RU2289021C2 - Method for determining formation parameters during inspection of low-debit non-flowing wells - Google Patents

Abstract

FIELD: oil-extractive industry, in particular, hydro-dynamic methods for inspecting wells, possible use for determining formation parameters during inspection of low-debit non-flowing wells using method of successive change of stationary conditions.

SUBSTANCE: in accordance to method, after standard processing of actual influx curve, on its basis, pressure tracking time graph is built. For known value of bed pressure straight line is drawn on graph, connecting point of known bed pressure to bending point, which matches time of appearance of filtration resistances during filtration of liquid. Along this line time is counted, standing for theoretically optimal formation inspection period during influx. Then on actual influx curve bending point is placed, determined from pressure tracking graph, connected to point of intersection of optimal bed inspection time during influx and bed pressure and hypothetical influx curve is produced. Resulting curve is processed in accordance to unstable filtration method while determining hydrodynamic parameters of bed - productiveness, hydro-conductivity, penetrability and skin-factor.

EFFECT: expanded functional capabilities of method due to possible determining of larger number of hydro-dynamic and filtration parameters.

1 tbl, 1 ex, 3 dwg

Description

The invention relates to the oil industry and, in particular, to hydrodynamic methods for researching wells.

A known method of determining the parameters of the reservoir according to the pressure recovery curve [1]. The disadvantage of this method is that the hydrodynamic parameters of the formation are determined only when researching wells by the method of transient filtration.

There is a method of determining the parameters of the reservoir by the method of successive changes in stationary states (curve tracking level, pressure) [1]. The disadvantage of this method is that according to the results of the study, only the reservoir productivity coefficient is determined.

The proposed method is aimed at improving the existing methods of research by the method of successive changes of stationary states (tracking level, pressure) in low-flow non-overfill wells with determination of hydrodynamic and filtration parameters of the formation.

As a result of processing the research data in a known manner (tracking the level, pressure), according to the proposed method, in contrast to the standard ones listed above, it becomes possible to determine such hydrodynamic and filtration parameters as productivity, hydraulic conductivity, permeability, piezoconductivity, and also calculate the value of the skin factor.

Technology of work.

The studies are carried out according to the standard scheme - lowering the back pressure in the wellbore (lowering the level in the wellbore), followed by tracking and recording changes in the level (pressure) in the well. After that, the interpretation of the data is performed.

The following should be noted.

As you know, the main condition for solving the problem of determining the parameters of the reservoir, according to M.Masket, is the knowledge of the values of the initial and current reservoir pressures in exploration and production wells. Moreover, according to M. Musket, in the absence of accurate information about the value of reservoir pressure, it is possible to determine only the productivity of the reservoir [1].

The authors propose the solution of the problem with the definition of productivity, hydraulic conductivity, permeability, piezoelectric conductivity of the reservoir according to the inflow curve, which is as follows.

After standard processing of the inflow curve in coordinates Р _С -Т according to the Krylov method, the well productivity coefficient (K _SLE ) is estimated according to the graph of dependence Р _С ^СР dP / dt [1]. If the true reservoir pressure (P _PL ) is not unambiguously determined by this method, then the productivity coefficient is recalculated taking into account the correction for the existing reservoir pressure deficit (dP ₀ ) [2].

With a known value of R _PL on the graph R _C ^CP -dP / dt, a straight line is drawn connecting the point of the known reservoir pressure with an inflection on the same graph for determining K _PROD .

This inflection point means the time of occurrence (onset of manifestation) of filtration resistances (skin factor, Jamen effect) during fluid filtration due to the manifestation of the structural and mechanical properties of liquids, as well as the properties of low-permeability reservoirs associated with their lithological features. From this straight line, time is calculated, which means the theoretically optimal period of formation study for inflow.

At the same time, it is assumed that the inflow reaches the wellhead in some “certain” time, exceeding the time of the actual study, but already in the absence or minimal influence of the above, additional resistance (skin factor, Jamen effect).

In reality, a real inflow in a “certain” time due to the influence of the skin factor will come to a point on the pressure axis, indicating the next conditional reservoir pressure. And if you leave the well to the natural restoration of pressure (level), then the inflow to the mouth will come in hundreds of hours.

Then on the graph P _C -T there is an inflection point corresponding to the hypothetical time of the inflow study (t ₀ -t _n ) and the known reservoir pressure. And, in accordance with the logistic shape of the initial section of the real inflow curve, the inflection point, determined by the pressure tracking schedule, is connected by a straight line with the intersection point of the optimal tracking time and reservoir pressure.

The hypothetical curve obtained in this way is processed using one of the known methods of transient filtering. For example, by the tangent method with obtaining the hydrodynamic parameters of the formation: hydraulic conductivity, permeability, piezoconductivity and skin factor.

Example

Consider processing the inflow curve in well R-347 (SE ₂ in the interval 2360-2374 m) of the Koshilsky field.

When testing the object, a non-diverting oil flow was obtained with a flow rate of 7.5 m ³ / day at N _DYN ^SR = 850 m.

Figure 1 shows the actual flow curve. The productivity coefficient calculated by the Krylov method is 1.65 m ³ / day × atm.

