Di Qingyun

Modeling and analysis of CSAMT field source effect and its characteristics

Controlled-source audio-frequency magnetotellurics (CSAMT) has been a highly successful geophysical tool used in a variety of geological exploration studies for many years. However, due to the artificial source used in the CSAMT technique, two important factors are considered during interpretation: non-plane-wave or geometric effects and source overprint effects. Hence, in this paper we simulate the source overprint effects and analyzed the rule and characteristics of its influence on CSAMT applications. Two-dimensional modeling was carried out using an adaptive unstructured finite element method to simulate several typical models. Also, we summarized the characteristics and rule of the source overprint effects and analyzed its influence on the data taken over several mining areas. The results obtained from the study shows that the occurrence and strength of the source overprint effect is dependent on the location of the source dipole, in relation to the receiver and the subsurface geology. In order to avoid source overprint effects, three principle were suggested to determine the best location for the grounded dipole source in the field.

Adaptive equalization for logging telemetry based on OFDM

In order to solve the equalization of the logging telemetry based on the Orthogonal Frequency Division Multiplexing, a self-adaptive channel equalization method is proposed and realized. After analysis of telemetry system, through transform of the system structure, according to the characteristics of frame operation, the channel Signal Noise Ratio measurement and real-time dynamic update method are realized, it ensure the logging telemetry no interruption of the premise and real-time dynamic adjustment of the rate according to the channel change. This method enhances the reliability and stability of the system, and improves the efficiency of logging operation.

Dynamic inclination measurement at-bit based on MEMS accelerometer

Geo-Steering Drilling technology is one brand oil field engineering technology, which integrates well drilling, well logging and reservoir engineering technology. The measurement of At-Bit geology parameters and At-Bit drilling parameters are the core of down hole measurement technology. The trajectory information of drilling is indicated by the angle of the well in the measurement of the drilling parameters. Traditional instruments that measures the deviation of drilling, and other drilling parameters sensor probe distance is far from the bit, although here the measurement environment compared with near bit is good. But it cannot reflect the trajectory timely that is a big problem, especially in thin reservoir of directional drilling operation. The closer distance of the measuring sensor is, the worse the influence of vibration, shock, temperature and so on, which puts forward a very high demand for the development of the At-Bit Geo-Steering Drilling tools. The dynamic inclination measurement unit at At-Bit based on MEMS acceleration is using five axis MEMS accelerometer and four compartments Geological Steering tool. The sensor is near by the bit less than one meter and it can be real-time measurement of drill attitude and trajectory information. In order to meet the dynamic situation of inclination measurement, the image measuring and compensating for dynamic filtering method are used, makes the dynamic measuring precision of hole deviation control in less than 0.5 degrees, static measuring accuracy within 0.3 degrees. This Unit meets the demand of LWD logging in high precision Geo-Steering Drilling.

Synchronization method for logging telemetry based on OFDM

The application of Orthogonal Frequency Division Multiplexing to logging telemetry can obtain high data transmission rate. The problem of synchronization is the key to the performance of the telemetry system. The process includes the clock synchronization, symbol synchronization and frame synchronization. For the logging telemetry, the down hole transmission clock is drift with the temperature and environment changing, the surface system must acquire and track the clock. In this thesis, we propose the method of inserting pilot frequency to obtain and track the surface system frequency, and use the pseudo random sequence to achieve symbol synchronization. This algorithm has the advantages of less computation, fast convergence and so on. It has been used in the sets of logging equipment. The establishing time is short and training result is in good agreement.