RU2748894C1 - Method for determining effective hydrogen index of fluids that fully or partially saturate pore space of naturally saturated rock samples - Google Patents

Abstract

FIELD: mining industry.SUBSTANCE: invention relates to the determination of the characteristics of formation fluids simultaneously located in the pore space of a rock sample. When implementing the method, several naturally saturated samples of rock belonging to the same formation are selected, so that there are 2 samples per one place of collection. Samples from the first group are crushed and pieces larger than 3 mm in size are selected. The volume of the solid phase Vsol.ph.1iis determined on each selected sample of crushed rock using a helium porosimeter. The apparent volume of pore fluids Vf.ap.1iis determined by nuclear magnetic resonance (hereinafter – NMR) at HI=1. The crushed sample is placed in prepared cups made of a filter paper. The cups with the sample are placed in Soxhlet apparatuses for cleaning samples by extraction in an alcohol-benzene mixture. After the extraction, the sample cups are dried, desalted in distilled water if necessary, and re-dried, at a temperature of 105ºC. The volume of the solid phase Vsol.ph.2iis determined using a helium porosimeter. The apparent volume of pore fluids Vf.ap.2iis determined by NMR at HI=1. The true volume of fluids that occupied the pore space is calculated, according to a given mathematical dependence. Then the apparent volume of fluids, which occupied the pore space, is calculated at HI=1 according to a given mathematical dependence. Next, the effective hydrogen index of the fluids located in the pores of naturally saturated samples is calculated. The samples are then placed under a layer of fluid in the form of kerosene or a model of formation water and kept under vacuum until the release of air bubbles stops, after which the samples are placed in a saturator, where they are kept for at least 2 hours with an excess pressure of 15 MPa. The apparent coefficient of total porosity Cp100appis determined by NMR at 100% filling of the pore space with fluids. The hydrogen index of the fluid HIfl.satwith which the samples were saturated with is determined. The effective hydrogen index of all fluids in the pore space is calculated for samples in a naturally saturated state with pre-saturation with fluid, followed by the calculation of the true coefficient of total porosity of samples pre-saturated with kerosene.EFFECT: increased information content and reliability of the definition is achieved.1 cl, 3 tbl

Description

The invention relates to methods for determining the properties of formation fluids, namely the effective hydrogen index of all fluids simultaneously located in the pore space of a rock sample, with subsequent refinement of the value of the total porosity coefficient of these samples.

The hydrogen index (HI) is the ratio of the number of hydrogen atoms in a given volume of the test fluid to the number of hydrogen atoms in the same volume of distilled water at standard values of pressure and temperature.

The effective hydrogen index (HI) is the ratio of the number of hydrogen atoms in a given volume of several investigated fluids to the number of hydrogen atoms in the same volume of distilled water at standard values of pressure and temperature.

The volume of fluids, determined using the NMR method - NMR signal from the measured sample, normalized to the volume.

The volume of the solid phase, determined using the gas-volumetric method, is the volume not filled with helium. It includes both the volume of the mineral skeleton and the volume of fluids in the sample.

There are various methods for determining the hydrogen index of fluids saturating the pore space of rocks.

Literature sources indicate the following methods for determining the hydrogen index of fluids saturating a rock.

In the book [Kleinberg R. L., Vinegar H. J., 1996. NMR Properties of Reservoir Fluids. The Log Analyst, 37, 6.20 - 32] indicates several methods for determining VI.

Gaymard and Poupon suggested that hydrocarbons can be represented by alkanes and introduced the correlation dependence of the hydrogen index on the HC density. However, as experiments have shown, this assumption is satisfactory only for pure methane at high pressures and for pure alkanes under atmospheric conditions.

Kleinberg and Vinegar presented the dependence of the hydrogen index on the density of hydrocarbons, based on measurements of real oil in atmospheric conditions.

