Method for determining spontaneous or artificial ignition of a reservoir

Abstract

The present invention relates to a method for determining whether to use spontaneous combustion or artificial ignition in an oil reservoir, which comprises the following steps: step one, using an accelerating calorimeter to determine the spontaneous combustion temperature; step two, considering the oxidation time required to reach a certain spontaneous combustion temperature when heat loss is taken into account; step three, determining whether to use spontaneous combustion or artificial ignition; the spontaneous combustion temperature is determined by experiment, and the oxidation time required to reach the spontaneous combustion temperature is calculated in step two; if the decrease in oil production caused by the delay of combustion results in a decrease in income that is greater than the cost of artificial ignition, then artificial ignition is used, otherwise, spontaneous combustion is used. The present invention can design a more economically efficient oil production method, and if the oil reservoir can spontaneously combust, expensive artificial ignition equipment does not need to be invested.

Description

TECHNICAL FIELD

[0001] The present invention relates to enhanced oil recovery technology in the process of air injection development of oil field, in particular to a method for determining whether to use spontaneous combustion or artificial ignition of oil reservoir. BACKGROUND

[0002] In the development of oil field, in order to improve oil production (oil production rate), water or gas is often injected into the oil reservoir. The gas can be nitrogen, hydrocarbon gas, carbon dioxide or air. If air injection is used, the oxygen in the air will react with the oil. The oxidation reaction will produce some heat to increase the temperature of the oil reservoir. When the temperature of the oil reservoir reaches the ignition temperature, spontaneous combustion will occur, resulting in partial combustion of the oil to produce more heat energy to facilitate the production of more oil. However, the oxidation process takes time, and if the oxidation time is too long, spontaneous combustion will not occur. Sometimes the ignition temperature is not reached, and spontaneous combustion will not occur. In these cases, artificial ignition must be used, so artificial ignition is generally used directly at present, but artificial ignition requires more cost, so a method for determining whether to use spontaneous combustion or artificial ignition is needed. SUMMARY

[0003] The purpose of the present invention is to provide a method for determining whether to use spontaneous combustion or artificial ignition of oil reservoir, which is used to determine whether to use artificial ignition or spontaneous combustion, which method has higher recovery rate and economic effect.

[0004] The technical scheme adopted by the present invention to solve its technical problems is that the method for determining whether to use spontaneous combustion or artificial ignition of oil reservoir comprises the following steps:

[0005] Step 1: use an accelerated calorimeter to experimentally determine the temperature of spontaneous combustion;

[0006] Step 2: consider the oxidation time required to reach a certain spontaneous combustion temperature when heat loss is considered;

[0007] 2.1 Establish a heat loss model:

[0008] Through the analytical solution of heat E lost by unit interface area to the overlying and underlying strata: b , unit: kcal / m 2 .℃:

[0009]

[0010]

[0011] I N = T N d N + p N (d N ) 2 + 2q N (d N) 3 (3)

[0012]

[0013] In the above equation, E b The unit is kcal / m 2 .℃; λ is the thermal conductivity of the overlying or underlying rock, in kcal / (md℃); κ is the thermal diffusivity, in m 2 / day; d is the diffusion length, in meters, equal to t k This refers to the diffusion time, expressed in days; T is the interface temperature, expressed in °C, which is equal to the reservoir temperature at any given time t; the intermediate parameter p is expressed in °C / m, and q is expressed in °C / m. 2 The superscript N indicates the previous time step;

[0014] 2.2 Considering the oxidation time required for heat loss, from the initial interface temperature T ri Calculate the oxidation time required to reach any interface temperature T, assuming the reservoir is a cube with unit interface area and reservoir thickness, and the reservoir's heat balance is the heat H generated or released from the oxidation time Δt. gen Subtract the heat increment H of the oxidation zone during time Δt in E is equal to the heat loss E of the overlying and underlying rocks. b (Δt, t), the mathematical equation is:

[0015] H gen -H in =E b (Δt, T) (5)

[0016]

[0017] H in =h(ρC) r (ΔT) (7)

[0018] E b (Δt, T) = E b (t,T)-E b (t N T N (8)

[0019] Obtain the reservoir temperature or interface temperature from T ri Oxidation time required to rise to T:

[0020] Step 1: Set the initial reservoir temperature T ri Given the auto-ignition temperature Tz, calculate the oxidation time t. SI ,

[0021]

[0022] wherein: is the effective void fraction, decimal; (pC) r is the thermal capacity of the reservoir, kcal / (m 3 ·°C); T ri and T z are the initial temperature and autoignition temperature of the reservoir, respectively; B is a constant in K; E is the activation energy of the oxidation reaction, J / mol, R is the universal gas constant equal to 8.3147 J / (mol·K); S org is the remaining oil saturation under gas injection conditions, decimal; p o is the density of the oil, kg / m 3 ; is the oxygen partial pressure, atm; A o is the frequency factor, (kg O2 / kg oil)·day -1 ·atm -n ; n is the reaction order, dimensionless; H is the enthalpy of the corresponding reaction, kcal / kg O2; T SI , E, A o and p O2 are obtained from the accelerated calorimeter experiment;

