RU2143065C1 - Method of prognostication of condensate content in formation gas and its cumulative recovery for pools with high content of condensate - Google Patents

Abstract

FIELD: oil and gas producing industry. SUBSTANCE: method includes sampling of separation gas and wet condensate; experimental determination of formation losses of condensate by investigation of phase behavior of formation gas sample on laboratory plants and prognostication of condensate change in formation gas by calculation. Investigations are carried out for determination of dependence of formation pressure on withdrawal of dry gas content of gas components in degassed condensate found in laboratory plant in composition of precipitating wet condensate. The entire period of deposit development is divided into period of operation beginning from initial formation pressure to pressure of beginning of condensation and into period of operation beginning from pressure of beginning of condensation to pressure of 0.101 MPa with change of condensate content in formation gas. The second period is divided into stages. Volumes of dry gas at the end of each stage are determined by formula. EFFECT: higher accuracy of prognostication of condensate content on formation gas. 2 cl, 2 dwg, 1 tbl

Description

 The invention relates to the oil and gas industry, in particular, to methods for designing development of fields with a high condensate content in the formation gas, and can be used in the development of gas condensate deposits with a high condensate content.

 A known method for predicting the condensate content and its total production, including the experimental determination of reservoir condensate losses at pVT units and a calculation method for predicting changes in the condensate content in the reservoir gas and its production during development at the depletion mode at the stage of exploration of the reservoir [1].

 The disadvantage of this method, taken as a prototype, is that it does not take into account the peculiarities of the phase behavior of gas condensate systems with a high condensate content. The method for predicting the current instruction is based on the condition that the dependence of reservoir pressure is straightforward. In fact, this condition is not fulfilled. This is the first assumption that is not acceptable for high condensate gas condensate systems.

 Another disadvantage of the method is that the condensate content prediction formula is valid only for saturated deposits (the pressure of the onset of condensation is equal to reservoir), and for deep deposits with a high condensate content, it can be justifiably stated that at least 50% of them are unsaturated. The difference between the reservoir pressure and the pressure of the onset of condensation affects the distribution of condensate in the reservoir and in the produced products, and therefore the conditions for predicting the condensate content in the reservoir gas and its production during development.

 The objective of the invention is to improve the accuracy of predicting the condensate content in the reservoir gas and its total production for design development in the depletion mode of deposits with a high condensate content. The problem is solved in that in a method for predicting the condensate content in the formation gas and its total production, including sampling the separation gas and crude condensate, creating a recombined formation gas sample from them, experimentally determining the formation condensate losses by modeling the development of the reservoir in the pVT installation, experimental studies of a recombined formation gas sample at the pVT installation to determine the dependence of formation pressure on relative dry gas withdrawals . Predicted values of reservoir pressure are determined not by conditionally accepted straight-line dependence, but by graphical dependence for a specific reservoir, constructed on the basis of experimental data of differential condensation of a recombined reservoir gas sample of the reservoir under study.

 The problem is also solved by the fact that they additionally determine the content of gas components in the degassed condensate located in the pVT chamber as a part of the crude precipitated condensate, and amend the reservoir condensate losses.

(1)
где

относительный отбор сухого газа из залежи при снижении давления в ней от начального до давления в конце m-го этапа;

- относительный отбор сухого газа при снижении давления от начального до давления начала конденсации; n - число этапов; m - порядковый номер этапа (0, 1, 2... n);

- относительный объем сухого газа, отобранного при снижении давления от начального до давления начала конденсации

и остающийся в пласте при снижении давления до 0,101 МПа в газовой фазе и растворенном состоянии (

).The problem is also solved by the fact that the entire development period of the reservoir is divided into a period of operation from the initial reservoir pressure to the pressure of condensation onset and a period of operation from the pressure of condensation onset to 0.101 MPa, with only the second period being divided into n stages, and the relative dry gas withdrawals at the end each stage is determined by the formula

(1)
Where

relative selection of dry gas from the reservoir with a decrease in pressure in it from the initial to the pressure at the end of the mth stage;

- relative selection of dry gas with a decrease in pressure from the initial to the pressure of the beginning of condensation; n is the number of stages; m is the sequence number of the stage (0, 1, 2 ... n);