These methods have a number of disadvantages: for example, the first method has nothing to do with real high-viscosity hydrocarbons and bitumen. On the one hand, the dependence is not always observed, especially for heavy hydrocarbons, on the other hand, the pore space of rocks contains not only hydrocarbons, but also residual water, which affects the value of the effective hydrogen index. The proposed methods do not allow determining the effective hydrogen index of residual water and hydrocarbons, or more fluids.

In the book [Jafarov I.S., Syngaevsky P.E., Khafizov S.F. 2002. Application of the method of nuclear magnetic resonance to characterize the composition and distribution of formation fluids, 439. Chemistry, Moscow] describe the calculation method for determining the hydrogen index, based on the recalculation of the proton density by the formula:

where ρ is the density g / cm ³ ;

nH is the number of hydrogen atoms;

MW is molecular weight;

0.11 the density of protons in distilled water mol / cm ³ .

The disadvantages of this method include a complex procedure for determining the values of MW and pN due to the complex composition of real hydrocarbons, especially high-viscosity hydrocarbons and bitumen. Also, this method does not allow to determine the effective hydrogen index of residual water and hydrocarbons or more fluids.

In the book [Jafarov I.S., Syngaevsky P.E., Khafizov S.F. 2002. Application of the method of nuclear magnetic resonance to characterize the composition and distribution of formation fluids, 439. Chemistry, Moscow] shows the palettes for determining the VI of fluids depending on the density of hydrocarbons.

The disadvantages of determining the hydrogen index by this method include the following points:

This method can only determine the hydrogen index of hydrocarbons, while the studied section may contain residual water, heavy and light hydrocarbons, as well as bitumen, which affect the effective hydrogen index.

To determine the hydrogen index, it is necessary to determine the density of the hydrocarbons. However, the density of hydrocarbons produced from the formations of the Bazhenov formation or from formations containing highly viscous hydrocarbons or bitumen is not always equal to the density of hydrocarbons remaining in the formation.

In the book [Jafarov I.S., Syngaevsky P.E., Khafizov S.F. 2002. Application of the method of nuclear magnetic resonance to characterize the composition and distribution of formation fluids, 439. Chemistry, Moscow] a method for determining the VI fluid based on comparing the amplitude of the NMR signal from the test fluid and distilled water is presented as follows.

where A _f and A _d are the measured amplitudes of the NMR signal of the test fluid and distilled water, respectively;

V _f and V _d - volumes of the investigated fluid and distilled water, respectively;

This method has disadvantages similar to the previous methods for determining the hydrogen index, namely:

In this way, the hydrogen index of hydrocarbons and residual water can be determined separately and the effective value of the hydrogen index of the residual water and hydrocarbons can be calculated, or it is possible to mix the model water sample and the hydrocarbon sample and measure the effective hydrogen index. But for the calculation and measurement, it is necessary to know how much residual water and how much hydrocarbons are contained in the reservoir under study, which represents additional costs for additional experiments.

To determine the hydrogen index, a hydrocarbon sample is required. However, the composition of hydrocarbons produced from the Bazhenov formation or reservoirs containing high-viscosity hydrocarbons or bitumen is not always identical to the composition of the hydrocarbons remaining in the formation. Accordingly, the hydrogen indices of produced hydrocarbons and those remaining in the formation will differ.

There are various methods of obtaining information about the volume of pore space in the rock, filled with hydrocarbons in the collection, the core of an unconventional reservoir of the Jurassic high-carbon formation [RU 2681801 C1, IPC G01N33 / 24, G01N1 / 28, E21B 49/00, publ. 03/12/2019.] The method for determining the volume of the pore space is that the hydrocarbons in the pore space are divided into groups according to the degree of connectivity and mobility, and the mass fraction of hydrocarbons of each group is determined step by step. To determine the total volume of the pore space, the linear resources of oil and gas (q [t / m ² ]) are calculated for each group, and then they are summed up.

This method has disadvantages.

