1. Gas injection scheme
Study on (1) Numerical Simulation
According to the geological research results, a three-dimensional geological model of the experimental area is established. The numerical simulation grid is divided into four grids vertically, forming a grid system with variable depth. The grid direction on the plane is basically consistent with the long axis of the structure, and the total number of grids is 40×42= 1680. On the basis of three-dimensional geological modeling, the indoor experimental data of gas injection flooding are fitted.
PVT phase state experiment fitting: The phase state simulation software Winprop is used to fit the high-pressure PVT experimental data of crude oil in Fang 48 well area, which mainly includes characterization, component combination, saturation pressure calculation, single flash experiment fitting, isocomponent expansion experiment fitting, multi-stage degassing experiment fitting, CO2 injection expansion experiment fitting and phase diagram calculation. Finally, the fluid PVT parameter field which can reflect the actual property change of formation fluid is obtained.
Pseudo-component division: the formation crude oil in Fang 48 well area is combined into six pseudo-components: CO2, N2-C 1, C2-C6, C7-C 16, C 17-C30, C3 1+. In the process of parameter optimization, the fitting effect of saturation pressure, gas-oil ratio, density and other components and fluid viscosity, which have great influence on crude oil properties and flow properties, is emphatically considered.
Study on slim tube experiment fitting and gas injection miscible flooding: Through slim tube experiment fitting, the minimum miscible pressure of CO2 injection into reservoir fluid in Fang 48 well area is determined, and the P-X phase diagram and pseudo-ternary phase diagram of multi-stage contact during gas injection are simulated and calculated. The miscibility and characteristics of reservoir fluids during CO2 injection in Fang 48 well area are analyzed.
Fitting of long-core displacement experiment: The purpose of fitting of long-core displacement experiment is to appropriately correct the parameters such as relative permeability curve and capillary pressure curve by matching the gas injection method with the experimental results, so as to provide practical basic seepage characteristic data for 3D reservoir numerical simulation research. Three long core displacement experiments with CO2 gas injected at different pressures are fitted (Table 6-28).
Table 6-28 Fitting Results of CO2 Gas Injection Long Core Displacement Experiment
On the basis of geological modeling and experimental data fitting, the numerical simulation indexes of six different gas injection rate schemes are predicted (Table 6-29). As can be seen from the table, with the increase of gas injection rate, the oil recovery rate increases. Mainly due to the increase of gas injection rate, the formation pressure keeps rising horizontally, which is more conducive to improving oil displacement efficiency. However, with the further increase of gas injection rate, the oil exchange rate decreases.
Table 6-29 Prediction Results of Main Indicators of Numerical Simulation of Different Gas Injection Rates
From the relationship between gas injection speed and cumulative oil increase (Figure 6-20), with the increase of gas injection speed, the cumulative oil increase has little change, indicating that increasing gas injection speed has no obvious influence on development effect.
Figure 6-20 6-20 Relationship between CO2 Injection Rate and Cumulative Oil Increase
(2) Scheme design results
According to the results of laboratory experiments and numerical simulation, when CO2 15t is injected daily, the prediction index of the scheme is good, and the oil recovery increases with the increase of gas injection rate. At the end of the simulation, the cumulative oil production is 6. 14× 104t, and the recovery ratio is 24.02%. Considering that there is a certain error between the indoor experiment and numerical simulation and the actual situation of the mine, in order to facilitate the actual operation on site, the test process should be accelerated as much as possible, and the conclusion of CO2 flooding test should be drawn as soon as possible. At the beginning of the scheme design, we will inject 20 tons of gas every day, and at the same time, we will follow up and adjust according to the dynamic changes of gas injection wells and connecting wells.
2. Petroleum production technology
(1) implantation process
Pipe: Through the comparative analysis of FRP pipe, NiP permeable pipe and corrosion-resistant alloy steel pipe, J55 steel grade and flat NiP permeable pipe are optimized.
Injection string: Y34 1- 1 14 packer is an integral injection string, which consists of downhole circulation valve, Y34 1- 165438 packer, ball seat and bell mouth. The downhole tools are made of alloy steel with CO2 corrosion resistance, and the pipe string can achieve CO2 corrosion resistance.