[0023] Step 2: the oxidation time t is longer than t SI from Step 1 when heat loss is considered, set t = t SI + δ0, δ0 is an arbitrary incremental time;

[0024] Step 3: use t to calculate d, I N , p, q, E b (Δt, T), H in and H gen ;

[0025] Step 4: calculate the heat ratio R H = (H gen - H in ) / E b (Δt, T) within Δt;

[0026] Step 5: if R H deviates negatively from 1, add δ1 to t to increase heat generation, δ1 is the time increment; if R H deviates positively from 1, subtract δ1 from t to reduce heat generation, because H gen increases faster than E b over time, H in is the heat increment at the set autoignition temperature Tz;

[0027] Step 6: Repeat steps 2 to 5 using the new t from step 5 until R H is about 1, then t is the oxidation time needed to reach the autoignition temperature Tz set in step 1 considering heat loss;

[0028] Step 7: Set the autoignition temperature 10 degrees higher than step 1, repeat steps 1-6. At step 2, t=

[0029] t N +t SI -t SI N ;

[0030] Step 8: Repeat step 7 until the ignition temperature is reached, then t is the oxidation time needed considering heat loss;

[0031] Step 3, decide whether to autoignite or manually ignite; the autoignition temperature measured by experiment is Tz, and the oxidation time needed to reach the autoignition temperature calculated in step 2 is t SI , due to the delay of combustion resulting in the reduction of oil production, if the reduction of oil production brings the reduction of income greater than the cost of manual ignition, adopt manual ignition method, otherwise, adopt autoignition.

[0032] The specific method of step 1 in the above scheme is:

[0033] First, heat the accelerated calorimeter to the required temperature and keep it for a period of time to reach thermal equilibrium; check if the heating rate is less than the pre-set rate of 0.02℃ / min, if it is, the accelerated calorimeter continues to execute the pre-selected temperature step, following the heating-wait-search sequence, until the self-heating rate is greater than the pre-set rate, at this time, the accelerated calorimeter is kept in adiabatic conditions until the experiment is completed.

[0034] 1. The method of deciding whether to autoignite or manually ignite the oil reservoir proposed in the present application can design a more economically beneficial oil production method. That is, if the oil reservoir can autoignite, there is no need to invest in expensive manual ignition equipment.

[0035] 2. If the oil reservoir cannot autoignite, it may not use the air injection method to produce oil, because even if manual ignition is successful near the well bottom, if it is extinguished in the deep part of the oil reservoir, the air injection combustion method has failed.

[0036] 3. In recent years, new energy such as hydrogen energy has developed rapidly. Air injection and crude oil combustion can generate hydrogen. Therefore, the present application can be beneficial to the optimal design of hydrogen production. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 Follow the heating-wait-search (HWS) sequence.

[0038] Figure 2The oxidation time required to reach different reservoir temperatures, taking heat loss into account. Detailed implementation method:

[0039] The present invention will be further described below with reference to the accompanying drawings:

[0040] This method for determining whether an oil reservoir will spontaneously combust or be manually ignited includes the following steps:

[0041] Step 1: Use an accelerating calorimeter to experimentally determine the temperature of spontaneous combustion;

[0042] In an ARC (Accelerating-rate calorimeter) experiment, the ARC is first heated to the desired temperature and held for a period of time to reach thermal equilibrium. The heating rate is then checked to ensure it is less than the preset rate (e.g., 0.02 °C / min). If so, the ARC continues to execute the pre-selected temperature step (e.g., 5 °C), following a Heating-Wait-Search (HWS) sequence, until the self-heating rate exceeds the preset rate. During this time, the ARC remains under adiabatic conditions until the experiment is complete. Figure 1 As shown. When the temperature suddenly rises, this temperature should be the auto-ignition temperature. Figure 1 In this case, the corresponding auto-ignition temperature is approximately 75°C.

[0043] Step 2: Considering heat loss, the oxidation time required to reach a certain temperature is considered. In oil reservoirs, some of the heat generated by LTO may be lost to the overlying and underlying rocks. In laboratory experiments, heat will be lost through the experimental system.

