RESUMEN
Many oil and gas fields, especially non-conventional shale and compacted sand reservoirs, have formation anisotropy. The acoustic anisotropy measurement of cores in these reservoirs can guide drilling, well logging, and exploitation. However, almost all core holders are designed for cylinder cores, which are not suitable for all-directional measurements. A three-dimensional measurement device was designed on the basis of the cross-hole sonic logging method. This device mainly consisted of two pairs of transducers, a signal generator, an oscillograph, an omnidirectional positioning system, and a computer control system. By adjusting the measurement latitude and longitude circle automatically, this device scanned spherical sample rocks and obtained full-wave waveforms in all directions. Experiments were performed taking granite from the Jiaodong Peninsula, China, as an example, and the arrival times and velocities of the longitudinal and shear waves were calculated based on the full-wave waveforms. Thereafter, anisotropic physical characterizations were carried out on the basis of these velocities. These data play an important role in guiding formation fracturing and analyzing the stability of borehole walls.
Asunto(s)
Acústica , Transductores , Anisotropía , ChinaRESUMEN
Well logging is performed in oil and gas exploration wells to obtain the physical characteristics of underground formations. Thereafter, these wells are cased. Through-casing logging is important in mature fields and for wells that are cased without logging due to borehole stability issues. Acoustic through-casing logging is a challenging issue due to the strong interference of casing waves in formation waves, especially when the casing and formation are poorly bonded. An acoustic tool with dual-source transmitters is developed, in which an additional transducer is added to suppress casing waves. First, the operation principle and the overall design of the tool are carried out, including the span distance between the two transmitting transducers and the spacing distance between the transmitting transducer and the receiving transducers. Thereafter, a dual-source transmitting circuit is designed to send out two excitation signals of opposite polarities. These signals possess good consistency, high emission power, and precise signal adjustment. Lastly, the tool is tested in cased exploration wells in China. The experiment endings show that about 90% of the casing waves are canceled. By suppressing the casing wave amplitude, the cased-hole acoustic logging can be used commercially to obtain trustworthy formation information.
RESUMEN
To obtain qualified logging while drilling (LWD) data, a new acoustic LWD tool was designed. Its overall design is introduced here, including the physical construction, electronic structure, and operation flowchart. Thereafter, core technologies adopted in this tool are presented, such as dominant exciting wave bands of dipole source, a sine wave pulse excitation circuit, broadband impedance matching, and an intellectualized active reception transducer. Lastly, we tested this tool in the azimuthal anisotropy module well, calibration well, and normal well, working in the model of the cable, sliding eye, and logging while drilling. Experiments showed that the core technologies achieved ideal results and that the LWD tool obtained qualified data.
RESUMEN
An anisotropic physical model is constructed to evaluate the anisotropy measurement. The model consists of a series of equally spaced thin limestone slab sheets cemented with concrete, resulting in a transversely isotropic medium. For the anisotropy measurement evaluation, the borehole model is tested by a standard multipole acoustic tool. The measurement finds an S-wave anisotropy magnitude about 20% and determines the fast S-wave polarization along the alignment direction of the slab sheets. The results of the work not only validate the borehole measurement technology, but also provide a testing facility for calibrating the measurement acoustic tool.
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A hybrid method based on the finite-difference method and equivalence principle to simulate elastic wave scattering of three-dimensional objects is proposed. In this method, the near fields are first calculated in a rectangular volume containing the object by the finite-difference method. Then the displacements and tractions on a virtual surface are transformed to the far field by the application of the equivalence principle in elastodynamics. The feasibility is verified by comparing modeling results with the analytical solution for the canonical point force source radiation problem. Modeling for complex scatterer structures shows the advantage of this method in handling multi-scale scattering problems.
