# Study on Autogenous Heat Technology of Offshore Oilfield: Experiment Research, Process Design, and Application

Authors: Yanping Sun; Chengsheng Wang; Jun Sun; Shuliang Ren; Hua Peng; Yueyue Fang; Fangxue Xu
Journal: Geofluids
 (2021)

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## Abstract

Conventional heavy oil has abundant reserves and low recovery efficiency in offshore oilfields. Autogenous heat technology uses 2-3 kinds of inorganic salt solution to produce inert gas and release a lot of heat under the action of a catalyst. It is applied to improve heavy oil recovery of the offshore oilfield. This paper applies experimental schemes such as viscosity reduction rate evaluation, heat conditions, gas production conditions, reaction rate control, and effect of environmental factors. This paper evaluates the performance of the autogenous heat system, optimizes the process parameters, and designs the process scheme and construction scheme according to the oil well production. This paper researches an autogenous heat system with nontoxic and high heat production and optimizes the catalyst type, concentration, and time to reach exothermic peak. When the concentration of the thermogenic agent is 1.5 mol/L in the autogenous heat system, the range of temperature rise is 67°C, which achieves the target requirement of more than 50°C. Field application shows that the autogenous heat system can effectively reduce the viscosity of heavy oil, dissolve solid paraffin, clean organic scale, improve reservoir permeability, and increase heavy oil production. This paper applies autogenous heat technology to improving the efficiency of heavy oil recovery of the offshore oilfield. Research conclusions show that the autogenous heat system can effectively reduce the viscosity of heavy oil, improve reservoir permeability, and increase heavy oil production.


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## Body

## 1. Introduction

Autogenic heat technology originated from an invention patent of the Shell Company. The principle of heat generation is mixing 2-3 kinds of inorganic saline solution, with catalysis; the exothermic chemical reaction occurs to produce inert gases and generate a large amount of heat [1]. In theory, the complete reaction of a 1 m3 5 mol/L heat generation system can release 1×106 kilojoules of heat. The thermochemical reaction formula is(1)A+B⟶cat.C+D↑2H2O+QThe autogenic heat system releases a large amount of heat after reacting in the reservoir, which can increase the reservoir temperature and reduce the viscosity of crude oil. At the same time, increasing the oil fluidity of reservoirs by chemical viscosity reduction and the reaction products have no effect on the formation [2]. Autogenic heat technology is mainly used in high viscosity and high pour point reservoirs. According to the existing offshore process conditions, it is an attempt to develop offshore heavy oil by using autogenic heat chemical synergistic technology with less investment and quick response.Heavy oil thermochemical synergistic technology is relatively mature in onshore oilfields [3, 4], but compared with an onshore oilfield, an offshore oilfield has its particularity, so it is necessary to carry out thermochemical synergistic technology research according to the characteristics of the offshore oilfield [5].


## 2. Study on Autogenic Heat System

### 2.1. Optimization of Autogenic Heat System

There are mainly two kinds of commonly used autogenic heat systems.System 1:(2)NO2−+NH4+⟶cat.N2↑+2H2O+332.58kJ/molSystem 2:(3)NaNO2+12CONH22+HCl⟶cat.NaC1+N2↑+12CO2+32H2O+213kJ/molAccording to Figures1 and 2, both systems can increase the temperature of the wellbore or formation [6]. Under the same peak temperature difference, the concentration of system 1 is obviously lower than that of system 2; system 1 can obtain higher heating temperature with lower system concentration [6]. During the experiment, a large amount of gas was produced in both systems, and the colorless and odorless gas N2 was produced in system 1. At the same time, system 2 produces a lot of brown-red toxic gases [7], which are by-products of the experimental reaction, NO and NO2. Therefore, system 1 was selected for further experiments.Figure 1
Relationship between concentration and peak time or peak temperature difference of autogenic heat system 1.Figure 2
Relationship between concentration and peak time or peak temperature difference of autogenic heat system 2.


### 2.2. Study on the Performance of Autogenic Heat System

The reaction of NO2- and NH4+ ions at low temperature follows the general law of chemical reaction. The reaction rate equation is as follows:(4)dCNO2−dt=KCαNO2−⋅CβNH4+In the formula, K is a constant of reaction rate, and it is a function of temperature. Usually, the K value will increases by 2~4 times when the temperature increases by 10°C, anddCNO2−/dt is the rate of change of instantaneous NO2- concentration with time. CNO2- and CNH4+ are the instantaneous concentrations of NO2- and NH4+, respectively, and α and β are the characteristic constants of the equation [8].It can be seen from the above equation that the higher the temperature, the greater the initial concentration of reactants and the faster the reaction rate. In order to minimize the heat loss and make full use of the heat released by the reaction to heat the reservoir, it is necessary to establish a method to control the heating rate. According to the chemical reaction mechanism, for an exothermic chemical reaction, when the concentration of the reactant is given, the heat released is a certain amount; only the reaction speed is variable. The factors that affect the reaction rate are temperature, pressure, and the type and concentration of catalyst. From the relationship between the saturated vapor pressure of water and temperature, we can know that the saturated vapor pressure of water is 0.1175 MPa at 119°C, and the pressure in formation is far greater than the saturated vapor pressure of water at this temperature. Therefore, it is not necessary to study the effect of pressure on the heating rate. The main research objects are temperature and the type and concentration of catalyst.


#### 2.2.1. Calorific Value of Autogenic Heat System under Ideal Conditions

It can be seen from formula (4) that after mixing different concentrations of the NaNO2 aqueous solution with different concentrations of the NH4Cl aqueous solution, a large amount of heat can be generated, which greatly increases the temperature of basic brine. Table 1 shows the heat release calculated according to the data of standard molar enthalpy of formation in formula (4).Table 1
Calorific value of autogenic heating reaction.
0.5 m3 NaNO2 solution0.5 m3 NH4Cl solutionTheoretical heat produced by mixing (MJ)mol/L%mol/L%0.56.440.55.0883.11.012.51.010.16166.31.519.361.515.24249.42.025.02.020.32332.52.532.22.525.4415.73.037.53.030.48498.8From the above table, it can be seen that the mixture of 0.5 m3 of the NaNO2 aqueous solution whose concentration is 3.0 mol/L with 0.5 m3 of NH4Cl aqueous solution whose concentration is 3.0 mol/L can theoretically produce 498.8 MJ of heat, 33.6 m3 (0.1 MPa, 25°C) of nitrogen, and 1.5 mol/L of NaCl aqueous solution (which is harmless to most oil and gas reservoirs) and can also make it possible for the temperature of base brine to increase by 119°C.


#### 2.2.2. Calorific Value of Autogenic Heating System under Laboratory Condition

Different concentrations of heating agent solution were added to the high temperature and high pressure reactor, and the vessel was sealed immediately to observe the temperature change in the reactor. According to the experimental results in Table2 and Figure 3, it is found that (1) under the same heating agent concentration and base brine temperature, the higher the concentration of the heating agent, the more heat generated, and the larger the heating range of the system. However, when the concentration of the heating agent is lower than 1.0 mol/L, the reaction speed is lower, and the reaction time is prolonged, resulting in the increase of heat loss in the experimental process. (2) Due to the limitation of the solubility of inorganic salts, when the concentration of the heating agent exceeds 2.5 mol/L, it is difficult to prepare the heating system and to dissolve other additives in the system. Therefore, it is suggested that the concentration of the heating agent should be controlled in the range of 1.0 mol/L-2.5 mol/L.Table 2
Experimental data of heat generation in autogenic heat system.
Concentration (mol/L)Peak temperature (°C)Temperature range (°C)Experiment conditions0.5634100 mL 1.0 mol/L NaNO2 solution+100 mL 1.0 mol/L NH4Cl solution1.07919100 mL 2.0 mol/L NaNO2 solution+100 mL 2.0 mol/L NH4Cl solution1.512767100 mL 3.0 mol/L NaNO2 solution+100 mL 3.0 mol/L NH4Cl solution2.014282100 mL 4.0 mol/L NaNO2 solution+100 mL 4.0 mol/L NH4Cl solution2.515797100 mL 5.0 mol/L NaNO2 solution+100 mL 5.0 mol/L NH4Cl solution3.0178118100 mL 6.0 mol/L NaNO2 solution+100 mL 6.0 mol/L NH4Cl solutionNote: catalyst concentration: 0.3%; base brine: 60°C.Figure 3
Relationship between heat concentration and peak temperature or temperature rise range.


