RU2069263C1 - Method for evaluation of active volume of oil-saturated pores of producing formations - Google Patents

Abstract

FIELD: geology; applicable in calculation of hydrocarbon resources on newly discovered deposits. SUBSTANCE: method for evaluation of active volume of oil-saturated pores of producing formations includes measurement of gamma activity hum and injection of drilling mud saturated with indicator and forced into formation; measurement of gamma activity, and repeated injection of drilling mud saturated with indicator; determination of effective thickness and dynamic porosity of formations; correction of value of dynamic porosity by effect of redistribution of indicator between solid and liquid phases of drilling mud, between movable and immovable parts of fluid in pore spaces of formation and by the depth of penetration of indicator into formation. Value of volume of oil-saturated pores is determined as the sum of product of corrected dynamic porosity and effective thickness of each volume object. EFFECT: higher efficiency. 6 dwg, 1 tbl

Description

 The invention relates to the field of geology, namely, to the calculation of hydrocarbon reserves in newly discovered fields.

 The aim of the present invention is the realization of the possibility of determining the potential (active) hydrocarbon reserves in the conditions of bedding and increasing the reliability of calculating the coefficient of dynamic porosity.

This goal is achieved by the fact that in the known method for the study of productive formations, including background measurement of gamma-ray logging (GC), pumping the γ-indicator and selling it into the formations with measurements of the intensity of gamma radiation after each operation with determination of the effective thickness (h _eff ) and dynamic porosity formations (K _g) according to the invention, a sample of the well drilling fluid filling, assert it and determine indicator distribution coefficient in liquid and solid phase of the mud, and calculating a correction for ne distribution of the indicator between the liquid and solid phases of the drilling fluid, a bulk multisection collapsible reservoir model is made, the overall porosity of the model is determined, it is saturated with an inactive drilling fluid filtrate, it is pushed out with a “labeled” drilling fluid filtrate in a volume equal to one pore volume of the model, it is completely disassembled in the direction from top to bottom measure the intensity of g-radiation from each layer, determine the dependence of the change in the relative intensity of the g-radiation of the indicator on the penetration depth Diving it deeper into the model, the correction for the dynamic porosity parameter for the indicator mass transfer between the mobile and the stationary liquid phase in the pore space of the permeable formation is carried out at the well in the same mode, two indicator fluid are pushed into the formation and one is pushed deep into the formation by an inactive liquid, taking into account the results of which a correction to the dynamic porosity parameter for the depth of penetration of the indicator into the reservoir and, based on the results of the determinations, correct the value of the previously calculated dyne value the formation porosity on the influence of the indicator redistribution between the solid and liquid phases of the drilling fluid, between the mobile and the stationary part of the fluid in the pore space of the formation, for the depth of penetration of the indicator into the formation, and the volume of oil-saturated pores is determined as the sum of the products of adjusted dynamic porosity and effective power for each counting object.

 Additionally, the search for related fields of technology did not confirm the popularity of these features, therefore, we can assume that the specified set of features meets the criterion of "materiality of differences."

(1)
где I_n гамма-аномалия, обусловленная проникновением индикаторной жидкости в пласт; I_p интенсивность γ-поля, обусловленная индикаторной жидкостью в стволе скважины; d_п, δ_и, δ_р- плотность породы, индикаторной жидкости и бурового раствора соответственно; f(δ_и, ln) функция, характеризующая насыщенность индикаторной жидкостью ствола скважины по гамма-излучению; η_э, η_эр
поправки, учитывающие положение прибора при проведении индикаторного ГК и ГК-распределения.The method is as follows. Before carrying out work in the studied section of the well, the background measurement of the HA is taken. The solution injected into the well is marked with a radioactive substance and placed by pushing drill pipes through the string into the interval of the studied formations. GC is removed to represent the distribution of the indicator in the study interval (GK distribution). Then, the indicator pushes into the reservoirs by performing reciprocating movements of the drilling tool at a distance of 30–40 m. After washing the research interval, a GK-indicator is performed. Then, the obtained g-effects from the penetration of radon into the formation are compared with the value that would have been obtained if the solution of the indicator of this concentration (which is judged by the GK distribution) penetrated into this reservoir to a depth above the radius of the zone of study of the formation by GK. In this case, the porosity of the reservoir is considered equal to effective, determined according to the dependence of core geophysics. This resistance allows one to judge the degree of formation saturation with an indicator, taking into account which the value of dynamic porosity is determined. For "saturated" formations, the dynamic porosity coefficient is determined by the formula:

(one)
where I _n gamma-anomaly due to the penetration of the indicator fluid into the reservoir; I _{p the} intensity of the γ-field due to the indicator fluid in the wellbore; d _p , δ _and , δ _p - the density of the rock, indicator fluid and drilling fluid, respectively; f (δ _and , ln) a function that characterizes the saturation of the indicator fluid of the wellbore with gamma radiation; η _e , η _er
corrections taking into account the position of the device during the indicator GK and GK distribution.

