CN102828733B - Method for extracting residual crude oil in oil field by using foam compound system - Google Patents

Abstract

The invention relates to a method for exploiting remaining crude oil in an oil field by using a foam composite system, and belongs to the technical field of oil field tertiary oil recovery. It is characterized in that the following steps are adopted: (1) water flooding in the early stage of the oilfield; (2) the main slug is injected into the foam composite system, and the foam composite system injected by the main slug is composed of a ternary composite system and nitrogen gas at a ratio of 1:1. The volume ratio is alternately injected to form; (3) the auxiliary slug is injected into the foam composite system, and the foam composite system injected by the auxiliary slug is formed by alternately injecting the ternary composite system and nitrogen at a liquid-to-gas volume ratio of 0.25:1; (4) Subsequent water flooding in the oil field; wherein, the ternary composite system in the step (2) and step (3) is 1.2% (weight) NaOH, 0.3% (weight) surfactant, 0.15% (weight) partial hydrolytic polymerization Acrylamide HPAM, balance water. The invention can better exploit the remaining oil in the middle and low permeability layer, and increase the economic benefit.

Description

A method for exploiting remaining crude oil in an oil field using a foam composite system

technical field

The invention belongs to oil field tertiary oil recovery technology, and specifically relates to a foam composite system and a method for exploiting remaining crude oil in an oil field by using the foam composite system.

Background technique

At present, many oil fields in China are in the stage of high water cut and high recovery degree, low comprehensive recovery rate, low production of many wells. In the 1980s, my country developed chemical flooding tertiary oil recovery technology. Tertiary oil recovery is the use of physical, chemical and biological means to continue to exploit the remaining oil in the ground. Now the chemical flooding technology is in a vigorous development stage, and the research work on chemical flooding mainly includes polymer flooding, binary compound flooding of surfactant-alkali/polymer, and ternary compound flooding of alkali-surfactant-polymer Drive and so on.

However, because the polymer is controlled by its oil displacement mechanism, generally it can only increase the recovery rate by about 7-15%. The application of binary compound flooding is also limited due to the large amount of chemicals required, high cost and relatively low economic benefits. ASP flooding takes into account the dual advantages of surfactant flooding and polymer profile control, the oil-water interfacial tension can be effectively reduced, and the oil displacement efficiency can be greatly improved on the basis of cost reduction, but the recovery factor still needs to be further improved .

Most of the foam in the foam flooding agent used in the oil field is prepared from gas and solution on the ground, or by means of the agitation of the bottom hole gas and the addition of surfactants to make the bottom hole fluid become foam, and the bubbles are stable Poor performance, uneven distribution in the formation, greatly restricted in field application.

Contents of the invention

The invention provides a method for exploiting remaining crude oil in an oil field by using a foam composite system. Foam composite flooding is the introduction of gas phase into the ASP flooding system, and the gas phase and liquid phase form foam.

Take the following steps:

(1) Water flooding in the early stage of the oilfield;

(2) The main slug is injected into the foam composite system, and the foam composite system injected into the main slug is formed by alternately injecting the ternary composite system and nitrogen at a liquid-to-gas volume ratio of 1:1;

(3) The auxiliary slug is injected into the foam composite system, and the foam composite system injected by the auxiliary slug is formed by alternately injecting the ternary composite system and nitrogen at a liquid-to-gas volume ratio of 0.25:1;

(4) Subsequent water flooding in the oil field;

Wherein, the ternary composite system in the step (2) and step (3) is 1.2% (weight) NaOH, 0.3% (weight) surfactant, 0.15% (weight) partially hydrolyzed polyacrylamide HPAM, the balance for water.

Preferably, the surfactant is alkylbenzene sulfonate ORS-41.

Preferably, wherein the slug size of the foam composite system injected by the main slug in the step (2) is 0.1-0.3PV (Porous Volume, pore volume multiple).

Preferably, wherein the slug size of the foam composite system injected by the auxiliary slug in the step (3) is 0.05PV.

