RU2057927C1 - Method of determination of location and intensities of absorption zones - Google Patents

Abstract

FIELD: geological prospecting. SUBSTANCE: method uses shock hydrodynamic pressure waves formed in hole. Parameters of wave fields characterizing interaction of pressure waves with environment and contact surface in hole are measured by transducers installed in hole and are registered in the form of shock diagrams on screen of oscillograph. Produced oscillograms are used to determine location and intensity of absorption zones. Use of the method makes it possible to reduce considerably time for examination of hole and to enhance authenticity of obtained results of examination even in those cases when it is impossible to perform examination by traditional methods (presence of cavities, poor strength of borehole walls close to examination zone, high temperature in shaft of hole). EFFECT: enhanced authenticity of examination with simultaneous decrease of examination time. 3 dwg

Description

 The invention relates to determining the location of the zones of absorption of drilling fluid during drilling of exploration, oil and gas wells and can be used in well research during exploratory and production drilling.

 When drilling a well in the presence of wash fluid absorption, one of the main tasks to determine the possibility of eliminating complications is to determine the location of the absorbing formation. It is known that the absorption of flushing fluid in a well being drilled is usually determined by the pressure drop at the wellhead, as well as by a partial loss of circulation. This method is based on repeated measurements of the flow rates of the fluid entering and leaving the circulating system at various pump flows.

 To identify the intervals in which the absorption of the washing fluid is most likely, a complex of field-geophysical methods for studying the absorbing formations is carried out: measurements with an electrothermometer, resistive meter; photographing the walls of the well; micro-logging; radioactive logging; acoustic logging.

 Hydrodynamic research methods, along with determining the intervals of the absorption zones, provide information on the intensity of the absorbing formation, and determine its permeability.

 In the prototype of the present invention (ed. St. N 1208212) the dynamic state of the well is created by forcing through the sealant the mouth of compressed air. Using a downhole flowmeter manometer at various points along the wellbore, after establishing a constant injection mode, measure the air flow rate above the static liquid level, as well as the flow rate and pressure on the flooded section of the well. Based on the data obtained, a flow chart is constructed showing the nature of the change in air flow at different depths of the well. It took 15 minutes to take measurements at two points.

 The aim of the invention is to increase the reliability of the results of the study while reducing the time of the study.

 The goal is achieved in that the dynamic state of the water-filled well is created by means of a hydraulic shock and the location and intensity of the absorption zones are determined by the change in the magnitude of the drop in the pulsed hydrodynamic pressures at the moment the shock wave travels through the absorption zone and the value of its travel time from the wellhead to the absorption zone.

 The essence of the invention is based on the patterns of propagation of shock waves in a compressible viscous fluid, the interaction of pulsed hydrodynamic pressure waves with the environment and the contact surface, and the influence of absorption zones on wave processes in the well.

 The method is based on the use of hydrodynamic shock pressure waves resulting from shock compression of a column of fluid filling a well under the influence of an external impact in the form of a hydraulic shock and analysis of wave field parameters characterizing the behavior of shock waves near absorption zones.

 To determine the qualitative and quantitative characteristics of the absorbing formation and to study the mutual influence of wave processes in the well and fluid flow filtered through the contact surface of the absorption zone, the basic equations are derived that describe the transient fluid movement in the wellbore and in the filtration zone.

 When considering a non-stationary process on the scale of the length of the well, the idea of I. A. Charny was accepted about the possibility of considering the connection between the local characteristics of the hydrodynamic flow stationary [1] The movement is considered isothermal, the well is considered as a vertical absolutely rigid pipe.

 To derive the water hammer equations, we consider a pipe section selected in two horizontal sections X and X + ΔX in the interval of the absorption zone (Fig. 1). Introduced designations: l pipe length, d pipe diameter; P is the average pressure in cross section; v average velocity in cross section; t time; w average filtration rate (real); τ is the viscous shear stress between the fluid and the pipe wall.