- the relative volume of dry gas taken when the pressure decreases from the initial to the pressure of the beginning of the condensation

and remaining in the reservoir with a decrease in pressure to 0.101 MPa in the gas phase and in the dissolved state (

)

где q_к.п.г ^o начальное содержание конденсата в пластовом газе, г/м³; q_к.п.г ^m - содержание конденсата в пластовом газе в конце m-го этапа (m=1, 2. ..n), г/м³; q_к.п.к ^m - пластовые потери конденсата в конце m-го этапа, г/м³.The problem is also solved in that the condensate content in the reservoir gas for the undersaturated reservoir is determined by the formula

where q _kpg ^{o the} initial condensate content in the reservoir gas, g / m ³ ; q _c.p.g ^m - the condensate content in the reservoir gas at the end of the m-th stage (m = 1, 2. ..n), g / m ³ ; q _cpc ^m - reservoir condensate losses at the end of the m-th stage, g / m ³ .

где q $\genfrac{}{}{0ex}{}{\text{m}}{\text{Σк.п.г}}$ - суммарная добыча конденсата в составе пластового газа, извлеченного из пласта к концу m-го этапа, г/м³.The problem is also solved in that the total production of condensate in the composition of the reservoir gas extracted from the reservoir is determined by the following formula

where q $\genfrac{}{}{0ex}{}{\text{m}}{\text{Σk.p.g}}$ - the total production of condensate in the composition of the reservoir gas extracted from the reservoir by the end of the m-th stage, g / m ³ .

(4)
где

- относительный отбор сухого газа из залежи при снижении давления в ней от начального до давления в конце m-го этапа; m - порядковый номер этапа;

относительный объем газа, остающегося в пласте в газовой фазе и растворенном состоянии при давлении 0,101 МПа.For a saturated reservoir, the problem is solved in that the entire development period is divided into n stages, and the relative dry gas withdrawals at the end of each stage are determined by the formula

(4)
Where

- the relative selection of dry gas from the reservoir with a decrease in pressure in it from the initial to the pressure at the end of the m-th stage; m is the sequence number of the stage;

the relative volume of gas remaining in the reservoir in the gas phase and dissolved state at a pressure of 0.101 MPa.

где q_к.п.г ^m - содержание конденсата в пластовом газе, г/м³.The problem is also solved by the fact that in the case of forecasting for a saturated reservoir, the prediction of the condensate content in the reservoir gas is determined by the formula

where q _c.p. ^{m m} is the condensate content in the reservoir gas, g / m ³ .

(6)
где q_к.п.г ^m - суммарная добыча конденсата в составе пластового газа, извлеченного из пласта к концу m-го этапа, г/м³.The problem is also solved by the fact that the total production of condensate in the composition of the reservoir gas extracted from the reservoir for a saturated reservoir is determined by the formula

(6)
where q _c.p.g ^m is the total production of condensate in the composition of the reservoir gas extracted from the reservoir by the end of the m-th stage, g / m ³ .

построенной на основании экспериментальных данных дифференциальной конденсации пластового газа.Distinctive features of the claimed invention are the following:
1. Conduct a study of the recombined formation gas sample at the pVT installation to determine the dependence of the reservoir pressure on the relative dry gas withdrawals, and the predicted value of the reservoir pressure is determined by the graphical dependence

constructed on the basis of experimental data of differential condensation of the reservoir gas.

 2. Additionally, the content of gas components in the degassed condensate deposited in the pVT chamber is determined, and corrections are made in the calculation of reservoir condensate losses.

 3. The reservoir development period is divided into the reservoir development period from the initial reservoir pressure to the start condensation pressure and the development period from the beginning of the condensation pressure to 0.101 MPa, and this period is divided into n stages, and the relative dry gas withdrawals at the end of each stage of the development period are determined by formula above.

 4. The material balance equations for saturated and undersaturated deposits, which are used to calculate the desired predicted indicators.

 The above significant distinguishing features were not known to us from the patent and scientific and technical information, and we believe that they are "new." These essential features are not obvious to the average person skilled in the art and therefore meet the criterion of "inventive step".