#### 2.2.3. Gas Production Rate of Autogenic Heat System under Laboratory Conditions

Figure4 shows the experimental process of the autogenous heating system for gas generation. The gas volume obtained by the reaction is collected by the drainage method. The total amount of gas collected is recorded after the experiment is completed. The gas yield of the system under formation or wellbore conditions is controlled and mastered by changing the concentration of the heating agent. Table 3 and Figure 5 show the relationship between the concentration of the heat generating agent and the amount of gas generated.Figure 4
Experimental process of autogenous heating system for gas generation.Table 3
Experimental data of gas production rate of autogenic heat system.
Concentration (mol/L)Quantity of gas (N mL)Experiment conditions0.51545100 mL 1.0 mol/L NaNO2 solution+100 mL 1.0 mol/L NH4Cl solution1.03495100 mL 2.0 mol/L NaNO2 solution+100 mL 2.0 mol/L NH4Cl solution1.55850100 mL 3.0 mol/L NaNO2 solution+100 mL 3.0 mol/L NH4Cl solution2.08155100 mL 4.0 mol/L NaNO2 solution+100 mL 4.0 mol/L NH4Cl solution2.510192100 mL 5.0 mol/L NaNO2 solution+100 mL 5.0 mol/L NH4Cl solution3.012500100 mL 6.0 mol/L NaNO2 solution+100 mL 6.0 mol/L NH4Cl solutionNote: catalyst concentration: 0.3%; base brine: 60°C.Figure 5
Relationship between heating agent concentration and gas quantity.


#### 2.2.4. The Control of Thermal Peak of Autogenic Heat System

Taking the same initial temperature, let two kinds of heat-generating agents react exothermically under an apparent adiabatic condition. By changing the type and amount of the catalyst, we can understand the relationship between the amount of catalyst and the reaction speed.Tables4 and 5 and Figures 6 and 7 show the same catalyst concentration and base brine temperature.(1)
The thermochemical reaction of sodium nitrite and ammonium chloride can hardly be observed at room temperature without adding acid, and only when the solution is heated to more than 60°C can the reaction occur, and the reaction rate is very slow(2)
The thermochemical reaction rate of sodium nitrite and ammonium chloride can be increased by either liquid acid or solid acid and strong acid or weak acid(3)
The catalytic intensity of acid to the reaction between sodium nitrite and ammonium chloride is related to strength of the acid. The higher the catalyst concentration and strength, the greater the rate of thermochemical reaction. It can be seen from the experimental results that the catalytic strength of phosphoric acid is almost the same as that of hydrochloric acid and nitric acid. This is because phosphoric acid is a polybasic acid; when the temperature rises, its dissociation constant increases, providing more H+ ions for the reaction(4)
The higher the catalyst concentration and strength, the shorter the peak time of the system, but the peak temperature is not affected by the catalyst concentrationTable 4
The effect of catalyst concentration on heat generation rate of system.
Catalyst concentration: 0.5% HClCatalyst concentration: 1.0% HClCatalyst concentration: 1.5% HClTime (min)Temperature (°C)Time (min)Temperature (°C)Time (min)Temperature (°C)025 (indoor temperature)025 (indoor temperature)025 (indoor temperature)528529534103110321041153315341545203720402050254025422552304330463052354535483551404640524050454745524549504850505049555155495548605060496047Concentration of system: 100 mL 2.0 mol/L NaNO2 solution+100 mL 2.0 mol/L NH4Cl solution.Table 5
The effect of catalyst types on heat generation rate and thermal peak.
Catalyst: 1% benzoic acidCatalyst: 1.0% HClCatalyst: 1.0% phosphoric acidCatalyst: 1.0% MXTime (min)Temperature (°C)Time (min)Temperature (°C)Time (min)Temperature (°C)Time (min)Temperature (°C)025 (indoor)025 (indoor)025 (indoor)025 (indoor)52852953452810291032104110311531153715451535203420402050203825362542255225413038304630523045353935483551354940414052405040524542455245494553504450505049505555455549554855576045604960476055654465486547655470437048704670527543754775457551Concentration of system: 100 mL 2.0 mol/L NaNO2 solution+100 mL 2.0 mol/L NH4Cl solution.Figure 6
The effect of catalyst concentration on heat generation rate of system.Figure 7
The effect of catalyst types on heat generation rate and thermal peak.When the catalyst concentration is high (the concentration limits of different catalysts are different), the pyrogenic reaction will be accompanied by brown gas, mainly nitric oxide and nitrogen dioxide (toxic). Therefore, when using the pyrogenic system, the concentration of acidic catalyst should be controlled to reduce the production of toxic products.(5)
The addition of a very small amount of acid can greatly increase the rate of thermochemical reaction, indicating that the thermochemical reaction of sodium nitrite and ammonium chloride in acid solution is a typical acid-catalyzed reaction(6)
When the concentration and type of catalyst change, the peak position of the pyrogenic system will change(7)
Catalyst MX reacted smoothly and slowly released H+, and no brown by-product gases such as NO and NO2 were produced during the experiment


#### 2.2.5. The Effect of Ambient Temperature on Autogenic Heat System

The relationship between ambient temperature and reaction rate can be understood by changing the ambient temperature of the heating system under the condition of same heating agent concentration, the same catalyst type and concentration, and the apparent adiabatic. The result shows that the higher the ambient temperature is, the faster the heat generation rate of chemical reaction is. Table6 and Figure 8 show the influence of ambient temperature on heat generation rate and heat peak.Table 6
The effect of ambient temperature on heat generation rate and thermal peak.
Ambient temperature: 60°CAmbient temperature: 75°CAmbient temperature: 85°CTime (min)Temperature (°C)Time (min)Temperature (°C)Time (min)Temperature (°C)025 (indoor)025 (indoor)025 (indoor)1—1—1—223232242326341363437457480543578586652685694764783792872889789910751010111111Concentration of system: 100 mL 2.0 mol/L NaNO2 solution+100 mL 2.0 mol/L NH4Cl solution catalyst: 1.0% HCl.Figure 8
The effect of ambient temperature on heat generation rate and thermal peak.


### 2.3. Evaluation of Application Effect of Autogenic Thermochemical Synergistic System

#### 2.3.1. The Viscosity-Reducing Property of Autogenic Thermochemical Synergistic System

A certain amount of simulated crude oil from an oil field is placed in a beaker, and the autogenous heat system components are added to the beaker in turn to make it react fully in the beaker, and the temperature changes are recorded. The viscosities of the system of the “thermal peak” and at the end of the reaction are measured by parallel experiments. According to Table7 and Figure 9, the experimental results show that the heat generated during the reaction can effectively reduce the viscosity of heavy oil. And the viscosity of heavy oil can be reduced from 2984 mPa·s to 121 mPa·s when the reaction reaches the peak. The temperature of the mixture can be maintained above 60°C for more than 30 minutes during the reaction process, and the obvious viscosity reduction effect can also be maintained at the end of the reaction.Table 7
Viscosity reduction properties of autogenic heat system.
Temperature (°C)Indoor temperature“Thermal peak”The end of the reactionViscosity (mPa·S)2984121578Figure 9
The variation of temperature with reaction time of autogenic heat system.


