阅读说明：本技术 一种裸眼井差分电导率处理方法 (Open hole differential conductivity processing method ) 是由 刘鹏程 沈建国 于 2019-04-16 设计创作，主要内容包括：一种裸眼井差分电导率处理方法,属于石油工程测井施工中套管井地层物理参数测量技术领域,该方法用同一源距相邻深度测量的波形相减可以去掉响应中的所有无用信号(包括井内液体、水泥环的二次场响应),得到间隔Δ深度两个深度点所测量地层(区域)的二次场差；用响应差(代替视电导率差)和差分几何因子差进行反褶积反演,还原了地层电导率曲线,用差分反演的方法解决了地层电导率曲线的求取问题；在差分几何因子源距选择正确的情况下,可以完全还原地层电导率,提高了地层分辨率。(A kind of open hole differential conductivity processing method, it is the well stratum physical parameter measurement technical field of the casing in the petroleum engineering well logging construction, this method can remove all unnecessary signals (including the secondary field response of liquid, cement sheath in the well) in the response by the waveform subtraction of the adjacent depth measurement of the same source distance, get the secondary field difference of the stratum (area) measured by two depth points of interval delta depth; deconvolution inversion is carried out by using the response difference (replacing the difference of the apparent conductivity) and the difference of the differential geometric factors, a stratum conductivity curve is reduced, and the problem of solving the stratum conductivity curve by using a differential inversion method is solved; under the condition that the source distance of the differential geometric factor is correctly selected, the formation conductivity can be completely reduced, and the formation resolution is improved.)

1. A method for processing open hole differential conductivity is characterized by comprising the following steps: the specific method comprises the following steps:

step one, transient electromagnetic logging is excited by adopting a step signal, and electromagnetic induction signals excited by an eddy current field with an interval delta depth are taken according to the characteristics of waveforms, namely transient electromagnetic induction receiving waveforms, wherein the induced electromotive force U of a receiving coil comprises information of a primary field and a secondary field, and a waveform 3 is obtained by using a signal waveform 1 and a waveform 2 with the interval delta depth to make a difference, because the primary fields with different depths are the same at the same moment, the primary field is eliminated in the waveform 3, and only the secondary field difference with the interval delta depth is left;

subtracting transient electromagnetic induction receiving waveforms of two depth points with the interval delta to obtain a response difference waveform 3, wherein the primary fields of the adjacent depth points are equal in size and same in phase, so that the primary fields can be eliminated by difference making, and the obtained receiving waveform difference is the product of the difference of the conductivity of view and the constant of a known instrument;

step three, obtaining the difference of the visual conductivity and the known difference geometric factor g_ΔPerforming deconvolution inversion on the difference to obtain a stratum conductivity curve, wherein sigma is the stratum conductivity curve;

step four, debugging a proper differential geometric factor g_ΔBecause the source distances L of the geometric factors are different, the shapes of the geometric factors are also inconsistent, the results obtained by inversion are also different, the correct geometric factors are obtained by debugging, and the deconvolution result is closest to the stratum conductivity curve;

and step five, obtaining the stratum conductivity after the steps one, two, three and four are executed, and comparing the stratum conductivity with an original curve.

Technical Field

The invention belongs to the technical field of measurement of formation physical parameters of a cased well in logging construction of petroleum engineering, and particularly relates to a method for processing differential conductivity of an open hole well.

Background

In the exploration and development of petroleum, well logging is a very important means of assessing hydrocarbon reservoirs. In the aspect of a logging technology, a transient electromagnetic logging technology is developed and perfected by using a geophysical prospecting method, a transmitted signal is a step signal, transient excitation is adopted, and transient response waveforms of different source distances in a well are measured. The transmitted electromagnetic signal forms an eddy current in the medium outside the well, a secondary field generated by the eddy current is received by the receiving coil again, and the formation conductivity information is contained in the secondary field.

The received signals also include directly coupled signals (i.e., primary field) and secondary field signals, and the conventional method cannot eliminate the primary field irrelevant to the formation conductivity, so that the secondary field and the apparent conductivity cannot be acquired, and further the formation conductivity cannot be obtained. The waveform measured by the same source distance and the adjacent depth is subtracted to remove all useless signals (the primary field and the secondary field response of liquid and cement sheath in the well) in the response and obtain the secondary field difference of the stratum (area) measured by the adjacent two depth points.

Disclosure of Invention

Aiming at the problem in the prior art that the actual formation conductivity cannot be reduced due to the limitation of knowledge of the secondary field difference, the invention provides a method for processing the open hole differential conductivity, which deduces the relationship between the difference and the visual conductivity and the formation conductivity sequence on the basis of the secondary field difference measured by two adjacent depth points, reduces a formation conductivity curve by using a deconvolution method, and reduces a formation resistivity curve by calculating the reciprocal.