 The invention has successfully passed laboratory and field tests, and in this regard, we believe that the invention meets the criterion of "industrial applicability".

 A method for predicting the condensate content in the reservoir gas and its total production for designing development on the depletion mode of deposits with a high condensate content will be shown using an example of a well study. 74 of the West Sopless gas condensate field.

When conducting field studies, samples are taken of the separation gas and crude condensate. The initial reservoir pressure (p ₀ ) at this time is 45.0 MPa.

Для этого загружают в камеру pVT газ сепарации, затем, в соответствии с замеренным на промысле удельным содержанием, загружают в камеру pVT сырой конденсат. Приводят камеру pVT к начальным пластовым условиям по температуре и давлению. После перемешивания убеждаются, что вся жидкая фаза полностью растворилась в газе. Затем моделируют процесс разработки залежи на режиме истощения методом дифференциальной конденсации, при котором снижение давления производят за счет отбора газовой фазы при сохранении постоянными температуры и объема, при этом выпуск газа производят поэтапно. На каждом этапе снижают давление за счет увеличения объема камеры pVT и после установления фазового равновесия (интенсивного перемешивания и выдержки) производят выпуск газовой фазы при постоянном давлении до момента, когда объем рабочей камеры не станет равным первоначальному. Затем производят очередное снижение давления. Выпуск газа в газометр производят через минусовую ловушку. Причем ловушку после каждого опыта подогревают до плюс 35^oC, а газ направляют в газометр.The study of the phase behavior of reservoir gas is carried out from experience in determining the dependence of reservoir pressure on relative gas withdrawals

To do this, the separation gas is loaded into the pVT chamber, then, in accordance with the specific content measured at the field, crude condensate is loaded into the pVT chamber. The pVT chamber is brought to the initial reservoir conditions in temperature and pressure. After mixing, make sure that the entire liquid phase is completely dissolved in the gas. Then, the reservoir development process is simulated using the depletion method by differential condensation, in which the pressure is reduced by taking the gas phase while keeping the temperature and volume constant, while the gas is released in stages. At each stage, the pressure is reduced by increasing the volume of the pVT chamber and after establishing phase equilibrium (intensive mixing and holding), the gas phase is released at constant pressure until the volume of the working chamber becomes equal to the original. Then produce another decrease in pressure. The gas is released into the gas meter through a minus trap. Moreover, the trap after each experiment is heated to plus 35 ^o C, and the gas is sent to a gasometer.

 After measuring the gas volume in the gas meter, its composition is determined by the chromatographic method, the mass of the liquid phase is determined by the weight method, and then the composition of the liquid phase is determined by the chromatographic method.

 Based on the results of the qualitative and quantitative characteristics of the gas and condensate released in the trap, the volume and composition of dry gas are calculated. Then, the process of differential condensation of the recombined sample is divided into 6-10 stages in terms of gas production and the following experiments are carried out in a similar way. First of all, at the beginning of the experiment, the first period in the behavior of the formation gas during the development of the reservoir in the depletion mode is determined: the development of the reservoir from the initial pressure to the pressure of the beginning of condensation. When the pressure is reduced by visual method, the pressure of the onset of condensation is determined. When the pressure decreases slightly below the pressure of the onset of condensation, the experiment is terminated, gas is measured in the gas meter and condensate is measured in the trap.

(см. фиг. 1) выделяют этап разработки при снижении давления от начального до давления начала конденсации:

(нулевой этап). Давление начала конденсации было установлено равным 34,2 МПа (см. фиг. 1). При этом давлении относительный отбор сухого газа составляет 0,035. Оставшийся период разработки делят на 10 равных частей по отбору газа. Значение отборов к концу каждого этапа определяют по формуле (1).Based on the results of the studies, the dependence of the reservoir pressure content on the relative gas withdrawals is constructed (see Fig. 1). After that, a series of studies is carried out to determine the reservoir loss of condensate, and the composition of the degassed condensate released in the pVT chamber is determined. The results of studies to determine reservoir losses are shown in the table and in FIG. 2, curve 1. In the dependency graph

(see Fig. 1) distinguish the development stage with a decrease in pressure from the initial to the pressure at the beginning of condensation:

(stage zero). The condensation onset pressure was set to 34.2 MPa (see FIG. 1). At this pressure, the relative dry gas recovery is 0.035. The remaining development period is divided into 10 equal parts for gas sampling. The value of the selections at the end of each stage is determined by the formula (1).

