The frequency domain electromagnetic method has already been widely used for tomographic imaging or electromagnetic well logging. However, different from open hole logging, the metal casing existing in production well...The frequency domain electromagnetic method has already been widely used for tomographic imaging or electromagnetic well logging. However, different from open hole logging, the metal casing existing in production well logging has a strong shielding effect on the electromagnetic waves, thus bringing some difficulties to the application of the frequency domain electromagnetic method in production well logging. According to the relation of the field source geometry to the ring around the mandrel, the general expressions of frequency domain electromagnetic responses in axially symmetrical layered conductive medium are deduced. The propagation effects caused by the low-frequency electromagnetic waves in cased hole are also analyzed. The distribution curves of eddy current density and magnetic flux density along the radial direction in the mandrel indicate that the eddy loss within the mandrel is proportional to the transmission signal frequency and the mandrel conductivity. The secondary field responses of different casing materials show that the transmission frequency has an important effect on the ability of electromagnetic waves penetrating the metal casing. The transmission frequency should be ultra-low in order to enable the electromagnetic signal to penetrate the casing easily. The numerical results of frequency responses for different casing physical parameters show that the casing thickness has a significant impact on the choice of the transmission frequency. It is also found that the effect of the casing radius on the transmission frequency can be neglected.展开更多
Carbonate dissolution during the process of burial and evolution by percolating acid fluid was simulated using core plugs to analyze the characteristics and controlling factors of Cambrian carbonate rock dissolution i...Carbonate dissolution during the process of burial and evolution by percolating acid fluid was simulated using core plugs to analyze the characteristics and controlling factors of Cambrian carbonate rock dissolution in the Tarim Basin. The results showed that mineral composition and reservoir space type control selective dissolution. In the carbonate rock strata with high calcite content, the calcite is likely to dissolve first to form secondary dissolution pores; gypsum and anhydrite in the carbonate rock can be dissolved to form mold pores in contemporaneous and penecontemporaneous stages. Porous carbonate has mainly enlargement of matrix pores, with porosity and permeability increasing correspondingly, but not obviously. In comparison, dominant channels for fluid are likely to occur in fractured carbonate or porous carbonate forming cracks under high pressure, resulting in a relative reduction in the dissolution volume, but great increase of permeability. With the rise of temperature and pressure, corrosion ability of acid fluid to carbonate rock increases first and then decreases, there exists an optimum range of temperature and pressure for dissolution, which corresponds to the buried depth of 2 250-3 750 m of the Cambrian. Considering reservoir characteristics of the study area, it is concluded that calcite in the penecontemporaneous period is the material basis for the development of dissolution pore, and carbonate rock were mainly dissolved by early atmospheric fresh water, superimposed and reformed to form high quality reservoirs by multiple acid fluids including deep hydrothermal fluid and acid fluid generated during the process of organic thermal evolution under burial condition.展开更多
基金supported by the National Natural Science Foundation of China (No.50974103, No.61003196)the Specialized Research Plan of Shaanxi Province Education Department (No.2010JK787)
文摘The frequency domain electromagnetic method has already been widely used for tomographic imaging or electromagnetic well logging. However, different from open hole logging, the metal casing existing in production well logging has a strong shielding effect on the electromagnetic waves, thus bringing some difficulties to the application of the frequency domain electromagnetic method in production well logging. According to the relation of the field source geometry to the ring around the mandrel, the general expressions of frequency domain electromagnetic responses in axially symmetrical layered conductive medium are deduced. The propagation effects caused by the low-frequency electromagnetic waves in cased hole are also analyzed. The distribution curves of eddy current density and magnetic flux density along the radial direction in the mandrel indicate that the eddy loss within the mandrel is proportional to the transmission signal frequency and the mandrel conductivity. The secondary field responses of different casing materials show that the transmission frequency has an important effect on the ability of electromagnetic waves penetrating the metal casing. The transmission frequency should be ultra-low in order to enable the electromagnetic signal to penetrate the casing easily. The numerical results of frequency responses for different casing physical parameters show that the casing thickness has a significant impact on the choice of the transmission frequency. It is also found that the effect of the casing radius on the transmission frequency can be neglected.
基金Supported by the China National Science and Technology Major Project(2016ZX05005-004-006)
文摘Carbonate dissolution during the process of burial and evolution by percolating acid fluid was simulated using core plugs to analyze the characteristics and controlling factors of Cambrian carbonate rock dissolution in the Tarim Basin. The results showed that mineral composition and reservoir space type control selective dissolution. In the carbonate rock strata with high calcite content, the calcite is likely to dissolve first to form secondary dissolution pores; gypsum and anhydrite in the carbonate rock can be dissolved to form mold pores in contemporaneous and penecontemporaneous stages. Porous carbonate has mainly enlargement of matrix pores, with porosity and permeability increasing correspondingly, but not obviously. In comparison, dominant channels for fluid are likely to occur in fractured carbonate or porous carbonate forming cracks under high pressure, resulting in a relative reduction in the dissolution volume, but great increase of permeability. With the rise of temperature and pressure, corrosion ability of acid fluid to carbonate rock increases first and then decreases, there exists an optimum range of temperature and pressure for dissolution, which corresponds to the buried depth of 2 250-3 750 m of the Cambrian. Considering reservoir characteristics of the study area, it is concluded that calcite in the penecontemporaneous period is the material basis for the development of dissolution pore, and carbonate rock were mainly dissolved by early atmospheric fresh water, superimposed and reformed to form high quality reservoirs by multiple acid fluids including deep hydrothermal fluid and acid fluid generated during the process of organic thermal evolution under burial condition.