#### 2.3.2. The Dissolving Paraffin Performance of Autogenic Thermochemical Synergistic System

A certain amount of solid paraffin was placed in a beaker, and those components of the system were added to the beaker in turn to make it react fully in the beaker. The residual solid paraffin content was measured at the end of the reaction, and the reaction time was recorded. It can be seen from the experimental results in Table8 that the autogenic thermochemical system has a good dissolution effect on the fixed paraffin. With the increase of the concentration of the heating agent, the amount of dissolving solid paraffin increases, and the time of dissolving solid paraffin is shorter.Table 8
The dissolving paraffin performance of the system.
Concentration (%)4510Quantity of paraffin dissolved (g)14.721.537.3Time (min)1186Dissolution rate (g/min)1.332.686.21Percentage of paraffin dissolved (%)29.44374.6


#### 2.3.3. The Cleaning Organic Fouling Performance of Autogenic Thermochemical Synergistic System

A certain amount of rock particles adhering to heavy oil and organic matter were placed in a beaker, and then, those components of the system were added to the beaker in turn to make it react fully in the beaker. At the end of the reaction, the amount of residual organic matter was measured, and the cleaning capacity of the 100°C distilled water was compared with that of the system. It can be seen from the experimental results in Table9 that the autothermal system has a good cleaning effect on heavy oil and organic matter, compared with 100°C distilled water, and the autothermal system has a better cleaning organic fouling performance.Table 9
The cleaning organic fouling performance of autogenic thermochemical synergistic system.
TypeAutothermic with plugging removal system100°C distilled waterCleaning effect83.60%57.30%PhenomenonSurface of rock particles is basically clean, floating heavy oil, and organic matter on the surface of liquidSome heavy oil and organic matter melt to the liquid surface, and black heavy oil remains on the surface of the rock particlesThe SARA of heavy oil is as follows: saturated hydrocarbon 41.04%, aromatic hydrocarbon 26.24%, resin 14.13%, and asphaltene 18.59%. And the calculation method of the cleaning effect is as follows: reduced weight after cleaning/total weight before cleaning.


#### 2.3.4. The Plugging Removal Performance of Autogenic Thermochemical Synergistic System

The test core is the Minghua formation oil sands in the Bohai oilfield (core pipe:25mm∗100mm). Core basic parameters are permeability 3130 md, porosity 28%, and oil saturation 71.5%, consistent with reservoir parameters.Crude oil is an oil sample from a well in the Bohai oilfield (degassing viscosity at 50°C 1931 mPa·s).The system formulation is as follows:(i)
Base solution: 2%KCl solution(ii)
Acid system: 10% HCl+6% HBF4(iii)
Autogenic heating composite system: 2.0 mol/L NaNO2+2.0 mol/L NH4Cl and acid system is alternately injected by 3 slugsAccording to Table10 and Figure 10, the experimental results show that the core permeability is significantly increased than the benchmark permeability, the permeability is increased by more than 2.0 times, and the increase range of core permeability is large, which indicates that the plugging removal effect of the self-heating system combined with the HBF4 system can relieve the pollution of the Bohai heavy oil wells.Table 10
The acidizing effect on core flow test of autogenic heating combined with plugging removal system.
K/K0Pad fluid 1Pad fluid 2Autothermic combined with plugging removal solutionPosterior base liquid10.18933.13232.0281Figure 10
The core flow test of autogenic heating combined with plugging removal system.


## 2.1. Optimization of Autogenic Heat System

There are mainly two kinds of commonly used autogenic heat systems.System 1:(2)NO2−+NH4+⟶cat.N2↑+2H2O+332.58kJ/molSystem 2:(3)NaNO2+12CONH22+HCl⟶cat.NaC1+N2↑+12CO2+32H2O+213kJ/molAccording to Figures1 and 2, both systems can increase the temperature of the wellbore or formation [6]. Under the same peak temperature difference, the concentration of system 1 is obviously lower than that of system 2; system 1 can obtain higher heating temperature with lower system concentration [6]. During the experiment, a large amount of gas was produced in both systems, and the colorless and odorless gas N2 was produced in system 1. At the same time, system 2 produces a lot of brown-red toxic gases [7], which are by-products of the experimental reaction, NO and NO2. Therefore, system 1 was selected for further experiments.Figure 1
Relationship between concentration and peak time or peak temperature difference of autogenic heat system 1.Figure 2
Relationship between concentration and peak time or peak temperature difference of autogenic heat system 2.


## 2.2. Study on the Performance of Autogenic Heat System

The reaction of NO2- and NH4+ ions at low temperature follows the general law of chemical reaction. The reaction rate equation is as follows:(4)dCNO2−dt=KCαNO2−⋅CβNH4+In the formula, K is a constant of reaction rate, and it is a function of temperature. Usually, the K value will increases by 2~4 times when the temperature increases by 10°C, anddCNO2−/dt is the rate of change of instantaneous NO2- concentration with time. CNO2- and CNH4+ are the instantaneous concentrations of NO2- and NH4+, respectively, and α and β are the characteristic constants of the equation [8].It can be seen from the above equation that the higher the temperature, the greater the initial concentration of reactants and the faster the reaction rate. In order to minimize the heat loss and make full use of the heat released by the reaction to heat the reservoir, it is necessary to establish a method to control the heating rate. According to the chemical reaction mechanism, for an exothermic chemical reaction, when the concentration of the reactant is given, the heat released is a certain amount; only the reaction speed is variable. The factors that affect the reaction rate are temperature, pressure, and the type and concentration of catalyst. From the relationship between the saturated vapor pressure of water and temperature, we can know that the saturated vapor pressure of water is 0.1175 MPa at 119°C, and the pressure in formation is far greater than the saturated vapor pressure of water at this temperature. Therefore, it is not necessary to study the effect of pressure on the heating rate. The main research objects are temperature and the type and concentration of catalyst.


### 2.2.1. Calorific Value of Autogenic Heat System under Ideal Conditions

It can be seen from formula (4) that after mixing different concentrations of the NaNO2 aqueous solution with different concentrations of the NH4Cl aqueous solution, a large amount of heat can be generated, which greatly increases the temperature of basic brine. Table 1 shows the heat release calculated according to the data of standard molar enthalpy of formation in formula (4).Table 1
Calorific value of autogenic heating reaction.
0.5 m3 NaNO2 solution0.5 m3 NH4Cl solutionTheoretical heat produced by mixing (MJ)mol/L%mol/L%0.56.440.55.0883.11.012.51.010.16166.31.519.361.515.24249.42.025.02.020.32332.52.532.22.525.4415.73.037.53.030.48498.8From the above table, it can be seen that the mixture of 0.5 m3 of the NaNO2 aqueous solution whose concentration is 3.0 mol/L with 0.5 m3 of NH4Cl aqueous solution whose concentration is 3.0 mol/L can theoretically produce 498.8 MJ of heat, 33.6 m3 (0.1 MPa, 25°C) of nitrogen, and 1.5 mol/L of NaCl aqueous solution (which is harmless to most oil and gas reservoirs) and can also make it possible for the temperature of base brine to increase by 119°C.


