SU1603327A1 - Method of determining abnormal high seam pressure - Google Patents

Abstract

This invention relates to well seismic surveys and can be used in oil and gas exploration. The aim of the invention is to improve the accuracy of determining the zone of abnormally high reservoir pressure (AHP) below the bottom of the well by taking into account the influence of lithology and saturation of rocks. To achieve the goal, the acoustic rigidity of the rock is used as a prognostic parameter, which is determined on the basis of well seismic data and core testing. The calculation of the prognostic parameter for the unopened part of the section is made on the basis of the reflection coefficients determined from seismic survey data. 1 tab.

Description

This invention relates to well seismic surveys and can be used in oil and gas exploration. The purpose of the invention is to improve the accuracy of determining the AHA zone below the bottom of a well by taking into account the influence of lithology and rock saturation,.

The basis of the method is the use of the acoustic rigidity of the rock as a prognostic parameter, which is more sensitive to the presence of AVPD zones in comparison with the traditionally used parameters (for example, the velocity of propagation of elastic waves).

The calculation of the prognostic parameter for the unopened part of the section is carried out on the basis of the reflection coefficients.

determined by well seismic data.

The method is carried out as follows.

Using the sludge (core) selected during the bureni process, the density and the rate of propagation of elastic oscillations in it are determined and acoustic is calculated. hardness. Elastic vibrations are excited on the surface from at least two points of the explosion, one of which is located at the wellhead and the other at a distance equal to the current depth of the well. Such an arrangement of another point of explosion provides the highest accuracy in determining the velocity of elastic waves in borehole seismic exploration. Elastic seismic oscillations are recorded in the well.

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nor by the obtained records on the vertical profile is calculated as a function of the depth. The values of acoustic stiffness, reflection coefficients and seismic wave velocities reflected from boundaries below the bottom of the well. Next, the dependence of the previously determined acoustic sludge magnitude (core) is corrected using acoustic stiffness data determined after the drilling process (according to well seismic survey data). The location and size of the zone of abnormally high reservoir pressure is determined by the decrease in the value of the corrected acoustic stiffness as a function of the depth of the well.

To implement the method, an observation system was used in the experimental area, in which one of the explosion points was fixed at the wellhead, and the subsequent points were located on four profiles.

Elastic vibrations were recorded by a digital seismic station. The deep seismic receivers of the borehole multichannel probe were placed on a vertical profile taking into account the actual size of the entire array of devices, respectively, at depths of 820 m — the upper device, 970, 1120, 1270 and 1570 m. At the same time, a correlation overlap of at least one seismic receiver was ensured. . Another point of the explosion was placed at a distance from the wellhead 820, 970, 1120, 1270, 1470 and 1570 m. Ensuring that the blast distance from the wellhead is equal to the depth of the well provided the highest accuracy in estimating Vi + i velocities using well seismic data. It should be noted that to implement the method, high quality of the original records in the signal / interference ratio of at least 10 is necessary.

The error in determining the reflection coefficients Ki for the three reflecting horizons did not exceed 3–4% (see tab.), Which ensures the accuracy of determining the values of acoustic rigidity not below the specified limits.

Using the expression for the reflection coefficient

.. / oi-HVi-H - / 0 | Y | / E | + iVi h-1 -f-piVi

whether the density pi of the rock and the velocity Vi of the propagation of elastic waves in it were determined from the analysis of the sludge (core), the acoustic stiffnesses of the exposed

parts of the section and corrected them using seismic acoustic stiffness data at the correlation overlap points.

Using the proposed method as a prognostic parameter of acoustic stiffness eliminates the influence on the detection of an AHFP zone such factors as lithological variability of rocks due to joint

Claims (1)

analysis of borehole seismic data and core studies (cuttings). The Invention Method for determining abnormally high formation pressure (AHF); including excitation at the surface and recording elastic waves in wells, determining their propagation velocity, taking sludge or core during the drilling process and determining its density, revealing the AHF zone to reduce the prognostic parameter relative to the line of the normal change of the prognostic parameter with a depth that in order to improve the accuracy of AOPP zones below the well bottom by taking into account the influence of lithology and rock saturation, while drilling, additionally determine the speed of propagation of elastic waves over the cuttings or core and calculate the acoustic stiffness of the slurry or core as a function of depth, the excitation of elastic waves on the surface is carried out after the completion of drilling in at least two points, one of which is located at the mouth and the other at a distance equal to the current depth of the well, the depths of the reflection coefficients in the unopened drilling and acoustic rigidity in the exposed part of the section according to well seismic data correct the values of acoustic rigidity determined by the part of the section opened by the drilling and cutting and cores using the acoustic impedance values, obtained from borehole seismic data, calculate for the intervals below the bottom of the well the value of acoustic rigidity and use the latter as a prognostic parameter of the zone AU is below the bottom of the well. The reflection coefficients when implementing the method