Article pubs.acs.org/EF
Selectivity of Pore-Scale Elastic Microspheres as a Novel Profile Control and Oil Displacement Agent Chuanjin Yao,* Guanglun Lei, Lei Li, and Xuemei Gao School of Petroleum Engineering, China University of Petroleum (East China), No. 66 Changjiang West Road, Qingdao Economic and Technological Development Zone, Qingdao 266580, Shandong, People’s Republic of China ABSTRACT: Pore-scale elastic microspheres were prepared controllably and their swelling property, stability, and creeprecovery property in brine water were analyzed in laboratory. The goal of the research was to study the selectivity of the porescale elastic microspheres as a novel profile control (water injection profile modification) and oil displacement agent. The matching factor between particle size of elastic microspheres and pore throat diameter of sand pack model was introduced to characterize their matching relationship. The results indicate that the optimal matching factor is 1.35−1.55. Besides, the profile control and oil displacement effect were studied using a series of heterogeneous double-tube sand pack models with optimal matching factors. The shunt flow experiments show that when the matching factor is an optimal value, the elastic microspheres prefer to plug the high-permeability layer selectivity and almost do not clog the low-permeability layer. The oil displacement experiments show that the elastic microspheres have the characteristic of plugging water without plugging oil and can improve the sweep status and oil displacement effect of low-permeability layer and low-permeability area in the high-permeability layer. According to the experimental results and actual situation of Block Liu 28-1, an optimal program for the profile control and oil displacement of elastic microspheres was proposed and conducted. The results show that the elastic microspheres can improve the water injection profile effectively. The results also confirm that the matching factor is an appropriate measure to evaluate the profile control and oil displacement effect of elastic microspheres and to guide the field test. the polyacrylamine-Cr6+ gels used for reducing the water/oil ratio.9 Liang et al. found these gels could reduce water permeability more than oil permeability.10 Herbas et al. set up a model to study polymer gels treatment test to improve the injection profile and the sweep factor in a water injector.11 Gels for high-temperature water control and in situ gels have also been studied in recent years.12−14 Chang et al. obtained “colloidal dispersion gels” by cross-linking low concentration polymer solution with small amounts of chromium acetate or aluminum citrate.15 Chauveteauu et al. invented the microgels for profile control.16−18 These microgels are colloidal particles of acrylamide-based polymeric gels cross-linked with zirconium whose properties are easily affected by salinity, pH, shear rate, etc. Therefore, their resistance is weak. The preformed particle gels, which were prepared by using an initiator, acrylamide monomer, cross-linker, and additive had also been used to improve the water injection profile.19−21 These powdered millimeter-sized gel particles can be obtained from crushing and then sieving dry gels, which can swell several fold in water to form a suspension. These particle gels can tolerate high salinity and high temperature and are suitable to improve the development effect of oilfields with strong heterogeneity, high water-cut, and large porous channels.22−24 However, they have no defined shape and surface plugging can easily form, because of their large size.25 An ideal chemical agent for water control treatment in oil reservoirs should have the following properties: tolerance to