The method is suitable only for a reservoir of a Jurassic high-carbon formation; accordingly, it is impossible to determine the capacitive properties of rocks of other high-carbon formations, rocks containing high-viscosity hydrocarbons, bitumen and / or highly saline formation waters in the pore space. In this way, it is possible to obtain information about the pore space only in mass fractions, which does not allow the calculation of reserves by the volumetric method. This method does not determine and does not take into account the volume of water in the capillaries and the volume of water sorbed on the surface of clay minerals. Without taking into account the water volume, it is impossible to reliably determine the total porosity coefficient.

The problem to be solved by the claimed technical solution is a method for determining the effective hydrogen index simultaneously of all fluids located in the pore space of the naturally-saturated sample under study, fully or partially saturated with one or more fluids, when carrying out laboratory measurements by the method of nuclear magnetic resonance (NMR ), or the studied rock interval during nuclear magnetic logging (NML).

EFFECT: obtaining the effective value of the hydrogen index simultaneously for all fluids contained in the pore space of the studied samples. Possibility of clarifying the value of the total porosity coefficient obtained on naturally-saturated, naturally-saturated with fluid saturation, samples by the NMR method in laboratory conditions, and clarifying the value of the total porosity coefficient obtained using nuclear magnetic logging directly in the studied interval of the formation. Refinement of the coefficient of total porosity is carried out by dividing the value of the coefficient of total porosity, obtained by the method of nuclear magnetic resonance, by the value of the effective hydrogen index.

The specified technical result is achieved in that the method for determining the effective hydrogen index of fluids completely or partially saturating the pore space of naturally-saturated rock samples is characterized by the following sequence of actions: several naturally-saturated rock samples are taken from one formation, so that on one sampling site accounted for 2 samples, samples from the first group are crushed and pieces larger than 3 mm are separated, on each sample of crushed rock, the volume of the solid phase Vt.f. 1i is determined using a helium porosimeter, the apparent volume of pore fluids Vf.k. is determined. 1 _i ; using the NMR method (at VI = 1), place the crushed sample into prepared cups made of filter paper, place the cups with the sample into Soxhlet apparatus for cleaning the samples by the extraction method in an alcohol-benzene mixture (or other solvents and their mixtures), after the end of the extraction the cups with the sample are dried , if necessary, demineralized in distilled water and re-dried at a temperature of 105 ° C, determine the volume of the solid phase Vt.f. 2 _i using a helium porosimeter, determine the apparent volume of pore fluids by the NMR method Vf.c. 2 _i (at VI = 1 ), calculate the true volume of fluids that occupied the pore space according to the mathematical relationship

then the apparent volume of fluids (at VI = 1) that occupied the pore space is calculated according to the mathematical relationship

the effective hydrogen index of fluids in the pores of naturally-saturated samples is calculated from the mathematical dependence

где n - число исследуемых проб дробленой горной породы,

where n is the number of samples of crushed rock under study,

then, on samples from the second group, the apparent porosity coefficient is determined by the NMR method (at VI = 1) at natural saturation Kp _{each at e.n.} , the true coefficient of porosity is calculated by the mathematical dependence

then the samples are placed under a fluid layer (kerosene, a model of formation water, etc.) and kept under vacuum until the release of air bubbles stops, then the samples are placed in a saturator, where they are kept for at least 2 hours with an excessive division of 15 MPa, the apparent coefficient of total porosity according to NMR at 100% filling of the pore space with fluids Кп _100kаzh , determine the hydrogen index of the fluid with which the samples were saturated with VI _fl.nas , calculate the effective hydrogen index of all fluids in the pore space for samples in a naturally saturated state with additional saturation with fluid according to mathematical dependence

where V _is.u. ^{_ the} true volume of fluids at natural saturation (determined by the NMR method taking into account the correction for the hydrogen index), ml

VI _Eff.u. - effective hydrogen index of fluids at natural saturation

V _{fl. Sat.} ^{- the} true volume of fluid entering the sample is determined as the ratio of the mass difference in air after and before saturation to the density of the fluid, ml

VI _fl.nas - hydrogen index of the fluid, which was used to saturate the sample up to 100% filling of all pores with fluids.

