RU2539811C1 - Determination of rock water saturation - Google Patents

Abstract

FIELD: oil-and-gas industry.

SUBSTANCE: invention relates to oil production and can be used for determination of reservoir properties of fractured rocks. This method is designed to define the rock specimen maximum moisture content c_rock. It consists in placing in retort chamber of metallic imitator in volume equal to that of rock specimen, said chamber being heated to 140-150°C to define initial moisture content c₀ in said retort. Defined are the retort calibration ratio and constant factor α, universal for used retort. Water is evaporated from rock specimen at 140-150°C in closed retort. Rock specimen water content is calculated by the formula: $$S_w=\frac{({с}_{rock}-{с}_0)(V_0-V_{spec})}{\alpha V_{pore}}(1)$$

, where S_w is specimen water saturation; c_rock is measured maximum moisture content of said specimen; c₀ is moisture content in retort without specimen defined directly before evaporation at 140-150°C; V₀ is volume of retort with feed components; V_spec is volume of rock specimen; α is constant factor, universal for this retort; V_pore is the volume of specimen pores.

EFFECT: higher validity and accuracy.

3 cl, 2 dwg, 2 tbl

Description

The invention relates to the field of oil industry and can be used to determine the reservoir properties of rock samples, mainly fractured.

A known method for determining water and oil saturation using a polychromatic X-ray system with a control of the saturation of the reservoir rocks with liquids by absorbing X-ray radiation (Kuznetsov AM Scientific and methodological foundations and studies of the influence of the properties of reservoir rocks on the efficiency of hydrocarbon extraction from the subsoil. Abstract of dissertation for the degree of doctor Engineering Sciences. M., 1998). Data on the intensity of x-ray radiation is collected during the movement of the x-ray tube, the collimator and the detector as units of a cell along the horizontal axis of the sample from the input section to the output. Model reservoir conditions. The water saturation of the rock sample is calculated based on Lambert’s law, using the linearity of the semi-logarithmic dependence of x-rays measured at 100% saturation of the sample with labeled liquid and 100% saturation of unlabeled liquid according to the mathematical formula, which measures the current intensity of x-rays transmitted through a dry sample ; X-ray intensity at 100% saturation with labeled liquid.

The disadvantage of this method is the insufficiently high accuracy, since changes in the amount of water in the sample during the experiment are not taken into account. This method is lengthy, requiring time-consuming procedures for the saturation of the sample with oil at 100%.

A known method for determining the oil and water saturation of rock samples, including sequential measurement of the weight of the oil-saturated sample, placing the sample in deuterated water, measuring the amplitude of the NMR signal from the sample with deuterated water, placing the sample in distilled water, measuring the weight and amplitude of the signal from the sample with distilled water drying the sample at the temperature of evaporation of water from the sample until the ratio of the current signal amplitude to the amplitude of the signal from the sample from deuteri is reached Anna water equal to (0.7-0.8) units, the saturation of the sample with kerosene, the measurement of the amplitude of the signal from the sample with kerosene, and the amount of oil and water in the sample is determined by the corresponding formulas (RF patent No. 2175764, G01N 24/08, publ. 2001). The method is time consuming and requires expensive equipment.

A known method for determining the water saturation of rock samples in an airtight retort, taken as a prototype. The method consists in evaporating water from a rock sample at a temperature of 140-150 ° C in a closed retort, condensing water vapor in a liquid cooler and collecting condensed liquid in a measured burette. The water saturation of a rock sample is defined as the ratio of the volume of condensed water to the pore volume of the sample. Measurement of water saturation by the retort method, as a rule, is carried out on standard rock samples with a diameter of about 30 mm and a length of 40-60 mm with a porosity of more than 10%. Measurements are carried out in the range from 20% to 100% water saturation. (EA Polyakov. Methods of studying the physical properties of oil and gas reservoirs, M., Nedra, 1981 - p. 116)

The disadvantages of the method is that there is a loss of condensed liquid in the liquid refrigerator, in addition, the volume of the condensed liquid in the measuring tubes is determined with an error of + -0.5 division, i.e. about 0.05 ml. These limitations lead to the fact that the determination of water saturation of samples is possible only in the range from 20% to 100%. When water saturation is lower than 20% on standard rock samples or when measuring water saturation on fractured rock samples with low porosity, the relative error in determining water saturation exceeds the allowable measurement methods of 10%.

