CN110162878B - Method for determining lower limit of crude oil filling pore throat of tight reservoir - Google Patents
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Abstract
The invention relates to a calculation method in the field of petroleum geology research, in particular to a method for determining the lower limit of a crude oil filling pore throat of a tight reservoir, which comprises the following steps: (1) Based on the relation between the power and the resistance in the filling process, when the residual pressure P is equal to the capillary force Pc, the lower filling limit is reached; (2) And calculating and determining the lower limit of the filling pore throat of the crude oil according to a balance relation of power and resistance in the filling process. The invention deepens the understanding of the mechanism of filling the compact oil, supplements the geological theory of the compact oil reservoir formation, and provides an effective means for predicting the distribution range of the compact oil, thereby having great guiding value and wide application prospect in the current and future unconventional oil and gas exploration fields.
Description
Technical Field
The invention relates to a calculation method in the field of petroleum geology research, in particular to a method for determining a compact reservoir interface of an oil-gas-containing basin and a lower limit of a filling pore throat of crude oil in a reservoir by means of a basin numerical simulation method.
Background
Dense oil is an important exploration field of current and future oil and gas resources, and the accumulation mechanism of the dense oil, such as a filling mechanism, a seepage mechanism, an occurrence mechanism and an aggregation mechanism, is not clearly known. The lower limit of the filling pore throat of the dense oil and the change of the lower limit of the filling pore throat in the process of accumulation are the primary problems to be solved. The pore throat filling lower limit is the minimum physical boundary of the oil and gas to overcome migration resistance under specific geological conditions so as to fill the reservoir in the oil and gas reservoir forming process. Thus, different reservoir conditions have different pore throat filling lower limits that vary during the reservoir evolution even under specific reservoir conditions.
The research institute Zou Cai of petroleum exploration and development can add the thickness of the bound water film and the maximum diameter (4 nm) of the asphalt molecules to calculate that the pore throat lower limit of the compact oil reservoir is 54nm, and a calculation model is shown in figure 1, wherein B in figure 1 is a local section of A in figure 1, (a) is the critical pore throat radius of 54nm, (B) is the pore throat diameter of 200nm, and (c) is the average thickness of the bound water film of 50nm. The estimation method adopting the summation of the thickness of the bound water film and the diameter of the oil molecule is simple, convenient and quick, and can obtain an approximate lower limit of pore throat. However, this method is limited to static descriptions, departs to some extent from actual geological conditions and hydrocarbon reservoir conditions, and fails to account for changes in the lower fill throat limit during crude oil filling. The lower filling pore throat limit and the change of the filling pore throat limit in the crude oil filling process are determined by the balance condition of power and resistance, and are comprehensively influenced by a plurality of factors such as the intrinsic characteristics of a reservoir stratum, the characteristics of source rocks, the properties of the crude oil, the burial depth and the burial history.
According to the statistical relationship between the residual oil content and the average pore diameter, the medium petroleum exploration and development institute Cui Jingwei and the like think that the filling lower limit of the seven-segment compact oil of the extended group length of the Ordos basin is about 15nm. This example statistics demonstrates that the lower dense oil filling pore throat limit can be smaller, unlike the theoretical value that Zou Cai can yield, etc. However, the method is completely based on the statistical relationship between the aperture and the residual quantity, on one hand, the statistical data points are too few to reflect the actual geological condition, and on the other hand, the limit values of the oil-containing layer and the non-oil-containing layer are determined based on the mutation points on the statistical relationship and lack of geological basis.
The physical simulation experiment of dense oil reservoir formation such as China university of Petroleum (Beijing) Wu Kangjun and the like obtains that the lower limit of the filling pore throat of dense oil to form a large-scale oil reservoir is 0.12 mu m. The physical simulation experiment shows that the lower fill orifice throat limit is related to the source reservoir pressure differential. However, the experimental conditions of the physical simulation experiment are far from the actual geological conditions, the selected samples are not continuous, and a relationship formula with a dynamic connotation in a general sense is established on the basis of data and knowledge obtained by the physical simulation experiment, so that a more accurate lower filling limit of the pore throat can be deduced.