1. INTRODUCTION The oil recovery of reservoirs is mainly controlled by the sweep factor and oil displacement efficiency.1,2 For the heterogeneous oilfields, the sweep factor of water flooding is an important evaluation parameter. It not only represents the sweep status of water flooding, but also influences the ultimate recoverable reserves and oil recovery.3 In most oil reservoirs, there are many layers with different permeability. Even in the same layer, it can be heterogeneous or many preponderance flow paths may exist.4,5 The injected water will prefer to flow along the higher permeability layer and the preponderance flow path. A common problem for oilfields is the excessive water production and a rapid decline of oil production. The result is often a premature shut-in of oil wells because the production has become uneconomical. However, there is still a lot of remaining oil in the lower permeability area and the oil recovery is very low.6 In recent years, many chemical agents have been used to control water and enhance oil recovery of heterogeneous oilfields through improving the water injection profiles in water injection wells. Koch and McLaughlin used an inorganic gel to control profile in water injection wells and solved the water breakthrough problem successfully.7 Chen researched a nonpolymer in situ gel for water control treatment of reservoirs.8 Inorganic gel and nonpolymer gel have the advantage of low viscosity and can be pumped at any rate using the ordinary field mixing and injection equipment. However, because of their low selectivity on oil, the success rate of construction was low and the profile control and flooding technology based on crosslinked polymer gels got a better development and application, because of their relatively low cost and supposed selectivity, i.e., only the water permeability was reduced. Nanda et al. studied © 2012 American Chemical Society
Received: April 24, 2012 Revised: July 2, 2012 Published: July 10, 2012 5092
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high salinity and hardness, compatibility with any mix water including seawater, thermal stability, low viscosity, excellent suspension dispersibility, insensitivity to shear, and ability to penetrate into the oil formation deeply, among others.8,26,27 In the early 21st century, a new chemical agent“elastic microspheres”was proposed and has attracted extensive concern of scholars. Some small-scale field tests have been performed in Shengli, Jidong, Dagang Oilfield in China and a better effect of water control and enhanced oil recovery was obtained.28−30 So far, although the matching relationship between elastic microspheres and reservoirs is one of the most important parameters for successful water control and enhanced oil recovery, few studies have comprehensively investigated the effect of elastic microspheres particle size on the profile control and oil displacement behavior. Therefore, in the present paper, a sample of elastic microspheres with a particle size of 4.27− 39.98 μm was prepared controllably through inverse suspension polymerization of acrylamide (AM) and N,N′-methylene bisacrylamide (MBA) in oil phase when [Span80 and Tween80] and APS was used as the dispersion stabilizer and the initiator, respectively. The stability and creep−recovery property of the elastic microspheres in brine water were studied. The matching factor between the particle size of elastic microspheres and the pore throat diameter of sand pack model was introduced to characterize the matching relationship between the elastic microspheres and reservoirs. The plugging, shunt flow, and oil displacement properties then were studied using a series of single-tube sand pack models and heterogeneous double-tube sand pack models under different matching factors. On the basis of these results, we optimized the particle size, concentration, and injection volume of the elastic microspheres, and we performed a field test in the Jidong Oilfield. In addition, the effects of elastic microspheres particle size on the profile control and oil displacement behavior are also presented.
Figure 1. Experimental flow for chemical flooding.