### 2.2.2. Calorific Value of Autogenic Heating System under Laboratory Condition

Different concentrations of heating agent solution were added to the high temperature and high pressure reactor, and the vessel was sealed immediately to observe the temperature change in the reactor. According to the experimental results in Table2 and Figure 3, it is found that (1) under the same heating agent concentration and base brine temperature, the higher the concentration of the heating agent, the more heat generated, and the larger the heating range of the system. However, when the concentration of the heating agent is lower than 1.0 mol/L, the reaction speed is lower, and the reaction time is prolonged, resulting in the increase of heat loss in the experimental process. (2) Due to the limitation of the solubility of inorganic salts, when the concentration of the heating agent exceeds 2.5 mol/L, it is difficult to prepare the heating system and to dissolve other additives in the system. Therefore, it is suggested that the concentration of the heating agent should be controlled in the range of 1.0 mol/L-2.5 mol/L.Table 2
Experimental data of heat generation in autogenic heat system.
Concentration (mol/L)Peak temperature (°C)Temperature range (°C)Experiment conditions0.5634100 mL 1.0 mol/L NaNO2 solution+100 mL 1.0 mol/L NH4Cl solution1.07919100 mL 2.0 mol/L NaNO2 solution+100 mL 2.0 mol/L NH4Cl solution1.512767100 mL 3.0 mol/L NaNO2 solution+100 mL 3.0 mol/L NH4Cl solution2.014282100 mL 4.0 mol/L NaNO2 solution+100 mL 4.0 mol/L NH4Cl solution2.515797100 mL 5.0 mol/L NaNO2 solution+100 mL 5.0 mol/L NH4Cl solution3.0178118100 mL 6.0 mol/L NaNO2 solution+100 mL 6.0 mol/L NH4Cl solutionNote: catalyst concentration: 0.3%; base brine: 60°C.Figure 3
Relationship between heat concentration and peak temperature or temperature rise range.


### 2.2.3. Gas Production Rate of Autogenic Heat System under Laboratory Conditions

Figure4 shows the experimental process of the autogenous heating system for gas generation. The gas volume obtained by the reaction is collected by the drainage method. The total amount of gas collected is recorded after the experiment is completed. The gas yield of the system under formation or wellbore conditions is controlled and mastered by changing the concentration of the heating agent. Table 3 and Figure 5 show the relationship between the concentration of the heat generating agent and the amount of gas generated.Figure 4
Experimental process of autogenous heating system for gas generation.Table 3
Experimental data of gas production rate of autogenic heat system.
Concentration (mol/L)Quantity of gas (N mL)Experiment conditions0.51545100 mL 1.0 mol/L NaNO2 solution+100 mL 1.0 mol/L NH4Cl solution1.03495100 mL 2.0 mol/L NaNO2 solution+100 mL 2.0 mol/L NH4Cl solution1.55850100 mL 3.0 mol/L NaNO2 solution+100 mL 3.0 mol/L NH4Cl solution2.08155100 mL 4.0 mol/L NaNO2 solution+100 mL 4.0 mol/L NH4Cl solution2.510192100 mL 5.0 mol/L NaNO2 solution+100 mL 5.0 mol/L NH4Cl solution3.012500100 mL 6.0 mol/L NaNO2 solution+100 mL 6.0 mol/L NH4Cl solutionNote: catalyst concentration: 0.3%; base brine: 60°C.Figure 5
Relationship between heating agent concentration and gas quantity.


### 2.2.4. The Control of Thermal Peak of Autogenic Heat System

Taking the same initial temperature, let two kinds of heat-generating agents react exothermically under an apparent adiabatic condition. By changing the type and amount of the catalyst, we can understand the relationship between the amount of catalyst and the reaction speed.Tables4 and 5 and Figures 6 and 7 show the same catalyst concentration and base brine temperature.(1)
The thermochemical reaction of sodium nitrite and ammonium chloride can hardly be observed at room temperature without adding acid, and only when the solution is heated to more than 60°C can the reaction occur, and the reaction rate is very slow(2)
The thermochemical reaction rate of sodium nitrite and ammonium chloride can be increased by either liquid acid or solid acid and strong acid or weak acid(3)
The catalytic intensity of acid to the reaction between sodium nitrite and ammonium chloride is related to strength of the acid. The higher the catalyst concentration and strength, the greater the rate of thermochemical reaction. It can be seen from the experimental results that the catalytic strength of phosphoric acid is almost the same as that of hydrochloric acid and nitric acid. This is because phosphoric acid is a polybasic acid; when the temperature rises, its dissociation constant increases, providing more H+ ions for the reaction(4)
The higher the catalyst concentration and strength, the shorter the peak time of the system, but the peak temperature is not affected by the catalyst concentrationTable 4
The effect of catalyst concentration on heat generation rate of system.
Catalyst concentration: 0.5% HClCatalyst concentration: 1.0% HClCatalyst concentration: 1.5% HClTime (min)Temperature (°C)Time (min)Temperature (°C)Time (min)Temperature (°C)025 (indoor temperature)025 (indoor temperature)025 (indoor temperature)528529534103110321041153315341545203720402050254025422552304330463052354535483551404640524050454745524549504850505049555155495548605060496047Concentration of system: 100 mL 2.0 mol/L NaNO2 solution+100 mL 2.0 mol/L NH4Cl solution.Table 5
The effect of catalyst types on heat generation rate and thermal peak.
Catalyst: 1% benzoic acidCatalyst: 1.0% HClCatalyst: 1.0% phosphoric acidCatalyst: 1.0% MXTime (min)Temperature (°C)Time (min)Temperature (°C)Time (min)Temperature (°C)Time (min)Temperature (°C)025 (indoor)025 (indoor)025 (indoor)025 (indoor)52852953452810291032104110311531153715451535203420402050203825362542255225413038304630523045353935483551354940414052405040524542455245494553504450505049505555455549554855576045604960476055654465486547655470437048704670527543754775457551Concentration of system: 100 mL 2.0 mol/L NaNO2 solution+100 mL 2.0 mol/L NH4Cl solution.Figure 6
The effect of catalyst concentration on heat generation rate of system.Figure 7
The effect of catalyst types on heat generation rate and thermal peak.When the catalyst concentration is high (the concentration limits of different catalysts are different), the pyrogenic reaction will be accompanied by brown gas, mainly nitric oxide and nitrogen dioxide (toxic). Therefore, when using the pyrogenic system, the concentration of acidic catalyst should be controlled to reduce the production of toxic products.(5)
The addition of a very small amount of acid can greatly increase the rate of thermochemical reaction, indicating that the thermochemical reaction of sodium nitrite and ammonium chloride in acid solution is a typical acid-catalyzed reaction(6)
When the concentration and type of catalyst change, the peak position of the pyrogenic system will change(7)
Catalyst MX reacted smoothly and slowly released H+, and no brown by-product gases such as NO and NO2 were produced during the experiment


### 2.2.5. The Effect of Ambient Temperature on Autogenic Heat System

The relationship between ambient temperature and reaction rate can be understood by changing the ambient temperature of the heating system under the condition of same heating agent concentration, the same catalyst type and concentration, and the apparent adiabatic. The result shows that the higher the ambient temperature is, the faster the heat generation rate of chemical reaction is. Table6 and Figure 8 show the influence of ambient temperature on heat generation rate and heat peak.Table 6
The effect of ambient temperature on heat generation rate and thermal peak.
Ambient temperature: 60°CAmbient temperature: 75°CAmbient temperature: 85°CTime (min)Temperature (°C)Time (min)Temperature (°C)Time (min)Temperature (°C)025 (indoor)025 (indoor)025 (indoor)1—1—1—223232242326341363437457480543578586652685694764783792872889789910751010111111Concentration of system: 100 mL 2.0 mol/L NaNO2 solution+100 mL 2.0 mol/L NH4Cl solution catalyst: 1.0% HCl.Figure 8
The effect of ambient temperature on heat generation rate and thermal peak.