определяют значение пластового давления к концу каждого этапа. Результаты расчетов приведены в таблице.According to the schedule of dependence

determine the value of reservoir pressure at the end of each stage. The calculation results are shown in the table.

_{Using the} q _qpc = f (p _pl ) dependency graph, the value of reservoir losses by the end of each stage is determined and the predicted dependence of the condensate content in the formation gas is determined by formula (2), and the predicted dependence of the total condensate production on formula (3) reservoir.

 For this example, the calculation results are shown in the table and in FIG. 2 (curves 2, 3).

 The claimed invention in comparison with the prototype allows you to take into account the peculiarities of the phase behavior of gas condensate systems with a high content of condensate deposits and to increase the reliability of the forecast of the condensate content in the reservoir gas and its total production as a part of the produced gas when designing the development of deposits in the depletion mode.

Literature
1. Instruction for a comprehensive study of gas and gas condensate reservoirs and wells. - M .: Nedra, 1981, p. 301.

Claims (2)

1. A method for predicting the condensate content in formation gas and its total production during the design process for developing a gas condensate field for deposits with a high condensate content, including sampling separation gas and crude condensate, experimental determination of formation condensate losses by studying the phase behavior of a recombined formation gas sample in plants pVT and forecasting changes in the condensate in the reservoir gas for the entire development period by the calculation method, characterized in that о conduct research on a recombined sample at the pVT unit to determine the dependence of reservoir pressure on relative dry gas withdrawals

determine the content of gas components in the degassed condensate located in the pVT chamber as a part of the precipitated crude condensate, and amend the reservoir loss of condensate, and to predict the desired parameters of the undersaturated reservoir during the design process, the entire period of development of the gas condensate field is divided into the period of operation from the initial reservoir pressure to pressure of the beginning of condensation and for the period of operation from the pressure of the beginning of condensation to a pressure of 0.101 MPa when the content of the condens the condensate in the reservoir gas, while only the second period is divided into n stages, and the relative volumes of dry gas at the end of each stage are determined by the formula 1

Where

relative selection of dry gas from the reservoir with a decrease in pressure in it from the initial to the pressure at the end of the mth stage;
m is the sequence number of the stage of the second development phase;

relative selection of dry gas from the initial pressure to the pressure of the beginning of condensation;

the relative volume of dry gas taken when the pressure decreases from the initial to the pressure of the beginning of the condensation;
the condensate content for the undersaturated reservoir gas is determined by the formula 2

where q $\genfrac{}{}{0ex}{}{\text{m}}{\text{c.p.}}$ - the condensate content in the reservoir gas at the end of the m-th stage (1, 2 ..., m, ... n), g / m ³ ;
n is the total number of stages;
q $\genfrac{}{}{0ex}{}{\text{°}}{\text{c.p.}}$ - the initial content of condensate in the reservoir gas, g / m ³ ;
q $\genfrac{}{}{0ex}{}{\text{m}}{\text{c.p.}}$ - reservoir condensate losses at the end of the m-th stage, g / m ³ ;
while the total production of condensate in the composition of the reservoir gas extracted from the reservoir is determined by the formula 3

where q $\genfrac{}{}{0ex}{}{\text{m}}{\text{Σk.p.g}}$ - the total production of condensate in the composition of the reservoir gas extracted from the reservoir by the end of the m-th stage, g / m ³ . 2. The method according to claim 1, characterized in that for a saturated reservoir the whole period is divided into n stages, and the relative dry gas withdrawals at the end of each stage are determined by formula 4

Where

relative selection of dry gas from the reservoir with a decrease in pressure in it from the initial to the pressure at the end of the mth stage;
m is the sequence number of the stage;

the relative volume of gas remaining in the reservoir in the gas phase and dissolved state at a pressure of 0.101 MPa;
the condensate content in the reservoir gas for a saturated reservoir is determined by the formula 5

and the total production of condensate in the composition of the reservoir gas extracted from the reservoir is determined by the formula

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