Advantages of the invention

The foam composite system provided by the invention can react to form foam under formation conditions, and the generated foam is stable and evenly distributed. The foam composite system solution added has high flow resistance and good fluidity control ability, and can expand displacement Larger swept volume, enhanced oil washing capacity, and the injection system can selectively enter the middle and low permeability layers, better exploit the remaining oil in the middle and low permeability layers, and increase economic benefits.

Description of drawings

Fig. 1 Comparison of core flooding experimental effects of several displacement methods;

Fig. 2 Comparison of injection pressure of several displacement methods;

Fig. 3 The relationship curve between the water content of the central well and the injection pore volume multiple;

Fig. 4 The relationship curve between the recovery factor of the central well and the injection pore volume multiple.

detailed description

In order to further understand the present invention, the preferred embodiment of the present invention is described below in conjunction with Daqing Oil Field No. 1 Plant and No. 6 Plant Development Examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than to the claims of the present invention limit.

Example one:

The No. 1 oil production plant pile 106 in Daqing Oilfield has an oil-bearing area of 1.5km ² , a crude oil reserve of 1.12 million tons, and a calibrated recovery rate of 29.7%. The thickness of the oil layer in the eastern block is between 2.3 and 9.1 meters, and the oil layer is roughly distributed in an east-west direction. It is a high-pressure porosity and medium permeability oil layer, with an average porosity of 33.9%, and an air permeability of 556.7mD. The selectivity is medium. The relative density of surface crude oil is 0.9382-0.9552, the viscosity of crude oil is 340mPa·s, the wax content is 9.43-11.83%, the freezing point is low, the original formation pressure is 14.08MPa, and the pressure coefficient is 1.017. The salinity of formation water is 2710~3666mg/L, among which the mass concentration of chloride ion is 1167~1697mg/L, which is MaHCO ₃ water type.

The mining is mainly carried out in the east of Zhuang 106 block. There are 9 oil and water wells in the east of Zhuang 106 block. 7. Well 106-45.

Comparison of oil displacement effects of injection foam composite systems. Four sets of water flooding + foam compound flooding, water flooding + ASP flooding, water flooding + polymer flooding, and water flooding were designed in the indoor experiment to compare the oil displacement effects. The results show that water flooding + foam flooding has the least amount of remaining oil and the largest range of enhanced oil recovery. Figure 1. This is because the foam composite system utilizes the ultra-low interfacial tension, high viscosity, and high fluidity control ability of the ternary composite system to effectively block high-permeability layers, control water channeling, and increase oil displacement. Efficiency and increased sweep volume. A large number of laboratory experiments and field data show that the recovery of multi-component foam composite flooding is about 8% higher than that of ASP flooding. Among them, water flooding + ASP flooding, water flooding + polymer flooding, and water flooding are all carried out by methods known in the art.

Wherein water flooding+foam composite flooding of the present invention adopts following steps:

Firstly, the ternary composite system is prepared as 1.2% (weight) NaOH, 0.3% (weight) surfactant, 0.15% (weight) partially hydrolyzed polyacrylamide HPAM, and the balance is water. Then use the following steps to extract oil:

(1) Water flooding in the early stage of the oilfield;

(2) The main slug is injected into the foam composite system formed by alternately injecting the ternary composite system and nitrogen at a liquid-to-gas volume ratio of 1:1;

(3) Auxiliary slug injection is a foam composite system formed by alternating injection of ternary composite system and nitrogen at a liquid-gas volume ratio of 0.25:1;

(4) Subsequent water flooding in the oilfield.

Determination of main slug size for injected foam composite systems. Five sets of schemes of 0.1PV, 0.2PV, 0.3PV, 0.4PV and 0.5PV for the main slug injection composite system were designed by indoor simulation, see Table 1. The simulation results show that after injecting the foam composite system, the oil production increases obviously, but the accumulative oil increase range of each scheme is the same. From the perspective of the cost of chemical dosage, the injection slug size of Scheme S1 is 0.1PV, which is more economical, has strong technical feasibility, and has the largest output-input ratio. From this point of view, the choice of scheme S1 for injecting the main slug, that is, injection of 0.1PV foam composite system is the best for oil displacement, followed by injection of 0.2PV.

