RU2097743C1 - Method designed to determine wettability parameter of container-rock pore channels - Google Patents

Abstract

FIELD: examination and analysis of materials. SUBSTANCE: specimen is prepared for examination, and its permeability is determined. Then specimen is centrifuged in different modes of centrifuge rotation. In this case, dependence of capillary pressure of draining of specimen effective pore space from water saturation and dependence of capillary pressure of absorption of specimen dynamic pore space from water saturation are determined. Normalized differential curves of dependence of radius occurrence frequency of pore channels from their size for dynamic and effective pore space are plotted by obtained dependences. Wettability parameter for definite radius of pores or their range is determined on basis of the above-indicated curves. EFFECT: higher results of analysis. 3 dwg

Description

 The invention relates to the field of studying the properties of porous materials, in particular to determining the wettability parameter of pore channels of natural reservoir rocks, and can be used in calculating oil and gas reserves, as well as in the design of rational oil field development systems.

A known method for determining the wettability of reservoir rocks, according to which experimentally determines the permeability, porosity, conduct double capillarimetry by displacing water with oil and oil with water, asking a number of discrete pressure values. The thickness of the water and oil films held by the pore surface of each sample is determined, according to these data, the samples are divided into hydrophilic and hydrophobized, and the value of the contact angle is determined by the corresponding formulas. Establish a correlation between the wetting angle and the humidity parameter, build a reference graph for these two parameters. The formation moisture parameter is calculated, and the wettability of the rocks is determined from the fixed value of the last of the reference graph [1]
However, this method is intended to determine only the integral wettability of the rocks with formation fluids.

Closest to the proposed method is a method for determining the wettability of reservoir rocks, according to which a sample is taken from the studied formation, it is extracted, dried, the permeability of the sample is measured, it is saturated with mineralized water, the sample is immersed in kerosene, centrifuged at a constant speed of 7000 rpm within 2 hours; then this sample is placed in mineralized water, centrifuged again in the same mode, the absorption capillary pressure is determined, and the dependence of the absorption capillary pressure of the dynamic pore space on water saturation is constructed (Fig. 1, curve "a"). Next, the same sample is immersed in kerosene, centrifuged, the capillary pressure of the drainage is determined, a curve of the dependence of the capillary pressure of the dynamic pore space drainage on water saturation is constructed (Fig. 1, curve b), and the wettability parameter (W) is determined by the formula:
W lq A ₁ / A ₂
where: A _{1 is the} area between the axis of water saturation and the capillary pressure curve of the drainage;
A ₂ area between the axis of water saturation and the capillary absorption pressure curve [2]
However, the known method allows only the integral wettability of the rocks, i.e. for the whole sample.

 The aim of the present invention is to provide the ability to determine the differential wettability parameter for specific values of the radii of the pores or their range.

где r₁ минимальный радиус выбранного диапазона радиусов поровых каналов;
r₂ максимальный радиус выбранного диапазона радиусов поровых каналов;
F_д(r) нормированная дифференциальная частота встречаемости радиусов поровых каналов динамического порового пространства;
F_э (r) нормированная дифференциальная частота встречаемости радиусов поровых каналов эффективного порового пространства;

площадь между осью радиусов поровых каналов и нормированной дифференциальной кривой частоты встречаемости радиусов поровых каналов динамического порового пространства;

площадь между осью радиусов поровых каналов и нормированной дифференциальной кривой частоты встречаемости радиусов поровых эффективного порового пространства.This goal is achieved by the fact that in the known method for determining the wettability parameter of the pore channels of reservoir rocks, according to which a sample is taken from the formation being studied, it is extracted, dried, the permeability of the sample is measured, it is saturated with mineralized water, the sample is immersed in kerosene sequentially and then in mineralized water and centrifuged it after each immersion, determine the dependence of the capillary pressure of absorption and capillary pressure of drainage of the pore space the wettability of the sample and the data obtained indicate that it is wettable; centrifugation of the sample is carried out under various centrifuge rotation modes to obtain a sample with residual water and oil saturation; in this case, after centrifuging the sample placed in kerosene, the dependence of the capillary pressure of drainage is determined effective pore space of the sample on saturation, and after centrifugation of the sample placed in mineralized water, the dependence of capillary pressure Nia absorption dynamic pore space of the sample of water saturation in the range of K _s to 1 K _it, where K _s water saturation factor, K _it - the coefficient of residual oil saturation, followed by the obtained dependence build normalized differential curves of the frequency of the radii of the pore channels of size for efficient and dynamic pore space, and the wettability parameter is determined by the formula:

where r _{1 is the} minimum radius of the selected range of radii of the pore channels;
r _{2 the} maximum radius of the selected range of radii of the pore channels;
F _d (r) the normalized differential frequency of the radii of the pore channels of the dynamic pore space;
F _e (r) normalized differential frequency of occurrence of the radii of the pore channels of the effective pore space;

the area between the axis of the radii of the pore channels and the normalized differential curve of the frequency of occurrence of the radii of the pore channels of the dynamic pore space;

the area between the axis of the radii of the pore channels and the normalized differential curve of the frequency of occurrence of the radii of the pore effective pore space.