The relation between the water film thickness and the throat radius is established by Wang Weiming and the like of China university of Petroleum (east China) at different formation pressures, and the chart is shown in figure 2, wherein a straight line C represents that the water film thickness is equal to the pore throat diameter, an area A above the straight line C represents that the throat radius is smaller than the water film thickness, and an area B represents that the throat radius is larger than the water film thickness. And obtaining a filling porosity lower limit according to the relation between the water film thickness and the porosity. Analysis shows that when the radius of the throat is smaller than the thickness of the water film, the corresponding pore throat and the controlled micro pores are saturated by bound water, and only when the radius of the throat is larger than the thickness of the water film, the throat can become an effective filling channel for dense oil. The focus of this understanding is, however, the relationship of the water film thickness to the formation pressure, and whether the throat is fully occupied by a water film, the emphasis being on "whether there is residual space that can be filled with crude oil". In fact, there is such a residual space that the crude oil does not necessarily fill in.
Based on a filling mechanical equilibrium relationship, the research institute Zhang Hong for petroleum exploration and development obtains filling pore throats of compact oil source storage interfaces of an Ordorsi basin extension group, a Jurassic system in a Sichuan basin and a Bakken group in a West basin in the United states, wherein the lower limits of the filling pores near the storage interfaces are respectively 15.74nm, 29.06nm and 14.22nm, and the lower limits of the filling pores in a storage layer are respectively 39.45nm, 37.20nm and 52.32nm. The basic principle to which this method applies is also a charge kinetic equilibrium relationship, recognizing that the pore-throat charge lower limits at the source-reservoir interface and the reservoir interior are different, refining the knowledge of the charge mechanism. However, in this method, the conversion of both the source reservoir pressure differential and the residual pressure within the reservoir due to hydrocarbon production pressurization to maximum depth of burial is simplistic, especially in the presence of lift-and-subsidence (over time), the changes in source reservoir pressure differential and residual pressure are not simply directly correlated with depth. It is questionable that the application of formation fracture pressure without fluid pressure in the event of a formation fracture may be questionable because even if the formation fractures, the fluid pressure in the formation is present and not fully released. In addition, the selection of key parameters in the method can not obtain the change of the pore throat filling lower limit in the occlusion process, thereby causing the undersea understanding of the filling process.
Disclosure of Invention
Aiming at the defects of the prior art and the research, the invention provides a calculation method for determining the lower limit of the filling pore throat of crude oil in a reservoir interface and the reservoir based on a basin numerical simulation method and an oil-gas filling dynamic balance principle.
The invention provides a method for determining the lower limit of a crude oil filling pore throat of a tight reservoir, which comprises the following steps:
(1) Based on the relation between the power and the resistance in the filling process, when the residual pressure P is equal to the capillary force Pc, the lower filling limit is reached;
(2) And calculating and determining the lower limit of the filling pore throat of the crude oil according to a balance relation of power and resistance in the filling process.
Wherein, the balance relation of the power and the resistance in the filling process in the step (2) is as follows:
wherein, P is charging power and MPa; pc is filling resistance, namely capillary force, MPa; sigma is the gas-water interfacial tension, N/m; theta is the wetting angle, °; r is the critical pore throat radius of filling, m.
When the filling pore throat is positioned on the reservoir interface, the evolution process of the residual pressure of the reservoir interface is obtained by a basin simulation method and quantified as a function of time; when the filling pore throat is positioned in the reservoir, the residual pressure in the reservoir is calculated by a fluid state equation, and a formation temperature evolution history is obtained by using a basin simulation method, so that a quantitative expression of the residual pressure evolution in the reservoir can be obtained.
Wherein the relation of the residual pressure of the reservoir interface changing along with the time is as follows:
P S-R ＝f(t)
wherein, P S-R The residual pressure at the reservoir interface, MPa; t is time, ma.
Wherein, the lower limit of the crude oil filling pore throat of the compact reservoir interface is as follows:
wherein d is S-R Filling the reservoir interface with crude oil down the throatLimit, m, typically converted to nm; r is a radical of hydrogen S-R The crude oil filling pore throat radius, m, for the reservoir interface is typically converted to nm.
Wherein the relation of the residual pressure in the reservoir varying with the formation temperature is as follows:
wherein, P R The residual pressure inside the reservoir, MPa; p F Is the fluid pressure, MPa, inside the reservoir; p w Is the hydrostatic pressure, MPa, inside the reservoir; r = 8.3145J/(mol · K); t is the formation temperature, k; v m Is the molar volume of the crude oil, ml/mol; a =3.0346V w -5.43；B＝0.1975A 2.0679 ；α＝3.1725A 3.0456 ；β＝1.539ω+2.071；V w Is the molar volume of formation water, V w =150mL/mol; ω =0.68; rho is the density of the formation water, kg/m3; g is the gravity acceleration, and the value is 9.8N/kg; h is the formation burial depth, m.