Table 1. Key Parameters of Sand Pack Models sand pack model
porosity [φ] (%)
permeability, k (μm2)
average pore throat radius, r (μm)
matching factor, δa
1
38.00
0.60
7.11
3.25
2
36.17
0.82
8.52
2.71
3
37.15
1.28
10.50
2.20
4
37.44
2.21
13.74
1.68
5
37.41
2.85
15.61
1.48
6
37.09
2.95
15.95
1.45
7
38.39
3.18
16.28
1.42
8
37.83
3.29
16.68
1.38
9
36.92
4.12
18.90
1.22
10
32.00
5.16
22.72
1.02
11
31.03
6.20
25.29
0.91
12
30.10
8.10
29.35
0.79
13
38.96 37.51
3.42 0.64
16.77 7.40
1.38 3.12
14
38.58 39.92
3.42 0.35
16.85 5.33
1.37 4.34
15
38.48 39.44
3.42 0.54
16.87 6.62
1.37 3.49
16
38.83 39.15
2.93 0.62
15.54 7.12
1.49 3.24
17
38.81 38.69
2.81 0.54
15.22 6.68
1.52 3.46
18
38.57 38.45
3.22 0.71
16.34 8.01
1.41 2.89
2. EXPERIMENTAL SECTION 2.1. Materials. The materials included acrylamide (AM, purity of >98.5%), dispersion stabilizer (D, Span80 and Tween80), N,N′methylene bisacrylamide (MBA, purity of >98.0%), ammonium persulfate (APS, purity of >98.0%), sodium chloride (NaCl, purity of >99.5%), ammonium hydroxide (NH4OH, purity of >99.5%), and plant oil. All reagents were used without any further purification. Deionized water was used for the preparation of all aqueous solutions. The brine water with salinity of 5000 mg/L was prepared according to the produced water from Block Gudao in the Shengli Oilfield in China. The produced sand with particle size of 10−100 mesh was obtained from Block Gudao in the Shengli Oilfield in China. A simulated oil sample with viscosity of 16 mPa·s and density of 942.7 kg/m3 at 60 °C was prepared using degassed crude oil from Block Gudao in the Shengli Oilfield in China and mixing it with a certain proportion of kerosene. 2.2. Equipment. The main equipment was the experimental flow for chemical flooding, as shown in Figure 1. The inner diameter and length of the sand pack tube were 2.7 and 82.0 cm, respectively. Other equipment included a Rise-2008 laser particle size analyzer, a XSP8CA microscope, a Nikon Model L110 digital camera, a RheoStress 600 rheometer, a LVDV-II+Pro viscosimeter, an injector, a four-neck flask, a mechanical stirrer, a reflux condenser, dropping funnels, and a constant-temperature water bath. The sand pack models used in this study were all packed with sand from Block Gudao in the Shengli Oilfield, China. Table 1 gives some key parameters of sand pack models. In Table 1, the average pore
a
The average particle size of elastic microspheres for calculation of the matching factor (δ) is 23.10 μm.
throat radius of sand pack model (r, given in units of μm) was calculated as follows:31 5093
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8k φ
where Q is the injection rate (given in units of mL/s), μ the fluid viscosity (given in units of mPa s), A the sectional area of sand pack model (A = πd2/4, expressed in units of cm2), and k0 the initial permeability of sand pack model (expressed in units of μm2). 2.3.4. Profile Control Property Analysis. Three heterogeneous double-tube sand pack models (Nos. 13−15) were used in this study. The temperature of the thermostat was kept fixed at 60 °C, and the injecting rate was 1.0 mL/min (5.24 cm/h). The matching factor between elastic microspheres and high-permeability tube was 1.37− 1.38. First, the brine water with a salinity of 5000 mg/L was injected for 0.5 PV. The elastic microsphere solutions with concentrations of 1000, 2000, and 3000 mg/L then were injected in the three heterogeneous double-tube sand pack models, respectively. Finally, the brine water was injected again for 1.0 PV to investigate the resistance of elastic microspheres to water flushing. The injection pressure (ΔP, given in units of 10−1 MPa) and shunt flow volume (QH and QL, mL) were measured. The shunt rate was defined as the ratio of shunt flow volume (QH or QL) to total flow volume (QH + QL). The permeability was calculated using eq 3 and the ability of profile improvement (f, expressed in units of %) was calculated using eq 5.
