Clock Synchronization And Signal Acquisition Research Of Underground Large Power Pulsed Field Sources

Combined with the current shortage of oil resources and prices, it is particularly important to dynamic monitoring residual oil production Wells in the mid-late oil field,Break through the outside casing detection formation of remaining oil research methods and theory is relatively mature.However, progress in the development of exploration instrument behind the theory, there is no commercial market promotion, Design of underground power pulse source of this paper is based on the time domain electromagnetic survey method, particularly, the use of transient electromagnetic method (TEM) to reflect the electrical is sensitive,method that uses pulsed electromagnetic field emission source to send pulsed electromagnetic fields to the formation, and produce induced current (primary field) in the space of formation, in the off-time of primary field, we are to measure secondary field eddy current attenuation characteristics in the formation mediators by the time, so we can detect the position of the formation of irregularities, and estimate its size and electrical properties, detection range corresponding to the time and the low-frequency component of the electromagnetic signals can effectively break through the metal casing shielding effect, maximum working on the target layer, thereby significantly improve the resolution of the target body.High power pulse source of this paper is mainly acting on downhole,Introduce achieved high power source in the metal casing of fast storage and instantaneous release.Through the underground of high power pulse source instantaneous discharge,, because of the large instantaneous power and the center frequency is low,break through the shield absorption of the metal sleeve,low frequency electromagnetic field excitation and ground measurements of weak signals in a metal casing, enabling borehole transient electromagnetic survey.To understand the ground working principle of transient electromagnetic method,the source is turned off, receiver to receive the secondary field of underground medium,so requires the synchronization of source and receiver, GPS antenna to the transmitter and receive configuration, main control unit receives satellite time signal.Combined with the actual oil field production, downhole conditions of GPS signal shielding, downhole instrument can’t receive GPS signals,So conduct a GPS time on the ground, instrument under the well should be carried out within the time.To ensure the realization of synchronous acquisition in the underground, high precision clock circuit design is necessary,the core issue is the high-precision clock circuit stability crystal devices,the stability of the crystal by ambient temperature changes the oscillation frequency changes accordingly, there is a cumulative error. With the change of temperature downhole drilling depth also changes, if no compensatory measures, the system is difficult to guarantee the accuracy.The field source is placed deep underground, thousands of meters deep, problems will inevitably lead to inaccurate measurements.So imagine using GPS to face with temperature-compensation crystal oscillator cooperate method of downhole, complementary advantages.Common oscillator built-in temperature compensation circuit curve, it is possible to generate a stable reference frequency signal,GPS can work normally, the ground can pair second pulse signal control precision of the borehole field source.When the GPS fails to work under the wells, it can be substituted with TCXO second pulse, easing the reliance on the GPS system, so the system is more precise.For transient electromagnetic system, transmit pulse current source is also an important part of the collection,By the clock signal,On the one hand it is used to synchronize TCXO, on the other hand for the single-chip ADC sampling circuit control acquisition,after overlay, ground-sensing signal associated with the role after doing convolution,presented information about the formation resistivity,to evaluate the distribution of remaining oil production wells downhole electromagnetic detection method provides the observation system.