ρ(x)•v(x)-

(x+

x)•v(x+dx)-πdρ(x)•w(x)dx (1) Учитывая, что
M ≃

ρ(x)dx где М количество массы в выделенном элементе ΔХ. Уравнение неразрывности примет вид:

+

(2) Уравнение баланса количества движения для выделенного элемента, используя теорему импульсов, запишется как

ρ(x)v²(x)+

P(x)+

gρ(x)-
-

ρ(x+dx)v²(x+dx)-

(x+dx)-πdτdx (3) С учетом того, что
L ≃

ρ(x)v(x) где L количество движения в выделенном элементе, уравнение импульсов имеет вид

+

+ ρg (4) Третьим уравнением в системе волновых уравнений взято уравнение

-C²

(5) где С скорость звука в жидкости, заполняющей скважину.The equation of mass balance of the selected element ΔX is written as

ρ (x) • v (x) -

(x +

x) • v (x + dx) -πdρ (x) • w (x) dx (1) Given that
M ≃

ρ (x) dx where M is the amount of mass in the selected element ΔX. The continuity equation takes the form:

+

(2) The equation of momentum balance for a selected element, using the momentum theorem, can be written as

ρ (x) v ² (x) +

P (x) +

gρ (x) -
-

ρ (x + dx) v ² (x + dx) -

(x + dx) -πdτdx (3) Given that
L ≃

ρ (x) v (x) where L is the momentum in the selected element, the momentum equation has the form

+

+ ρg (4) The third equation in the system of wave equations is the equation

-C ²

(5) where C is the speed of sound in the fluid filling the well.

((2πrdrdx)ρm) ρ(r)w(r)2πrd×ρ(r)-ρ(r)w(r+dr)2π(r+dr)dx (6) После соответствующих преобразований уравнение (6) примет вид
m

-r

(rρw) (7) Закон Дарси в дифференциальной форме имеет вид
w⁽¹⁾=

•

(8) Учитывая, что

-C²•

κ ρ•

Уравнение фильтрации примет вид
κ

κr

r

(9) Таким образом, система уравнений, описывающих закономерности распространения и взаимодействия с контактной поверхностью импульсных гидродинамических волн давления, имеет вид

+

+

+ρg

-C

(10)
w⁽¹⁾

•

κ•r

r

Решая уравнения системы последовательным интегрированием конечно-разностными методами n точек (n число разбиений интервала интегрирования), вдоль оси по всей длине скважины, находят функции решения Р_i(х, t), где i

Исключая из Р_i(х,t) составляющие экспоненциального затухания амплитуды сигнала, обусловленного потерями энергии волнового процесса в окружающую среду, определяемыми формулой
P_mi=exp (-β_ср·x) (11) где β_ср коэффициент затухания;
х расстояние.When drawing up the equations of filtration, a section of the absorbing layer selected by two cylinders with a height Δ X and radii r and r + Δ r was considered (Fig. 2). Introduced notation: w ⁽¹⁾ , P ⁽¹⁾ radial distribution of velocity and pressure around the well (w ⁽¹⁾ w; P ⁽¹⁾ P, at rd / 2) χ piezoelectric conductivity coefficient, μ fluid viscosity coefficient, k permeability coefficient; m porosity. The mass conservation equation for the selected area is written as

((2πrdrdx) ρm) ρ (r) w (r) 2πrd × ρ (r) -ρ (r) w (r + dr) 2π (r + dr) dx (6) After the corresponding transformations, equation (6) takes the form
m

-r

(rρw) (7) Darcy's law in differential form has the form
w ⁽¹⁾ =

•

(8) Given that

-C ² •

κ ρ •

The filtration equation takes the form
κ

κr

r

(9) Thus, the system of equations describing the laws of propagation and interaction with the contact surface of pulsed hydrodynamic pressure waves has the form

+

+

+ ρg

-C

(ten)
w ⁽¹⁾

•

κ • r

r

Solving the equations of the system by successive integration of n points by finite-difference methods (n is the number of partitions of the integration interval), along the axis along the entire length of the well, find the solution functions P _i (x, t), where i

Excluding from P _{i (} x, t) the components of the exponential decay of the signal amplitude due to the energy loss of the wave process into the environment, defined by the formula
P _mi = exp (-β _sr · x) (11) where β _{sr is} the attenuation coefficient;
x distance.

P (12) Решение уравнений системы (10) численными методами с использованием ЭВМ подтвердило возможность определения местоположения и интенсивности зон поглощений.Among the remaining components P _i (x, t) find the point i of the beginning of the pressure drop. The parameter x of this point determines the distance from the beginning of the integration section (wellhead) to the absorption zone. The pressure drop ΔР determines the absorption intensity Q
Q

P (12) Solving the equations of system (10) by numerical methods using a computer confirmed the possibility of determining the location and intensity of absorption zones.

