RU2043488C1 - Method for development of viscous oil pool - Google Patents

Abstract

FIELD: oil producing industry. SUBSTANCE: method for development of viscous oil pool includes determination of foaming capacity of degassed oil by passing gas through oil under formation conditions. Determined results are used to calculate ratio of injection volumes of gas and water by respective formula. EFFECT: higher efficiency.

Description

 The invention relates to the oil industry, in particular, to methods for developing oil fields.

 There is a method of developing an oil deposit by injecting the rims of the solvent and dry gas in a ratio that ensures the liquid state of the mixture in reservoir conditions, in the amount of 30-60% of the pore volume [1] Then, water is pumped as a pushing agent until water breaks into production wells, after which injects gas and water in the amount of 5-10% of the pore volume before the gas breaks into production wells.

 The disadvantage of this method is the need to use a solvent, as well as the decomposition of viscous oil under the influence of a solvent into two components: the lightest part of a viscous oil, which dissolves in a solvent and does not dissolve in a solvent, a solid or semi-solid precipitate consisting of heavy fractions of oil, paraffin, resins and asphaltenes, as well as rapid breakthrough of gas in a heterogeneous formation.

 Closest to the invention in technical essence and the achieved result is a method of developing oil deposits by pumping into injection wells alternating rims of gas and water and oil selection from production wells [2] (prototype).

 As a rule, the ratio of injected volumes of gas and water is assumed to be equal to unity.

 The disadvantage of this method is a slight increase in the oil recovery coefficient (5-7%) under the condition of immiscible displacement.

, где β соотношение закачиваемых объемов газа и воды в пластовых условиях, безразмерная величина;
r пенообразующая способность (кратность пены) дегазированной нефти при пропускании через нее закачиваемого газа в пластовых условиях, безразмерная величина;
b объемный коэффициент нефти, обусловленный растворением в ней закачиваемого газа, безразмерная величина;
ΔG растворимость закачиваемого газа в нефти, выраженная в м³ газа в пластовых условиях, растворяющихся в 1 м³ пластовой нефти, безразмерная величина;
m_н нефтенасыщенность коллектора, безразмерная величина.The aim of the invention is to increase oil recovery of formations containing viscous oil, by preventing gas breakthroughs. This goal is achieved by the fact that in the method of developing an oil deposit, including the injection of alternating rims of gas and water into the injection wells and the selection of oil from the producing wells, the foaming ability of the oil (the multiplicity of the foam) is determined prior to the injection of the rims of gas and water when passing through it displacing gas in reservoir conditions, and the ratio of injected volumes of gas and water in reservoir conditions is determined by the formula:
β =

where β is the ratio of injected volumes of gas and water in reservoir conditions, dimensionless quantity;
r foaming ability (multiplicity of foam) of degassed oil when passing injected gas through it under reservoir conditions, dimensionless quantity;
b volumetric coefficient of oil, due to the dissolution of the injected gas in it, dimensionless quantity;
ΔG is the solubility of the injected gas in oil, expressed in m ^{3 of} gas under reservoir conditions, dissolving in 1 m ^{3 of} reservoir oil, dimensionless quantity;
m _n reservoir oil saturation, dimensionless quantity.

It is known that water-gas treatment is generally not recommended for oil reservoirs containing oil with a density of more than 850 kg / m ³ , a viscosity of more than 10 cPs with a resin and asphaltene content of more than 10-15%. However, studies have shown that oil with a viscosity of more than 10-20 cPs and resins and asphaltenes content of more than 10-15% in a certain temperature range have the ability to foam when gas passes through them. At the same time, gas in the form of tiny bubbles is occluded in the oil, increasing its volume. This property of oil has not yet been used for gas and water-gas exposure.

 The aim of the invention is to increase oil recovery by using this effect by preventing gas breakthroughs.

In the proposed method for developing viscous oil deposits by means of gas-water treatment, the ratio of injected volumes of gas and water is selected so that all injected gas in the first exposure period is dissolved and occluded in the oil. For this purpose, the foaming ability (multiplicity of the foam) of the oil as it passes through the displacing gas under reservoir conditions is preliminarily evaluated. Based on the value of the foam multiplicity under these conditions, which characterizes the degree of increase in oil volume due to the displacing gas occluded in it, and the solubility of this gas in oil, expressed in m ^{3 of} formation gas, dissolving in 1 m ^{3 of} formation oil, the ratio of injected gas volumes is estimated and water. Experimental studies have shown that the process of such displacement leads to the fact that viscous oil increases significantly in volume, mobility increases, the oil displacement coefficient increases, and since there is practically no free gas in the first period of development, the period of pre-breakdown oil displacement by gas increases.

