RU2464418C1 - Method of defining productive bed water permeability factor by varying gravity - Google Patents

Abstract

FIELD: oil and gas production.

SUBSTANCE: proposed method comprises measuring gravity field g and bed pressure P, determining relationship between said magnitudes and calculating water permeability factor. The latter is defined as

for gas bed and

for oil bed where P is atmospheric pressure, R_k and r_c are radii of well feed circuit and well proper, respectively, A=γ+aα, A₁=γ₁+aα₁. Note here that γ, a and α γ₁ and α₁ are defined as factors of direct

for gas bed or direct

for oil bed and direct

plotted by experimental points of gravity field g variation relationship and variation of values

ΔP=P_f-P_w, where P_f and P_w are pressure at feed circuit and wellhead in monitoring of deposit development from total volume Q=qt of hydrocarbons extracted from the well for time t at volume yield q.

EFFECT: faster measurements, higher accuracy.

2 cl, 3 dwg

Description

The invention relates to gravimetric exploration, and in particular to a gravimetric method for monitoring oil and gas fields - to a method for determining the main complex characteristics of productive formations - the coefficient of hydraulic conductivity by variations of gravity.

A known method for determining the current gas reserves in a field, its distribution and movement of fluid masses over the field area, including measuring the gravitational field and reservoir pressure, identifying the relationship between these values and its application to determining the current gas reserves, its distribution and movement in the field (see patent RU 2307379, class G01V 7/00, publ. 09/27/2007).

However, this method does not allow to determine the complex characteristics of oil and gas reservoirs, including it is impossible to determine the coefficient of hydraulic conductivity of the reservoirs using it. In the practice of field development, the coefficients of these dependencies are determined empirically from the data of well research under steady-state conditions. Wells are studied in five to six modes, in each of which the flow rate is measured and the bottomhole pressure is determined. The process is associated with the closure or shutdown of wells after each research regime. According to this technique, the well pressure values correspond to almost the same time (the duration of the well shut-off time can be neglected), but to different well modes. According to these measurements, indicator charts are built. However, this method is too costly, and measurements require large periods of time and periodic downtime of the wells.

- для газового пласта и как

для нефтяного пласта, где Р_ат - атмосферное давление, R_k и r_с - радиусы контура питания скважины и самой скважины соответственно, а А=γ+аα, А₁=γ₁+aα₁, причем γ, а и α, γ₁ и α₁ определяют как коэффициенты прямых

в случае газового пласта или прямой

в случае нефтяного пласта и прямой

, построенных по экспериментальным точкам зависимостей изменения гравитационного поля g и изменения значений

, ΔР=Р_к-Р_з, где Р_к и Р₃ - давления на контуре питания и на забое скважины за время мониторинга разработки месторождения от суммарного объема Q=qt углеводородов, извлеченных из скважины за время t при объемном дебите q. Для пласта с линейным фильтрационным потоком коэффициенты а и α₁ устанавливают равными нулю.The objective of the invention is to remedy these disadvantages. The technical result consists in reducing the time of measurement and increasing the accuracy of the data. The problem is solved, and the technical result is achieved by the fact that according to the method for determining the coefficient of hydraulic conductivity of a hydrocarbon reservoir, including measuring the gravitational field and reservoir pressure, identifying the relationship between these values and calculating the coefficient of hydraulic conductivity, the coefficient of hydraulic conductivity is determined as

- for gas reservoir and how

for an oil reservoir, where P _at is atmospheric pressure, R _k and r _c are the radii of the well supply circuit and the well itself, respectively, and A = γ + a α, A ₁ = γ ₁ + a α ₁ , with γ, a and α , γ ₁ and α _{1 are} defined as the coefficients of the lines

in case of gas reservoir or direct

in case of oil reservoir and direct

constructed from the experimental points of dependences of the change in the gravitational field g and the change in values

, ΔР = Р _к -Р _з , where Р _к and Р ₃ are the pressures on the supply circuit and on the bottom of the well during the monitoring of field development from the total volume Q = qt of hydrocarbons extracted from the well during time t at volumetric flow rate q. For a formation with a linear filtration flow, the coefficients a and α ₁ are set equal to zero.