The residual pressure inside the reservoir is mainly related to the formation temperature, the molar volume and the formation burial depth, the change of the molar volume is mainly caused by the change of components in the oil production process, a quantitative expression of the evolution of the residual pressure inside the reservoir can be obtained by utilizing the history of the evolution of the formation temperature along with time and the history of the evolution of the formation burial depth along with time, and the relational expression of the fluid pressure inside the reservoir along with the change of the formation temperature is as follows:
P F ＝f(T)＝f'(t)
wherein T is the formation temperature, k; t is time, ma;
the formation burial depth can be determined as a function of time by a basin simulation method, so the evolution process of the hydrostatic pressure is as follows:
P W ＝f”(t)；
the residual pressure inside the reservoir as a function of time is:
P R ＝P F -P W ＝f'(t)-f”(t)。
wherein, the lower limit of the filling pore throat of the crude oil in the compact reservoir is as follows:
wherein d is R Filling the lower pore throat limit, m, for the crude oil inside the reservoir, typically converted to nm; r is R The pore throat radius, m, is filled with the crude oil inside the reservoir, typically converted to nm.
The invention has the beneficial effects that: the invention discloses a method for determining a lower limit of a crude oil filling pore throat of a tight reservoir, (1) the method indicates that the lower limit of the crude oil filling pore throat is changed in the reservoir forming process and is not a fixed value; (2) the crude oil filling process is illustrated as a residual pressure decay process, and the corresponding pore throat filling lower limit is gradually increased; (3) the change characteristics of the lower pore throat filling limit are explained from the aspect of the dynamic mechanism, and a calculation formula of the lower pore throat filling limit is established. The invention deepens the understanding of the mechanism of filling the compact oil, supplements the geological theory of the compact oil reservoir formation, and provides an effective means for predicting the distribution range of the compact oil, thereby having great guiding value and wide application prospect in the current and future unconventional oil and gas exploration fields.
Drawings
FIG. 1 is a graphical representation of a derivation of the lower dense pore throat fill threshold based on adsorbed water film thickness;
FIG. 2 is a graphical depiction of the relationship of water film thickness to throat radius under different formation pressure conditions;
FIG. 3 is a graphical representation of the residual pressure at the reservoir interface as a function of time for an implementation of the present invention;
FIG. 4 is a graphical representation of formation temperature as a function of time for an implementation of the present invention;
FIG. 5 is a graphical representation of the formation burial depth as a function of time for an implementation of the present invention, wherein FIGS. 5A and 5B are corresponding schematic and graphical representations;
fig. 6 is a graph of the change in residual pressure during inflation and the corresponding lower throat fill limit for an implementation of the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings and examples.
The method for determining the lower limit of the filling pore throat of crude oil at the compact reservoir interface and in the reservoir comprises the following steps:
(1) Based on the relation between the power and the resistance in the filling process, when the residual pressure (P) is equal to the capillary force (Pc), the lower filling limit is reached;
(2) The evolution process of the residual pressure of the reservoir interface is obtained by a basin simulation method and quantified as a function of time;
the functional relationship between the residual pressure evolution of the reservoir interface obtained by the basin simulation method and the time is as follows:
P S-R ＝f(t)；
wherein, P S-R The residual pressure at the reservoir interface, MPa; t is time, ma.
In the invention, the evolution process of the residual pressure in the reservoir is obtained by a fluid state equation;
wherein, P R The residual pressure inside the reservoir, MPa; r = 8.3145J/(mol · K); t is the formation temperature, k; v m Is the molar volume of the crude oil, ml/mol; a =3.0346V w -5.43；B＝0.1975A 2.0679 ；α＝3.1725A 3.0456 ；β＝1.539ω+2.071；V w Is the molar volume of formation water, V w =150mL/mol; ω =0.68; rho is the density of the formation water, kg/m3; g is the gravity acceleration, and the value is 9.8N/kg; h is the formation burial depth, m.
The residual pressure in the reservoir is mainly related to the temperature of the stratum, the molar volume and the buried depth of the stratum, and the change of the molar volume is mainly caused by the change of components in the crude oil process, so the crude oil component change is not considered for the moment. Therefore, the evolution quantitative expression of the residual pressure in the reservoir can be obtained by utilizing the evolution history of the formation temperature along with time and the evolution history of the formation burial depth along with time.