 From the current level of technology, we are not aware of methods for determining the differentiated wettability parameter for specific radii of pore channels or their range. This is ensured only by the proposed method due to the following.

 A pore channel that has a certain wettability and is saturated, in one case, with a wetting phase and in another with a non-wetting phase, under the same conditions of external action (in our case, centrifugal forces) provides respectively different penetration volumes, both in the first and second cases into the pore channel of the external phase surrounding this channel. The ratio of these volumes and characterizes the wettability of the pore channel. The proposed comparison of the structure of effective pore space and dynamic pore space, the parameters of which are normalized, allows us to determine the above volume ratio for specific radii or their range. Due to this, the differentiation of the volumes of the external phases, each of which is included in the same pore channel, is carried out along the radii of the pore channels. As a result, it is possible to study the wettability of porous media not as an integral, but as a differential characteristic.

 In the proposed method, the wettability parameter varies from 0 to 1.

 In FIG. 1 shows the curves of two dependencies, namely: capillary pressure of the absorption of dynamic pore space from water saturation (curve a) and capillary pressure of the drainage of dynamic pore space from water saturation (curve "b") obtained by implementing the method known in the prior art.

 In FIG. 2 shows curves of two dependencies, namely: capillary pressure of drainage of effective pore space from water saturation (curve "a") and capillary pressure of absorption of dynamic pore space from water saturation (curve "b") obtained by the proposed method; in FIG. 3 normalized differential curves of the frequency of occurrence of the radii of the pore channels versus their size for the effective pore space (curve a) and dynamic pore space (curve b).

An example implementation of the method:
For research, sample No. 333 of well 25 of the Mazuninskoye field was selected. A sample was taken from the water-saturated part of the Bashkir deposits. Studies of porosity (K _p ) and permeability (K _o.ch. ) respectively gave the following results: K 0.111 d.ed. and K 0.024 microns.

где P_к капиллярное давление;
Δρ - разность плотностей двух фаз;
N частота вращения ротора;
R расстояние от оси вращения до внутреннего торца образца;
H высота образца;
рассчитывали капиллярное давление (P_к) дренирования эффективного порового пространства, а по формуле
K 1 V_в/V_h,
где V_в объем жидкости, вышедшей из образца;
V_н объем открытых пор,
рассчитывали коэффициент водонасыщенности K. По полученным данным строили кривую зависимости P_к от K_в, представленную на фиг. 2, кривая "а".The specified sample was extracted, dried, saturated with 4 normal sodium chloride solutions, immersed in kerosene and centrifuged at various rotation modes of the centrifuge rotor from 100 to 11000 rpm, while recording the amount of water displaced. Further, according to the formula:

where P _to capillary pressure;
Δρ is the density difference of the two phases;
N rotor speed;
R is the distance from the axis of rotation to the inner end of the sample;
H is the height of the sample;
calculated capillary pressure (P _to ) drainage of the effective pore space, and according to the formula
K 1 V _in / V _h ,
where V _{is the} volume of liquid exiting the sample;
V _{n the} volume of open pores,
calculated water saturation coefficient K. The data obtained curve was from K _to P _in of FIG. 2, curve "a".

Then this sample saturated with kerosene with residual water saturation was mixed in a 4 normal sodium chloride solution, centrifuged, and the amount of extruded kerosene was recorded at various rotor rotation modes from 100 to 11000 rpm. Then, the capillary absorption pressure of the dynamic pore space and the oil saturation coefficient were determined using the above formulas. Then, a curve was built of the dependence of the capillary pressure of absorption on water saturation in the range from K _s to 1 - K _he (curve "b" of Fig. 2), (K _s residual water saturation, K _he residual oil saturation).

Next, we built a normalized differential curve of the frequency of occurrence of the radii of the pore channels on their size for the effective pore space. To this end, for each interval of values of P _to determined the interval of the radii of the pore channels: Δr _i = r _{i + 1} - r _i
wherein:
r _i = 2σ • cosθ / P _to
where σ is the surface tension at the boundary of two phases;
P _to capillary pressure;
θ is the wettability angle.

The average radius of the interval is calculated:
Then, respectively, for each interval of values of P _to determined the amount of released water:
ΔK _{Bi Bi} = K - K _{Bi + 1}
where K _{is the} coefficient of water saturation of the sample.

.The differential non-normalized frequency of occurrence of the radii of the pore channels was calculated by the fraction of released water per unit radius in each interval Δr _i :
F _i = ΔK _Bi / Δr _i
The sum of all frequencies ΣF _{i was} determined. The differential normalized frequency of occurrence of the radii of the pore channels was calculated by the formula:

.