The specific method principle and description of the open hole differential conductivity processing method are as follows:

step one, transient electromagnetic logging is excited by adopting a step signal, and electromagnetic induction signals excited by an eddy current field with an interval delta depth are taken according to the characteristics of waveforms, namely transient electromagnetic induction receiving waveforms, wherein the induced electromotive force U of a receiving coil comprises information of a primary field and a secondary field, and a waveform 3 is obtained by using a signal waveform 1 and a waveform 2 with the interval delta depth to make a difference, because the primary fields with different depths are the same at the same moment, the primary field is eliminated in the waveform 3, and only the secondary field difference with the interval delta depth is left;

subtracting transient electromagnetic induction receiving waveforms of two depth points with the interval delta to obtain a response difference waveform 3, wherein the primary fields of the adjacent depth points are equal in size and same in phase, so that the primary fields can be eliminated by difference making, and the obtained receiving waveform difference is the product of the difference of the conductivity of view and the constant of a known instrument;

step three, obtaining the difference of the visual conductivity and the known difference geometric factor g_ΔPerforming deconvolution inversion on the difference to obtain a stratum conductivity curve, wherein sigma is the stratum conductivity curve;

step four, debugging a proper differential geometric factor g_ΔBecause the source distances L of the geometric factors are different, the shapes of the geometric factors are also inconsistent, the results obtained by inversion are also different, the correct geometric factors are obtained by debugging, and the deconvolution result is closest to the stratum conductivity curve;

and step five, obtaining the stratum conductivity after the steps one, two, three and four are executed, and comparing the stratum conductivity with an original curve.

Compared with the prior art, the open hole differential conductivity processing method has the beneficial effects that:

(1) signals of the receiving coil comprise primary field (useless signals) and secondary field signals, and the traditional method cannot eliminate the primary field irrelevant to the formation conductivity, so that the secondary field and the formation conductivity information cannot be acquired. According to the invention, all useless signals (including cased hole response and secondary field response of liquid and cement sheath in a well) in response can be removed by subtracting waveforms measured at the same source distance and adjacent depths, so that the secondary field difference of the stratum (region) measured by two points with the interval delta depth is obtained;

(2) the invention further indicates that the secondary field difference can be described by the difference of the geometric factors, the response difference is the secondary field difference, the secondary field difference is in direct proportion to the difference of the apparent conductivity, and the difference of the apparent conductivity can be regarded as the convolution result of the formation conductivity and the geometric factor difference; deconvolution is carried out by using the response difference (replacing the difference of the apparent conductivity) and the longitudinal differential geometric factor difference, and a formation conductivity curve is restored;

(3) when the source distance of the differential geometric factor is properly selected, the formation conductivity curve can be completely reduced, the formation resolution is improved, and the exploration of the residual oil layer is facilitated.

Drawings

FIG. 1 is a process data flow diagram of the present invention;

FIG. 2 is a doll differential geometry map with a source spacing of 0.6 m;

FIG. 3 is a plot of the difference in the formation conductivity curve and the waveform of two depth points spaced Δ =0.1m apart;

FIG. 4 is a graph of deconvolution with a differential geometry factor of 0.5m source-to-source distance and a waveform difference plot of two depth points spaced Δ =0.1 m;

fig. 5 is a graph of deconvolution performed with a geometric factor difference of 0.6m source distance and a waveform difference plot of two depth points spaced by Δ =0.1 m.

Detailed Description

The invention is further described with reference to the following figures and specific data processing examples, but the scope of the invention is not limited thereto.

The key point of the invention is that a useless primary field signal is eliminated by a method of making difference between waveforms of two depth points with the interval delta =0.1m, and the difficulty is that information of the stratum conductivity is extracted in an electromagnetic induction signal with large amplitude by a data processing mode. The problem that primary field signals cannot be processed is solved, and the convolution relation between the difference of the apparent conductivity and the difference of the longitudinal geometric factor is connected according to the linear relation between the difference of the response waveforms and the difference of the apparent conductivity, so that a formation conductivity curve is obtained, and the distribution of the residual oil layer can be evaluated.

Referring first to fig. 1, the steps of the processing method are shown, including the steps of:

step one, as shown in FIG. 2, obtaining a doll differential geometric factor graph with a source distance of 0.6m through definition calculation;

step two, as shown in fig. 3, subtracting the received waveforms of two depth points with an interval Δ =0.1m to obtain a curve of the difference of the received waveforms (response difference), wherein the difference is in direct proportion to the difference of the apparent conductance;

step three, as shown in fig. 4, deconvolution inversion is carried out on the selected differential geometric factor with the source distance of 0.5m, and the large fluctuation can be seen, and the fluctuation of the maximum value exceeds the amplitude of the real stratum;

step four, the difference of the differential geometric factors of the source distances of 0.6m is selected in fig. 5 to perform deconvolution inversion, so that the variation trends of the inverted and reduced stratum and the real stratum are the same, the amplitude is slightly deviated due to the initial value selection, and the source distance selection can be considered to be correct.