Font Size: a A A

Research On Reservoir Characteristics And Fracture Initiation Mechanism Based On Fractal Theory

Posted on:2011-01-06Degree:DoctorType:Dissertation
Country:ChinaCandidate:W LiFull Text:PDF
GTID:1100360305978022Subject:Oil-Gas Well Engineering
Abstract/Summary:PDF Full Text Request
Hydraulic fracturing has been widely used in the reconstruction of low-permeability reservoirs, and becomes an effective method of stimulation for low-permeability oilfield since its first successful application in the late 1940's. In order to increase the success ratio of fracturing operation and further improve the efficiency of hydraulic fracturing, researches on fracture mechanism which based on rock fracture mechanics have been done by scholars. We can draw a conclusion that induced fracture's direction of extending and expanding which is perpendicular to single plane cracks of minimum principal stress. This conclusion has become the basis of shapes analysis and numerical simulation of hydraulic fracturing.Along with further development of oilfield, reservoirs needing to reform become more complex, and scholars have gradually recognized that single-plane cracks theorem can not give a perfect explanation on fracturing operation under complex situations in theory. The considerable field practices show that fractured reservoir has multi-fracture extending at the same time and the fracture shape may not be flat. And this situation is especially obvious in fractured reservoir. This paper, by means of fractal theory study, analyzes fracture shape of hydraulic fracturing and its influential factors via the study on the fracture initiation mechanism under different reservoirs by laboratory experiments and field data.To ensure dissertation, this study use the approach of combining theoretical research with experimental analysis. In the aspect of theory, first, analyzing fractal features of reservoir media with the method of fractal theory and setting up the effective stress fractal model.Then, analyzing fracture initiation mechanism of fractured and porosity reservoirs according to new stress condition equations of rock around borehole.In the aspect of experimental analysis, firstly, fractal dimensions of pore texture are determined by means of scanning electron microscope (SEM), mercury porosimetry method (MPM) and fractal dimensions of fractured texture are measured by coring.That provides data basis of fractal features for analysis of reservoir storage medium in fractal method. Then, it analyze the fracture initiation mechanism of fractured and porosity reservoirs on the basis of large dimension hydraulic fracturing simulation experiments as the experimental base on theoretical investigation.The main contents and outcomes are as following:1. Analyzing the microscopic feature of porous media using fractal geometric methods. To meet the filed requirement, effective stress fractal model is built according to fractal model of pore structure characteristics and simplified effective stress model is introduced. Coordinating connections between pore fluid and skeletal grains of pore structure on support total stress are quantitatively described by this model as well as the micro-parameters of porous medium are linked with the macro-parameters.2.Fractal model based on effective stress of porous medium derives new stress condition equation of rock around borehole and gets fracturing discrimination criteria with fractal parameters in the condition of casingless completion and perforation completion on further derivation.New model introduces fractal parameters describing the structure characteristics of porous medium.It is the basis of analysing fracture initiation mechanism of reservoir by use of fractal model.3. Analyzing the structural feature of porous media by use of fractal geometric methods. Establishing 3-D visualization platform such as VB.Net & OpenGL.3-D distribution of Budate formation's fracture system is simulated on the base of distribution rules of fracture medium by use of deterministic scattered modeling approach. In terms of simulation results, fractal theory can reflect randomness of single fracture and complexity of fracture system and it is an effective modeling method.4. Analyzing fracture criterion (rock fracture toughness) according to fractal geometry model. By using fractal method, shape and propagation direction of fracture are given. The fractal character is introduced into the fracture toughness, as a result, the fracture toughness values of type-â… , type-â…¡and mixed rocks are obtained.5. Using large dimension hydraulic fracturing simulant installation, the study analyze factors of fracture initiation mechanism according to the results of hydraulic fracturing simulation experiment. Experiments show that natural fracture has a significant influence on initiation pressure and fracture propagation shapes. The existence of natural fracture reduces the fracture pressure of rock, and makes the fracture geometry more complex.6. Analyzing the distribution rules of natural fracture by use of fractal methods, and ascertaining the relationship between porosity fractal parameters and permeability fractal parameters.Thus, Analyzing fractal parameters'influence on fracture length and fracture width according to PKN and KGD model which are 2-D.Fracture creation of hydraulic fracturing is a rock fracture process.Several different factors make the process more complex. This dissertation briefly concerns the effects of various factors on rock fracture, especially when natural fractures exist. This research deepened our understanding of fracture initiation mechanism and can be used for further research as well as direction of field fracturing practice in theory and technology.
Keywords/Search Tags:reservoir characteristics, hydraulic fracturing, fractal, effective stress, reservoir modeling, simulation experiment, fracture initiation mechanism
PDF Full Text Request
Related items