## 2.2.1. Calorific Value of Autogenic Heat System under Ideal Conditions

It can be seen from formula (4) that after mixing different concentrations of the NaNO2 aqueous solution with different concentrations of the NH4Cl aqueous solution, a large amount of heat can be generated, which greatly increases the temperature of basic brine. Table 1 shows the heat release calculated according to the data of standard molar enthalpy of formation in formula (4).Table 1
Calorific value of autogenic heating reaction.
0.5 m3 NaNO2 solution0.5 m3 NH4Cl solutionTheoretical heat produced by mixing (MJ)mol/L%mol/L%0.56.440.55.0883.11.012.51.010.16166.31.519.361.515.24249.42.025.02.020.32332.52.532.22.525.4415.73.037.53.030.48498.8From the above table, it can be seen that the mixture of 0.5 m3 of the NaNO2 aqueous solution whose concentration is 3.0 mol/L with 0.5 m3 of NH4Cl aqueous solution whose concentration is 3.0 mol/L can theoretically produce 498.8 MJ of heat, 33.6 m3 (0.1 MPa, 25°C) of nitrogen, and 1.5 mol/L of NaCl aqueous solution (which is harmless to most oil and gas reservoirs) and can also make it possible for the temperature of base brine to increase by 119°C.


## 2.2.2. Calorific Value of Autogenic Heating System under Laboratory Condition

Different concentrations of heating agent solution were added to the high temperature and high pressure reactor, and the vessel was sealed immediately to observe the temperature change in the reactor. According to the experimental results in Table2 and Figure 3, it is found that (1) under the same heating agent concentration and base brine temperature, the higher the concentration of the heating agent, the more heat generated, and the larger the heating range of the system. However, when the concentration of the heating agent is lower than 1.0 mol/L, the reaction speed is lower, and the reaction time is prolonged, resulting in the increase of heat loss in the experimental process. (2) Due to the limitation of the solubility of inorganic salts, when the concentration of the heating agent exceeds 2.5 mol/L, it is difficult to prepare the heating system and to dissolve other additives in the system. Therefore, it is suggested that the concentration of the heating agent should be controlled in the range of 1.0 mol/L-2.5 mol/L.Table 2
Experimental data of heat generation in autogenic heat system.
Concentration (mol/L)Peak temperature (°C)Temperature range (°C)Experiment conditions0.5634100 mL 1.0 mol/L NaNO2 solution+100 mL 1.0 mol/L NH4Cl solution1.07919100 mL 2.0 mol/L NaNO2 solution+100 mL 2.0 mol/L NH4Cl solution1.512767100 mL 3.0 mol/L NaNO2 solution+100 mL 3.0 mol/L NH4Cl solution2.014282100 mL 4.0 mol/L NaNO2 solution+100 mL 4.0 mol/L NH4Cl solution2.515797100 mL 5.0 mol/L NaNO2 solution+100 mL 5.0 mol/L NH4Cl solution3.0178118100 mL 6.0 mol/L NaNO2 solution+100 mL 6.0 mol/L NH4Cl solutionNote: catalyst concentration: 0.3%; base brine: 60°C.Figure 3
Relationship between heat concentration and peak temperature or temperature rise range.


## 2.2.3. Gas Production Rate of Autogenic Heat System under Laboratory Conditions

Figure4 shows the experimental process of the autogenous heating system for gas generation. The gas volume obtained by the reaction is collected by the drainage method. The total amount of gas collected is recorded after the experiment is completed. The gas yield of the system under formation or wellbore conditions is controlled and mastered by changing the concentration of the heating agent. Table 3 and Figure 5 show the relationship between the concentration of the heat generating agent and the amount of gas generated.Figure 4
Experimental process of autogenous heating system for gas generation.Table 3
Experimental data of gas production rate of autogenic heat system.
Concentration (mol/L)Quantity of gas (N mL)Experiment conditions0.51545100 mL 1.0 mol/L NaNO2 solution+100 mL 1.0 mol/L NH4Cl solution1.03495100 mL 2.0 mol/L NaNO2 solution+100 mL 2.0 mol/L NH4Cl solution1.55850100 mL 3.0 mol/L NaNO2 solution+100 mL 3.0 mol/L NH4Cl solution2.08155100 mL 4.0 mol/L NaNO2 solution+100 mL 4.0 mol/L NH4Cl solution2.510192100 mL 5.0 mol/L NaNO2 solution+100 mL 5.0 mol/L NH4Cl solution3.012500100 mL 6.0 mol/L NaNO2 solution+100 mL 6.0 mol/L NH4Cl solutionNote: catalyst concentration: 0.3%; base brine: 60°C.Figure 5
Relationship between heating agent concentration and gas quantity.


## 2.2.4. The Control of Thermal Peak of Autogenic Heat System

Taking the same initial temperature, let two kinds of heat-generating agents react exothermically under an apparent adiabatic condition. By changing the type and amount of the catalyst, we can understand the relationship between the amount of catalyst and the reaction speed.Tables4 and 5 and Figures 6 and 7 show the same catalyst concentration and base brine temperature.(1)
The thermochemical reaction of sodium nitrite and ammonium chloride can hardly be observed at room temperature without adding acid, and only when the solution is heated to more than 60°C can the reaction occur, and the reaction rate is very slow(2)
The thermochemical reaction rate of sodium nitrite and ammonium chloride can be increased by either liquid acid or solid acid and strong acid or weak acid(3)
The catalytic intensity of acid to the reaction between sodium nitrite and ammonium chloride is related to strength of the acid. The higher the catalyst concentration and strength, the greater the rate of thermochemical reaction. It can be seen from the experimental results that the catalytic strength of phosphoric acid is almost the same as that of hydrochloric acid and nitric acid. This is because phosphoric acid is a polybasic acid; when the temperature rises, its dissociation constant increases, providing more H+ ions for the reaction(4)
The higher the catalyst concentration and strength, the shorter the peak time of the system, but the peak temperature is not affected by the catalyst concentrationTable 4
The effect of catalyst concentration on heat generation rate of system.
Catalyst concentration: 0.5% HClCatalyst concentration: 1.0% HClCatalyst concentration: 1.5% HClTime (min)Temperature (°C)Time (min)Temperature (°C)Time (min)Temperature (°C)025 (indoor temperature)025 (indoor temperature)025 (indoor temperature)528529534103110321041153315341545203720402050254025422552304330463052354535483551404640524050454745524549504850505049555155495548605060496047Concentration of system: 100 mL 2.0 mol/L NaNO2 solution+100 mL 2.0 mol/L NH4Cl solution.Table 5
The effect of catalyst types on heat generation rate and thermal peak.
Catalyst: 1% benzoic acidCatalyst: 1.0% HClCatalyst: 1.0% phosphoric acidCatalyst: 1.0% MXTime (min)Temperature (°C)Time (min)Temperature (°C)Time (min)Temperature (°C)Time (min)Temperature (°C)025 (indoor)025 (indoor)025 (indoor)025 (indoor)52852953452810291032104110311531153715451535203420402050203825362542255225413038304630523045353935483551354940414052405040524542455245494553504450505049505555455549554855576045604960476055654465486547655470437048704670527543754775457551Concentration of system: 100 mL 2.0 mol/L NaNO2 solution+100 mL 2.0 mol/L NH4Cl solution.Figure 6
The effect of catalyst concentration on heat generation rate of system.Figure 7
The effect of catalyst types on heat generation rate and thermal peak.When the catalyst concentration is high (the concentration limits of different catalysts are different), the pyrogenic reaction will be accompanied by brown gas, mainly nitric oxide and nitrogen dioxide (toxic). Therefore, when using the pyrogenic system, the concentration of acidic catalyst should be controlled to reduce the production of toxic products.(5)
The addition of a very small amount of acid can greatly increase the rate of thermochemical reaction, indicating that the thermochemical reaction of sodium nitrite and ammonium chloride in acid solution is a typical acid-catalyzed reaction(6)
When the concentration and type of catalyst change, the peak position of the pyrogenic system will change(7)
Catalyst MX reacted smoothly and slowly released H+, and no brown by-product gases such as NO and NO2 were produced during the experiment


## 2.2.5. The Effect of Ambient Temperature on Autogenic Heat System

The relationship between ambient temperature and reaction rate can be understood by changing the ambient temperature of the heating system under the condition of same heating agent concentration, the same catalyst type and concentration, and the apparent adiabatic. The result shows that the higher the ambient temperature is, the faster the heat generation rate of chemical reaction is. Table6 and Figure 8 show the influence of ambient temperature on heat generation rate and heat peak.Table 6
The effect of ambient temperature on heat generation rate and thermal peak.
Ambient temperature: 60°CAmbient temperature: 75°CAmbient temperature: 85°CTime (min)Temperature (°C)Time (min)Temperature (°C)Time (min)Temperature (°C)025 (indoor)025 (indoor)025 (indoor)1—1—1—223232242326341363437457480543578586652685694764783792872889789910751010111111Concentration of system: 100 mL 2.0 mol/L NaNO2 solution+100 mL 2.0 mol/L NH4Cl solution catalyst: 1.0% HCl.Figure 8
The effect of ambient temperature on heat generation rate and thermal peak.


