SU1427312A1 - Method of seismic probing for predicting geological section - Google Patents

Description

(21) 4123270 / 24-25

(22) 06.26.86

(46) 09/30/88. Bul R 36 (71) Southern Branch of the All-Union Scientific Research Institute of Geophysical Methods of Exploration (72) MM Radjabov

(53) 550.834 (088.8)

(56) Gurvich I.N. Seismic exploration. M.: Nedra, 1980, p. 87-294.

.Membey V.I. Petodika multiple overlaps in seismic exploration. M .: Nedra, 1985, p. 99, fig. 46a.,

(54) METHOD OF SEPSMOZONDRO VANIYA FOR FORECASTING GEOLOGICAL CUT

(57) The invention relates to seismic exploration and can be used in exploration in the design of drilling exploratory wells. The goal is to improve the accuracy and detail of the prediction of the geological section and its volumetric dismemberment along the vertical, to any depth in the area specified on the day surface. The method is based on the longitudinal profile.

With a center in a given region, the excitation of oscillations in points located along this profile and symmetrically to its center, the reception of oscillations of reflected waves in points located on equal segments of combined longitudinal and transverse profiles, the centers of which are symmetrical with the points of excitation relative to the center of the longitudinal profile, determining the spatial drift, and performing the selection of the vertical radial velocity field over two sections, which makes it possible to increase its noise immunity and more accurately find the Determination of average values of peak speeds and the corresponding vertical times, which determine reservoir (interval) speeds, after which, at identical depths, the ratio of reservoir velocities determined separately by systems of transverse and longitudinal profiles is found, according to their magnitude and changes with depth, they predict geological section and judge the degree of its heterogeneity. 1 il.

i

(L

j you

with

The invention relates to seismic exploration and can be used in geological prospecting to predict a geological section, including the withdrawal section and the near-well surface of the designed, drilled and drilled wells not only at the depth interval discovered by the well, but also below the bottom hole. tO

The aim of the invention is to increase the detail and accuracy of studying a geological section within an area observation system, limiting the area under investigation. 15

The drawing shows the scheme of observations.

The diagram shows the line 1 of observation, the secant of the center of the area under study, the base 2 of the area under study, the center 3 of the base, which coincides with the center of the line of observation, the system and 4 probing, the combined system 5 of reception, the sources 6 of excitation.

The method is carried out as follows.

The observation line 1 is split, the center of which coincides with the center of the study area, and the base 2 of the study area is determined to be equal to half the lengths of the segments of the longitudinal and transverse arrangements. The length of the segments forming the combined system 5 is established from the condition of the necessary accuracy of determining the effective speed, the value of which is used to determine the radial velocity. The accuracy of calculating the effective velocity is influenced by a series of factors, the main of which is the length of the hodograph section of the reflected wave. The ratio relating the length of the section of the hodograph to the desired effective velocity can be represented as

t - V T | cJV / V |

50

- the length of the section of the hodograph, where the measurement of the effective velocity

V -

- the absolute error in measuring the time of the reflected waves is absolute; - extreme relative

Error in determining the speed.

The effective velocities of the reflected waves increase with increasing distance from the excitation source, tending to the highest reservoir velocity pc. maize study interval cut. Therefore, pr in V, m

formula (1) we will present

 PA Wdxc

in all:

Idtl

Tdv7vT

 square Max

(2)

Formula (2) determines the minimum allowable length of the hodograph segment of the reflected wave to determine the effective velocity.

For a transverse arrangement, L is the length of a segment, measured in one direction from the projection, onto which the source of excitation, i.e. The full length of the transverse locus consists of two segments. To ensure the necessary accuracy in determining the effective velocities, it is sufficient to take the minimum allowable length of each segment of the arrangements included in the reception system, equal to

 2L

2V

max max

TO,

(3)

where k

Idtl

IdV / Vl

Since the transverse arrangement consists of two segments, its full length is equal to

4V

PA.MOKS

to.

(four)

Consequently, in the combined system, the minimum permissible length of the transverse arrangement is twice the length of the minimum permissible length of the longitudinal distribution, determined from the relation

2 v

PL MO KS,

to.

(five)

50

In practice, the arrival time of the waves is subject to the greatest errors. It is understood that Idtl varies from 0.02 to 0.002 s and the average value of the relative error IdV / v in the definition of velocity is determined with an accuracy of 5%. With these values, 0.04 K? I :. 0.4. The minimum length of each segment of the reception system in this case can be determined from the condition:

0.08 U „„ L 0,8 U ,,.

When V

Pl, mmc

0.1 km

 1.5

4 km / s.

x 0.15

 6 km / s 0.5 L ё.

