Transient Pulse Radar Imaging Well-logging And Experimental Research

The exploration area of oil-gas resources are gradually from shallow reservoirs to deep reservoirs, the exploration areas gradually widen; the exploration depth is becoming deeper and deeper, and becoming more and more difficult for exploration. However, the conventional well-logging instruments have short radial detection ranges and inefficiency, so that it is very difficult to identify the reservoirs with strong heterogeneity, the micro-cracks growth areas, the tight reservoirs with low porosity and permeability. The transient pulse radar imaging well-logging technology depends on its long detection range and relatively high resolution, and can image the stratigraphic structures surrounding the well. These advantages can make up for the flaws of the conventional well-logging instruments, so the transient pulse radar imaging well-logging technology has been the focus of research for countries around the world. In order to overcome the challenges of complex oil-gas exploration in China, this paper aims to develop the first transient pulse radar imaging well-logging system of China for oil-gas resources exploration, therefore, we focus on the transient pulse radar imaging well-logging and experimental researches.The transient pulse radar imaging well-logging technology is a new method of geophysical exploration. Based on the development of borehole radar technology, the transient pulse radar imaging well-logging system emits transient impulses into the subsurface and uses its transmission characteristics to capture strati-graphic information. The different electronic parameters of formation surrounding the well is an essential prerequisite for transient pulse radar imaging well-logging, according to the analysis of the transmission properties of the transient pulse in the formation, so the paper provides an application condition of transient pulse radar imaging well-logging system, that is, the work frequency and formation parameters need satisfy ζ/ωε<<1. The transient pulse radar imaging well-logging system has two work patterns: cross-hole tomography pattern and single-hole reflection pattern. The former is mainly used for evaluating the electronic parameters between the two boreholes; however, the latter is for detecting the anomaly targets surrounding the well, and obtaining the targets’ location information by directional antennas.Single-hole reflection imaging is the main work pattern in the real exploration procedures, which can offer more strati-graphic information in one measurement, economical and efficient. Considering the condition of the oil wells and analyzing the disadvantages of the directional method of the abroad borehole radar, this paper proposes a new directional method for transient pulse radar imaging well-logging system. It takes a dipole with the discrete resistor loading as the transmitting antenna, and several directional antennas along the axis with different radiation directions form the receiving array. This kind of directional method can locate the targets without rotating the receiving antennas, which greatly reduces the complexity of the transient pulse radar imaging well-logging system. Meanwhile, the key technology research of transient pulse radar imaging well-logging prototype system applying to hydrocarbon resource exploration is carried out.In order to test and verify the performance of the transient pulse radar imaging well-logging prototype system, at first, we carried out experiments in an imitate-well by this prototype system as well as MALA borehole radar system, and analyzed the experimental results from the both systems. Then, we adopted the finite difference time domain(FDTD) method to do some relevant numerical simulation. Finally, we took the transmission characteristics study of transient pulse in complex medium surrounding the well by means of combining the physical experiments with numerical simulation.The transient pulse radar imaging well-logging prototype system I uses two omnidirectional dipoles as the transmitting and receiving antennas, respectively. The single-hole reflection imaging experiment is carried out in imitate-well I in a limestone formation. The results of both physical experiments and numerical simulation demonstrate that: the fractures will change the transmission paths of the transient pulses, which are not benefit for collecting the echo signals; the prototype system I can detect the targets that about 10 m from the well in the formation with fractures; a simulated 5000 m cable module added onto the cable ends for simulating the data communication in a deep well, the communication status is in good condition, which shows that the prototype system I has the basic functions for oil-gas reservoirs exploration. While the transient pulse radar imaging well-logging prototype system II is equipped with an omni-directional dipole transmitting antenna and a receiving array with four ferrite composites directional antennas. The single-hole reflection and cross-hole tomography experiments are carried out in imitate-well II in a sandstone formation. Both the experiments and simulation results indicate that: the attenuation of transient pulse is very serious in sandstone formation with high conductivity, which is unfavorable for the transmission of transient pulses; the conductivity of the test field is a serious constraint to radial detection range of the transient pulse radar imaging well-logging prototype system.The transient pulse radar imaging well-logging prototype system III employs an omni-directional dipole as the transmitting antenna, while the receiving array consists of two directional antennas along the axis with 180° difference. This prototype with the conventional well-logging instruments is carried out in an oil well with 1596 m depth and filled with mud. A novel method to obtain the energy curve is proposed. Through processing the radar data from the well-logging experiments, the energy curve is in good agreement with the conventional resistivity curves. Because the prototype system has a long radial detection range, so it can better reflect the original state formation surrounding the well; the radar profile maps in typical angles show that the transient pulse radar imaging well-logging prototype system III has certain directionality. The experimental results between the transient pulse radar imaging well-logging prototype system and conventional well-logging instruments have a high level of consistency; moreover, the prototype has a good working performance in the oil well with high temperature and high pressure as well as filled with mud. Therefore, the transient pulse radar imaging well-logging prototype system can provide a new means for formation evaluation.