Wellhead of water injection well: CO2 corrosion resistance of wellhead of water injection well can be divided into DD, EE and FF levels. DD wellhead materials are 35CrMoEE wellhead materials. The key parts in contact with corrosive media, such as valve core, spacer ring and gland, are made of CO2-resistant alloy steel, while other parts are made of 35CrMoFF wellhead materials, all of which are made of CO2-resistant alloy steel. According to the pressure data, select the well head of water injection well KQ65-35-FF with high pressure and good sealing; Install a one-way valve at the wellhead.
Auxiliary anti-corrosion process: while using anti-corrosion tubing and casing, the tubing uses diesel as isolation fluid and is pretreated with corrosion inhibitor; Corrosion inhibitor is added to the oil casing for pressure balance and corrosion protection to protect the oil and casing. At present, the better corrosion inhibitors at home and abroad mainly include propargyl alcohol, organic amine, imidazoline and quaternary amine. Imidazoline corrosion inhibitors with different concentrations and different partial pressures were tested in Zhongyuan Oilfield, and the corrosion inhibition rate reached 86.7% ~ 96.0%, indicating that imidazoline corrosion inhibitors can well prevent CO2 corrosion. After the tubing string goes down the well, the preservative is replaced in reverse circulation to fill the annulus of the tubing casing, and the preservative is supplemented intermittently in the later injection process. When placing bets, the tubing is extruded into isolated diesel oil first, and then extruded into preservative for tubing pretreatment.
(2) Pumping lifting technology
Tubing and sucker rod: NiP treatment technology mainly relies on NiP layer (thickness 20 ~ 40μ m) to isolate the contact between steel body and corrosive medium, thus achieving the purpose of anticorrosion. The advantages of this technology are simple process and low cost. Considering the compatibility with the testing technology, the oil well adopts the flat combined tubing with thickened outside of the small coupling, that is, the small coupling with nickel and phosphorus penetration outside the thickened tubing is used in the upper 800m, and the flat tubing with nickel and phosphorus penetration is used in other intervals.
The sucker rod adopts Ф 25× Ф 22×Ф19 MMH surface nickel-phosphorus co-infiltration sucker rod; 32mm cylindrical pump is selected as the oil well pump; The pumping unit is YCYJ 10-3-37HB energy-saving pumping unit; In order to meet the requirements of dynamic monitoring and consider CO2 corrosion prevention, the eccentric 250-EE wellhead is selected.
(3) Matching technology of mechanical oil recovery
Air-proof technology: In order to improve the pump efficiency and prevent air lock, an air anchor is installed under the oil well pump.
Wax removal and prevention process: the wax removal and prevention agent adopts oil-soluble wax removal and prevention agent.
Anti-corrosion technology: after the production well takes effect, the mixture of gas, water and oil is corrosive to some extent. In the production process, corrosion inhibitors are used to prevent corrosion, and the dosing system is determined according to the CO2 monitoring quantity of the produced liquid.
Anti-scaling technology: According to the test in Jiangsu Oilfield, scaling occurred in CO2 flooding production wells, and the measure taken was to drip anti-scaling agent into the annulus of oil casing. In 2000, the No.8 Oil Production Plant of Daqing Oilfield studied the underground solid anti-scaling technology, and the main agents were aminotrimethylphosphonic acid and sodium polyacrylate. The indoor experimental results show that the scale inhibitor concentration is in the range of 2.0 ~ 6.0 mg/L, and the scale inhibition rate can reach 90.2% ~ 98.4%. Solidify the scale inhibitor, install it at the lower part of the oil well pump, and enter the well with the production string. The field test results show that the concentration of scale inhibitor in the produced fluid of the test well can be controlled within the effective concentration range, and the validity period is 1 year, which plays a good role in scale prevention. Therefore, in production wells, solid scale inhibitors and scale inhibitors are put into underground oil casings to prevent scaling.