As shown in fig. 4, the formation temperature may be determined by basin simulation method as the evolution process:
T＝f'(t)；
wherein T is the formation temperature, k; t is time, ma.
As shown in fig. 5, the stratum burial depth can be determined by the basin simulation method as follows:
h＝f”(t)；
the function relationship between the residual pressure in the reservoir and the time is as follows:
P R ＝f(T)-ρgh＝f'(t)-f”(t)；
the capillary force is
Wherein, sigma is the gas-water interfacial tension, N/m; theta is the wetting angle, °; r is the critical pore throat radius, m;
the pore throat fill lower limit of the reservoir interface of one of the present invention is:
wherein d is S-R The lower limit of the reservoir interface crude oil filling pore throat, m, is usually converted to nm; r is S-R The crude oil filling pore throat radius, m, for the reservoir interface is typically converted to nm.
The pore throat fill lower limit inside the reservoir of one aspect of the invention is:
wherein, d is R Filling the lower pore throat limit, m, for the crude oil inside the reservoir, typically converted to nm; r is S-R The pore throat radius, m, is filled with the crude oil inside the reservoir, typically converted to nm.
The invention has the beneficial effects that: the lower throat filling limit is illustrated as varying during occlusion, and is not a fixed value; the crude oil filling process is illustrated as a residual pressure decay process, and the corresponding pore throat filling lower limit is gradually increased; the change characteristics of the lower pore throat filling limit are explained from the aspect of the dynamic mechanism, and a calculation formula of the lower pore throat filling limit is established. The invention deepens the understanding of the mechanism of filling the compact oil, supplements the geological theory of the compact oil reservoir formation, and provides an effective means for predicting the distribution range of the compact oil, thereby having great guiding value and wide application prospect in the current and future unconventional oil and gas exploration fields.
FIG. 3 shows a formation pressure evolution process obtained by a basin numerical simulation method; as shown in fig. 3, the evolution process of the residual pressure at the reservoir interface is fitted as a function of time:
P S-R ＝f(t)＝-0.00008t 5 +0.004t 4 -0.101t 3 +0.951t 2 -5.299t+32.11；
wherein, P S-R The residual pressure at the reservoir interface, MPa; t is time, ma.
The capillary force calculation formula is as follows:
wherein, sigma is the gas-water interfacial tension, N/m; theta is the wetting angle, °; r is the critical pore throat radius, m;
according to the dynamic equilibrium relation at the pore throat filling lower limit, the pore throat filling lower limit of the reservoir interface can be obtained as follows:
wherein σ =0.172 × ρ oil -113.55；ρ oil ＝916kg/m 3 (ii) a θ =0 °; t is between 20Ma and 0 Ma.
As shown in fig. 6, the evolution process of the residual pressure at the reservoir interface between 20Ma and 0Ma and the corresponding variation process of the pore throat filling lower limit can be obtained.
And calculating according to a fluid state equation to obtain the residual pressure inside the reservoir as follows:
P R the residual pressure inside the reservoir, MPa; p F Is the fluid pressure, MPa, inside the reservoir; p w Hydrostatic pressure, MPa, inside the reservoir; r = 8.3145J/(mol · K); t is the formation temperature, k; v m Is the molar volume of the crude oil, ml/mol; a =3.0346V w -5.43；B＝0.1975A 2.0679 ；α＝3.1725A 3.0456 ；β＝1.539ω+2.071；V w Is the molar volume of formation water, V w =150mL/mol; ω =0.68; rho is the density of the formation water, kg/m3; g is the gravity acceleration, and the value is 9.8N/kg; h is the formation burial depth, m.
The fluid pressure inside the reservoir may be expressed as a function of formation temperature:
P F ＝f(T)＝f'(t)＝-0.009t 2 -0.086t+59.9
wherein T is the formation temperature, k; t is time, ma.
The formation burial depth can be determined as a function of time by a basin simulation method, so the evolution process of the hydrostatic pressure is as follows:
P W ＝f”(t)＝-0.003t 3 +0.094t 2 -1.841t+38.63
the residual pressure inside the reservoir as a function of time is:
P R ＝P F -P W ＝f'(t)-f”(t)＝0.003t 3 -0.103t 2 +1.755t+21.27
according to the dynamic balance relation at the pore throat filling lower limit, the pore throat filling lower limit in the reservoir can be obtained as follows:
wherein σ =0.172 × ρ oil -113.55；ρ oil ＝916kg/m 3 (ii) a θ =0 °; t is between 20Ma and 0 Ma.