(рис. 1), так как по результатам однократной закачки это сделать сложно. После этого в интервале исследований закачивается жидкость, аналогичная жидкости-носителю, но не содержащая меченного вещества. Объем, которым ИЖ помещается в интервал исследований, берется из вышепроведенных закачек РВ. Неактивной жидкостью производится оттеснение индикатора вглубь пласта, результаты которого фиксируются по данным ГК-оттеснения. Данные этого ГК дают возможность определить глубину оттеснения (ln) индикатора вглубь пласта с использованием зависимости (рис.2)

где I_о, I значения γ-активности до и после оттеснения.Then, in the same mode as the first injection, the second injection is performed, which is completed by flushing the wellbore in the volume of a half-cycle of circulation; according to its results, the formations characterized by the above technique as being “saturated” by γ-radiation are monitored, formations are found for which petrophysical dependence K _e (K _p ) is incorrect, and for the "unsaturated" formations, approximately the depth of penetration of the indicator fluid is determined using the form of the known dependence of the saturation function

(Fig. 1), since according to the results of a single injection, this is difficult to do. After that, a fluid similar to the carrier fluid, but not containing the labeled substance, is pumped into the test interval. The volume with which IL is placed in the study interval is taken from the above RV downloads. Inactive fluid displaces the indicator deep into the reservoir, the results of which are recorded according to the GK-displacement. The data of this GC make it possible to determine the depth of displacement (ln) of the indicator deep into the reservoir using the dependence (Fig. 2)

where I _about , I values of γ-activity before and after displacement.

 For those formations against which the intensity as a result of repeated injection doubled or changed by an amount close to the first intensity value, one can judge the penetration depth by the results of pushing the indicator deeper into the reservoir with an inactive solution. In the work “Prospects of the radon indicator method” (Oil industry, 1988, N 9, p. 40-43) V. A. Yudin and others showed that the change in the relative intensity of g-radiation of the indicator rim when pushing it deeper into the reservoir does not depend on its thickness occurs exponentially (see Fig. 2). Taking the ratio of intensities for each layer, you can find a point on curve 2 and the corresponding depth l. The results of the displacement can serve as a check of the results of re-injection of the indicator for formations "saturated" with indicator fluid, which were mentioned above.

 Due to this distribution of technological operations, it is not necessary to know exactly the volume of labeled fluid pumped into the layers, since this parameter is not used in the calculations. However, when choosing an indicator injection mode, it is necessary to know such an injection volume that can be used to create an indicator penetration zone even in low-permeability formations. In this case, you can use the formula proposed by V. Yudin.

(3)
где

средневзвешенное по толщине значение проницаемости;
K $\genfrac{}{}{0ex}{}{\text{min}}{\text{пр}}$ минимальное значение проницаемости исследуемых пластов;

среднее значение пористости в исследуемом интервале;
L_м минимально обнаружимая толщина зоны проникновения меченного раствора по данным ГК;
d_c диаметр скважины.

(3)
Where

thickness-average permeability value;
K $\genfrac{}{}{0ex}{}{\text{min}}{\text{etc}}$ the minimum value of the permeability of the studied formations;

the average value of porosity in the studied interval;
L _{m the} minimum detectable thickness of the zone of penetration of the labeled solution according to the data of the Civil Code;
d _c borehole diameter.

, K_п, d_c. Параметр L_м оценивается, исходя из наименьшей пористости слабопроницаемых коллекторов

, прогнозируемой концентрации индикатора в жидкости-носителе по известной в теории ГК формуле. Причем расчетное значение интенсивности от такого пласта, активированного индикатором должно быть выше удвоенного значения квадратного корня из фоновой γ-активности против этого пласта.In the calculations of V _min estimated values of the parameters are used

, K _p , d _c . The parameter L _m is estimated based on the lowest porosity of low permeability reservoirs

, the predicted concentration of the indicator in the carrier fluid according to the formula known in the theory of HA. Moreover, the calculated value of the intensity from such a layer activated by the indicator should be higher than twice the square root of the background γ activity against this layer.

