Research On Seismic Prediction And Evaluation For The Fracture In The Compact Clastic Rock Reservoir

Aimed at fracture prediction-a world-class problem, the paper developed a set of effective method and technique series for seismic integrative prediction and evaluation for the fracture in the compact clastic rock reservoir through systematic research, so, the paper developed a new approach for the exploration and exploitation of the fractured reservoirs in compact clastic rock in Sichuan basin and so on.(1) Based on the analysis of the forming, shape types and scale features of the clastic rock fracture, the paper summarized the reservoir types and fracture types in Xujiahe formation, indicated that the reservoir types include fracture-pore type and pore type, and the fracture types consist of sedimentary fracture, diagenetic and structural fracture. The paper also concluded that the geologic and geophysical response patterns, the logging response variation properties and seismic wave variation properties of the clastic rock reservoirs. Taking the complicated and changeful variation properties of the fracture scales, and geologic and geophysical properties of the fractures in clastic rock reservoirs in Xujiahe formation as the science evidences and stable foundations, the paper developed a set of fracture prediction and evaluation methods and techniques suitable for the compact clastic rock reservoir. These methods and techniques are comprised of prestack and poststack seismic attribute prediction technique, seismic high resolution nonlinear inversion method, nonlinear parameter prediction and seismic nonlinear fracture evaluation technique. These methods and techniques are specialized fracture prediction techniques, which filled up the domestic blank of specialized fracture technique.(2) Poststack seismic attribute fracture prediction techniques consist of coherent volume analysis technique, improved dip adjusting coherent volume analysis technique, reflection strength analysis technique and so on. The coherent volume analysis technique performs fracture prediction by using the similarity of the seismic wave, and can gain good fracture prediction effects if 3D seismic volume is used. Poststack seismic attribute fracture prediction technique has high validity and reliability for the fractures with large size.(3) Based on the analysis of elastic wave transmission properties and physical model in anisotropic fractured medium, the paper developed prestack multi-azimuth seismic attribute prediction techniques comprising of AVA (or AVO), FVO, VVA and IPVA techniques, which is a quantitative prediction technique for small-size fracture, and can provide such information as fracture intensity and fracture orientation. This prestack fracture prediction technique was applied to predict the fractures in Shaximiao reservoir, and determine the fracture orientation and distribution properties in Shaximiao reservoir, and good geologic effects have been obtained. Therefore, this technique provided new technical supports for fracture prediction problems.(4) Seismic high resolution nonlinear inversion method is a combination of self-adaptive clustering intelligent algorithm and neural network technique (BP algorithm), and is a new seismic inversion method which inserts BP algorithm into the interior of the clustering intelligent algorithm and integrates the advantages of the two methods. This new seismic inversion method utilizes the characteristic that the particles can search the regional optimum solution in the whole interval by pursuing the local optimum particle, and utilizes the characteristic that BP operator will converge nearby the optimum point rapidly and accurately, so this method can find the optimum point and obtain the optimum solution quickly and accurately; this new seismic inversion method can establish the nonlinear mapping relationships with the seismic data of the traces nearby the borehole and update the mapping relationships with the constraint of the fracture intensity data of the imaging logging; this method can automatically realize fracture intensity inversion, and gain fracture intensity section. Therefore, this new seismic inversion method is the optimal estimate method for fracture intensity, is a quantitative fracture prediction technique, and is a sort of core technique for fracture prediction.(5) Based on catastrophe parameter, fractal dimension parameter (or relevancy dimension) and Lyapunov exponent can be direct indicators of fracture growth situations, the paper developed a new, complete and effective fracture prediction technique, which consists of pinchout point catastrophe fracture prediction technique, relevancy dimension fracture prediction technique, stochastic fractal fracture prediction technique, Lyapunov chaos fracture prediction technique and nonlinear fracture evaluation technique.Pinchout point catastrophe prediction technique researches discontinuous phenomenon and its properties on the basis of the catastrophe theory; relevancy dimension and fractal fracture prediction technique are relied on the fracture system has self-similarity and the relevancy dimension (or fractal dimension) can reflect fracture scale information; Lyapunov chaos fracture prediction technique is based on Lyapunov exponent more than 1 reflects the divergent sedimentary environment and the telogenetic divergent geologic reconstruction action.Nonlinear fracture evaluation technique is a new self-adaptive fuzzy neural network method based on a model formed by combining adaptive neural fuzzy inference system(ANFIS), and applied genetic algorithm to optimize the linking weights of the network. This evaluation technique utilizes parameter space formed by three kinds of nonlinear parameters for fracture evaluation, and can gain the integrative parameters after evaluation, which represent the fracture development extent, so these integrative parameters are called as fracture development indexes, which can be used as evaluation indexes for fracture development extent.(6) These fracture prediction techniques are successfully applied in such areas as central and west Sichuan and so on, and good geologic effects and rich innovative research results have been gained. The application and research results indicated that the research results are suitable for the complicated variability and fracture scale variation properties of fracture systems with different types.Among the fracture prediction technique series, each technique can be applied alone, and also can be combined to use, so they are very flexible; among them, there are qualitative prediction technique and quantitative prediction techniques which can be combined to use to improve the prediction effects; moreover, the fracture prediction technique series include not only linear prediction technique, but also nonlinear prediction technique, which are adaptable for the complex and changeful features of the fracture system in the reservoir. The paper developed a new approach for fracture prediction and evaluation, and provided powerful technical supports for the exploration and exploitation of the fractured reservoir. Therefore, these techniques will have wide application prospects and popularizing values.