Design Of Downhole Transient Electromagnetic Large Power Source

Oil and gas as nonrenewable resources are important strategic materials which directly related to the country’s strategy safety and people’s daily life. Our country’s demand for petroleum is steadily on the increase. For example, in2011, the proportion of our country’s petroleum depend on foreign supply had surpassed56percent,according to the amount of Chinese oil and gas resources that have been ascertained, we see the increase of yield gains by improving recovery ratio of develop oil zone a little, will produce earnings far more than invest heavily in new exploration zone and cost little risk. The development and use of advanced technology to dynamic monitoring of oil deposit in exploiting, real-time understanding of the water flooding or gas drive reservoir oil-water or oil-gas interface changes,and to guide further exploration and development,improve the recovery ratio of oil and gas field, achieve increasing reserves and production or stable tapping the potential in limited resources case, all have great significance.So far, although there are many evaluation of reservoir oil and gas, compared to the formation water resistivity,oil and gas have significant differences in the resistivity, Resistivity is still the main parameters of judgment and evaluation of reservoir hydrocarbon potential. Resistivity is closely related to porosity and pore fluid properties, saturation.Since the famous Archie formula proposed, electrical and electromagnetic methods have been quantitative evaluation of the most direct and reliable method for reservoirs containing oil and gas. A large number of ground electromagnetic exploration methods, in the time domain electromagnetic exploration methods with high resolution, anti-interference ability and low production costs, especially the transient electromagnetic method (TEM) are more sensitive to reflection of the electrical layer, is the exploration stage structure prediction of hydrocarbon potential, and evaluation and development phases of the preferred method for dynamic monitoring of hydrocarbon reservoirs.With most of our country’s oil fields have exploited to the middle and latter period, it becomes more and more important to dynamic monitoring producing well for increase the effective oil production and also decrease the cost of exploration. Cased-hole resistivity logging can provide straight reference material, at present, our national cased-hole resistivity logging tools are imported from abroad almost. We don’t have the cased-hole resistivity logging tools or equipment with independent intellectual property rights.This paper first describes the design of take advantage of transient electromagnetic pulse source cased-hole measure resistivity, then the paper has studied total design program of large power the transient electromagnetic source system for cased-hole resistivity logging, mainly presents achieve the excitation of low frequency electromagnetic field in the metal-casing and weak signal detection, meantime,we give simulation test proposal about cased-hole resistivity logging weak signal detection, we can obtain information on the formation resistivity, according to the signal within the casing, it offers viewing system for well electromagnetic detection method of evaluate distribute state of the remaining oil in producing well.Cased-hole resistivity logging large power transient electromagnetic pulse system can be divided into the transmitter and the receiver system.The transmitter system adopts SCR shift phase to control AC provide boost voltage for the input of transfhormer, the principle is charge up big capacitor, after fill up the big capacitor, cut off charge circuit to isolate against big capacitor, lead with the constant temperature crystal oscillator, through optically controlled switches make the SCR on, according to time-domain transient electromagnetic method. Via put coil within casing as antenna for emit electromagnetic pulse signal, focused on the current acquisition of the emission source, used the C8051F060microcontroller programming achieve the current collection.Take advantage of calibration the current sensor of V8that made by Canadian Phoenix, and then use it to measure the emission current in circuit.Receiver system adopts electromagnetic sensors fixed up at suitable position, receive the second turbulence eletromagnetic field of cased-hole after formation affect, we adopt TI company TMS320VC5509A chip and analog-digital converter CS5381as receiving device. Synchronization of precise time provide guarantee for the post-data processing. It introduces TI DSP software development, CCS integrated development environment and system software processes. Using FAT32file system to read and write data on the SD card and giving the detailed design of an external program download, using C language to complete the preparation of the underlying module, the difficulty of the program lies in weak signal detection.Through two years of exploration, to prove the feasibility of the program, made in the way, the transmitter has large power, low frequency.The test results fully illustrate:excitation and observation of electromagnetic fields change in cased borehole,obtains the distribution information of formation resistivity around casing well. And then prove that the electromagnetic detection method for the distribution of the remaining oil in the evaluation of the development of reservoir wells is feasible.