, (4)
Причем значения In и ln берутся по результатам первой закачки.In the case of mismatch of the depths l _n that took place after the first selling and pushing, their average value is taken. Given the updated depth data, the dynamic porosity value is determined by the formula:

, (4)
Moreover, the values of In and ln are taken according to the results of the first injection.

In order to increase the reliability of determining the indicated coefficient K _g, experimentally determine the corrections P ₁ and P ₂ , previously not determined by anyone and depending on the proportion of the indicator redistributed between the liquid and solid phases of the drilling fluid (P ₁ ) and the uneven concentration of the indicator in the formation in the radial direction (P ₂ ).

 By laboratory tests on models, the authors found that the influence of these factors on the intensity recorded against the reservoir and the results of determining dynamic porosity can be significant.

, (5)
где V_o объем сосуда (4) с индикатором;
V_в, V_ж объем воздушной и жидкой фаз системы.The correction (P ₁ ) for the redistribution of the indicator in the drilling fluid is as follows: a sample of the drilling fluid is taken, which upon sedimentation makes it possible to obtain about 0.5 L of filtrate (for the convenience of the experiment), and sedimentation is carried out until the filtrate is obtained in a volume of at least 30 % of the total sample volume. Moreover, it was found experimentally that an increase in the fraction of the filtrate slightly changes the value of the correction P ₁ . In a known manner using the installation shown in Fig. 3, there is a distribution coefficient of the indicator in the liquid and solid phases of the drilling fluid. In both cases, Bobrov’s apparatus is filled with the studied fluid, an indicator is introduced into system (4), the intensity from it is determined (I _о in the chamber (4), it is sealed by the system, air is circulated using the pump (3). During the circulation, intensity measurements are made with the device (8.9) to stabilize the readings of the γ-radiometer (I). From the radon balance equation (for this system), the distribution coefficient of the indicator can be written as follows:

, (5)
where V _{o the} volume of the vessel (4) with an indicator;
V _in , V _{W the} volume of the air and liquid phases of the system.

, (6)
где V_ф объемная доля фильтрата в буровом растворе.Correction P ₁ is found after the value of the distribution coefficient of the indicator in the filtrate α _f and the solid phase α _{tcr was determined} by the formula:

, (6)
where V _{f the} volume fraction of the filtrate in the drilling fluid.

An experiment performed according to the described scheme for a lime-bitumen solution showed that of the total amount of radon introduced into the solution, 80% remains in the filtrate (diesel fuel), and 20% goes into the solid phase, that is, the correction P ₁ was 0.8 for IDB. For each type of mortar used during drilling, the coefficient is re-determined.

 The effect of mass transfer of an isotope between a mobile and a stationary fluid in the pore space of the reservoir on the γ-activity readings is performed using the setup shown in Fig. 4.

 An indicator solution in the filtrate is passed through a bulk sectional model (1 4) filled with a vacuum method of a drilling fluid filtrate. In this case, the total volume of the pore space of the model is estimated. After passing a fixed volume of the indicator (equal to one pore volume of the model), samples of the bulk medium from each section are taken in cuvettes of the same volume and measured at the installation. For the analysis, the ratio of intensity from each section to its maximum value is taken. The obtained curves (Fig. 5) show that after passing one pore volume of the indicator fluid through the model, the distribution of the radioactive substance along the length of the model, its uneven concentration decreases to the output part of the model. Studies show that the difference between a real displacement process and a piston one is explained by the redistribution of a radioactive substance from a moving carrier into a motionless liquid film on the solid phase of the rock. This process can lead to an overestimation of the value of dynamic porosity compared to its actual value. Overstatement can be large (2-30 times) if the distribution coefficient of the radioactive substance in the mobile liquid is many times greater than in the stationary liquid forming a film on the surface (for example, for an aqueous solution of an indicator).

(7)
где I_о, С_о максимальные значения интенсивности и концентрация индикатора по слоям модели (в данном случае С_о начальная концентрация R_н);
I_i, С_i интенсивность и концентрация индикатора в i-том слое модели.The correction P ₂ for the mass transfer of the indicator from the moving fluid to the still fluid is determined by the formula:

(7)
where I _about , With _{about the} maximum values of the intensity and concentration of the indicator in the layers of the model (in this case, With _{about the} initial concentration R _n );
I _i , C _{i the} intensity and concentration of the indicator in the i-th layer of the model.