The main objective of the invention is the creation of a method for determining the water saturation of rock samples with high accuracy, including for fractured rocks with low porosity (less than 1%).

The technical result of the method is to increase the accuracy and reliability of determining the water saturation of rock samples with low porosity.

The technical result is achieved in that in the known method for determining the water saturation of rock samples, including evaporating water from the sample at a temperature of 140-150 ° C in a closed retort, in addition to the retort chamber, a metal simulator is placed with a volume equal to the volume of the rock sample, the chamber is heated to a temperature of 140- 150 ° C and determine the initial humidity of the retort from ₀ , determine the calibration dependence of the retort and a constant coefficient α, universal for the retort used, and when evaporating water from rock samples, determine they add maximum moisture to the sample from the _rock , while the water saturation of the rock sample is determined from the expression:

Where

S _in - water saturation of the rock sample;

from _rock - the measured maximum humidity of the rock sample;

с ₀ - humidity in a retort without a rock sample, determined immediately before the experiment at an evaporation temperature of 140-150 ° С;

V ₀ is the volume of the retort with supply connections;

V _arr is the volume of the rock sample;

α is a constant coefficient universal for the retort used;

V _pore is the pore volume of the sample.

The initial humidity in the retort with _{0 is} necessary to determine the water saturation of the rock sample by expression (1), which increases the accuracy and reliability of the determination of water saturation.

From the calibration dependence of the retort, a constant coefficient α is determined that is universal for the retort used, which is used to calculate the water saturation of the rock sample, which increases the accuracy and reliability of determining water saturation.

The evaporation temperature of 140-150 ° C is optimal for the correct determination of the maximum humidity in the retort chamber. With increasing temperature, the rate of evaporation of water from the sample increases and the maximum from the _rock can be determined incorrectly. With decreasing temperature, the measurement time increases.

Significant differences make it possible to experimentally determine the water saturation of samples, including fractured rock samples with low porosity (from 0.1% to 1%) with a small relative error.

Figure 1 shows a diagram of the installation for measuring.

Figure 2 shows the dependence of the measured humidity on the volume of evaporated water in the retort.

The installation for measuring (Fig. 1), which implements the inventive method, comprises a retort 1, a digital moisture meter 2 with a semiconductor sensor (relative measurement error 2%), a manometer for indicating pressure in the system 3, receiver 4, emergency relief valve system 5.

The inventive method is implemented as follows.

The sample is placed in the retort chamber 1. A digital moisture meter 2 with a semiconductor sensor is connected to the chamber. Retorts with connecting tubes and a receiver are located inside the thermostat, in which the temperature is maintained at a temperature of 140-150 ° С during the experiment. The temperature of stable operation of the semiconductor sensor is 100 ° C; therefore, the housing of the moisture meter is located outside the thermostat and is connected to the system with a Teflon tube (or a PEEK tube). Overpressure for stable operation of the sensor should not exceed 0.3 atm, therefore, the system provides a receiver - a container with a movable piston connected to a gas cylinder with an overpressure of about 0.1 atm (not shown in Fig.). A pressure gauge 3 is connected to indicate the pressure in the system. In the event of an emergency increase in pressure in the system, there is a valve to relieve excess pressure 5.

The invention is illustrated by the following examples.

To implement the proposed method, rock samples were used from wells of the N field in Western Siberia. Fractured cylindrical rock specimens were selected.

Example 1

A metal simulator is placed in the retort chamber with a volume equal to the volume of the rock sample, the chamber is heated to a temperature of 140-150 ° C and using the digital moisture meter 2, the initial humidity of the chamber is determined with ₀ - the air humidity in the heated chamber. with ₀ = 44.52%.

