(Urumqi 8300 1 1 of Northwest Petroleum Bureau of Xinxing Oil Company)
Tahe 1 and No.2 oilfields adopt the mode of "horizontal well+vertical well" to exploit the Lower Triassic Oil Formation and Middle Triassic Oil Formation. Through the analysis of the breakthrough time of vertical well and horizontal well bottom water and its influencing factors, we can draw the following conclusions: No matter whether the single well production allocation of horizontal wells is higher or lower than its critical production, the water-free oil production of horizontal wells is greater than that of vertical wells under the same geological conditions. If a horizontal well is put into production below the critical production, its waterless period is much longer than that of a vertical well.
In practical application, the effective vertical permeability around the wellbore can be determined or verified according to the water breakthrough time of the bottom water reservoir. If the actual water breakthrough time is far beyond the theoretical waterless period, it can be preliminarily judged that there is an interlayer near the wellbore. Combined with the analysis of adjacent wells in waterless period, the distribution of interlayer can be roughly judged, and combined with the logging curve of horizontal section of horizontal well, it is helpful to judge the water outlet position of horizontal section
Breakthrough time of bottom water, vertical permeability, critical production of waterless oil production
Tahe 1 No.2 Oilfield adopts "horizontal well+vertical well" to exploit Triassic Lower Oil Formation and Middle Oil Formation. By analyzing the breakthrough time of vertical well and horizontal well bottom water and its influencing factors, we can draw the following conclusions: under the same geological conditions, the waterless oil production of horizontal well is higher than that of vertical well, regardless of whether the single well allocation production of horizontal well is higher or lower than its critical production. That is, when the production allocation of horizontal wells is higher than its critical production (at this time, it is also higher than the daily production of vertical wells under the same conditions), the breakthrough time of bottom water is equivalent. If a horizontal well starts production below the critical production, theoretically the waterless period is infinite. In practice, because the daily output of a single horizontal well cannot always be lower than the critical output of declining varieties, it will also encounter water, but its waterless period is much longer than that of a vertical well.
In principle, when the vertical permeability near the wellbore of a single well is known, the water breakthrough time formulas (1- 1) and (1-4) of horizontal wells and vertical wells in bottom water reservoirs can be used to predict the water-free period of a single well. According to full-diameter core analysis, the ratio of vertical permeability to horizontal permeability in Tahe 1 and No.2 oilfield development layers is 1: 1.5, 1: 1. In practical application, due to the influence of factors such as the number of coring wells, limited full-diameter analysis interval, heterogeneity on the reservoir plane, vertical permeability, etc., it will be reduced due to the vertical distribution of interlayer in the reservoir, especially in the oil-bearing interval. If the same numerical calculation is applied, it will bring great errors, and different wells should determine the values according to specific conditions. Therefore, it is of little significance to predict the breakthrough time of bottom water for Tahe 1 and No.2 oilfields with serious reservoir heterogeneity. On the contrary, from the actual water-free period, according to the formulas (1- 1) and (1-4), the effective vertical permeability near the wellbore of a single well can be calculated, and this important parameter can be obtained. After determining the effective vertical permeability near the wellbore of each well in the oilfield, if the actual water breakthrough time far exceeds the theoretical waterless period, combined with the analysis of the waterless period of adjacent wells, it can be preliminarily judged that there is an interlayer near the wellbore; Based on the analysis of water-free period of horizontal well and the logging curve of horizontal section of horizontal well, it is helpful to judge the water outlet position of horizontal section.
This paper mainly analyzes the breakthrough time of bottom water in Tahe 1 and No.2 oilfields and its influencing factors, and tries to apply it in this oilfield in order to help and draw lessons from reservoir analysis and oil production.
1 water breakthrough time of bottom water reservoir
As we all know, when the cumulative oil production without water is constant, the higher the single well allocation, the shorter the breakthrough time of bottom water. The production allocation of horizontal wells is higher than that of vertical wells, so is the waterless oil production period necessarily longer than that of vertical wells?
1. 1 vertical bottom hole water breakthrough time
Sobocinski formula and Cornelivs formula for breakthrough time of vertical wells in bottom water reservoirs and their symbolic meanings are as follows:
Essays on exploration and development of oil and gas fields in northern Tarim basin
Where: TBT-water breakthrough time (d);
μ 0-viscosity of underground crude oil (MPa s);
ψ-porosity;
H—— oil layer thickness (m); -Water breakthrough time (dimension1);
ρw and ρ 0-density of formation water and formation oil (g/cm3);
Kv, KH—— vertical permeability (10-3 μ m2);
M—— water-oil mobility ratio;
α-m < 1 is 0.5, 1 < m < 10 is 0.6;
Z—— the height of water cone (dimension1);
Hp—— thickness of perforation section (m);
Bo-volume coefficient of underground crude oil;
Q-Oil production (m3/day).
