RU2476669C1 - Method for determining filtration parameters of formation - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: method involves the following sequence of actions: after continuous well operation cycle during at least 30 days, a long-term (at least 3 days) level recovery curve is recorded, as per which current productivity of formations is evaluated; then, on the basis of comparison of current productivity with the initial one, it is determined, how much the skin factor has been changed. Besides, in order to obtain continuous time variation curves of pressure and skin factor, repeated interpretation of pressure and flow rate change curves is performed during the whole time period of observations since the well has been started up.

EFFECT: improving reliable determination of skin factor reduction points for opened hydraulic formation fracturing of low-permeable formation.

2 dwg

Description

The invention relates to oil production technologies, and in particular to methods for conducting, interpreting and analyzing the results of hydrodynamic studies of production wells (well) equipped with electric centrifugal pumps (ESP).

Well-known well test methods (for example, application for invention No. 2008118158/03, 10/02/2006), involving the registration of the pressure change curve in the well during one or more cycles of its start, stop, or cyclic change of operating modes according to which, according to the results of the well test interpretation reservoir filtration parameters, performance characteristics of the autopsy, primarily the skin factor, and reservoir pressure.

However, these methods have a significant drawback: very low accuracy in the operation of low-permeable formations, opened by hydraulic fracturing (Fracturing).

This disadvantage is due to the fact that for the formation of a pseudo-radial flow regime in the well, which is necessary for a reliable assessment of the filtration-capacitive properties, a long operating time is required in a stable mode of well selection or idle time. This is not always technically feasible due to the low unstable productivity of the formation and, in addition, is impractical for economic reasons.

More acceptable in such conditions is the technology for determining the filtration parameters, the initial and current values of the skin factor and reservoir pressure, which consists in long-term monitoring of the change in time of the bottomhole pressure and downhole flow rate, starting from the moment the well is put into operation (for example, US Patent No. 6101447 08.08.2000).

The rate of pressure drop and flow rate during the day after the well’s start-up is used to judge the filtration properties of the formation and the initial value of the skin factor, and the nature of the change in the above parameters during the long-term (more than 30 days) well operation shows the change in the skin factor over time ( with independently obtained data on the current reservoir pressure).

However, this technology has a drawback. The accuracy of determining the nature of the change in time of the skin factor in the absence of data on the current reservoir pressure is very low. This disadvantage is due to the fact that the change in time of the skin factor and reservoir pressure almost equally affect the results of measurements in the well.

This does not allow for well logging to reliably identify wells where the skin factor has decreased and to make an informed decision on the stimulation of the inflow (for example, on repeated hydraulic fracturing), which leads to losses in oil production.

The objective of the invention is to increase the reliability of determining the nature of the reduction of the skin factor over time for an opened fracturing of a low permeability formation.

с начальной

определяют, насколько изменился скин-фактор.To do this, in the well-known technology for determining the filtration parameters, skin factor and reservoir pressure (US Patent No. 6101447), which consists in long-term monitoring of the change in time of the bottomhole pressure and downhole flow rate, starting from the moment the well is put into operation, after a continuous cycle of well operation in for at least 30 days, a long (at least 3 days) level recovery curve is recorded. This curve estimates the current productivity of the formation. Then, based on a comparison of current productivity

from the initial

determine how much the skin factor has changed.

To calculate the current skin factor S _TEK (under conditions when the composition of the product and the phase permeability of the formation practically do not change in time), use the ratio:

,

,

where S _NACH is the initial skin factor, R _{KP is the} radius of the power circuit, R _{c is the} radius of the well.

After that, re-interpretation of the pressure and flow rate curves is carried out throughout the entire observation time (from the moment the well was launched). The result of the calculations performed during the interpretation are continuous curves of changes in time of reservoir pressure and skin factor.

Thus, reliable data are obtained for each well about the deterioration of the skin factor over time in the absence of information about the current reservoir pressure.

An example of a practical implementation of the method is presented in figures 1 and 2.

Figure 1 shows the results of long-term monitoring of pressure P, flow rate at the bottom of Q, and cumulative production of Q _Σ , starting from the moment the well was launched (KSD ₁ ) into operation for a period of 60 days.

The graph shows the following lines:

1 - measured flow rate;

2 - cumulative production;

3 - measured pressure;

4 - the results of reproducing the curve of the change in flow rate and cumulative production during interpretation during the entire time of observations (from the moment the well was launched);

5 - calculated curve of reservoir pressure over time.

Figure 2 shows the results of pressure measurement in the HLC cycle on a diagnostic Log-Log scale.

The graph shows the following lines:

1 - pressure;

2 - logarithmic derivative;

R ₀ is the position of the asymptote to the derivative in the interval of the radial flow.

The dots represent the measurement results, thin solid lines represent the results of the reproduction of the named parameters during interpretation.

=1,13 м³/сут МПа).Based on the results of studies in the cycle, the permeability of the formation (0.5 mD) and the initial integral skin factor (-5.6), as well as the initial productivity (

= 1.13 m ³ / day MPa).

It is impossible to assess how the skin factor has changed over time for this research cycle, since the nature of the measurement of the current reservoir pressure over the drained well section of the reservoir (size of the site) is not known.

Therefore, after a continuous cycle of well operation, a long (10 days) level recovery curve was recorded (HLC cycle in Fig. 1). Then the well was again launched in the mode of technological selection (KSD cycle ₂ in figure 1).

It is also impossible to evaluate the current skin factor from the results of this study, since the duration of the HLE under these conditions (low permeability of the formation, the presence of a hydraulic fracture) is insufficient for the formation of a radial flow regime in the formation (Fig. 2).

=1.05 м³/сут МПа.However, current productivity is determined with reasonable accuracy. She makes up

= 1.05 m ³ / day MPa.

Further, in accordance with formula (1), the value of the current skin factor was calculated, which amounted to -5.5.

And, finally, after re-interpreting the pressure and flow rate curves during the entire observation time from the time the well was launched, continuous curves of the change in time of reservoir pressure and skin factor were obtained (Fig. 1).

By the time the study was completed, reservoir pressure had dropped from 20.0 to 16.7 MPa. At the same time, the skin factor increased slightly, which indicates that contamination of the hydraulic fracture has begun.

Claims (1)

A method for determining formation filtration parameters, including long-term monitoring of changes in time of pressure and downhole flow rate, starting from the moment the well is put into operation, characterized in that after a continuous cycle of operation of the well for at least 30 days, a long, at least 3 days, the recovery curve of the level, which assesses the current productivity of the formation, then re-interpret the pressure and flow curves over the entire observation time from the start of the well zhiny and based on comparison with the initial current efficiency is determined how much the skin factor.

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