The calibration dependence of the retort is determined in the following way: in the chamber of the retort with a volume of 268 cm ³ place a metal simulator of a rock sample with a volume of 170 cm ³ with a ceramic box. A predetermined volume of water of the fifth _{century is} poured into the box. The chamber is again heated to a temperature of 140-150 ° C and the maximum air humidity is determined in it - with _caliber . The measurement is repeated for different predetermined volumes of water in the chamber. Build a calibration dependence of the measured maximum humidity on the volume of water in the chamber (figure 2). Calibration dependence is a universal characteristic for the retort used.

The measured humidity is related to the volume of water in the rock sample by the dependence:

,

,

where s _caliber is the maximum air humidity of a chamber with a ceramic casing;

с ₀ - humidity in a retort without a rock sample, determined immediately before the experiment at an evaporation temperature of 140-150 ° С;

α is a constant coefficient universal for the retort used;

V _in - the volume of water in the box;

V ₀ is the volume of the retort with supply connections;

V _arr is the volume of the rock sample.

The constant coefficient α is determined from the calibration dependence of the measured maximum humidity on the volume of water in the retort (figure 2) when approximating the experimental data by a linear dependence. The slope tangent of the approximating dependence tanφ is equal to the ratio α / (V ₀ −V _arr ).

The constant coefficient α is universal for the retort used. In this experiment, α = 6891.

In the next step, the length and diameter of the samples, as well as the pore volume, are determined. The length and diameter of the samples were measured with an electronic caliper. Length and diameter measurements for each sample were carried out at three different points; the obtained values were averaged. The pore volume of the samples was measured by the Preobrazhensky method when the sample was saturated with liquid at 100% in accordance with GOST 26450.1-85.

A rock sample with unknown water saturation is taken with the parameters:

length - 4.447 cm

diameter - 7.00 cm

V _arr = 171.141 cm ³ ,

V _then = 1,029 cm ³ .

A rock sample is placed in the retort chamber and water is evaporated from the rock sample in a closed retort at a temperature of 140-150 ° C. When evaporating water from the sample, the maximum moisture content from the _{rock is} determined. For this sample from the _breed = 84.63%.

The water saturation of the rock sample is determined from the expression:

The water saturation of the first sample of rock S _in = 0,548 units

Example 2

A rock sample with unknown water saturation has the following parameters:

length - 4.446 cm

diameter - 7.03 cm

V _arr = 172.572 cm ³ ,

V _then = 0.837 cm ³ .

All measurements are carried out as with a rock sample 1. As a result of measurements, we obtain:

from _breed = 82.73%.

The water saturation of the sample is determined by the expression (1):

S _in = 0.632 units

Example 3

A rock sample with unknown water saturation has the following parameters:

length - 4.460 cm

diameter - 7.03 cm

V _arr = 173.116 cm ³ ,

V _then = 0.658 cm ³ .

All measurements are carried out as with a rock sample 1. As a result of measurements, one obtains:

from _breed = 75.77%.

The water saturation of the sample is calculated by the expression (1):

S _in = 0.654 units

Example 4

A rock sample with unknown water saturation has the following parameters:

length - 4.450 cm

diameter - 7.02 cm

V _arr = 172.236 cm ³ ,

V _then = 0.796 cm ³ .

All measurements are carried out as with a rock sample 1. As a result of measurements, one obtains:

from _breed = 69.64%.

The water saturation of the sample is calculated by the expression (1):

S _in = 0.439 units

Example 5

A rock sample with unknown water saturation has the following parameters:

length - 4.450 cm

diameter - 7.02 cm

V _arr = 172.236 cm ³ ,

V _then = 0.889 cm ³ .

All measurements are carried out as with a rock sample 1. As a result of measurements, one obtains:

from _breed = 78.51%.

The water saturation of the sample is calculated by the expression (1):

S _in = 0.532 units

Example 6

A rock sample with unknown water saturation has the following parameters:

length - 4.450 cm

diameter - 7.01 cm

V _arr = 171.746 cm ³ ,

V _then = 0.747 cm ³ .

All measurements are carried out as with a rock sample 1. As a result of measurements, one obtains:

from _breed = 77.43%.