(1)
where k is the permeability of sand pack model, μm ; φ is the porosity of sand pack model, dimensionless. The matching factor (δ) between the particle size of elastic microspheres and the pore throat diameter of sand pack model was defined as follows: 2
δ=
dave 2r
(2)
where dave is the average particle size of elastic microspheres (given in units of μm). 2.3. Methods. 2.3.1. Preparation of Microspheres. The elastic microspheres were prepared through inverse suspension polymerization.32−34 The preparation was carried out in a 250-mL four-neck flask. The four-neck flask was equipped with a mechanical stirrer, a reflux condenser, a dropping funnel, and a constant-temperature water bath. First, 100.00 g of plant oil and 12.00 g of dispersion stabilizer (m(Span80): m(Tween80) = 3:1) were introduced into the flask. The flask was then placed in the water bath at a constant temperature of 30 °C with a mixing speed of 360 rpm. Immediately after mixing, half of the aqueous solution of AM, MBA, and APS (6.65 g of AM, 0.16 g of MBA, and 0.33 g of APS were dissolved in 44.00 g deionized water) in the dropping funnel was dripped into the flask within 15 min. When the water phase was suspended in the oil phase completely, the temperature was increased to 75 °C to initiate the polymerization of monomers. Simultaneously, the remaining half of the aqueous solution of AM, MBA, and APS was dripped into the flask at an appropriate dripping rate. NH4OH (20 wt %) was added to adjust the pH to ∼7.0. After reaction for 60 min, the mixture in the flask was cooled and filtered. Thus, the sample of elastic microspheres was obtained. 2.3.2. Physical Property Analysis. A Rise-2008 laser particle size analyzer was used to determine the initial particle size of elastic microspheres in deionized water at 25 °C. The particle size change was measured to characterize the stability of elastic microspheres in brine water with a salinity of 5000 mg/L at different temperatures. Six parallel measurements were performed, and the temperature was 25, 50, 60, 70, 80, and 90 °C, respectively. The average particle size of elastic microspheres was calculated using a Rise-2008 laser particle size analyzer. The shape of elastic microspheres in brine water with a salinity of 30000 mg/L at different temperatures was observed using an XSP-8CA microscope. A LVDV-II+Pro viscosimeter was used to measure the viscosity of elastic microspheres in brine water with a salinity of 5000 mg/L at 60 °C. The concentration of elastic microspheres solution was 1000−3000 mg/L. The creep and recovery property of elastic microspheres was measured using a RheoStress 600 rheometer at 60 °C. First, a constant shear stress of 1.0 Pa was applied on the elastic microspheres system and the linear viscoelastic range was obtained. The constant shear stress then was eliminated and the strain of elastic microspheres versus time was studied.35 2.3.3. Plugging Property Analysis. In this study, 12 single-tube sand pack models with different permeability (numbered 1−12) were used. The temperature of the thermostat was kept fixed at 60 °C, and the injecting rate was 1.0 mL/min (10.48 cm/h). First, the brine water with a salinity of 5000 mg/L was injected for 0.5 PV. The elastic microspheres solution with a concentration of 2000 mg/L then was injected for 2.5 PV. At last, the brine water was injected again for 1.0 PV. The injection pressure difference (ΔP, given in units of 10−1 MPa) was measured and the permeability of sand pack model in the displacement process (k′, given in units of μm2) and the plugging rate of the sand pack model (η, expressed in units of %) were calculated using the following equations:36,37
k′ =
QμL AΔP
η (%) =
k 0 − k′ × 100% k0
f (%) =
(Q H1/Q L1) − (Q H2/Q L2) × 100% (Q H1/Q L1)
(5)
where QH1 and QH2 are the shunt flow volumes of the sand pack tube with high permeability before and after profile control (given in mL); QL1 and QL2 are the shunt flow volume of the sand pack tube with low permeability before and after profile control (given in mL). 2.3.5. Oil Displacement Property Analysis. A heterogeneous sandpacked glass model (10 cm × 10 cm × 0.1 cm) was used to explain the displacement efficiency of elastic microspheres. The middle area, with a width of 4 cm, had a high permeability and both sides of the middle area had a low permeability, as shown in Figure 2. First, the model was
Figure 2. Schematic diagram of heterogeneous sand-packed glass model (10 cm × 10 cm × 0.1 cm).