(8)
а
F(I_i/I_o) = (b₁+b₂+1)•exp(-μδ_пX), (9)
где а₁, а₂, b₁, b₂ коэффициенты, зависящие от физико-химических свойств индикаторной жидкости и пластового флюида, определяемые экспериментально с помощью модели (рис.4);
μ массовый коэффициент поглощения g-излучения
Х толщина слоя модели до i-того.Function

(8)
a
F (I _i / I _o ) = (b ₁ + b ₂ +1) • exp (-μδ _пX ), (9)
where a ₁ , a ₂ , b ₁ , b _{2 are} coefficients depending on the physicochemical properties of the indicator fluid and reservoir fluid, determined experimentally using the model (Fig. 4);
μ mass absorption coefficient of g-radiation
X layer thickness of the model to i-th.

It was experimentally established that within the limits of change in fractions of the bulk model 0.1 3 mm, the values of the correction P ₂ change little, ceteris paribus.

Elementary active volumes are determined for each geophysically homogeneous element and productive stratum (layer) according to the formula:
V _ea K _gi • h _i , (10)
where h _{i is the} effective thickness of the reservoir, determined according to the indicator method in a known manner. Summing up in the well the elementary specific active volumes included in the counting object (well), determine the specific active volume for this well.

на среднее значение плотности нефти и пересчетного коэффициента.Potential active hydrocarbon reserves are determined by multiplication

on the average oil density and conversion factor.

 All of the above is confirmed by the example that is attached to the application materials.

 The economic efficiency from the application of the proposed method is determined by the fact that with a more accurate assessment of oil and gas reserves, their distribution by volume of deposits is more accurately established. This avoids the additional cost of drilling unreasonably designed production wells and ensures a rational development mode, which will lead to increased oil recovery.

Example
In the well. 4T, the radon indicator method (IMR) was carried out in order to determine the potential (linear) reserves of productive deposits in the interval 5019.0-5247.0 m.

The studied (deposits) formations are represented by carbonate differences of Carboniferous age, clean of clay material, dense, fractured. The porosity values determined by the GIS complex vary from 1.9 to 4.7%
Indicator studies were carried out using the following technology (in accordance with the stated proposal):
Radon in the amount of 15 MKi was introduced into the study interval by a series of operations by dissolving it in 2.5 m ^{3 of} drilling mud filtrate (in diesel fuel), by portion injection of this volume in a mixture with lime-bitumen solution (IDB) with CA / 320 aggregate (0, 5 m ³ indicator, 1 m ₃ IDB) to obtain a uniform distribution of the indicator in the study interval by selling drill pipe along the string in the study interval (volume 44 m ³ ). After removing the GK distribution of radon in the research interval with the drill pipes raised (above the research interval), the drilling tool was paced in the research interval (30 times per candle) to form a zone of penetration of the activated filtrate into the reservoir. As experience with a radon indicator showed, this method is the most universal and it is possible to achieve indicator penetration even into low-capacity (low-permeability) reservoirs (Abstract of dissertation for the degree of candidate of technical sciences "Development of a method for determining the filtration-capacitive properties of permeable formations by the radon indicator method" Kilyakov V .N. M. 1990, 25 pp.). By injecting 30 cm ^{3 of the} solution through the drill string, the labeled solution that did not penetrate into the strata was displaced above the test interval. GK was measured on the productive part of the section. By injecting 30 m ^{3 of the} solution into the annulus, the indicator was returned to the research interval and the above operations were performed to sell the indicator into the reservoirs. Flushing the research interval from residual radon is combined with the injection of inactive diesel fuel in the research interval. After measuring the indicator GK, the boring tool was paced in the same mode as during sales (with the same speed of descent, ascent).

 The third indicator measurement allows you to judge the displacement of the indicator inactive fluid inland.

 The obtained indicator curves are shown in Fig. 6 for the section of the studied interval.

Consideration of the results of the studies in combination with other geophysical methods of oil and gas exploration (NSC), HF core studies makes it possible, according to the algorithm described in the application, to evaluate the values of dynamic porosity (Table 1). Moreover, the depth of penetration of the indicator into the strata at the first selling was estimated by the results of two sales (1,2) and one pushing (3) of the indicator deep into the strata (Table 1) and theoretical curves. In order to clarify the obtained values of dynamic porosity, we carried out a number of laboratory determinations to assess the effect of mass transfer (formula) in the application - coefficient P ₂ ). Moreover, for the case of filtering diesel fuel into an oil-saturated reservoir, coefficient a ₁ 0.87; and ₂ 0.42.