As shown in fig. 6, the evolution process of the residual pressure inside the reservoir between 20Ma and 0Ma and the corresponding variation process of the pore throat filling lower limit can be obtained.
The above-mentioned embodiments, objects, technical solutions and advantages of the present invention are further described in detail, it should be understood that the above-mentioned embodiments are only illustrative of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (5)
1. A method for determining a lower limit of a crude oil filling pore throat of a tight reservoir, comprising the steps of:
(1) Based on the relation between the power and the resistance in the filling process, when the residual pressure P is equal to the capillary force Pc, the lower filling limit is reached;
(2) Calculating and determining the lower limit of the filling pore throat of the crude oil according to a balance relation of the power and the resistance in the filling process, wherein the balance relation of the power and the resistance in the filling process in the step (2) is as follows:
wherein, P is filling power, MPa; pc is filling resistance, namely capillary force, MPa; sigma is gas-water interfacial tension, N/m; theta is the wetting angle, °; r is the radius of the filling critical pore throat, m;
when the filling pore throat is positioned on the reservoir interface, the evolution process of the residual pressure of the reservoir interface is obtained by a basin simulation method and quantified as a function of time; when the filling pore throat is positioned in the reservoir, the residual pressure in the reservoir is calculated by a fluid state equation, and a basin simulation method is utilized to obtain a formation temperature evolution history so as to obtain a residual pressure evolution quantitative expression in the reservoir;
the relation of the residual pressure in the reservoir along with the change of the formation temperature is as follows:
wherein, P R The residual pressure inside the reservoir, MPa; p is F Is the fluid pressure, MPa, inside the reservoir; p w Is the hydrostatic pressure, MPa, inside the reservoir; r = 8.3145J/(mol · K); t is the formation temperature, k; v m Is the molar volume of the crude oil, ml/mol; a =3.0346V w -5.43；B＝0.1975A 2.0679 ；α＝3.1725A 3.0456 ；β＝1.539ω+2.071；V w Is the molar volume of formation water, V w =150mL/mol; ω =0.68; rho is the density of the formation water, kg/m3; g is the gravity acceleration, and the value is 9.8N/kg; h is the formation burial depth, m.
2. The method of determining a lower crude oil charge pore throat limit for a tight reservoir of claim 1, wherein the residual pressure at the reservoir interface over time is related by:
P S-R ＝f(t)
wherein, P S-R Is the residual pressure at the reservoir interface, MPa; t is time, ma.
3. The method of determining a tight reservoir crude oil charge pore throat lower limit of claim 2, wherein the tight reservoir interface crude oil charge pore throat lower limit is:
wherein d is S-R The lower limit of the reservoir interface crude oil filling pore throat, m, is usually converted to nm; r is S-R The crude oil filling pore throat radius, m, for the reservoir interface is typically converted to nm.
4. The method for determining the lower limit of the crude oil filling pore throat of the tight reservoir as claimed in claim 1, wherein the residual pressure inside the reservoir is mainly related to the formation temperature, the molar volume and the formation burial depth, the change of the molar volume is mainly caused by the change of components in the oil production process, a quantitative expression of the evolution of the residual pressure inside the reservoir can be obtained by using the history of the evolution of the formation temperature with time and the history of the evolution of the formation burial depth with time, and the relation of the fluid pressure inside the reservoir with the change of the formation temperature is as follows:
P F ＝f(T)＝f'(t)
wherein T is the formation temperature, k; t is time, ma;
the formation burial depth can be determined as a function of time by a basin simulation method, so the evolution process of the hydrostatic pressure is as follows:
P W ＝f”(t)；
the residual pressure inside the reservoir as a function of time is:
P R ＝P F -P W ＝f'(t)-f”(t)。
5. the method of determining a lower limit of a tight reservoir crude oil filling pore throat according to claim 4, wherein the lower limit of the tight reservoir crude oil filling pore throat is:
wherein d is R Filling the lower pore throat limit, m, for the crude oil inside the reservoir, typically converted to nm; r is R The pore throat radius, m, is filled with the crude oil inside the reservoir, typically converted to nm.
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