岩石激发极化衰减谱的多指数反演

激发极化衰减谱比极化率具有更为丰富的储层信息,与地层的孔隙结构、渗透率、地层水电阻率以及泥质含量密切相关。衰减谱是一系列单指数衰减的线性叠加,因此,可以对衰减谱进行多指数反演,得到弛豫时间谱,从而可以更好地利用激发极化衰减谱来进行储层评价。一般的非负最小二乘反演的结果振荡剧烈,与实际情况不相符。这里采用阻尼最小二乘方法,结合奇异值分解技术对泥质砂岩的激发极化衰减谱进行了多指数反演,得到了光滑连续的弛豫时间谱,弛豫时间分布点数为32点~64点较合适,算法和软件对实际的岩心具有较好的效果。

MULTI-EXPONENTIAL INVERSION OF INDUCED POLARIZATION DECAY CURVE OF SHALY SAND

The induced polarization(IP) decay curve contains more information than the polarizability.It relates to the pore structure,permeability,formation water resistivity and shality.The decay curve can be inversed to form the relaxation spectrum.The normalized IP decay signal is a superposition of IP signal from individual pore and can be inversed to a relaxation time spectrum.The spectrum is very useful to characterize the reservoirs.The normal non-negative least-square method is unable to obtain the reasonable results.In this paper a damp least-squares inversion method combined with the singular value decomposition method is used to inverse the induced polarization relaxation spectra of the shaly sands.The resulted spectra are continuous.The appropriate number of relaxation arrangement points in relaxation data inversion ranges from 32 to 64.The algorithm and the software are suitable for the multi-exponential inversion of core samples.