1.2 Breakthrough time of bottom water
The theoretical formula for calculating the breakthrough time of horizontal bottom water proposed by Ozakan and Raghavan assumes that the oil-water interface of the reservoir is a constant pressure boundary and the breakthrough time of bottom water is:
Essays on exploration and development of oil and gas fields in northern Tarim basin
Where: FD-micro displacement efficiency (dimension1); E- sweep coefficient is a function of effective well spacing aD, dimension I length LD, dimension I vertical distance ZWD and dimension I wellbore radius rWD, that is, E=f(aD, LD, ZWD, rWD) (dimension I);
SWC- irreducible water saturation (decimal);
Sor- residual oil saturation (decimal);
LD- length (dimension1);
L—— length of horizontal section (m);
Zwd- vertical distance (dimension1);
Zw-vertical distance between horizontal section and oil-water interface (m); Other symbols have the same meanings as before.
The formula (1-4) can be rewritten as:
Essays on exploration and development of oil and gas fields in northern Tarim basin
2. Influencing factors of bottom water breakthrough time
2. 1 theoretical analysis
According to the formula (1-8), the water-free oil production is only related to the sweep coefficient function e of horizontal wells and vertical wells (other parameters depend on the reservoir properties and fluid properties of the formation). It can be seen that the key to improve the waterless oil production of bottom water reservoir is to find a completion method that can greatly improve the sweep efficiency, Tan, Tahe Oilfield Horizontal Well Reservoir Engineering Stage Research Report 1 No.2, Planning and Design Institute of Northwest Petroleum Bureau, 1999.
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Figure 1 shows the relationship between vertical well sweep coefficient function e, effective well spacing aD, vertical well opening b and size-borehole raDius rWD, and the definitions of ad and rWD are as follows:
Essays on exploration and development of oil and gas fields in northern Tarim basin
Where: rev-drainage radius of shaft (m); Other symbols have the same meanings as before.
Figure 1 shows that when rWD is constant, E is inversely proportional to B and directly proportional to aD, but aD only works when it is less than 2 (aD=2 can also be used to determine the spacing of vertical wells). Once the reasonable well spacing of vertical well pattern is determined, only the opening of vertical wells can be adjusted. When b = 25%, as can be seen from the figure 1, the corresponding E= 1.3.
Fig. 2 shows the relationship among sweep efficiency e, effective well spacing aD, size-length LD and size-vertical distance ZwD of horizontal wells in bottom water reservoirs.
Figure 2 shows that when ZWD is constant, the e of horizontal wells is proportional to aD and LD, but a. only works when it is 2 ~ 4 (at this time, ad = 2 ~ 4 can also be used to determine the well spacing of horizontal wells; In addition, the longer the L., the bigger the advertisement is needed. Once the reasonable spacing of horizontal wells is determined, the only way to effectively improve E is to increase the horizontal section of horizontal wells.
From the above analysis, it can be seen that the only way to effectively improve the sweep coefficient function is to increase the horizontal length of horizontal wells or reduce the opening of vertical wells.
Figure 1 vertical well displacement efficiency figure 1 vertical well displacement efficiency
Figure 2 Sweep coefficient of horizontal well Figure 2 Displacement coefficient of horizontal well
Fig. 3 shows the influence of dimensionless length LD and opening b on sweep coefficient function e of horizontal or vertical wells.
As can be seen from Figure 3, the range of vertical well sweep coefficient E is limited in the lower left corner of the figure: As 6 decreases from 1 to 0.0 1, E increases from 0.0 1 to1; The range of the horizontal well E can be divided into two parts: one part is surrounded by the vertical well E (the lower left corner of the dotted line), and the other part is unique to the horizontal well, which is much higher than the vertical well E. As can be seen from Figure 3, as long as the LD of the horizontal well is greater than 1(kv = KH, the homogeneous reservoir and the heterogeneous reservoir with kv=0. 1kh can be obtained from the formula 1. When LD= 1, the influence of the horizontal length of the horizontal well is 2h and 6.3 h) or the horizontal length is greater than 6.3h, then E means that the oil production of the horizontal well is much higher than that of the vertical well (because the horizontal section of the horizontal well cannot be less than 6.3 times of the oil layer thickness). That is to say, under the same daily output, the bottom water breakthrough time of horizontal wells is much longer than that of vertical wells; When the breakthrough time of bottom water is equal, the daily output of horizontal wells is much higher than that of vertical wells.
