porous reservoir. Fracture, dissolved pore, dissolved cavern, matrix pore and chicken wire pattern system due to their connection are main pore spaces of igneous reservoir.The triple porosity model which is built in this paper based on matrix, natural fracture and non-connected vug is suitable to the characteristic of igneous rock. Triple porosity model is suitable for all combinations of matrix, fracture and non-connected vug porosities. Moreover, it has significant directing sense for the reservoir evaluation of carbonate and metamorphic reservoir. The definition of porosity of each type is the key to use the triple porosity model. If nuclear magnetic resonance, micro-resistivity imaging logs and a variety of sonic imaging logs which permit reasonable estimates of some rock properties in complex reservoir are available, it will be easy to define porosity of each type. But, if they are not available, this paper tried to solve it by traditional logs.④on genetic optimization log interpretationOptimization log interpretation does not directly use limited log information and response equations to compute reservoir parameters, whereas according to generalized inversion theory of geophysics, it comprehensively uses all kinds of log information and relevant geology information, and utilize optimization mathematical approach, statistics probability, error theory and the technique of quality control to resolve geologic parameter and evaluate formation. Those parameters can reflect the original appearance of complex lithology formation.Genetic algorithm is a robust search algorithm which can be used to optimization computation in complex system. It has many merits.⑤on identifying fluid propertyThe geologic condition that igneous reservoir is formed is complex, and it has powerful anisotropism. First, the log responses vary a lot between different lithology, so it is very difficult to analyze the gas zone by using the same standard; Secondly, borehole wall collapse of igneous rock is serious, which makes the readings of density log curve less low and the readings of neutron log curve higher. Moreover, due to the different sensibility of igneous reservoir to logging suite, it is very difficult to directly establish the relationship between gas surveying data and gas-bearing reservoir. Therefore, on the basis of the existing logging and test data, it is a effective way to find gas-bearing reservoir in igneous rock by using qualitative and quantitative methods at the same time. The qualitative method is simple and audio-visual, but it requires good borehole. It accords with the geologic conditions of igneous rock when the qualitative method combined with the quantitative method.