根据电磁场基本理论,假设井下非均匀介质为关于发射井轴对称的柱状分层介质,推导了发射线圈通以交变电流时,井间磁偶极电磁测井模型的频域电磁场响应一般表达式。为井间电磁测井的正演计算和反演解释提供了理论依据。分析了井眼泥浆电导率和套管磁导率参数对井间电磁测井响应的影响,仿真结果表明,井眼中泥浆电导率的变化对电磁测井响应的影响极小,因此,井间电磁测井数据处理时没有必要进行泥浆影响校正。不同磁导率金属套管的电磁测井响应分析表明,井间电磁测井中,采用非磁性或弱磁性套管要优于一般的铁磁性套管。讨论了井间电磁测井对地层电导率变化的灵敏程度,计算结果表明,井间电磁测井响应可以灵敏地识别地层电阻率变化,证明了过套管电磁测井技术用于油气资源勘探的可行性和有效性。
By electromagnetic theory,assuming the subsurface inhomogeneous medium is axially symmetrical in respect of the bole axis where the transmitter is,the general expressions of frequency-domain electromagnetic responses for cross-well electromagnetic logging model are deduced for the case that the magnetic dipole source and the receiver are set in respective well.These expressions can provide theoretical foundation for forward modeling and inversion and interpretation in cross-well electromagnetic exploration.And the effects of the bore-hole mud and casing pipe on electromagnetic logging responses were analyzed.Simulation results indicates that the borehole mud has little effects on the electromagnetic responses,so we can ignore of the mud effect in casing hole environment in cross-well electromagnetic measurements.The numerical results of different magnetic permeability of the casing pipe show that in cross-well environments,non-magnetic or low-magnetic steel pipe is superior to magnetic iron pipe.Furthermore,the sensitivity analysis of the electromagnetic responses to the formation resistivity indicates that the electromagnetic responses are fairly sensitive to the formation resistivity.And the result proved the feasibility and effectiveness of cross-well electromagnetic logging technology applies to the field of oil and gas exploration.