Fig. 3 sweep efficiency e of horizontal and vertical wells.
If a horizontal well starts production below the critical production, theoretically the waterless period is infinite. In practice, because the daily output of a single horizontal well cannot always be lower than the critical output of declining varieties, it will also encounter water, but its waterless period is much longer than that of a vertical well.
Table 1 comparison table of horizontal wells and comparable vertical wells in Tahe oilfield 1 and table 2 1 Tahe 1, table 2 comparison table of horizontal wells and comparable vertical wells in Tahe oilfield.
2.2 Actual situation
Theoretical analysis shows that the waterless oil production of horizontal wells is higher than that of vertical wells under the same conditions, regardless of whether the single well allocation production of horizontal wells is higher or lower than its critical production. If the daily output of horizontal wells is much higher than that of vertical wells, the breakthrough time of bottom water is equivalent; If a horizontal well is put into production below the critical production, its waterless period is much longer than that of a vertical well. Table 1 can prove that the actual situation is the same: the daily output of TK 104H, TK 105H and TK20 1H are all higher than their critical output (55.2t/d, 106.75t/d, 32.45). While the reservoir thickness is basically the same as that of TK 105H (H. (H. = 21.1m). The production of equivalent TK 106H well (h0=22m) is slightly lower than the critical production (1m).
3 the application of bottom water breakthrough time
By knowing the breakthrough time of vertical bottom water, we can estimate the effective vertical permeability of the formation near the wellbore of the well, and then borrow the vertical permeability value of the formation near the vertical well adjacent to the horizontal well, we can get the theoretical waterless period which is more in line with the actual waterless period of the horizontal well.
The estimated vertical permeability is 3. 1
(1) vertical well
According to the horizontal permeability of the formation around the wellbore provided by the core data of a single well, the breakthrough time of bottom water of a vertical well is known, and its effective vertical permeability is calculated according to the formula, which can better reflect the actual situation of the formation around the wellbore. The formula is (1 1):
Essays on exploration and development of oil and gas fields in northern Tarim basin
The parameters of 7 vertical wells in Tahe Oilfield 1 and Well 2 are substituted into the formulas (1-3), (1-2) and (3- 1), and the calculation results are shown in Table 2. This shows that the formation kv/kh near each wellbore is different. Well TK 10 1 and well TK 103 in the table are not coring. The former refers to TK 102 data for porosity and horizontal permeability, while the latter takes the average value of the oilfield, so the obtained kv/kh is for reference only. For TK 103 and AN 1 wells, the possible reason why the value of kv/kh is greater than 1 is that the oil layer may have high permeability kx in the x direction and low permeability ky in the y direction, so its effective horizontal permeability is less than the high horizontal permeability kx in the x direction, and in this case, the effective horizontal permeability will be less than the vertical permeability kv.
Table 2 Calculation of ratio of vertical permeability to horizontal permeability in Tahe 1 and No.2 Oilfield Table 2 Calculation of ratio of vertical permeability to horizontal permeability in Tahe 1 and No.2 Oilfield
(2) Horizontal wells
Because the horizontal well sweep coefficient is obtained by looking up the map, it is a function of effective well spacing aD, size-length LD, size-vertical distance ZWD and size-wellbore radius rwD, that is, E = f (AD, LD, ZWD, RWD), L. It is also a function of kv/KH. For a given tBT, the ratio of vertical permeability to horizontal permeability of the formation near the wellbore of a horizontal well cannot be directly calculated like that of a vertical well, because the specific functional relationship of E cannot be calculated back, or even known. After borrowing the kv/kh values of adjacent vertical wells (S5 1, S56), the theoretical water breakthrough period (Table 3) is obtained according to formulas (1-4) ~ (1-7), which shows that the formation parameters of adjacent vertical wells are borrowed on the premise that the coring analysis data of vertical wells are relatively complete. In addition, Table 3 also shows that the theoretical waterless period calculated by using the effective length of horizontal section is highly consistent with the actual situation, so the effective length value is substituted in the calculation of relevant formulas of reservoir engineering.
Table 3 Calculation of Water Breakthrough Time of Horizontal Wells in Tahe Oilfield 1 and No.2 Bottom Water Drive Reservoir Table 3 Calculation of Cone Time of Horizontal Wells in Tahe Oilfield 1.2 Bottom Water Drive Reservoir
3.2 Preliminary judgment of interlayer distribution direction
(1) tk105h-tk103 well direction (NEE—SWW) may have interbeds.