 Examples of specific implementation of the method.

The studies were carried out on a linear model of a bulk porous medium with a length of 50 cm, a diameter of 3.5 cm, and a permeability of 0.8 μm ² .

Предварительно проводилась оценка с помощью камеры высокого давления со смотровыми стеклами вспенивающей способности (кратности пены) вязкой нефти Мордово-Озерского месторождения. Такая оценка проводилась при температуре 38^оС и давлении 12,5 сПз. Через камеру, заполненную на 1/3 нефтью, пропускали газ (азот). Кратность пены для Мордово-Озерской нефти составила r=1,2, объемный коэффициент для этой нефти за счет растворения в ней азота составил по расчету 1,02.As a viscous oil, oil of the Mordovo-Ozersky field with a viscosity of 150 cPs was taken. The ratio of volumes of injected rims was determined by the expression
β =

A preliminary assessment was made using a high-pressure chamber with sight glasses of the foaming ability (multiplicity of foam) of viscous oil of the Mordovo-Ozerskoye field. This evaluation was carried out at a temperature of 38 ^{° C} and a pressure of 12.5 cps. Through the chamber, 1/3 filled with oil, gas (nitrogen) was passed. The foam multiplicity for Mordovo-Ozerskaya oil was r = 1.2, the volumetric coefficient for this oil due to the dissolution of nitrogen in it was 1.02 as calculated.

The solubility of nitrogen in the Mordovian-Ozerskoye oil amounted to 9 st <% - 2> cdot <% 0> m ³ / m ^{3 of} oil or Δ G = 0,082 m ^{3 of} gas in reservoir conditions per 1 m ^{3 of} reservoir oil. The oil saturation of the formation was 0.75.

The sizes of the gas rims amounted to 0.024, and water 0.1. The experiment was carried out at a pressure of 12.5 MPa and t = 38 ^o C.

Results:
Displacement coefficient during pumping of 3 pore volumes 0.75
Injection volume during gas breakdown 0.92 pore
volume
For comparison with the prototype, the same oil was displaced by alternating rims of gas and water with a ratio of their volumes in reservoir conditions equal to unity. The experimental conditions were the same P = 12.5 MPa and t = 38 ^o C. The dimensions of the rims were 0.1 pore volume. Nitrogen was used as gas.

Experimental results: Oil displacement coefficient 0.63. Injection volume during gas breakdown 0.71 pore
volume
For comparison with the process of displacing Newtonian oils, which do not foam when displaced by gas, an experiment was carried out to displace oil with a viscosity of 17 cPs (transformer oil was used as an oil model) with gas and water rims with a ratio of 1. The rim sizes were 0.1.

Experiment Results:
Displacement ratio
when pumping 3 pore volumes of 0.55
Injection volume during breakdown of 0.51 pore gas
volume
The results of the 1st experiment are superior to the results of the 2nd experiment (comparison with the prototype). At the same time, the advantage of the present invention compared to the prototype is an increase in oil recovery by 15%. Comparison of the 1st experiment with the 3rd experiment shows that for oils that do not have foaming ability in the mode of immiscible displacement, the results are much worse. The oil displacement coefficient is lower than in the present invention by 27%

Claims (1)

METHOD FOR DEVELOPING VISCOUS OIL DEPOSITS, including the injection of alternating rims of gas and water into injection wells, and the selection of oil from production wells, characterized in that the foaming ability of the oil is determined prior to injection of the rims of gas and water when the injected gas is passed through it under reservoir conditions, and the ratio of injected volumes of gas and water in reservoir conditions is determined in accordance with the expression

where β is the ratio of injected volumes of gas and water in reservoir conditions;
r the foaming ability of oil (the ratio of the foam) when passing injected gas through it;
b volumetric coefficient of oil due to the dissolution of the injected gas in it;
DG is the solubility of the injected gas in oil, expressed in m ^{3 of} gas under reservoir conditions, dissolving in 1 m ^{3 of} reservoir oil;
m _n reservoir oil saturation.