V _{eats us + fl.} ^{_ the} total true volume of all fluids in the pore space of the sample, ml.

then the true coefficient of the total porosity of the samples, resaturated with kerosene, is calculated according to the mathematical dependence

The essence of the invention lies in the fact that from the central part of the core drilled using the isolating technology, or waxed in the well, several naturally-saturated rock samples are taken from one layer, so that there are 2 samples per sampling site.

One of the two images is crushed and pieces larger than 3 mm are isolated.

On each sample of crushed rock, the volume of the solid phase Vt.ph1 _i is determined using a helium porosimeter.

Determine the apparent volume of pore fluids Vf.c. 1 _i by NMR (with VI = 1).

Place the crushed sample in prepared filter paper cups. The cups with the sample are placed in Soxhlet apparatus for cleaning samples by extraction in an alcohol-benzene mixture (or other solvents and their mixtures).

After the end of the extraction, the cups with the sample are dried, if necessary, desalted in distilled water and dried again.

On a sample cleaned of hydrocarbons, desalted and dried at a temperature of 105 ° C, the volume of the solid phase Vt.f.2 _{i is} again determined.

Then the apparent volume of pore fluids is determined by the NMR method Vph.c.2 _i (with VI = 1).

Determine the true volume of fluids that occupied the pore space by the formula

Determine the apparent volume of fluids (with VI = 1) that occupied the pore space by the formula

The effective hydrogen index of fluids in the pores of naturally saturated samples is determined by the formula:

Where n is the number of crushed rock samples under study.

On the second cylindrical sample, the apparent porosity coefficient is determined by the NMR method (at VI = 1) at natural saturation Kp _{each pri.} - And the true coefficient of porosity is determined by the formula:

To determine the total porosity coefficient by the NMR method, 100% filling of the pore space with fluids is required. In this case, the naturally-saturated samples under study are placed under a fluid layer (kerosene, a model of formation water, etc.), with which it is necessary to saturate the samples to 100% filling the pore space. They are kept under a layer of fluid under vacuum until the release of air bubbles ceases, then the samples are placed in a saturator, where they are kept for at least 2 hours with an excessive division of 15 MPa.

After the test samples are saturated with fluid, the apparent coefficient of total porosity by NMR is determined at 100% filling of the pore space with fluids Kp _100kazh . In this case, there is a change in the amount and composition of fluids in the pore space of the samples and, accordingly, a change in the effective hydrogen index. In order to correctly determine the effective hydrogen index of all fluids in the pore space, including the fluid with which the samples were saturated, it is first necessary to determine the hydrogen index of the fluid with which the samples were saturated with VI _fl. To determine it, you can use a method based on comparing the amplitude of the NMR signal from the test fluid and distilled water [Jafarov I.S., Syngaevsky P.E., Khafizov S.F. 2002. Application of the method of nuclear magnetic resonance to characterize the composition and distribution of reservoir fluids, 439. Chemistry, Moscow]. Then the effective hydrogen index of all fluids in the pore space for samples in a naturally saturated state with additional fluid saturation will be calculated by the formula:

Where V is. _{E. N.} ^{_ the} true volume of fluids at natural saturation (determined by the NMR method taking into account the correction for the hydrogen index), ml

VI _eff.u. - effective hydrogen index of fluids at natural saturation

V _{fl. Sat.} ^{_ the} true volume of fluid entering the sample is defined as the ratio of the mass difference in air after and before saturation to the density of the fluid, ml

VI _fl.nas - hydrogen index of the fluid, which was used to saturate the sample up to 100% filling of all pores with fluids.

V _{nat. Sat. + Fl. Sat.} - the total true volume of all fluids in the pore space of the sample, ml.