## 2.3. Evaluation of Application Effect of Autogenic Thermochemical Synergistic System

### 2.3.1. The Viscosity-Reducing Property of Autogenic Thermochemical Synergistic System

A certain amount of simulated crude oil from an oil field is placed in a beaker, and the autogenous heat system components are added to the beaker in turn to make it react fully in the beaker, and the temperature changes are recorded. The viscosities of the system of the “thermal peak” and at the end of the reaction are measured by parallel experiments. According to Table7 and Figure 9, the experimental results show that the heat generated during the reaction can effectively reduce the viscosity of heavy oil. And the viscosity of heavy oil can be reduced from 2984 mPa·s to 121 mPa·s when the reaction reaches the peak. The temperature of the mixture can be maintained above 60°C for more than 30 minutes during the reaction process, and the obvious viscosity reduction effect can also be maintained at the end of the reaction.Table 7
Viscosity reduction properties of autogenic heat system.
Temperature (°C)Indoor temperature“Thermal peak”The end of the reactionViscosity (mPa·S)2984121578Figure 9
The variation of temperature with reaction time of autogenic heat system.


### 2.3.2. The Dissolving Paraffin Performance of Autogenic Thermochemical Synergistic System

A certain amount of solid paraffin was placed in a beaker, and those components of the system were added to the beaker in turn to make it react fully in the beaker. The residual solid paraffin content was measured at the end of the reaction, and the reaction time was recorded. It can be seen from the experimental results in Table8 that the autogenic thermochemical system has a good dissolution effect on the fixed paraffin. With the increase of the concentration of the heating agent, the amount of dissolving solid paraffin increases, and the time of dissolving solid paraffin is shorter.Table 8
The dissolving paraffin performance of the system.
Concentration (%)4510Quantity of paraffin dissolved (g)14.721.537.3Time (min)1186Dissolution rate (g/min)1.332.686.21Percentage of paraffin dissolved (%)29.44374.6


### 2.3.3. The Cleaning Organic Fouling Performance of Autogenic Thermochemical Synergistic System

A certain amount of rock particles adhering to heavy oil and organic matter were placed in a beaker, and then, those components of the system were added to the beaker in turn to make it react fully in the beaker. At the end of the reaction, the amount of residual organic matter was measured, and the cleaning capacity of the 100°C distilled water was compared with that of the system. It can be seen from the experimental results in Table9 that the autothermal system has a good cleaning effect on heavy oil and organic matter, compared with 100°C distilled water, and the autothermal system has a better cleaning organic fouling performance.Table 9
The cleaning organic fouling performance of autogenic thermochemical synergistic system.
TypeAutothermic with plugging removal system100°C distilled waterCleaning effect83.60%57.30%PhenomenonSurface of rock particles is basically clean, floating heavy oil, and organic matter on the surface of liquidSome heavy oil and organic matter melt to the liquid surface, and black heavy oil remains on the surface of the rock particlesThe SARA of heavy oil is as follows: saturated hydrocarbon 41.04%, aromatic hydrocarbon 26.24%, resin 14.13%, and asphaltene 18.59%. And the calculation method of the cleaning effect is as follows: reduced weight after cleaning/total weight before cleaning.


### 2.3.4. The Plugging Removal Performance of Autogenic Thermochemical Synergistic System

The test core is the Minghua formation oil sands in the Bohai oilfield (core pipe:25mm∗100mm). Core basic parameters are permeability 3130 md, porosity 28%, and oil saturation 71.5%, consistent with reservoir parameters.Crude oil is an oil sample from a well in the Bohai oilfield (degassing viscosity at 50°C 1931 mPa·s).The system formulation is as follows:(i)
Base solution: 2%KCl solution(ii)
Acid system: 10% HCl+6% HBF4(iii)
Autogenic heating composite system: 2.0 mol/L NaNO2+2.0 mol/L NH4Cl and acid system is alternately injected by 3 slugsAccording to Table10 and Figure 10, the experimental results show that the core permeability is significantly increased than the benchmark permeability, the permeability is increased by more than 2.0 times, and the increase range of core permeability is large, which indicates that the plugging removal effect of the self-heating system combined with the HBF4 system can relieve the pollution of the Bohai heavy oil wells.Table 10
The acidizing effect on core flow test of autogenic heating combined with plugging removal system.
K/K0Pad fluid 1Pad fluid 2Autothermic combined with plugging removal solutionPosterior base liquid10.18933.13232.0281Figure 10
The core flow test of autogenic heating combined with plugging removal system.


## 2.3.1. The Viscosity-Reducing Property of Autogenic Thermochemical Synergistic System

A certain amount of simulated crude oil from an oil field is placed in a beaker, and the autogenous heat system components are added to the beaker in turn to make it react fully in the beaker, and the temperature changes are recorded. The viscosities of the system of the “thermal peak” and at the end of the reaction are measured by parallel experiments. According to Table7 and Figure 9, the experimental results show that the heat generated during the reaction can effectively reduce the viscosity of heavy oil. And the viscosity of heavy oil can be reduced from 2984 mPa·s to 121 mPa·s when the reaction reaches the peak. The temperature of the mixture can be maintained above 60°C for more than 30 minutes during the reaction process, and the obvious viscosity reduction effect can also be maintained at the end of the reaction.Table 7
Viscosity reduction properties of autogenic heat system.
Temperature (°C)Indoor temperature“Thermal peak”The end of the reactionViscosity (mPa·S)2984121578Figure 9
The variation of temperature with reaction time of autogenic heat system.


## 2.3.2. The Dissolving Paraffin Performance of Autogenic Thermochemical Synergistic System

A certain amount of solid paraffin was placed in a beaker, and those components of the system were added to the beaker in turn to make it react fully in the beaker. The residual solid paraffin content was measured at the end of the reaction, and the reaction time was recorded. It can be seen from the experimental results in Table8 that the autogenic thermochemical system has a good dissolution effect on the fixed paraffin. With the increase of the concentration of the heating agent, the amount of dissolving solid paraffin increases, and the time of dissolving solid paraffin is shorter.Table 8
The dissolving paraffin performance of the system.
Concentration (%)4510Quantity of paraffin dissolved (g)14.721.537.3Time (min)1186Dissolution rate (g/min)1.332.686.21Percentage of paraffin dissolved (%)29.44374.6


## 2.3.3. The Cleaning Organic Fouling Performance of Autogenic Thermochemical Synergistic System

A certain amount of rock particles adhering to heavy oil and organic matter were placed in a beaker, and then, those components of the system were added to the beaker in turn to make it react fully in the beaker. At the end of the reaction, the amount of residual organic matter was measured, and the cleaning capacity of the 100°C distilled water was compared with that of the system. It can be seen from the experimental results in Table9 that the autothermal system has a good cleaning effect on heavy oil and organic matter, compared with 100°C distilled water, and the autothermal system has a better cleaning organic fouling performance.Table 9
The cleaning organic fouling performance of autogenic thermochemical synergistic system.
TypeAutothermic with plugging removal system100°C distilled waterCleaning effect83.60%57.30%PhenomenonSurface of rock particles is basically clean, floating heavy oil, and organic matter on the surface of liquidSome heavy oil and organic matter melt to the liquid surface, and black heavy oil remains on the surface of the rock particlesThe SARA of heavy oil is as follows: saturated hydrocarbon 41.04%, aromatic hydrocarbon 26.24%, resin 14.13%, and asphaltene 18.59%. And the calculation method of the cleaning effect is as follows: reduced weight after cleaning/total weight before cleaning.