Figure 2 shows that the transformed inflow curve in the coordinates of P _C ^CP -dP / dt does not reach the mark corresponding to the known reservoir (hydrostatic) pressure (P _PL = 237 atm), but indicates a value of 182 atm. This is the conditional reservoir pressure, determined according to the schedule P _C ^CP -dP / dt. Therefore, the productivity coefficient was recalculated taking into account the deficit of reservoir pressure. It turned out to be equal to 0.556 m ³ / day × atm.

Further interpretation is carried out according to the above method.

On the converted inflow curve, the inflection point is located at around 175 atm (Fig. 2). Then this point is connected with a known value of reservoir pressure on the axis of pressure.

Figure 2 shows that as a result of the construction, two indicator charts with different angular coefficients were formed. Qualitatively, these values of the angular coefficients correspond to the real and estimated (hypothetical) time of the inflow study. From this it follows that the line BC (figure 2) corresponds to the time of the study of the influx until it reaches the wellhead. The lines AB and VD mean, respectively, the influx time before the manifestation of additional filtering resistances and after their manifestation (figure 2). Figure 2 shows that the angular coefficient of the indicator diagram of the actual inflow curve is 3.62 times greater than the angular coefficient of the indicator diagram of the calculated inflow curve (tgα ₁ > tgα ₂ ). Consequently, the study time in the aircraft section will be longer than the study time in the VD section by the same amount. In our case, the total inflow time (the initial section without the influence of resistance + hypothetical pressure recovery time) was 60 hours.

It is assumed that, hypothetically, the influx reaches the wellhead in 60 hours, provided that there is no or minimal influence of additional resistances (skin factor).

Thus, it turns out that further construction and calculation of the formation parameters is carried out with the assumption that the well that opened the low-permeability reservoirs is hydrodynamically perfect and the inflow of oil from the formation into the wellbore is isotropic.

Based on this assumption, a graph of the calculated inflow curve was constructed with its likely continuation (Fig. 1, curve 2) and with the achievement of the true reservoir pressure after 60 hours. The solution to this calculation curve is made according to the well-known formula of the elastic regime:

where R _PL - reservoir pressure, Pa;

P _C (t) - bottomhole pressure, Pa, at time t, sec;

Q - flow rate, m ³ / s;

μ - oil viscosity, Pa · sec;

k - permeability, m ² ;

h is the effective thickness of the reservoir, m;

χ - piezoconductivity, m ² / s;

- приведенный радиус скважины, м.

- reduced well radius, m

In expression 1, the increment of bottomhole pressure decreases sharply over time.

Then the calculated (hypothetical) flow curve is processed by the tangent method (figure 3).

The obtained parameters of the reservoir, as a result of processing the hypothetical inflow curve according to the proposed method, are shown in table 1. Table 1 also shows the results of processing studies of the wells of the Koshilsky field according to the methods of Muravyov-Krylov, Fedortsova VK, Karnaukhova ML and Horner.

Table 1
Wells processing results of the Koshilskoye field No. of wells Reservoir interval, m Productivity coefficient, m ^{3 /} day.

TO _PRON. MD

S one 2 3 four 5 four 3 5 four 5 3 3 four four 347

1.65 0.6 0.8 0.7 - 0.93 1.17 2.2 2.0 3.0 38 88 -1.0 312

0.13 0.05 0.4 0.04 0.4 0.44 0.5 4.4 4.0 5,0 68 52 0.08 thirty

1,0 0.05 0,07 1.4 0.06 1.7 1,5 17 thirty 81 4.9 Note: 1 - processing the curve by the Muravyov-Krylov method, 2 - processing the curve by the method of Fedorsov V.K., 3 - processing the curve by the method of Karnaukhov ML, 4 - processing the curve by the proposed method, 5 - processing the curve by the method Horner.

As can be seen from the data in table 1, the processing results have satisfactory convergence.

LITERATURE

1. S.N. Buzinov, I.D. Umrikhin. Hydrodynamic research methods for wells and reservoirs. M., 1973, pp. 24-28; 50-84.

2. V.K. Fedortsov, A.K. Yagafarov. A method for determining the productivity of low-yield non-sinking oil wells. Modern hydrodynamic methods for researching wells. Proceedings of the Intern. Well Researchers Forum, M., 2004, pp. 290-295.

Claims (1)

The method of determining reservoir parameters from the results of research of low-producing non-correlating wells by successively changing stationary states by measuring and recording pressure, building and processing the actual flow curve with standard research technologies, characterized in that after standard processing of the actual flow curve, a follow-up time graph is built on its basis pressure and with a known value of reservoir pressure on the graph draw a straight line connecting the point formation pressure with an inflection point, which corresponds to the time of occurrence of filtering resistances during fluid filtration, the time is calculated using this straight line, which indicates the theoretically optimal period of formation study for inflow, then on the actual inflow curve the inflection point determined from the pressure tracking graph is connected to the intersection point the optimal time to study the reservoir for inflow and reservoir pressure and get a hypothetical inflow curve, which is processed by the method of the resulting filtration with the determination of the hydrodynamic parameters of the formation - productivity, hydraulic conductivity, permeability and skin factor.

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