Table 1 Effect of main slug size on oil increment

plan Slug size (PV) Cumulative fuel increase (square) Increased cost (10,000 yuan) Increased net income (10,000 yuan) S1 0.1 1532.34 86 138.46 S2 0.2 1719.95 172 120.78 S3 0.3 1802.805 258 112.23 S4 0.4 1893.325 344 101.37 S5 0.5 1954.28 430 94.35

Determination of the size of the auxiliary slug injected into the foam composite system. At the same time, indoor simulations designed five sets of schemes for injecting secondary slug composite systems of 0.05PV, 0.06PV, 0.07PV, 0.08PV, and 0.09PV under the fixed main slug size of 0.1PV, see Table 2. The simulation results show that after injecting the secondary slug of the foam composite system, the oil increment increases obviously on the original basis, but the accumulative oil increment of each scheme is the same. From the perspective of the cost of chemical dosage and the net income, the scheme S6 is more economical to inject a secondary slug with a size of 0.05PV, has strong technical feasibility, and has a large ratio of output to input. From this point of view, it is better to choose the scheme S6 for injecting the auxiliary slug, that is, injecting 0.05PV foam composite system for oil displacement.

Table 2 Effect of auxiliary slug size on oil production

plan Slug size (PV) Cumulative fuel increase (square) Increased cost (10,000 yuan) Increased net income (10,000 yuan) S6 0.05 752.46 43 63.92 S7 0.06 845.54 51.6 54.19 S8 0.07 913.43 60.2 47.10 S9 0.08 952.41 68.8 43.02 S10 0.09 985.91 77.4 39.52

Field effect after injecting foam composite system. According to the optimal parameters determined by the above simulation tests, it can be obtained from the actual application in Zhuang 106 Block of the No. 6 Oil Production Plant in Daqing. The flow resistance is increased, and the swept volume is enlarged. In the foam composite system flooding, the oilfield water flooding recovery rate is 28%, after the foam composite flooding, the recovery rate is finally increased by 4.92%, and the block water cut is reduced.

Economic benefits after injecting foam composite systems. Due to the economic input of 324.38 tons of chemical agents in foam flooding, the total chemical cost was 13.164 million yuan, and the site construction and equipment costs totaled 740,000 yuan, with a total investment of 13.904 million yuan. According to the forecast results, the accumulative increase of 11,424 tons of oil in 5 years, the crude oil price is 35 million yuan/ton, and the economic benefit will be 39.984 million yuan, and the output-input ratio will reach 2.88. From this point of view, this technology is economically feasible.

Example two:

Daqing Oilfield No. 1 Oil Production Plant is located in the northern part of the Sazhong Development Zone. It starts from the third row of the first area in the north, reaches the third row in the south, reaches the 98# fault in the west, and ends in the eastern transition zone in the east. The oil-bearing area of the Sapu oil layer is 25.79km ² , and the geological reserves are 16558.82×10 ⁴ t, of which the geological reserves of the Sa+Pu Group II oil layer are 11673.27×10 ⁴ t, accounting for 70.5% of the reserves of the Sapu oil layer in the block, and the reserve abundance is 452.62×10 ⁴ t/km ² . The Sa and Pu oil layers are a set of interbedded deposits of gray, gray-green, and brown sand-mudstones, and the bedding is mainly horizontal bedding, containing ostracod fossils. The reservoir space of the oil reservoir is dominated by primary intergranular pores, with a porosity of 22-26%, an average porosity of 24.32%, an original oil saturation of 56-76%, an air permeability of 200-1600mD, and an average permeability of 784mD.

According to the well selection principles and standards, the water wells in the fault-east oil layer area of the North 1 area were analyzed, and 8 water wells were selected for water flooding depth profile control, and the profile control well area was eight injection and twenty-one production. The profile control well group consists of North 1-41-P254, North 1-41-P261, North 1-44-P256, North 1-44-P262, Middle 11-P245, Middle 11-P252, Middle 12-P215, Middle 12- P216 consists of 8 water wells, 21 oil wells in the well area, and 6 production wells in the center.

