| The deep volcanic reservoirs in Daqing Oilfield is dense, its porosity (usually 3% to 20%) and permeability (0.01×10~3～10×10~3μm~2) are very low, and its non-homogeneous is strong. Since natural productivities of most wells are low, they must be fractured in order to achieve industrial production capacity. However, because gas reservoir of volcanic rocks are deep buried (usually 3000～4500m), geothermal gradient is high (usually 4～4.5℃/100m), lithology is complex and hard, fracture pressure is up to 80MPa or more, However, because of deep buried gas reservoir of volcanic rocks (usually 3000～4500m) and high geothermal gradient (usually 4～4.5℃/100m), as well as complex, hard lithology and up to 80MPa or more fracture pressure, the following questions will be appeared when traditional deep well fracturing is used in volcanic rock fracturing. (1) Temperature and pressure resistant indexes of fracturing tool are low. The domestic technical indexes of high temperature and high pressure fracturing tool are generally temperature resistant 150℃, working pressure 80MPa. They can meet the needs for general technologies of deep well fracturing. However, volcanic reservoirs can not be fractured when its temperature exceeds 150℃and formation fracture pressure is above 80MPa. And it limits further development of volcanic reservoirs. High-performance packer rubber is the core of fracturing packer's temperature and pressure resistant indexes. Packer rubbers both at home and abroad are made from HNBR, but the maximum allowable temperature which HNBR supports is only 160℃. This limits further performance improvement of packer rubber's technical indexes. Therefore, rubber materials with better performance are needed to be found and they are needed to be studied from such areas as formulation design, vulcanization technology, structure optimization of packer rubber and protection measures. (2) Fracturing scale is low. Deep volcanic rock wells could achieve higher production capacity after large-scale fracturing. But due to large-scale and long time construction, there are some serious wear and tear problems when fracturing tool are eroded in high-strength proppant, resulting in lower casing strength, especially high deformation in prone position and some accidents which happen while drawing. Therefore, string abrasion mechanism in large-scale fracturing is needed to be studied to determine the reason and position of the abrasion occurrence in order to develop high abrasion resistance well tools. (3) Hierarchical transformation can not be implemented. Volcanic reservoir has multiple vertical layers, and is non-homogeneous and strong, the formation fracture pressure of which is high. For the volcanic reservoir with 40～50MPa formation fracture pressure, its pressure of the ground construction is more than 80MPa. When the pressure of the ground construction is 80MPa , the axial tension F which actions on the string can be achieved 919.5kN. But the tubing in general card form isΦ76mm, and its threadlock anti-slip strength is only 846kN. When axial tension exceeds anti-slip strength connecting threadlock, the slip accident will appear for card form tubing. Therefore, deep well generally use test gas method by fracturing layer by layer. However, the method has some problems such as long time construction, high formation damage by many times killing, and low construction efficiency. (4) Existing cycle instruments are not adapted to deep gas well fracturing. At the end of the test gas, gas well fracturing string must be full cycled before killing. Therefore, the cycle instruments need to be designed in fracturing string device. There are two kinds of conventional cycle instruments: shear pin mode and hydraulic switch mode. But when they are implemented in deep gas well, there are some problems such as low temperature and pressure resistant indexes, poor wear resistance, low reliability. Therefore, new cycle instruments adapted to deep gas well fracturing need to be studied.In order to solve the practical problems faced by deep gas reservoir fracturing, the research of this thesis focus on 180℃, 100MPa deep gas well fracturing technologies including the following four main aspects:1. Plug-in hierarchical fracturing string is developed, and thus providing technical means for fracturing transformation of deep volcanic rocks. Plug-in hierarchical fracturing string takes drillable packer as layered plugging packer, and achieves hierarchical fracturing combined with plug-in fracturing string. Its characteristics include high construction efficiency, small formation damage, and it solves the problems that hierarchical fracturing string for two-card string of packer will be slipped when deep well is fractured. A non-linear static model of fractured string is established by using finite element method, which takes full account of the structure of fractured string, boundary conditions and various loads. And it correctly describes collision contact state between fractured string and the casing inner wall, constructs the conditions of contacting state. The results got by iterative calculation show that the deformation of fracturing siring in high temperature and high pressure working conditions meets strength requirements.2. Deep well fracturing packers Y344-115 and Y443-108 are developed, which are 180℃and 100MPa resistant. The closure issues during placing packer Y443 are solved through structural design and material selection. 180℃, 100MPa packer rubbers are developed from such areas as preferred selection of plastic materials, formulation design, curing process, structural design and plastic tube's protection, which significantly improve technical indexes of packer. And the performance indexes of packer achieve international advanced level.3. Fluent software is used to establish the internal flow field model of fracturing string. Fluid flow of different traffic, sand-ratio fracturing fluid in string is numerical simulated. And streamlines, velocity field, pressure field and solid-liquid phase distribution are obtained. Abrasive wear mechanism and the main abrasive positions while fracturing are determined. According to the theoretical research results, technical methods for solving abrasive problems of fracturing string with large volume of sand are proposed.4. Reverse circulation valve used in deep wells is studied, which has the characteristics including high technical indexes (180℃, 100MPa), sand and wear resistant, high reliability. It can be repeated used in high temperature and high pressure deep wells. It establishes an effective channel circle of killing to ensure safe construction of fracturing string in deep gas wells.Deep gas well fracturing techniques are used 111 times in field, fractures 121 layers, and the success rate of construction is 97.6%, maximum pressure of fracturing construction reaches 97.95MPa, the largest construction displacement is 6.0m~3/min, the largest volume of sand in single well is 130m~3. Theoretical studies and the indoor and field tests demonstrate that the 180℃, 100MPa plug-in hierarchical fracturing string and single-layer pressure pipe string which were developed at the first time in domestic satisfies deep volcanic reservoir fracturing technology needs from the aspects such as indexes of temperature and pressure resistant, hierarchical fracturing process, sand size, security and reliability, and achieves domestic advanced level. |
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