Thus, in the proposed method, changes in the values of the reservoir pressure and well production over time t are used, which correspond to different measurement times, but one well operation mode. This method does not require stopping wells and conducting special measurements - the time of gravimetric monitoring of field development is combined with the time provided for by the development technology of associated pressure measurements.

Figure 1 presents the experimental points reflecting the dependence of P ² / Q on g / Q;

figure 2 - dependence of g / Q on Q;

figure 3 presents the zone of change of different values of the permeability of the Cenomanian complex of deposits of the gas field of the Tyumen region.

The main and most applicable characteristics of reservoirs are as follows.

Water conductivity coefficient

where k _CR - the permeability of the reservoir in the area of the investigated wells; h is the working thickness of the reservoir; µ is the viscosity of a liquid or gas. The coefficient d is the most capacious characteristic of the reservoir, which determines its productivity in the well.

Conductivity coefficient

which characterizes fluid mobility in reservoir conditions in the well area. The coefficients d, d ₁ relate to the most widely used complex characteristics of productive strata of oil and gas fields, which take into account two or three of their main properties that affect the development of deposits.

The permeability coefficient of the formation k _pr is the main filtration characteristic of the formation.

Currently, these coefficients are determined from the corresponding indicator diagrams or lines using the productivity coefficient A ₁ (for an oil well) or filtration resistance coefficient A (for a gas well) obtained from them.

In the practice of field development, indicator charts are built according to experimental data from well research under steady-state conditions. Wells are studied in five to six modes, in each of which the flow rate is measured and the bottomhole pressure is determined. Then the well is closed, and the steady-state pressure at the bottom of a stopped well is taken as a contour.

According to the claimed method, the construction of indicator charts and the determination of all the above coefficients A ₁ , A, d, d ₁ and k _pr are carried out according to the values of gravity variations (changes in the gravitational field) obtained on the surface during monitoring of the development of oil and gas fields. The proposed method is low-cost, uses changes in the values of the gravitational field, flow rate of wells and reservoir pressure, and therefore does not require stopping the wells.

The method is as follows. Let us first consider the case of gas fields. In the practice of developing gas fields, an indicator diagram or indicator line is constructed using the dependence

where P _k and P _s are the pressures on the feed circuit and the bottom of the well, q is the volumetric flow rate of the well, A and B are the equality coefficients.

Denote

.

.

Then equality (3) takes the form

From here

This expression defines the equation of the indicator line, A and B are the coefficients of this line. In practice, the development of gas fields, these coefficients are determined by the method of researching wells in five to six steady-state modes, at each of which the flow rate is measured and the bottomhole pressure is determined. This technique, associated with well research in different modes and with their shutdown, requires a certain time and cost.

To determine these coefficients, it is proposed to use analytical expressions

where Q = qt is the total volume of gas extracted from the reservoir during time t (determined by well flow rates during time t), g, P are the changes in the gravitational field and reservoir pressure (gravity variations) obtained during monitoring of the field during time t , a , b, and γ, α are the coefficients of expressions (6) and (7).

We rewrite equations (6) and (7) as follows

These equalities also determine the equations of lines with coefficients a , b, and γ, α, which are constant for each given well and characterize the filtration resistance of the medium.

Comparing equations (5), (8) and (9), we see that they all have the same form and structure. Therefore, the coefficients A and B can be expressed in terms of the values of a , b and γ, α, and, therefore, it is possible to determine them in terms of the gravitational field, which is much easier and less costly.

After small transformations, from these equalities we obtain

These expressions make it possible to determine the coefficients of equation (3), therefore, the equations of the indicator line (5) through the coefficients of equalities (8) and (9), obtained from the values of the variations of gravity.

In the case of a circular reservoir, in the center of which there is a well, with a flat radial filtration flow, the equality coefficients are determined by the formulas

where P _at is the normal atmospheric pressure, ρ _at is the gas density under normal conditions, β is the volumetric compression coefficient of gas, R _k and r _c are the radii of the supply circuit of the well and the well itself.