With „,. 4.8 km

When operating on each reception system 5 located on one side of the center of the area under study, receive reflected waves excited from the excitation source 6 located on the other side of the center of the area under study. Subsequently, sequentially displacing the receiving system 5 and the excitation source 6 in opposite directions from the center of the study area and forming the sounding system 4, the indicated order of excitation and reception of reflected waves is maintained.

The interval between the centers of the reception system 5, located on one side of the center of the investigated excitation regions 6, located in the opposite direction from it, is determined from the condition:

 2uZ,

where L X - the interval between the centers

reception systems and excitation sources; uZ is the thickness of the reservoir with the smallest reservoir velocity 35 cut.

The use of the reservoir with the lowest reservoir cutting speed caused-. it is necessary to reveal the formation

and with greater reservoir velocity. This achieves a given degree of detail of the section being studied.

Between the values of L Z and V, „c there is the following relationship:

UZ 1,4 V,

PA M "N

TO.

(8) formula (7) in the form

can be preu X 2.8 V,

TO.

With the lowest reservoir velocity and a given error in determining the speed, equal to 5%, Jol tj K 0.04. Then

,, 8-V

n (|. min

0,1-U „d, min. (ten)

For reflected waves of different lengths recorded on each of the system profiles, radial velocities are found for the corresponding depths according to the formula:

 q-v

)

(eleven)

where q is a conversion factor, the acceptance is 0.98 for the sedimentary section and 0.95 for the consolidated section. Then, the depth is determined for the reflection points corresponding to the mid-hodograph of the reflected will. For transverse profiles, the depth is determined by the formula

Z popper 5 (tVd,) - (

for longitudinal profiles

Znpoq I - (t V,

 Ray

) 2-X2,

(12)

formula

(13)

thirty

35

40

45

50

55

where t is the arrival time of the reflected wave in the middle of the hodograph;

a y-distance from the projection of the corresponding excitation source on the transverse profile to the receiver where the arrival of the reflected beam corresponding to the middle of the locus is registered;

R is the perpendicular distance from the corresponding excitation source to the transverse profile line;

X is the distance on the longitudinal profile, measured from the excitation source, where the arrival of the reflected beam, corresponding to the middle of the hodograph, is recorded.

The radial velocities found for the corresponding depths according to the transverse and longitudinal profiles of the system are separately represented as a vertical radial velocity field. For further study, the vertical radial velocity fields are averaged. For this purpose, a given window is slid along each of the vertical radial-velocity fields, the value of which is determined from

51A273

relations (6), which, when received

conditions equal to D2

yx

0.075

, 05 km. With each averaging, the given window is moved in depth. To its value. Find the averaged values of the radial velocities of Udc „g. respectively, along the systems of transverse and longitudinal profiles, which are represented in the form of graphs of changes in averaged values of radial velocities with depth, and also found the corresponding vertical times by the formula:

(U)

.p

where Z-depth 5 corresponds to the average radial velocity value.

The found vertical times are presented in the form of graphs of changes in the depth of the vertical propagation times of the reflected: waves in which graphs of the distribution over the depth of reservoir velocities are plotted. Then find the relationship

1C

 square proA, .C "em,

(15)

V

square poper syst

characterizing the coefficient of heterogeneity of the reservoir. The value of the TC coefficient is presented in the form of a graph of changes in the coefficients of the inhomogeneity of the formation with depth. The strata are considered homogeneous if% 1, and heterogeneous if K 5 1.

A positive effect is achieved by adjusting the degree of detail of studying a geological section with multiple accumulations of information.

The application of the method allows vertical sounding, making it possible to predict a geological section with the necessary accuracy to any given depth.

with the release of layers with typilch.ipshi and higher speeds.

Claims (1)

Invention Formula A seismic sounding method for predicting a geological section, including the excitation of elastic vibrations at a number of points, located along a profile, recording vibrations at reception points that form a reception system consisting of segments of combined longitudinal and transverse profiles, the receiving system and the source airways are successively moved along the profile in opposite directions from the center of the study area with the same displacement step LH, which is so that, in order to increase the activity the accuracy of the geological, section Within an area observation system limiting the area under study, the minimum allowable length L of each transverse spread segment, counted in one direction from the projection onto the day surface of the excitation source, is taken to be equal to the length of the longitudinal spread segment, determined from the condition 0.08 ,, L 0, 8 V ,,. d, „,, where Vf ,. the weeping layer has the highest formation velocity expected in the section interval under study, km / s, and the displacement step D X is determined from the condition X   n „.„ n. where, Vn ,, ..;, is the smallest formation velocity of the cut, km / s. For each system of longitudinal and transverse arrangements, the distribution of averaged values of radial velocities and the corresponding vertical times for which reservoir velocities are determined is found, and the magnitude and nature of their changes with depth judge the degree of heterogeneity of the reservoir and predict a geological section. 2 .S