## 2.3.4. The Plugging Removal Performance of Autogenic Thermochemical Synergistic System

The test core is the Minghua formation oil sands in the Bohai oilfield (core pipe:25mm∗100mm). Core basic parameters are permeability 3130 md, porosity 28%, and oil saturation 71.5%, consistent with reservoir parameters.Crude oil is an oil sample from a well in the Bohai oilfield (degassing viscosity at 50°C 1931 mPa·s).The system formulation is as follows:(i)
Base solution: 2%KCl solution(ii)
Acid system: 10% HCl+6% HBF4(iii)
Autogenic heating composite system: 2.0 mol/L NaNO2+2.0 mol/L NH4Cl and acid system is alternately injected by 3 slugsAccording to Table10 and Figure 10, the experimental results show that the core permeability is significantly increased than the benchmark permeability, the permeability is increased by more than 2.0 times, and the increase range of core permeability is large, which indicates that the plugging removal effect of the self-heating system combined with the HBF4 system can relieve the pollution of the Bohai heavy oil wells.Table 10
The acidizing effect on core flow test of autogenic heating combined with plugging removal system.
K/K0Pad fluid 1Pad fluid 2Autothermic combined with plugging removal solutionPosterior base liquid10.18933.13232.0281Figure 10
The core flow test of autogenic heating combined with plugging removal system.


## 3. Field Test

There are 4 wells of two oil fields that have employed the thermochemical synergistic technology of heavy oil.


### 3.1. Chemical Deicing and Plugging Removal of a Well

In February 2011, the low temperature caused tube freezing from the Christmas tree to the sea level, and the length is about 14 m, which seriously affected the static pressure test and subsequent daily production of the well P2.


#### 3.1.1. Process Plan

(1) Dosage of System. The amount of autogenous heating system prepared and the number of solutions currently prepared are shown in Table 11.Table 11
Statistics of deicing and plugging removal agents.
Reagent typeConcentration (%)Dosage of reagent (kg)Available solution volume (L)NH4ClSaturated solution40107NaNO2Saturated solution4048Pour point reducer501020(2) Slug Design. According to the current situation of the well, the process design is shown in Table 12.Table 12
Design of deicing and plugging removal.
SlugNameDosage (L)EffectFirstPour point reducer solution2Reduce the solidification point of solution in wellboreSecondNH4Cl+NaNO2 supersaturated solution5The autothermic main agent was added to the solution in the wellbore and dissolvedThirdCatalyst solution of autothermal reaction0.5Accelerate the self-heating reaction to release heat quickly to melt the ice(3) Process Program. (1)
Close the main valve, open the paraffin removal valve after emptying, pour 2 L of the pour point reducer into the tubing, then close the paraffin removal valve to open the main valve(2)
Close the main valve, open the paraffin removal valve after emptying, pour 5 L of NaNO2+NH4Cl supersaturated solution into the tubing, then close the paraffin removal valve to open the main valve(3)
Close the main valve to open the paraffin removal valve, pour 0.5 L of the catalyst solution into the tubing, close the paraffin removal valve to open the main valve, shut down the main valve after the liquid flows into the wellbore, and let the solution of the autogenous heat system in the wellbore react for a certain time to release more heat(4)
Cycle above until removal of ice blockage in tubing


#### 3.1.2. Effect Analysis

(1)
Take deicing and plugging removal operations in this well, from March 10 to March 16, during which the actual operation lasted for four days, and the ice column in the plugged tubing was removed for nearly 14 m(2)
According to the location of the ice column in the well, adjust the operational scheme of the reagent to meet the needs of the field. It shows that the heat generating position and time of the solution can be controlled


### 3.2. Field Test of Plugging Removal in Well A23 by Autogenous Heat

The A23 well is located at the high part of the reservoir at the top formation. It initially produces the main oil layer of formation. The vertical depth of the perforated interval is 1645.6 m-1659.3 m and the vertical thickness of the oil layer is 13.7 m.The well carried out second plugging removal operations on April 15 to 16, 2010, and the effect of plugging removal was very good. But a month later, the liquid production began to decrease. The output of the well was low in October 2010, and the reservoir near the wellbore was damaged.


#### 3.2.1. Plugging Removal Process Design

(1)
injection mode: oil ring annulus reverse extrusion, alternate injection(2)
Construction discharge: 3.0-5.5 bpm, which can be adjusted according to spot pressure(3)
Construction pressure: <12 MPa (1740 psi)The fracture pressure gradient is calculated according to 0.017 MPa/m, and the formation fracture pressure is 28.1 MPa. The annular friction is 1 MPa/1000 m, and the maximum injection pressure at the wellhead is 12.45 MPa.Table13 shows how many the injection solutions are needed, and Table 14 estimates how the plugging removal and draining in a well will perform.Table 13
Scale design of injection solution.
Liquid nameLiquid levelNotem3bblsPrepad10.062.9Prepare one for each 30 m3 acid tankTreating fluid20.0125.8Prepare one for each 30 m3 acid tankAfterpad10.062.9Simultaneous prepare with the prepadAutogenic hydrothermal30.0188.7Prepare one for each 30 m3 acid tankSpacer fluid12.075.5Prepare one for each 30 m3 acid tankDisplacement fluid32.0201.3Prepare one for each 30 m3 acid tankTotal fluid volume114717.0Table 14
Program of plugging removal and draining in well A23.
StageFrequency (Hz)Running time (hr)Estimated drain speed (m3/hr)Discharge fluid volume every stage (m3)Estimated cumulative liquid discharge (m3)13545-7202024065-7305034585-740904Power frequency5-7>220Note: the estimated discharge velocity is calculated according to the rated displacement of the pump.


#### 3.2.2. Effect Tracking

Figure11 shows the production curve. As of July 1, 2012, the liquid production of the well increased from 85.8 m3/d to 275.3 m3/d, and the liquid production increased by 3.2 times. Oil production increased from 16.9 m3/d to 27.8 m3/d, and cumulative oil increment is 3052 m3.Figure 11
Production curve of well.


## 3.1. Chemical Deicing and Plugging Removal of a Well

In February 2011, the low temperature caused tube freezing from the Christmas tree to the sea level, and the length is about 14 m, which seriously affected the static pressure test and subsequent daily production of the well P2.