The theoretical waterless period of TK 105H is 49 days, which is far less than the actual waterless period 17 1 day. Since the well was changed to 5 mm choke production from May 7 to June 9, the average daily oil production in 34 days was 93.49 tons, which was lower than its critical production of 65,438+006.75 tons. Therefore, it is considered that the water was still in the original state at the end of these 34 days and there was no further coning. The remaining 138 days is still longer than the theoretical waterless period (the actual waterless period is shorter than the horizontal section of the well, and the oil production at the initial stage of production is affected by the short metering time), which is considered as one of the evidences that interlayer may exist in the formation near TK 105H borehole.
The vertical permeability of well TK 103 is greater than the horizontal permeability, which is another evidence that there may be an interlayer in the direction of TK 105h-TK 103. Although TK 103 drilling did not encounter interlayer in the oil layer, the effective permeability in the lateral direction was lower than that in the longitudinal direction due to the existence of low permeability layer in the direction of TK 105h-TK 103 within the oil control range of this well.
(2) Possible distribution of interbeds in the direction of TK105h-TK103.
From the fact that the theoretical waterless period of TK 105H is much smaller than the actual waterless period, it is considered that this interlayer is close to the oil-water interface. Because the closer the interlayer is to the oil-water interface, the more obvious the effect of inhibiting water cone is.
(3) Possible distribution of interbeds in the direction of TK105h-TK103.
Well TK 10 1 has a siltstone interlayer with a thickness of 2.5m at the oil-water interface. So, are the interlayers in TK 105h-TK 103 and TK 10 1 integrated or independent? If they are connected as a whole, the interlayer will be wide in the east-west direction and will inevitably spread in the north-south direction. In this way, the possibility of high north-south permeability in well TK 103 will be reduced; In addition, the bottom water of well TK 105H needs longer time to bypass a large range of interbeds before entering the wellbore. Therefore, it is considered that the interlayer in the direction of well TK 105h-TK 103 is separated and annihilated near well TK 103.
3.3 Auxiliary judgment of water outlet position of horizontal section.
From the vertical permeability reflected by the permeability logging curve of horizontal section of horizontal well, we can determine the difference of physical properties in the direction of horizontal section and the existence of high permeability zone in oil layer. Fig. 4 shows the vertical permeability distribution of horizontal section TK 104H. Take the 3m liquid supply section with the longest length (3 m) (5003 ~ 5006m) and high permeability (700× 10-3μm2) of this well, and calculate the water breakthrough time according to the output per unit length, assuming that all the output comes from here, and the result is 390 ~ 4 days (Table 3). Although the actual water breakthrough time is within this range, this range is very large. That is, it is difficult to determine the proportion of oil production in the 3m liquid supply section to the total oil production, so it cannot be said that the high permeability layer leads to water breakthrough in the horizontal well in advance. But at least one thing is certain, that is, under the mode of bottom water ridge, the high permeability layer not only contributed more oil at the initial stage, but also contributed more water after water breakthrough. Therefore, it is helpful to determine the location with more water by using the horizontal section logging curve to calculate the water breakthrough time in the liquid supply section.
Fig. 4 Vertical permeability distribution in horizontal section of well TK104h.
To sum up, according to the bottom water breakthrough time of bottom water reservoir, the effective vertical permeability around the wellbore can be determined or verified; If the actual water breakthrough time is far beyond the theoretical waterless period, it can be preliminarily judged that there is interlayer near the wellbore, and the distribution of interlayer can be roughly judged by combining the analysis of waterless period of adjacent wells. Assist the logging curve of horizontal section of horizontal well to judge the water outlet position of horizontal section.
refer to
[1] Wan Renpu. Horizontal well mining technology. Beijing: Petroleum Industry Press, 1995+033 ~ 360.
Prediction and application of water cone time in sandstone reservoir with bottom water
Yang Li Chengjun
(Planning and Design Institute of Northwest Petroleum Geology Bureau of Urumqi 8300 1 1)
Abstract: The Lower Triassic Formation and the Middle Triassic Formation in Tahe 1 2 Oilfield are mined by horizontal wells and vertical wells respectively. By analyzing the bottom water coning time of vertical wells and horizontal wells and its influencing factors, we can draw the following conclusions: under the same geological conditions, the waterless oil production rate of horizontal wells is higher than that of vertical wells, regardless of whether the single well production distribution of horizontal wells is higher or lower than its critical production. If a horizontal well is put into production at critical production, its waterless time is much longer than that of a vertical well.
In practice, we can verify the effective vertical permeability around the oil well according to the bottom water coning time; If the actual water-free time is much longer than the theoretical value, the fringe can be used to verify whether there is interlayer around the well, and combined with the water-free situation of adjacent wells and logging curves, it can help to judge the water-out position.
Keywords: bottom water coning time, vertical permeability, waterless oil production rate and critical oil production rate