Metering technology: according to the surface flow, the corresponding single well metering technology is determined, and the liquid level recovery method and wellhead oil tank metering or tipping bucket metering method are adopted for simultaneous metering.
3. Ground technology
Injection project: build 1 injection station in the experimental area, freeze and store liquid CO2, and then inject it under pressure. There is a 1 water injection station in the southwest of the water injection well. After CO2 is transported to the injection station by the tanker of CO2 station, it is pumped into 30m3 storage tank by the oil unloading pump. A refrigeration device is set to maintain the temperature of the storage tank at 0 ~ 10℃, and CO2 in the storage tank is injected into the wellhead through an injection pump. Because the liquid supply pump was not considered in the process, it could not run normally during the test, and then it was adjusted to a skid-mounted gas injection device, which met the gas injection requirements in the test area.
Crude oil gathering and transportation project: 5 new oil wells in crude oil gathering and transportation system adopt centralized oil pulling scheme. Single well metering adopts fixed dumper; The oil gathering pipeline is made of molten epoxy powder with a thickness of 350μm or more, which is prefabricated in the factory. The joint is a socket pipe joint, which is welded on site. The structure of the anticorrosive coating in the storage tank is: 2 coats of epoxy zinc-rich primer with dry film thickness of 80μm and 2 coats of epoxy antistatic coating topcoat with dry film thickness of120μ m. ..
4. Programme implementation
The gas injection well (Fang 188- 138) started trial injection in March 2003. This well only encounters F Ⅰ 7 layer, with sandstone thickness 10.3m and effective thickness of 6.0m, and it is injected directly without fracturing. The initial wellhead pressure is 14 ~ 15 MPa, and liquid CO25t is injected every day. By the end of June, 2004, the oil pressure was 13.0MPa, and liquid CO2 was injected about 3t every day. Due to injection conditions and other factors, only the injected liquid CO2596t is accumulated. Since July 2004, according to the plan, the average daily gas injection is about 20t. 65438+At the end of February, 2004, the injection pressure was about 12.5MPa, and the accumulated liquid CO25396t(0. 1079PV) was injected.
In 2005, gas injection continued as planned (about 20t days), and the whole well test was carried out for the gas injection well group from May to July. By the end of 2005, the injection pressure was 12.5 ~ 13.0 MPa, and liquid CO2 15000t(0.3PV) was injected cumulatively.
According to the oil well effect and gas channeling situation of well group, pulse gas injection was changed from June 5 to April 38, 2005, and the parameters such as pulse gas injection period and gas injection speed were optimized by numerical simulation technology. According to the optimized scheme, liquid CO25239t was injected in three stages. By the end of 2006, the cumulative gas injection was 20,373 t, with 0.407PV underground. In 2007, the gas injection was stopped in June 5438+0 ~ February according to the scheme requirements, and gas injection was resumed in April 1 1d, and * * co 2301t was injected; Affected by drilling and other factors, the gas injection wells stopped from May to September; On June+10/October, 5438, the field test of bidirectional profile control in gas injection wells was carried out, and 480m3 and CO2533t profile control agents were injected. By the end of 2007, a total of 220,674 t (0.413pv) had been injected.
The average thickness of sandstone drilled by four old oil wells in the experimental area is 12.9m, and the effective thickness is10.9m.. 199910 ~110, after perforation with YD-89 perforating gun, fracturing is carried out. The average thickness of fractured sandstone in a single well is 12.2m, the effective thickness is 65438+ the average daily oil production of a single well at the beginning is 3.5t, and the oil production intensity is 0.34t.. In August 2004, in order to speed up the test progress, the unfractured well 188- 137, which is 80m away from the gas injection well, was put into production. In the early stage of production, there was almost no natural productivity. In March 2005, the well was tested by huff and puff, and it began to take effect after huff and puff, with the highest daily oil production of1.5t. In July 2004, the test area began to take effect, and gas injection was seen in March 2005. After adjustment measures such as pulse gas injection and well opening between wells, the average daily oil production of a single well is 0.8t and the oil production intensity is 0.08t/d·m after five years of production.