### 3.1.1. Process Plan

(1) Dosage of System. The amount of autogenous heating system prepared and the number of solutions currently prepared are shown in Table 11.Table 11
Statistics of deicing and plugging removal agents.
Reagent typeConcentration (%)Dosage of reagent (kg)Available solution volume (L)NH4ClSaturated solution40107NaNO2Saturated solution4048Pour point reducer501020(2) Slug Design. According to the current situation of the well, the process design is shown in Table 12.Table 12
Design of deicing and plugging removal.
SlugNameDosage (L)EffectFirstPour point reducer solution2Reduce the solidification point of solution in wellboreSecondNH4Cl+NaNO2 supersaturated solution5The autothermic main agent was added to the solution in the wellbore and dissolvedThirdCatalyst solution of autothermal reaction0.5Accelerate the self-heating reaction to release heat quickly to melt the ice(3) Process Program. (1)
Close the main valve, open the paraffin removal valve after emptying, pour 2 L of the pour point reducer into the tubing, then close the paraffin removal valve to open the main valve(2)
Close the main valve, open the paraffin removal valve after emptying, pour 5 L of NaNO2+NH4Cl supersaturated solution into the tubing, then close the paraffin removal valve to open the main valve(3)
Close the main valve to open the paraffin removal valve, pour 0.5 L of the catalyst solution into the tubing, close the paraffin removal valve to open the main valve, shut down the main valve after the liquid flows into the wellbore, and let the solution of the autogenous heat system in the wellbore react for a certain time to release more heat(4)
Cycle above until removal of ice blockage in tubing


### 3.1.2. Effect Analysis

(1)
Take deicing and plugging removal operations in this well, from March 10 to March 16, during which the actual operation lasted for four days, and the ice column in the plugged tubing was removed for nearly 14 m(2)
According to the location of the ice column in the well, adjust the operational scheme of the reagent to meet the needs of the field. It shows that the heat generating position and time of the solution can be controlled


## 3.1.1. Process Plan

(1) Dosage of System. The amount of autogenous heating system prepared and the number of solutions currently prepared are shown in Table 11.Table 11
Statistics of deicing and plugging removal agents.
Reagent typeConcentration (%)Dosage of reagent (kg)Available solution volume (L)NH4ClSaturated solution40107NaNO2Saturated solution4048Pour point reducer501020(2) Slug Design. According to the current situation of the well, the process design is shown in Table 12.Table 12
Design of deicing and plugging removal.
SlugNameDosage (L)EffectFirstPour point reducer solution2Reduce the solidification point of solution in wellboreSecondNH4Cl+NaNO2 supersaturated solution5The autothermic main agent was added to the solution in the wellbore and dissolvedThirdCatalyst solution of autothermal reaction0.5Accelerate the self-heating reaction to release heat quickly to melt the ice(3) Process Program. (1)
Close the main valve, open the paraffin removal valve after emptying, pour 2 L of the pour point reducer into the tubing, then close the paraffin removal valve to open the main valve(2)
Close the main valve, open the paraffin removal valve after emptying, pour 5 L of NaNO2+NH4Cl supersaturated solution into the tubing, then close the paraffin removal valve to open the main valve(3)
Close the main valve to open the paraffin removal valve, pour 0.5 L of the catalyst solution into the tubing, close the paraffin removal valve to open the main valve, shut down the main valve after the liquid flows into the wellbore, and let the solution of the autogenous heat system in the wellbore react for a certain time to release more heat(4)
Cycle above until removal of ice blockage in tubing


## 3.1.2. Effect Analysis

(1)
Take deicing and plugging removal operations in this well, from March 10 to March 16, during which the actual operation lasted for four days, and the ice column in the plugged tubing was removed for nearly 14 m(2)
According to the location of the ice column in the well, adjust the operational scheme of the reagent to meet the needs of the field. It shows that the heat generating position and time of the solution can be controlled


## 3.2. Field Test of Plugging Removal in Well A23 by Autogenous Heat

The A23 well is located at the high part of the reservoir at the top formation. It initially produces the main oil layer of formation. The vertical depth of the perforated interval is 1645.6 m-1659.3 m and the vertical thickness of the oil layer is 13.7 m.The well carried out second plugging removal operations on April 15 to 16, 2010, and the effect of plugging removal was very good. But a month later, the liquid production began to decrease. The output of the well was low in October 2010, and the reservoir near the wellbore was damaged.


### 3.2.1. Plugging Removal Process Design

(1)
injection mode: oil ring annulus reverse extrusion, alternate injection(2)
Construction discharge: 3.0-5.5 bpm, which can be adjusted according to spot pressure(3)
Construction pressure: <12 MPa (1740 psi)The fracture pressure gradient is calculated according to 0.017 MPa/m, and the formation fracture pressure is 28.1 MPa. The annular friction is 1 MPa/1000 m, and the maximum injection pressure at the wellhead is 12.45 MPa.Table13 shows how many the injection solutions are needed, and Table 14 estimates how the plugging removal and draining in a well will perform.Table 13
Scale design of injection solution.
Liquid nameLiquid levelNotem3bblsPrepad10.062.9Prepare one for each 30 m3 acid tankTreating fluid20.0125.8Prepare one for each 30 m3 acid tankAfterpad10.062.9Simultaneous prepare with the prepadAutogenic hydrothermal30.0188.7Prepare one for each 30 m3 acid tankSpacer fluid12.075.5Prepare one for each 30 m3 acid tankDisplacement fluid32.0201.3Prepare one for each 30 m3 acid tankTotal fluid volume114717.0Table 14
Program of plugging removal and draining in well A23.
StageFrequency (Hz)Running time (hr)Estimated drain speed (m3/hr)Discharge fluid volume every stage (m3)Estimated cumulative liquid discharge (m3)13545-7202024065-7305034585-740904Power frequency5-7>220Note: the estimated discharge velocity is calculated according to the rated displacement of the pump.


### 3.2.2. Effect Tracking

Figure11 shows the production curve. As of July 1, 2012, the liquid production of the well increased from 85.8 m3/d to 275.3 m3/d, and the liquid production increased by 3.2 times. Oil production increased from 16.9 m3/d to 27.8 m3/d, and cumulative oil increment is 3052 m3.Figure 11
Production curve of well.


## 3.2.1. Plugging Removal Process Design

(1)
injection mode: oil ring annulus reverse extrusion, alternate injection(2)
Construction discharge: 3.0-5.5 bpm, which can be adjusted according to spot pressure(3)
Construction pressure: <12 MPa (1740 psi)The fracture pressure gradient is calculated according to 0.017 MPa/m, and the formation fracture pressure is 28.1 MPa. The annular friction is 1 MPa/1000 m, and the maximum injection pressure at the wellhead is 12.45 MPa.Table13 shows how many the injection solutions are needed, and Table 14 estimates how the plugging removal and draining in a well will perform.Table 13
Scale design of injection solution.
Liquid nameLiquid levelNotem3bblsPrepad10.062.9Prepare one for each 30 m3 acid tankTreating fluid20.0125.8Prepare one for each 30 m3 acid tankAfterpad10.062.9Simultaneous prepare with the prepadAutogenic hydrothermal30.0188.7Prepare one for each 30 m3 acid tankSpacer fluid12.075.5Prepare one for each 30 m3 acid tankDisplacement fluid32.0201.3Prepare one for each 30 m3 acid tankTotal fluid volume114717.0Table 14
Program of plugging removal and draining in well A23.
StageFrequency (Hz)Running time (hr)Estimated drain speed (m3/hr)Discharge fluid volume every stage (m3)Estimated cumulative liquid discharge (m3)13545-7202024065-7305034585-740904Power frequency5-7>220Note: the estimated discharge velocity is calculated according to the rated displacement of the pump.


## 3.2.2. Effect Tracking

Figure11 shows the production curve. As of July 1, 2012, the liquid production of the well increased from 85.8 m3/d to 275.3 m3/d, and the liquid production increased by 3.2 times. Oil production increased from 16.9 m3/d to 27.8 m3/d, and cumulative oil increment is 3052 m3.Figure 11
Production curve of well.


## 4. Conclusions

(1)
The autogenous heating system was optimized, which could produce high heat at low concentration and was nontoxic(2)
By controlling the type and concentration of the catalyst, the time to reach the thermal peak of the autogenic heating system can be controlled(3)
When the concentration of autogenous heating agent is 1.5 mol/L, the temperature rise is 67°C, which meets the performance requirements of more than 50°C(4)
The autogenic thermochemical synergistic system can effectively reduce the viscosity of heavy oil, dissolve solid paraffin and clean organic fouling, and effectively improve reservoir permeability and increase crude oil production



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*Source: 4988318-2021-09-17.xml*