Determination of main slug size for injected foam composite systems. Since the size of the slug affects the oil displacement effect and economic evaluation effect, five sets of schemes for injecting composite systems with main slugs of different sizes were designed by indoor simulation, as shown in Table 3. The simulation results show that the accumulative oil increment of each scheme is equal, and the scheme S3 has the highest net income when the main slug is injected with a size of 0.3PV, has strong technical feasibility, and has a large ratio of output to input. From this point of view, it is better to inject the main slug to select scheme S3, that is, to inject 0.3PV foam composite system for oil displacement.

Table 3 Effect of main slug size on oil production

plan Slug size (PV) Cumulative fuel increase (square) Increased cost (10,000 yuan) Increased net income (10,000 yuan) S1 0.1 1431.37 86 109.97 S2 0.2 1505.83 172 122.19 S3 0.3 1691.61 258 143.01 S4 0.4 1783.81 344 127.32 S5 0.5 1826.59 430 110.76

Determination of the size of the auxiliary slug injected into the foam composite system. The indoor simulation also designed five sets of schemes for injecting composite systems with different sizes of secondary slugs under the fixed main slug size of 0.3PV, see Table 4. The simulation results show that the injection of the secondary slug significantly improves the recovery again. However, there is little difference in the oil-increasing effects of the various schemes. Combining the cost of chemicals and the net income, scheme S6 is more economical to inject a secondary slug with a size of 0.05PV, has strong technical feasibility, and has a large ratio of output to input. From this point of view, it is better to inject 0.05PV foam composite system into the secondary slug to select scheme S6 for oil displacement.

Table 4 Effect of auxiliary slug size on oil production

plan Slug size (PV) Cumulative fuel increase (square) Increased cost (10,000 yuan) Increased net income (10,000 yuan) S6 0.05 843.41 43 54.42 S7 0.06 952.06 51.6 43.07 S8 0.07 1013.93 60.2 36.60 S9 0.08 1054.28 68.8 32.39 S10 0.09 1092.47 77.4 28.39

Field effect after injecting foam composite system. According to the optimal parameters determined by the above simulation tests, it can be obtained from the actual application in the first area of North Daqing Oil Production Plant. Compared with foam flooding and ASP flooding, the decrease in water cut is large and the period of low water cut is long, as shown in Figure 3. Foam flooding increases oil recovery by 30 percentage points compared with water flooding, and increases oil recovery by 10 percentage points compared with ASP flooding, as shown in Figure 4.

Economic benefits after injecting foam composite systems. Since 421.67 tons of chemical agents were put into the foam flooding, the total chemical cost was 15.127 million yuan, and the on-site construction and equipment costs totaled 894,000 yuan, totaling 16.021 million yuan. According to the forecast results, the accumulative oil increase will be 11,373.9 tons within 5 years, the crude oil price will be 35 million yuan/ton, the economic income will be 39,809,650 yuan, and the output-input ratio will reach 2.48.

Claims (2)

1. A method for exploiting remaining crude oil in an oil field, characterized in that the following steps are adopted: (1) Water flooding in the early stage of the oil field; (2) The main slug is injected into the foam composite system, and the foam composite system injected by the main slug is formed by alternate injection of the ternary composite system and nitrogen at a liquid-gas volume ratio of 1:1; (3) the secondary slug is injected into the foam composite system, and the foam composite system injected by the secondary slug is formed by alternate injection of the ternary composite system and nitrogen at a liquid-gas volume ratio of 0.25:1; (4) Subsequent water flooding in the oil field; Wherein, the ternary composite system in the step (2) and step (3) is 1.2wt% NaOH, 0.3wt% surfactant, 0.15wt% partially hydrolyzed polyacrylamide HPAM, and the balance is water; Wherein, the slug size of the foam composite system injected by the main slug in the step (2) is 0.2-0.3PV; wherein, the slug size of the foam composite system injected by the secondary slug in the step (3) is 0.05PV PV. 2. The method according to claim 1, characterized in that: the surfactant is alkylbenzenesulfonate ORS-41.