The method is as follows: In a well filled with water, using a source of hydraulic shock installed at a distance of X _gf from the wellhead, the propagation of pulsed hydrodynamic pressure waves is simulated. The wave caused by the disturbance propagates to the bottom of the well (direct wave) and, at a time
tt _o + (l X _gf ) / C, after reflection from the bottom (backward wave), returns to the place of installation of the source. To measure the parameters of the wave fields in the wellbore near the source of hydraulic shock at a distance of X _d1 and at a distance of X _d2 from the wellhead, the deep parts of the instruments with piezoelectric sensors are moved, the signals from which are recorded on the screen of a two-beam oscilloscope. Knowing the distance between the sensors and determining the travel time of this distance by the shock wave from the waveform, the propagation velocity of the shock wave is found
C (X _d2 -X _d1 ) / t. At the moment the absorber formation travels, part of the shock wave energy is spent interacting with the contact surface of the absorption zone, since the pressure at the front of the shock wave is the source of the secondary water hammer, the pressure wave of which penetrates the channels of the absorption zone. This phenomenon is noted on the shock diagram by a drop in pressure height. Determining from the diagram the travel time of the shock wave to the beginning of the pressure drop t * and multiplying its half by C, find the distance S that determines the location of the absorption zone relative to the wellhead. The magnitude of the pressure drop (ΔP *) on the shock diagram is determined by the formula (12) the intensity of the absorption zone.

The proposed method was confirmed by the results of studies of well N 699 Neftekamsky UBR, carried out during exploratory drilling. In a well with a depth of 750 m and a diameter of 152 mm filled with water, a hydraulic shock was created using a hydraulic hammer installed at a distance of 25 m from the wellhead by breaking a brass diaphragm with a liquid column under a pressure of 7 MPa. The parameters of the wave fields were measured by instruments installed at a distance of 30 m and 205 m from the wellhead with piezo-electric sensors of the LH-604 type, with an eigenfrequency of about 200 kHz, in the range of permissible pressures of 60 MPa, and a sensor surface area of about 0.78 cm ² and recorded in the form of shock diagrams on the screen of a CI-69 oscilloscope and a H0-27 geophysical photographic recorder.

1343 м/c
C2

1310 м/c
Диаграмма сигналов, измеряемых датчиком 2, и схема эксперимента показаны на фиг. 3.The values of C1 and C2, obtained as a result of the experiment by determining the distance between the two sensors from the shock diagrams of the travel time of the forward and backward shock waves, respectively, were
C1

1343 m / s
C2

1310 m / s
A diagram of the signals measured by the sensor 2 and the experimental design are shown in FIG. 3.

The diagram was analyzed as follows: The first pressure jump corresponds to the arrival of a direct wave at the point of registration at a time
(X _d2 -X _gf ) / C 0.134 s.

The second shock jump corresponds to the arrival at the registration point of the wave reflected from the bottom of the well at a time
(2l-X _d2 -X _gf ) / C 0.91 s.

 The influence of the absorption zone on the wave characteristics is marked by a drop in pressure height. Having determined the distance from the beginning of the pressure drop from the diagram, we found the distance that determines the location of the absorption zone relative to the wellhead.

 S C * t * / 2 (1343 0.25) / 2 167.5 m.

Having determined the magnitude of the pressure height drop, we found the intensity of the absorption zone
QK / μ · ΔP * 0.03 · 1.9 0.057 m ³ / s.

 The time spent on testing was fractions of a second, the obtained data S and Q are in good agreement with the theoretical estimate.

 Thus, the invention can significantly reduce the time of well research and increase the reliability of the obtained research results even in cases when it is impossible to conduct research using traditional methods (cavernosity, poor strength of the walls of the well near the study area, high temperature in the wellbore).

Claims (1)

 METHOD FOR DETERMINING LOCATION AND INTENSITY OF ABSORPTION ZONES, including creating a dynamic state of a well, registering a changing parameter of a well, highlighting intervals at which there is a change in the recorded parameter, determining the location of absorption zones from the data obtained, characterized in that a dynamic state of a well filled with water is created by means of a hydraulic shock , in the amount of a changing parameter, the hydrodynamic pressure in the well is measured, followed by the gerist using the diagrams of the change in hydrodynamic pressure over time and the determination of the propagation velocity of elastic waves in the well, the travel time of the shock wave of the distance to the beginning of the pressure drop and the magnitude of the hydrodynamic pressure drop, the location of the absorption zone is determined by the magnitude of the hydrodynamic pressure drop, and the intensity of the absorption zones is judged by the propagation velocity of elastic waves in the well and the travel time of the shock wave distance to the beginning of the pressure drop.

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