[0044] 2.1 Establishing a heat loss model:

[0045] Heat E lost per unit interface area to the overlying and underlying strata b The unit is kcal / m 2 Analytical solution for .℃):

[0046]

[0047]

[0048] I N =T N d N +p N (d N ) 2 +2q N (dN) 3 (3)

[0049]

[0050] In the above equation, E bkcal / m 2 .°C; λ is the thermal conductivity of the overlying or underlying rock in kcal / (m.d.°C); κ is the thermal diffusivity in m 2 / day; d is the diffusion length in m, equal to t k is the diffusion time in days; T is the temperature at the interface in °C, equal to the reservoir temperature at any time t; the intermediate parameters p have units of °C / m and q has units of °C / m 2 : the superscript N indicates the previous time step;

[0051] 2.2 Oxidation time required considering heat losses, to reach an initial interface temperature T ri The oxidation time required to reach any interface temperature T is calculated assuming that the reservoir is a cube with unit interface area (1 m 2 ) and reservoir thickness h (m), the heat balance of the reservoir is that the heat generated or released (H gen ) from the oxidation time Δt minus the heat increment (H in ) of the oxidized zone during the time Δt, should be equal to the heat loss (E b (Δt, t)) of the overlying rock and the underlying rock. The mathematical equation is:

[0052] H gen -H in = E b (Δt, T) (7)

[0053]

[0054] H in = h(ρC) r (ΔT) (9)

[0055] E b (Δt, T) = E b (t, T) - E b (t N , T N ) (10)

[0056] The above equation has two unknowns, t and T. In the exponential term, t and B have units of K, but elsewhere, t has units of °C. From equation 7, the oxidation time required when the reservoir temperature or interface temperature increases from T ri to T is obtained:

[0057] Step 1: Set a reservoir temperature slightly higher than the initial reservoir temperature, calculate the oxidation time t SI ,

[0058]

[0059] where: is the effective void fraction, decimal; (pC) r is the reservoir heat capacity, kcal / (m 3 · °C); T ri and T z are the initial reservoir temperature and autoignition temperature, respectively, °C, but in the terms involving B, the units are K; B is a constant, units K; E is the activation energy for the oxidation reaction, J / mol; R is the universal gas constant equal to 8.3147 J / (mol·K); S org is the remaining oil saturation under gas injection conditions, decimal; p o is the oil density, kg / m 3 ; is the oxygen partial pressure, atm; A o is the frequency factor, (kg O2 / kg oil)·day -1 · atm -n ; n is the reaction order, dimensionless; H is the enthalpy for the corresponding reaction, kcal / kg O2. T SI , E, A o , and p O2 in these equations are obtained from accelerated calorimeter experiments;

[0060] Step 2: The oxidation time t is longer than t SI from Step 1 when heat loss is considered, set t = t SI + δ0, δ0 is an arbitrary incremental time;

[0061] Step 3: Use t to calculate d, I N , p, q, E b (Δt, T), H in , and H gen ;

[0062] Step 4: Calculate the heat ratio R H = (H gen - H in ) / E b (Δt, T) over Δt;

[0063] Step 5: If R H deviates negatively from 1, add δ1 to t to increase heat production, δ1 is the time increment; if R H deviates positively from 1, subtract δ1 from t to decrease heat production, because H gen increases faster than E b over time, H in is the heat increment at the set autoignition temperature Tz;

[0064] Step 6: Repeat Steps 2 through 5 using the new t obtained from Step 5 until RH Approximately 1, where t is the oxidation time required to reach the auto-ignition temperature Tz set in step 1, considering heat loss.

[0065] Step 7: Set the auto-ignition temperature to 10 degrees higher than in Step 1, and repeat steps 1-6. In Step 2, t =

[0066] t N +t SI -t SI N ;

[0067] Step 8: Repeat step 7 until the ignition temperature is reached. At this point, t is the oxidation time required considering heat loss.

[0068] Table 1 Example data for calculating auto-ignition delay time

[0069]

[0070] Using the data in Table 1 and from the article by Vinsome and Westerveld (1980), κ = 0.0929m 2 / d,λ / κ=560.6kcal / m 3. ℃, and h=10m, the relationship between t and T is as follows Figure 2 As shown, the required oxidation time increases significantly with increasing heat loss; if the reservoir temperature is low, the oxidation rate is low, thus requiring a longer oxidation time to raise the reservoir temperature. When the reservoir temperature is high, the oxidation rate is high, requiring a shorter time to further raise the reservoir temperature. As shown in the figure, when the reservoir temperature is above 100°C, the oxidation time remains almost constant. Oxidation time is used instead of auto-ignition delay time because at low temperatures, the ignition temperature may not yet be reached.

[0071] Step 3: Decide whether to allow spontaneous combustion or artificial ignition; if the spontaneous combustion temperature measured by the experiment is T SI The oxidation time required to reach the auto-ignition temperature, calculated in step two, is t. SI Since the delayed combustion leads to a reduction in oil production, if the reduction in revenue caused by the reduction in oil production is greater than the cost of manual ignition, manual ignition should be used; otherwise, spontaneous combustion ignition should be used.