Amendment P ₁ (formula 5) was also determined experimentally using the setup described above. It amounted to 0.8 for the IBR solution.

The volume method has been used to calculate reserves for each i-th interval), for which one value K _{p is} taken from the GIS and three calculation parameters are estimated: effective thickness h _i , porosity K _pi , oil saturation K _ni and, accordingly, the elementary specific volume of oil-saturated pores is calculated.

V _en K _pi • h _i • K _ni , (11)
The total in the well elementary specific volumes of oil-saturated pores for all intervals included in the counting object determines the specific volume of oil-saturated pores in this well
V = ΣK _{un pi} • h _i • K _HI, (12)
Then, according to the counting object, a map of equal specific volumes of oil-saturated pores is constructed.

 The initial balance reserves of oil are determined by multiplying the total oil-saturated volume by the average value of the oil density and the conversion factor.

 Recoverable reserves are determined by multiplying the balance sheet reserves by the extraction coefficient (β).

 For the well under consideration, the elementary specific volumes of oil-saturated pores were calculated and summed.

(16)
Рассчитанный коэффициент нефтеотдачи согласуется с величиной β, принятого для данного месторождения (β 0,417).V _o.n. = ΣK _pi • h _i • K _нi = 5.3696, (13)
Using the data of the gamma indicator method, we determine the dynamic porosity of each layer and the elementary specific active volume by the formula
V _ea K _gi • h _i , (14)
Summing up the elementary specific active volumes, we determine the specific active volume for this well
V _u.a. = ΣK _gi • h _i = 2.1615, (15)
The marginal (physical) oil recovery coefficient for this well is

(16)
The calculated oil recovery coefficient is consistent with the value of β adopted for a given field (β 0.417).

 Recoverable reserves are determined by multiplying the balance reserves by the displacement coefficient, which can be determined either on core samples of a given field, or according to the results of trial operation or by analogy with a similar field.

 The following fact speaks about the efficiency of the method and its higher reliability compared to the standard one: according to the standard method, the recoverable reserves were calculated by the standard method, which amounted to 16 million tons of oil, while the oil saturation coefficient was adopted for core 0.9, and the coefficient crowding out 0.7.

 During the operation of the field, only 6 million tons were recovered. At the same field, our proposed method for studying productive formations was applied at the drilling (exploration) stage.

 The estimated potential (active) reserves using dynamic porosity amounted to about 6.7 million tons of oil, which differs from actually recovered by only 10%

Claims (1)

 A method for assessing the active volume of oil-saturated pores in productive formations, including measuring background gamma activity, injecting drilling fluid saturated with an indicator twice, pushing it into the formations and pushing them into the formations with measurements of gamma radiation intensity after each operation, determining the effective thickness and dynamic porosity of formations and determining the pore volume from the measurement results, characterized in that, in order to increase the reliability of the assessment of active hydrocarbon reserves, a sample of the injected of the new mud, defend it, determine the distribution coefficient of the indicator in the liquid and solid phases of the drilling fluid, calculate the correction for the redistribution of the indicator between them, make a bulk multisection collapsible model of the formation, determine the total porosity of the model, saturate it with an inactive mud filtrate, displace it with the mud filtrate saturated with an indicator in a volume equal to one pore volume of the model, disassemble it layer by layer in the direction from top to bottom, measure the intensity ha mma radiation from each layer, determine the dependence of measuring the relative intensity of indicator gamma radiation on the depth of its penetration into the model depth, find a correction to the dynamic porosity parameter for mass transfer of the indicator between the mobile and stationary liquid phases in the pore space of the permeable formation, drilling mud flow in the well saturated with the indicator, is carried out in one mode, the displacement of the drilling fluid saturated with the indicator deep into the reservoir, is carried out with an inactive mud filtrate pa, find a correction to the dynamic porosity parameter for the depth of penetration of the indicator into the formation and, based on the results, correct the previously determined value of the dynamic porosity of the formations, taking into account the corrections for the effect of redistribution of the indicator between the solid and liquid phases of the drilling fluid, determined as a result of the study of the sample taken from the well, between moving and stationary parts of the fluid in the pore space of the reservoir, and the depth of penetration of the indicator into the reservoir, determined as a result of the study based on a collapsible model, and the volume of oil-saturated pores is determined as the sum of the products of the adjusted dynamic porosity and effective thickness for each counting object.

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