saturated with a simulated oil sample and water was injected until the water-cut was 100%; then the elastic microspheres solution of 2000 mg/L was injected and, finally, only water was injected. Meanwhile, the fluids distribution photos were taken by Nikon L110 digital camera. The displacement rate was 0.2 mL/min. Three heterogeneous double-tube sand pack models (Nos. 16−18) were used in this study. The temperature of the thermostat was kept fixed at 60 °C, and the injecting rate was 1.0 mL/min (5.24 cm/h). The matching factor between the elastic microspheres and the highpermeability tube was 1.41−1.52. First, the sand pack models were all saturated by the simulated oil sample and the initial oil saturation (Soi, decimal) and initial oil volume (Voi, mL) were calculated. The brine water with a salinity of 5000 mg/L then was injected into the sandpacks until the water-cut was up to 98%, and the residual oil volume (Vr, mL) was calculated. The elastic microspheres solutions with different concentrations of 1000, 2000, and 3000 mg/L were injected for 0.5 PV, respectively. At last, the brine water was injected again until the water-cut was up to 98%. Simultaneously, the oil increment volume (ΔV, mL) was recorded and the oil recovery of water flooding (Rw, %) and enhanced oil recovery of elastic microspheres (EOR, %) was calculated using eqs 6 and 7.
(3)
(4) 5094
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Voi − Vr × 100% Voi
(6)
ΔV × 100% Voi
(7)
EOR (%) =
3. RESULTS AND DISCUSSION 3.1. Physical Properties of Elastic Microspheres. 3.1.1. Basic Physical Properties. The elastic microspheres prepared in this study are milk-white. The effective content of elastic microspheres sample is >94%. The density is ∼1.0 g/ cm3. The viscosity of elastic microspheres solution is 85%. 3.3. Effect of Heterogeneity on Plugging Property. Three heterogeneous double-tube sand pack models (Nos. 13− 15) were evaluated by the change of shunt rate and dimensionless permeability in the injection process of the elastic microspheres with different concentrations, as shown in Figure 12. The initial shunt rate of the high- and lowpermeability tubes while waterflooding is 90% and 10%, respectively. In the injection process of the elastic microspheres, the shunt rate of the high-permeability tube decreases and the shunt rate of the low-permeability tube increases with increasing injection volume of the elastic microspheres. When the injection volume is up to 1.5 PV (Figure 12a, No. 13, 1000 mg/L), 0.5 PV (Figure 12b, No. 14, 2000 mg/L), 0.2 PV (Figure 12c, No. 15, 3000 mg/L), the shunt rates of the highand low-permeability tubes all tended to 50% and the ability of profile improvement ( f) is >90%. The result indicates that the elastic microspheres can improve the water injection profile of a porous medium effectively. When the brine water is injected for 1.0 PV, again the shunt rate of the high- and low-permeability tubes is still maintained at ∼50%, indicating that the elastic microspheres have good resistance to water flushing and the strength of in-depth plugging is high. The figures also show that the permeability of the high-permeability tube is reduced by ∼80%, but the permeability reduction of the low-permeability tube is not obvious. This is mainly caused by the different matching factors of the two tubes. Many elastic microspheres can easily move into the high-permeability tubes with optimal matching factors of 1.38 (No. 13), 1.37 (No. 14), and 1.37 (No. 15), and the plugging rate is up to 80%. However, only some small elastic microspheres can move into the lowpermeability tubes with high matching factors of 3.12 (No. 13), 4.34 (No. 14), and 3.49 (No. 15), and the plugging rate is 85% as the criterion, the optimal matching factor is 1.35−1.55. With an optimal matching factor, the plugging rate obtains the ideal value and the permeability also decreases obviously. However, if the matching factor is extremely large or small, the plugging rate decreases rapidly and the reduction of the permeability is not obvious. When the matching factor is an optimal value of 1.42, the injection pressure presents a characteristic of wave-type variation as shown in Figure 11 (curve a). Although the
Figure 11. Injection pressure change in single-tube sand pack models with different matching factors [δ] (I, primary water injection; II, injection of elastic microspheres solution (2000 mg/L); and III, succeeding water injection).