Thus, the true coefficient of the total porosity of samples re-saturated with kerosene, which should be taken into account when calculating reserves by the volumetric method, is calculated using a formula similar to formula 8:

The advantage of this method over others is that the effective hydrogen index is determined simultaneously for all fluids filling the pore space of naturally saturated samples, the composition of the studied fluids corresponds to the composition of fluids in the places of occurrence. There is no need for a separate determination of the hydrogen index of each fluid filling the pore space, followed by the calculation of the effective value.

A feature of the claimed invention is that this method does not depend on the shape of the original sample and does not require additional measurements of the filtration-capacitive properties.

In practice, the method is applied as follows.

The claimed invention has been tested on naturally saturated core samples taken from well 3462-Em-Egovskoye field.

The objects of study in well 3462 of the Em-Egovskoye field are samples in a naturally-saturated state and in a naturally-saturated state with additional saturation with kerosene, taken from the sediments of the Bazhenov and Abalak formations. Core samples are mainly represented by clay-siliceous rock and siliceous-clay rock.

To determine the total porosity coefficient in laboratory conditions by the NMR method, 14 samples are taken: 7 samples from the YuK ₀ formation and 7 samples from the YuK ₁ formation from the naturally saturated core drilled using the isolation technology. To prevent the evaporation of fluids from the selected samples, they are wrapped in 2 layers of cling film and placed in bottles. Before starting NMR measurements, the geometric dimensions of the samples and the mass in air (Table 1, columns 4,5,6) are determined at natural saturation. Then, on the samples, the apparent porosity coefficient at natural saturation is determined by the NMR method (Table 1, column 7) using an NMR analyzer Chromatek-Proton 20M manufactured by ZAO SKB Khromatek and OOO NPP GEFES. The samples are placed under a layer of kerosene (kerosene hydrogen index VIker = 0.95) and kept under vacuum until air bubbles cease to evolve. Then the samples are kept in a saturator at an overpressure of 15 MPa for 2 hours. After saturation with kerosene to 100% filling the pore space with fluids, the sample is weighed in air (Table 1, column 8) and the apparent coefficient of total porosity is determined at 100% filling of the pore space with fluids by NMR (Table 1, column 9).

To determine the effective hydrogen index, 14 duplicate samples are taken with the same sampling site and sample composition. Samples are crushed and sieved on sieves with a mesh diameter of <3 mm, wrapped in 2 layers of cling film and placed in bottles to prevent moisture evaporation. On each naturally-saturated sample of the crushed sample, the volume Vf.c.1 of the fluids saturating the pore space of naturally-saturated samples of the crushed sample is determined by the NMR method (Table 2, column 5). Then, the volume of the solid phase Vt.ph.1 is measured using an UltraPore-300 helium porosimeter manufactured by CoreLab Instruments (Table 2, column 4).

Place the naturally saturated samples of the crushed sample into prepared filter paper cups. The cups with the sample are placed in Soxhlet apparatus for cleaning samples by extraction in chloroform and kept in this way for 14 days. After cleaning from hydrocarbons, the samples are dried at 105 ° C in a drying oven to constant weight.

Determine the volume of pore fluids Vf.c.2 by NMR (Table 2, column 7) and the volume of the solid phase Vt.f. 2 using a helium porosimeter (Table 2, column 6) after cleaning from hydrocarbons and drying.

Using formula 5, calculate the true volume of fluids that occupied the pore space of the samples of the crushed sample at natural saturation (Table 2, column 8). Formula 6 is used to calculate the apparent volume of fluids that occupied the pore space of the crushed sample samples at natural saturation (Table 2, column 9). Formula 7 is used to calculate the effective hydrogen index of pore fluids for each formation (Table 2, column 10).