Claims

1. A method for determining whether an oil reservoir will spontaneously combust or be ignited artificially, characterized in that... Includes the following steps: Step 1: Use an accelerating calorimeter to experimentally determine the temperature of spontaneous combustion; Step 2: Considering heat loss, determine the oxidation time required to reach a certain auto-ignition temperature; 2.1 Establishing a heat loss model: Heat E lost per unit interface area to the overlying and underlying strata b The unit is kcal / m 2 Analytical solution for .℃: I N =T N d N +p N (d N ) 2 +2q N (d N ) 3 (3) In the above equation, E b The unit is kcal / m 2 .℃; λ is the thermal conductivity of the overlying or underlying rock, in kcal / (md℃); κ is the thermal diffusivity, in m 2 / day; d is the diffusion length, in meters, equal to Δt is the oxidation time; T is the interface temperature, in °C, and equal to the reservoir temperature at any given time t; the intermediate parameter p is in °C / m, and the intermediate parameter q is in °C / m. 2 The superscript N indicates the previous time step. 2.2 Considering the oxidation time required for heat loss, from the initial interface temperature T ri Calculate the oxidation time required to reach any interface temperature T, assuming the reservoir is a cube with unit interface area and reservoir thickness, and the reservoir's heat balance is the amount of heat H generated or released from the oxidation time Δt. gen Subtract the heat increment H of the oxidation zone during time Δt in E is equal to the heat loss E of the overlying and underlying rocks. b (Δt, T), the mathematical equation is: H gen –H in =E b (Δt,T) (5) H in =h(ρC) r (ΔT) (7) E b (Δt,T)=E b (t,T)-E b (t N ,T N ) (8) Where h is the reservoir thickness, in meters; Obtain the reservoir temperature or interface temperature from T ri Oxidation time required to rise to T: Step 1: Set the initial reservoir temperature T ri Given the auto-ignition temperature Tz, calculate the oxidation time t. SI , in: It is the effective porosity, a decimal; (ρC) r It is the reservoir heat capacity, kcal / (m³). 3 Reservoir temperature (℃); T ri and T z These are the initial reservoir temperature and auto-ignition temperature, respectively; B is a constant in K; E is the activation energy of the oxidation reaction, J / mol; R is the universal gas constant, equal to 8.3147 J / (mol·K); S org It is the residual oil saturation under gas injection conditions, a decimal; ρ o It is the density of oil, kg / m³ 3 ; It is the partial pressure of oxygen, atmospheric pressure; A o It is the frequency factor, (kg O2 / kg oil)·day -1 Atmospheric pressure -n n is the reaction order, dimensionless; H is the enthalpy of the corresponding reaction, kcal / kg O2; T SI ,E,A o and p O2 Obtained by accelerated calorimetry experiments; Step 2: Considering heat loss, the oxidation time t is longer than t from step 1. SI Let t = t SI +δ0, where δ0 is an arbitrary time increment; Step 3: Calculate d and I using t. N ,p,q,E b (Δt,T),H in and H gen ; Step 4: Calculate the heat ratio R within Δt. H =(H gen -H in ) / E b (Δt,T); Step 5: If R H If the deviation from 1 is negative, then δ1 is added to t to increase heat generation, where δ1 is the time increment; if R H If the deviation from 1 is positive, then δ1 is subtracted from t to reduce heat generation, because H increases over time. gen E b It increases even faster, H in The heat increment at the set auto-ignition temperature Tz; Step 6: Repeat steps 2 through 5 using the new t obtained in step 5 until R. H Approximately 1, where t is the oxidation time required to reach the auto-ignition temperature Tz set in step 1, considering heat loss. Step 7: Set the auto-ignition temperature to 10 degrees higher than in Step 1, and repeat steps 1-6. In Step 2, t = t N +t SI -t SI N ; Step 8: Repeat step 7 until the ignition temperature is reached. At this point, t is the oxidation time required considering heat loss. Step 3: Decide whether to allow spontaneous combustion or artificial ignition; the spontaneous combustion temperature measured experimentally is Tz, and the oxidation time required to reach the spontaneous combustion temperature calculated in Step 2 is t. SI Since the delayed combustion leads to a reduction in oil production, if the reduction in revenue caused by the reduction in oil production is greater than the cost of manual ignition, manual ignition should be used; otherwise, spontaneous combustion ignition should be used.

2. The method for determining whether an oil reservoir will spontaneously combust or be artificially ignited according to claim 1, characterized in that: The specific method for step one is as follows: First, heat the accelerated calorimeter to the required temperature and maintain it for a period of time to reach thermal equilibrium. Check if the heating rate is less than the preset rate of 0.02℃ / min. If it is less, the accelerated calorimeter continues to execute the pre-selected temperature step, following the heating-waiting-search sequence, until the self-heating rate is greater than the preset rate. At this time, the accelerated calorimeter is kept under adiabatic conditions until the experiment is completed.

Images