average particle size of elastic microspheres is greater than the average pore throat diameter of sand pack, the elastic microspheres can still transport into the deep area of sand pack constantly, depending on their deformation and recovery properties. Thus, the elastic microspheres can plug the deep area of the sand pack effectively and the plugging rate is high. When the matching factor is a smaller value of 0.79 (i.e., the average pore throat size of the sand pack is larger), the elastic microspheres can be injected easily and transported in the sand pack smoothly. Thus, the elastic microspheres cannot plug the sand pack effectively and the plugging rate is very low. In addition the injection pressure is excessively small in the entire injection process, as shown in Figure 11 (curve b). When the
3.4. OIL DISPLACEMENT RESULTS Figure 13 shows the fluid distribution in a heterogeneous sandpacked glass model during the elastic microspheres injection process. In Figure 13a, the injected water will go through, along the high-permeability area first; the sweep region is mainly in the high-permeability area, and there is still a lot of remaining oil at both sides. In Figures 13b and 13c, the injected elastic microspheres prefer to the plug the high-permeability area 5097
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Figure 12. Change of shunt rate and dimensionless permeability in elastic microspheres injection process (I, primary water injection; II, injection of elastic microspheres solution [(a) model 13, 1000 mg/L; (b) model 14, 2000 mg/L; (c) model 15, 3000 mg/L]; III, succeeding water injection), and (d) plugging rate of sand pack tubes and injection volume of elastic microspheres for a shunt rate of 50%.
13d that the elastic microspheres can improve the displacement efficiency effectively. Table 2 gives the enhanced oil recovery of elastic microspheres in heterogeneous double-tube sand pack models (Nos. 16−18). Table 2 shows that the oil recovery of water flooding (Rw) is 64.14%−65.28%, and the enhanced oil recovery of elastic microspheres (EOR) is 10.15%−12.47%. Comparing the oil recovery and water-cut reduction of the high-permeability tube with that of the low-permeability tube in each model, it can be seen that the oil recovery mainly comes from the low-permeability tube and the water-cut reduction of the high-permeability tube is higher. This result indicates that the elastic microspheres prefer to plug high-permeability tubes with optimal matching factors of 1.49 (No. 16), 1.52 (No. 17), and 1.41 (No. 18) and improve the swept volume of the lowpermeability layer with high matching factors of 3.24 (No. 16),
Figure 13. Fluid distribution in the heterogeneous sand-packed glass model during (a) original water flooding, (b) the injection of elastic microspheres, (c) the end of elastic microspheres injection, and (d) subsequent water flooding.
(preponderance flow path forming after water flooding), to change the flow direction of subsequent fluid and displace the remaining oil at both sides. It can be seen from Figures 13a and
Table 2. Enhanced Oil Recovery of Elastic Microspheres in Heterogeneous Double-Tube Sand Pack Models Rw (%)
a
sand pack model
Cma (mg/L)
sand pack type
Soi
single
16 16
1000 1000
high-permeability tube low-permeability tube
0.78 0.68
17 17
2000 2000
high-permeability tube low-permeability tube
18 18
3000 3000
high-permeability tube low-permeability tube
EOR (%) total
single
total
78.18 52.37
65.28
5.44 12.26
10.15
0.81 0.65
83.07 46.90
64.99
4.79 14.59
12.20
0.76 0.66
80.37 48.24
64.14
4.66 14.43
12.47
Concentration of elastic microspheres solution (mg/L). 5098
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ultimate swelling times of elastic microspheres in brine water with a salinity of 5000 mg/L at 90 °C was 2.18. Targeting an optimal matching factor of 1.35−1.55, the elastic microspheres with average initial particle size of 21.0 μm (0.4−50 μm) were selected. In addition, the injection concentration was controlled at 1500−2000 mg/L by adjusting the flow rate of the proportioning pump. In the first slug, the elastic microspheres of 2000 mg/L and 20−50 μm was used to plug the large channels and in the second slug, the elastic microspheres of 1500 mg/L and 0.4−30 μm was used to perform in-depth profile control and oil displacement. The total injection time was ∼65 days. 4.3. Field Test Results and