After determining the value of the effective hydrogen index of fluids for the formations YuK ₀ and YuK ₁ using formula 8, calculate the true porosity coefficient for the samples measured by NMR at natural saturation (Table 3, column 4). The value of the effective hydrogen index of fluids saturating the pore space of samples saturated with kerosene is determined by formula 9. To do this, first determine the true volume of fluids for each naturally saturated sample (Table 3, column 5) by the formula:

Where V is. _{E. N.} - true volume of fluids at natural saturation, ml

Kp _{source at e.n.} - true coefficient of porosity at natural saturation,%

(The true porosity coefficient at natural saturation is the true volume of fluids, determined by the NMR method, reduced to the fraction of porosity).

Then determine the true volume of fluid - kerosene (Table 3, column 6), which entered the samples at saturation, according to the formula:

Where M ₁ is the mass of a naturally saturated sample, g

M ₂ is the mass of a naturally-saturated sample with additional saturation with kerosene, g 0.788 is the density of kerosene, g / ml.

The results of determining the effective hydrogen index of all fluids filling the pore space of samples saturated with kerosene are presented in Table 3 in column 7. The true coefficient of total porosity for samples saturated with kerosene is calculated using formula 10 (Table 3, column 8).

Thus, with the help of this invention, the results of laboratory determination of the coefficient of total porosity of naturally-saturated samples resaturated with kerosene are clarified.

Claims (16)

A method for determining the effective hydrogen index of fluids that completely or partially saturate the pore space of naturally-saturated rock samples, characterized by a sequence of actions: several naturally-saturated rock samples are taken from one layer, so that there are 2 samples per sampling site, samples from the first group are crushed and pieces larger than 3 mm in size are separated, on each sample of crushed rock, the volume of the solid phase Vt.f.1 _i is determined using a helium porosimeter, the apparent volume of pore fluids Vf.c. 1 _{i is} determined by the NMR method with VI = 1, place the crushed sample into prepared cups made of filter paper, place the cups with the sample into Soxhlet apparatus for cleaning samples by the extraction method in an alcohol-benzene mixture, after the end of the extraction the cups with the sample are dried, if necessary, desalted in distilled water and dried again at a temperature of 105 ° C is determined the volume of the solid phase Vt.f. 2 _i is determined using a helium porosimeter, the apparent volume of pore fluids is determined by the NMR method Vph.c.2 _i at VI = 1, the true volume of fluids occupying the pore space is calculated according to the mathematical dependence

then the apparent volume of fluids at VI = 1, which occupied the pore space, is calculated according to the mathematical relationship

calculate the effective hydrogen index of fluids in the pores of naturally saturated samples, according to the mathematical dependence

where n is the number of samples of crushed rock under study, then on samples from the second group, the apparent porosity coefficient is determined by the NMR method at VI = 1 at natural saturation Kp _{each at un.} , the true coefficient of porosity is calculated by the mathematical dependence

then the samples are placed under a fluid layer in the form of kerosene or a model of formation water and kept under vacuum until the release of air bubbles stops, then the samples are placed in a saturator, where they are kept for at least 2 hours with an overpressure of 15 MPa, the apparent coefficient of the total porosity by NMR at 100% filling of the pore space with fluids Кп _{100 kaz} , determine the hydrogen index of the fluid, which saturated the samples of VI _fl. , calculate the effective hydrogen index of all fluids in the pore space for samples in a naturally saturated state with additional fluid saturation according to the mathematical relationship

where V _is.u. ^{_ the} true volume of fluids at natural saturation (determined by the NMR method taking into account the correction for the hydrogen index), ml; VI _eff.u. - effective hydrogen index of fluids at natural saturation; V _{fl. Sat.} ^{_ the} true volume of fluid entering the sample is determined as the ratio of the difference in masses in air after and before saturation to the density of the fluid, ml; VI _fl.nas - hydrogen index of the fluid, which was used to saturate the sample up to 100% filling of all pores with fluids; V _{nat. Sat. + Fl. Sat.} ^{_ the} total true volume of all fluids in the pore space of the sample, ml; then the true coefficient of the total porosity of the samples resaturated with kerosene is calculated according to the mathematical dependence

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