строили искомую зависимость (кривая "а" фиг. 3). Далее на том же чертеже строили нормированную кривую дифференциального распределения радиусов поровых каналов для динамического порового пространства (кривая "б" фиг. 3). Для этого повторили вышеописанную процедуру определения частот встречаемости радиусов поровых каналов по данным кривой капиллярного давления впитывания динамического порового пространства. При этом при расчете дифференциальной нормированной частоты встречаемости радиусов поровых каналов сумма частот ΣF_i берется та же самая, полученная при обработке кривой капиллярного давления дренирования эффективного порового пространства.According to F _gi and

built the desired dependence (curve "a" of Fig. 3). Then, in the same drawing, a normalized curve of the differential distribution of the radii of the pore channels for dynamic pore space was built (curve "b" of Fig. 3). To do this, we repeated the above procedure for determining the frequency of occurrence of the radii of the pore channels according to the curve of the capillary pressure of absorption of the dynamic pore space. In this case, when calculating the differential normalized frequency of occurrence of the radii of the pore channels, the sum of the frequencies ΣF _i is taken to be the same obtained by processing the capillary pressure curve of the drainage of the effective pore space.

где r₁ минимальный радиус выбранного диапазона радиусов поровых каналов;
r₂ максимальный радиус выбранного диапазона радиусов поровых каналов;
F_д (r) нормированная дифференциальная частота встречаемости радиусов поровых каналов динамического порового пространства;
F_э (r) нормированная дифференциальная частота встречаемости радиусов поровых каналов эффективного порового пространства;

площадь между осью радиусов поровых каналов и нормированной дифференциальной кривой частоты встречаемости радиусов поровых динамического порового пространства;

площадь между осью радиусов поровых каналов и нормированной дифференциальной кривой частоты встречаемости радиусов поровых каналов эффективного порового пространства.In the resulting drawing (Fig. 3), the range of radii of the pore channels 40 120 μm was selected, for which the wettability parameter C _g 0.864 was calculated by the formula:

where r _{1 is the} minimum radius of the selected range of radii of the pore channels;
r _{2 the} maximum radius of the selected range of radii of the pore channels;
F _d (r) the normalized differential frequency of the radii of the pore channels of the dynamic pore space;
F _e (r) normalized differential frequency of occurrence of the radii of the pore channels of the effective pore space;

the area between the axis of the radii of the pore channels and the normalized differential curve of the frequency of occurrence of the radii of the pores of the dynamic pore space;

the area between the axis of the radii of the pore channels and the normalized differential curve of the frequency of occurrence of the radii of the pore channels of the effective pore space.

 According to a similar scheme, the wettability parameter was determined for other samples.

 Until now, existing methods for studying the wettability of natural reservoir rocks have made it possible to obtain wettability parameters that describe this property as an integral characteristic, not allowing, in particular, to distinguish the pore space region occupied by residual water saturation, and which, by its nature, is usually close to absolute Filnosti. As a result, the data obtained for the sample as a whole were transferred to a dynamic pore space, which plays a key role in the development of oil and gas fields. Moreover, the data turned out to be overestimated in the direction of flexibility.

 The proposed method allows for the first time to consider the wettability of porous media as a differential characteristic that describes various parts, areas, zones of the pore space, thereby increasing the accuracy and reliability of determining the wettability of precisely the filtering pore channels, which is the initial information for calculating oil and gas reserves, as well as for research issues of enhanced oil recovery (selection of chemicals, filtration modes, etc.).

Claims (1)

A method for determining the wettability parameter of pore channels of reservoir rocks, according to which a sample is taken from the formation being studied, it is extracted, dried, the permeability of the sample is measured, it is saturated with mineralized water, the sample is immersed sequentially in kerosene, and then it is mineralized water and centrifuged after each immersion, determine the dependence of the capillary pressure of absorption and capillary pressure of the drainage of the pore space on the water saturation of the sample and yes they are judged on wettability, characterized in that the centrifugation of the sample is carried out under various centrifuge rotation modes until a sample with residual water and oil saturation is obtained, while after centrifuging the sample placed in kerosene, the dependence of the capillary pressure of the drainage of the effective pore space of the sample on water saturation is determined, and after centrifugation of the sample placed in mineralized water, the dependence of the capillary pressure of absorption of the dynamic pore space is determined nstva sample by water saturation in the range of K _{of a} 1 _{o n} where K _{of a} coefficient of residual water saturation C _{o n} coefficient residual oil saturation, followed by the obtained dependence build normalized differential curves of the frequency of the radii of the pore channels of size for efficient and dynamic pore space, and the wettability parameter is determined by the formula

where r _{1 is the} minimum radius of the selected range of radii of the pore channels;
r _{2 the} maximum radius of the selected range of radii of the pore channels;
F _d (r) is the normalized differential frequency of occurrence of the radii of the pore channels of the dynamic pore space;
F _e (r) is the normalized differential frequency of occurrence of the radii of the pore channels of the effective pore space;

the area between the axis of the radii of the pore channels and the normalized differential curve of the frequency of occurrence of the radii of the pore channels of the dynamic pore space;

the area between the axis of the radii of the pore channels and the normalized differential curve of the frequency of occurrence of the radii of the pore channels of the effective pore space.

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