Discussion. After profile control and oil displacement of elastic microspheres, the injection pressure of water well L28-4 increased from 10 MPa to 14 MPa gradually. This result indicates that the elastic microspheres have been injected into the formation successfully. From the water injection profile change of well L28-4 (as shown in Figure 15b), it can be seen that the water absorption rate of the target layer (No. 46) with a optimal matching factor of 1.45 reduced from 72.8% to 25.8% and the water absorption of the main oil-bearing layers with high matching factors of 3.20 (No. 41), 3.12 (No. 43), and 2.56 (No. 44) increased greatly. These results indicate that the elastic microspheres have plugged the large channels and high-permeability layers effectively. After field testing, five oil wells achieved a better effect of water reduction and oil increase. From the oil production and water-cut change of oil well L28-2 as shown in Figure 15c, it can be seen that the oil production of oil well L28-2 increased from 1.2 t/d to 6.7 t/d and the water-cut reduced from 98.5% to 91.8%. In addition, the total oil production of Block Liu 28-1 increased from 72.5 t/d to 132.1 t/d, the water-cut reduced from 42.5% to 27.8%, and the increasing rate obviously slowed down (as shown in Figure 15d). Until December 2007, the cumulative incremental oil was 3520 t. These results indicate that the matching factor is an appropriate measure to evaluate the profile control and oil displacement effect of elastic microspheres and to guide the field test.
3.46 (No. 17), and 2.89 (No. 18). In addition, the water-cut decreases by ∼5.0%, but the oil production increases. This result indicates that the elastic microspheres have the effect of increasing oil production and decreasing water-cut. Another result can be seen that increasing the concentration of elastic microspheres can enhance oil recovery further, but the increase rate becomes smaller. Therefore, in order to obtain a better economic benefit, the concentration of elastic microspheres should be controlled reasonably.
4. FIELD APPLICATION 4.1. Overview of Block Liu 28-1. Block Liu 28-1 lies in the west of Liuzhong Anticline in the Jidong Oilfield and the oil-bearing formation is mainly the oil groups of Es32-I and Es33II. The oil-bearing area is 0.4 km2, the geological reserves are 136.5 × 104 t, the reservoir buried depth is 2750−3000 m, the initial reservoir temperature is ∼90 °C, and the salinity of formation water is ∼5000 mg/L. The reservoir is composed of feldspar sandstone and quartz sandstone, the oil layers are thick, and their distribution is stable. The oil layer belongs to fan-delta deposition with good physical properties. The porosity is 9%−22%, the permeability is 10−1000 × 10−3 μm2. This test region had been developed with water flooding for 16 years. Up to July 2007, there are six oil wells and five water wells, the oil production rate is 72.5 t/d, the total watercut is 42.5%, the cumulative oil production is 16.95 × 104 t, and the oil recovery is only 12.42%. Now, the water injection profiles in water wells are uneven and the development effect is becoming worse and worse. Thus, it is very important to take measures to control profile and enhance oil recovery further. 4.2. Optimization of Injection Parameter. Because of the low viscosity, excellent suspension dispersibility, insensitivity to shear, and high tolerance to salinity of the elastic microspheres, the original water injection pipelines and pump station do not need to be reconstructed, and the elastic microspheres can be conveniently injected online, using the apparatus and procedure described in Figure 14. Thus, the traditional way, using a big pump to control the profile only for a short time, is changed and the cost is also reduced. In July 2007, a field test was carried out in Block Liu 28-1 (as shown in Figure 15a) in the Jidong Oilfield of China. The target layer for profile control was layer No. 46 and some large channels might exist in this layer. According to the core analysis results, the pore throat size was 31.7 μm. In Figure 6, the
5. CONCLUSIONS A novel profile control and flooding agent “pore-scale elastic microspheres” with an effective content of >94%, a density of 1.0 g/cm3, and initial particle size of 4.27−39.98 μm is prepared by inverse suspension polymerization. The viscosity of the elastic microspheres solution is