When determining the main complex characteristics of productive strata of gas fields - the coefficients of hydraulic conductivity d (equality (1)) and conductivity d ₁ (equality (2)), only the value of coefficient A is used. From expressions (1), (2) and (11) we obtain

Using formula (10) we find

Dividing this expression by h, we obtain the value of the conductivity coefficient of the reservoir. In addition, knowing the value of µ, from equality (2) we can find the permeability coefficient of the formation k. And knowing k and µ, from the expression (1) it is possible to determine the thickness of gas-bearing deposits h.

In the case of oil fields, equality (3) has the form

Indicative Line Equation

Where

Equalities (9) and (8) for oil fields have the form

With these notations, to determine the coefficients A ₁ and d we obtain the expression

All of the above was related to the more general case of nonlinear oil and gas filtration in rocks.

In the case of a linear filtration flow, the above expressions are simplified. Equalities that determine the complex characteristics of oil and gas reservoirs take on a simpler form. The coefficients α and α ₁ are set equal to zero.

Knowing the coefficient of hydraulic conductivity d and the thickness of the formation h, from here it is possible to determine the coefficient of conductivity of the formation d ₁ , the permeability of the formation k _{pr is} determined from the values of h, μ and d ₁ Moreover, the coefficients for the case of linear filtration — the desired complex characteristics of productive formations — can only be determined by the values of the variations in gravity and reservoir pressure (bypassing the values of the flow rates of the wells).

The testing of the proposed method for constructing the indicator line of the well and determining the complex characteristics of the layers was carried out on the materials of one of the gas fields of the Tyumen region. Figure 1 and figure 2 presents graphs of changes in the dependencies (8) and (9) of one of the wells.

The values of the coefficients are found from the straight lines constructed from the dependency points:

a = -0.075, b = 0.000059, γ = 0.0286, α = 0.2817,

Given these coefficients, the values of A and B are determined by formulas (10):

A = 0.00747, B = 0.0000166.

Knowing the numbers R _k and r _c , using the well-known value A using the formula (13), it is easy to determine the value of the desired coefficient of hydraulic conductivity of the formation d, and then it is easy to find the numbers d ₁ and the permeability of the formation k.

In this way, the numbers A, d, d ₁ , and the permeability of the Cenomanian complex of deposits of the gas field under consideration were found. The zones of change in various values of the permeability of these deposits are shown in figure 3. The information in figure 3 is of great practical importance and is used in the development of oil and gas fields.

From the above material it follows that the proposed method allows you to build indicator charts and determine all of the above coefficients A, d, d ₁ and k from the values of the gravity variations obtained on the surface during monitoring of the development of oil and gas fields. The proposed method uses only changes in the values of the gravitational field, flow rates of wells and reservoir pressure, which means that it does not require special studies and shutdown of wells, which reduces the time of measurements while increasing the accuracy of the data obtained.

Claims (2)

1. The method of determining the coefficient of hydraulic conductivity of a hydrocarbon reservoir, including measuring the gravitational field g and reservoir pressure P, identifying the relationship between changes in these quantities and calculating the coefficient of hydraulic conductivity, characterized in that the hydraulic conductivity coefficient is determined as

- for gas reservoir and how

for an oil reservoir, where P _at is atmospheric pressure, R _k and r _c are the radii of the well supply circuit and the well itself, respectively, and A = γ + aα, A ₁ = γ ₁ + aα ₁ , with γ, a, and α, γ ₁ and α _{1 are} defined as the coefficients of the lines

in case of gas reservoir or direct

in case of oil reservoir and direct

constructed from the experimental points of dependences of the change in the gravitational field g and the change in values

,? P = -P _to P _s, where P _k and P _h - pressure on the supply circuit and the downhole monitoring during field development of the total volume Q = qt hydrocarbons extracted from a well at a time t volumetric production rate q. 2. The method according to claim 1, characterized in that for the formation with a linear filtration flow, the coefficients a and α ₁ are set equal to zero.

Images