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The seismoelectric interface electromagnetic characteristics have been studied for the finite offset Vertical Seismoelectric Profiling (VSEP) configuration. The approach consists of theoretical modeling and laboratory verification. The results show that the wave variation characteristics along the finite offset measurement line are markedly different from those along the zero-offset line. More interestingly, the wave characteristics for both configurations can be satisfactorily explained by the electric dipole model for the seismoelectric interface wave radiation. Besides, the experiment confirms the modeling result based on the seismoelectric coupling theory and validates the VSEP technique as an effective method for subsurface interface delineation.
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The development of acoustic source technology has been an important task for acoustic logging while drilling (LWD) and various source designs have been implemented. Using a multipole wave expansion theory, this study demonstrates that a LWD acoustic source can be represented as a combination of monopole, dipole, and quadrupole constituents and characterized by the contribution of each constituent. The theoretical analysis is experimentally demonstrated with a cylindrical pipe simulating the LWD collar. The result of this study can be used to provide a method for evaluating the performance of a LWD acoustic source.
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The interaction of a fluid-filled borehole with incident elastic waves is an important topic for downhole acoustic measurements. By analyzing the wave phenomena of this problem, one can simulate the detection of a borehole target using a source-receiver system in a remote borehole. The analysis result shows that the wave signals from the target borehole are of sufficient amplitude even though the borehole size is small compared to wavelength. Consequently, the target borehole can be detected when the two boreholes are far away from each other. The result can be utilized to provide a method for testing downhole acoustic imaging tools.
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The stopband of pipe extensional waves is an interesting natural phenomenon. This study demonstrates an important extension of this phenomenon. That is, the stopband can be effectively broadened by transmitting the waves across the joint of pipes of different thickness. The theoretical and experimental results reveal the detailed process of stopband forming along the pipe and the band broadening across the pipe joint. The result can be utilized to provide a method for logging while drilling acoustic isolation design.
RESUMEN
The aim of this article is to report the application of expanding retroauricular skin fascia flap, and autogenous costal cartilage for congenital microtia reconstruction. Microtia reconstruction was generally completed in 3 surgical stages. In the first surgical stage, a 50 or 80 mL kidney-shaped tissue expander was inserted subcutaneously in the retroauricular mastoid region. Inflation of saline volume increased up to 60 to 80 mL, and skin flap was expanded for 2 to 3 months postoperatively. In the second surgical stage, removal of tissue expander, formation of retroauricular skin flap, elevation of retroauricular fascia flap, and pedicles of both flaps in remnant ear side were performed. Costal cartilage was harvested from ipsilateral side chest to the ear for reconstruction. The 3D ear framework was sculpted with stabilization of structure, contour and erection. Simultaneously, intermediate full thickness skin graft of 4 x 8 cm was obtained from previous incision site from where costal cartilage was harvested. Cartilage ear framework was anchored between skin flap and fascia flap, and fixed it symmetrically to the opposite normal ear, inferior portion of the ear framework was wrapped by remnant ear lobule, expanded skin flap covered the anterior portion of the framework, fascial flap was draped to the posterior side of framework and helical rim, then fascial flap was surfaced by intermediate full thickness skin graft. Suction drain was inserted and coated between skin flap and framework, drain was removed fifth postoperative day. Tragus construction and conchal excavation with skin graft was performed in the third stage of microtia reconstruction. Between October 2000 and October 2007, 426 cases were diagnosed as unilateral microtia patients and 22 cases were bilateral microtia patients. Therefore, 448 microtia ears were treated with tissue expander and autogenous costal cartilage. In 262 cases, structure of the helix, tragus, conchal excavation, auriculocepahalic angle, and symmetry to opposite normal ear were satisfied in the follow-up period of 6 months to 4 years. Antihelix, triangular fossa, and scapha were prominent with good result in most of the patients. Expanded retroauricular skin flap combined with fascial flap can cover the different size and height of cartilage ear framework in single surgical stage. At the same time, on the basis of structure stability and contour reality of cartilage framework, we can achieve fine structure and erect stability of constructed auricle. This method affords ideal results in microtia reconstruction.