The water saturation of the sample is calculated by the expression (1):

S _in = 0.615 units

Example 7

A rock sample with unknown water saturation has the following parameters:

length - 4.480 cm

diameter - 7.01 cm

V _arr. = 172,904 cm ³ ,

V _then = 0.187 cm ³ .

All measurements are carried out as with a rock sample 1. As a result of measurements, one obtains:

from _breed = 53.29%.

The water saturation of the sample is calculated by the expression (1):

S _in = 0.647 units

Example 8

A rock sample with unknown water saturation has the following parameters:

length - 4.463 cm

diameter - 7.03 cm

V _arr = 173.232 cm ³ ,

V _then = 0.393 cm ³ .

All measurements are carried out as with a rock sample 1. As a result of measurements, one obtains:

from _breed = 63.60%.

The water saturation of the sample is calculated by the expression (1):

S _in = 0.669 units

The parameters of the fractured rock samples are shown in table 1.

Table 1 Parameters of cylindrical rock samples of deposit N. Sample Number Length cm Diameter cm V _then cm ³ V _arr , cm ³ The porosity of the samples,% one 4,447 7.00 1,029 171,141 0.601 2 4,446 7.03 0.837 172,572 0.485 3 4,460 7.03 0.658 173,116 0.38 four 4,450 7.02 0.796 172,236 0.462 5 4,450 7.02 0.889 172,236 0.516 6 4,450 7.01 0.747 171,746 0.435 7 4.48 7.01 0.187 172,904 0.108 8 4,463 7.03 0.393 173,232 0.227

The values of the measured humidity and calculated water saturation of the rock samples are shown in table 2.

table 2 Values of measured humidity and calculated water saturation of rock samples of field N. Sample Number The measured humidity,% Water saturation of samples, unit one 84.63 0.548 2 82.73 0.632 3 75.77 0.654 four 69.64 0.439 5 78.51 0.532 6 77.43 0.615 7 53.29 0.647 8 63.60 0.669

The inventive method allows to determine the water saturation of fractured rock samples with high accuracy and low measurement error.

Claims (3)

1. The method of determining the water saturation of rock samples, including the evaporation of water from the sample at a temperature of 140-150 ° C in a closed retort, characterized in that when evaporating water from the samples determine the maximum humidity of the rock sample (from the _rock ), and before evaporating water from the rock sample in the retort chamber was placed a metal simulator chamber is heated to a temperature 140-150 ° C and the initial moisture is measured in a retort (at _0), a calibration curve is determined and the retort constant factor α, for universal use ret mouths, and water saturation rock sample is determined according to the maximum moisture rock sample, the initial humidity of the retort chamber, the volume of the retort to bringing compounds rock sample volume constant coefficient, for the universal use of the retort, and pore volume of the rock sample. 2. The method according to claim 1, characterized in that the water saturation of the rock sample is determined by the formula:

Where
S _in - water saturation of the rock sample;
from _rock - the measured maximum humidity of the rock sample;
с ₀ - humidity in a retort without a rock sample, determined immediately before the experiment at an evaporation temperature of 140-150 ° С;
V ₀ is the volume of the retort with supply connections;
V _arr is the volume of the rock sample;
α is a constant coefficient universal for the retort used;
V _pore is the pore volume of the sample. 3. The method according to claim 1, characterized in that the calibration dependence of the retort is determined by placing in the retort chamber a metal simulator of a rock sample with a ceramic bottle with a given volume of water V _in , the chamber is heated to a temperature of 140-150 ° C and the maximum air humidity is measured - s _caliber , the measurement is repeated for different predetermined volumes of water in the chamber, a calibration dependence is built, and a constant coefficient α is determined by the calibration dependence, and the measured humidity is related to the water volume in the rock sample by the dependence:

,
where s _caliber is the maximum air humidity of a chamber with a ceramic casing;
с ₀ - humidity in a retort without a rock sample, determined immediately before the experiment at an evaporation temperature of 140-150 ° С;
α is a constant coefficient universal for the retort used;
V _in - the volume of water in the box;
V ₀ is the volume of the retort with supply connections;
V _arr is the volume of the rock sample.

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