Study on Technical Measures of Romashkino Oil Field after Entering Ultra-High Water Cut Stage

Romashkino oil field has large oilfield area, small formation dip, many reservoir layers, wide oil-water transition zone and complicated sedimentary environment. Since development, 3 overall development plannings and adjustments of individual block have been established. This achieves a high oil production. However, the recoverable reserves of major oil layer with high production become smaller and smaller and the water cut increases over time, the production ability of oil layer decreases. The development status of oil layer of mining siltstone, oil-water transition zone and oil layer with upswept injected water cannot be changed under present dilute well network condition, because there is no reinforced measurement to water well. This results the low oil production of Romashkino oil field. In order to improve oil production rate and reach the designed oil recovery, Romashkino oil field has been implemented many added cuttings since development. Resent researches about Romashkino oil field show: in later oilfield development stage, sidetrack and lateral drilling horizontal wells technology is very reasonable; formation hydraulic fracturing technology has been widely used in recent years; in tertiary oil recovery, sweep efficiency and flooding efficiency related technologies have been taken. This offers reference and guidance for the effective and reasonable oil field development in later period.


Introduction
Romashkino oil field lies in Tatarsta.It was found in 1948, and began industrial development in 1952.In 1954, Romashkino oil field began to inject water and it was a typical multi-layer oil field [1,2].The oily area of Romashkino oil field is 4255 km 2 , geological reserves is 45 × 108 m 3 , the recoverable reserves is 24 × 1088 m 3 , and the oil recovery is 53% [3,4].At present, this oilfield is in the production decline stage.In 1997, the crude oil production of Romashkino oil field is 1500 × 10 4 m 3 , the water cut is 0.88, the cumulative oil production is 20.3 × 10 8 m 3 , the recovery degree is 45.1% [5,6].The location map is shown in Figure 1.

Tectonic
The area of Romashkino oil field is large and the forma-tion dip is small, the tectonic area is 4500 km 2 , where the oil-water transition zone area is 70% of the total area, the formation dip is smaller than 0.5˚, and only reaches 2˚ in the side of south and west.The oil-bearing area of Devonian D-I layer is 4255 km 2 , tectonic high-point located in 1535 m below the sea leve [7][8][9] (see Figures 2 and 3) (North: 1480 -1482 m, South: 1489 -1490 m).

Sedimentary Facies
The oilfield stratigraphic section is composed of the Precambrian, Devonian, Carboniferous and Permian strata, the total sediment thickness is 2000 meters, in which car-bonate sediment thickness is about 1500 m, the thickness of the terrigenous is about 500 meters, where 89% of the proved reserves located in the Paxi Ya group DI sand layer and Ke Nuofu group D-0 sand layer of the Upper Devonian.The depositional environment of the sandstone reservoir is mainly the delta plain distributary channel, The lithology consists of quartz sandstone, siltstone, mudstone and limestone.The proven reservoirs of the o ers are established.The main oil production layer is D-I layer, the burial depth ranges from 1650 m to 1850 m. the oil layer temperature is 37.8 Degrees Celsius, the original formation pressure is 16.3 -18.2 MPa, and the OOIP is 45 × 10 8 t, other parameters are shown in Tables 1 and 2.
Fluid properti s The following shown parameters are the ters of the fluid properties of the production layer of Romashkino oil field.
Original formation pressure: 16.In a word, the major characteristics of Romashkino oil field are the followings: large area; big the formation dip; many oil layers; wide oil-water transition zone and complicated sedimentary environment.

Romashkino Oil Field Development Characteristics . Oil Developmen
Since development in 1952, Rom been made three total development program [11,12].
1) The first total development program (in 1956) p According to the geological structure, reserve pro d oil-water interface factors, Romashkino oil field is cutting into 21 development zone with water injection wells, the yearly oil production is 5400 × 10 4 ton.The injection and production of D-I layer is reasonable, the bottom-hole pressure of production well is 12.5 MPa, the wellhead pressure of injection well is 6 MPa, water line pressure is17.5 MPa (see Figure 4). 2

) The second total development program (in 1966)
The second total development program declined t with low and middle permeability.The main idea of this program is to keep stable production after entering high oil production; move the water line in completely flooded area, reservoir with good connectivity and homogeneous region; increase 50 percent oil production.The designed oil recovery of each cutting section is 40% to 55%.In order to solve the hierarchical differences, the development program formulates to take separate water injection and oil production.
3) The third total development program (in 1976 to   pt drilled, the wells network is encrypted and the production decline rate is controlled to reach the designed oil recovery.To reinforce water injection system needs the ratio of injection well and production well to be 1:3; for the independent well network with connectivity layer, the upper reservoir injection pressure should be higher than the lower reservoir; selective injection in the oil water transition band.

4) Key adjustment in five development Zones
In 1986, five developm ent period of Romashkino oil field were ma sted. 1) Establish separate point-like injection system in the disconti Rakhmanov block; carry out supplementary cutting in the high production oil layer and establish separate massive water injection system; 2) Establish supplementary cutting wells aims to develop periodic water injectio fu and Dongsuyefu development zone; 3) Establish stratified water injection system and supplementary cutting wells in the Qishiming ne; 4) Use the 600 × 600 m well network in the Saernuofu develo rizontal cutting; 5) In addition, carry out phased drilling in the low permeability layer ypt well spacing density to 300 × 600 m in the later period of Saernuofu development zone; do not drill well in the area with siltstone thickness less than 2 m and without wa njection system.

Division of Oilfield Devel
After introducing statistics to the Romashkino oil f gives Figures 5 and 6.

Ch
Characteristics of oil field development are shown Figures 7-9.
Figure 7 shows: in the second stage of development, the water cut lfield increases steadily.With the implementation of various adjustment measures of the oilfield, a downward trend of the line slope takes on; Figure 8 shows the second characteristic curve can be divided into three line section: the first line section means the completely development of oilfield blocks, water cut increases steadily; the second line section means the water cut increase faster and faster, because of the imperfect injection and production systems; in the third line section, the water cut keeps 0.87 with the implementation of different measures.The water cut of Romashkino oilfield increase slowly, duction and water production is low.This is related to the oil velocity and many measurements and adjustments.
1) Close the water well with high water cut; 2) Block high water cut layer; 3) Drill additional wells in low water cut area and improve oil production of oil well with little water; 4) Change the fluid flow direction by periodic water injection and adjust the water injection profile of water injection well.
Researches in recent years show: in later oilfield development stage, sidetrack and lateral drilling horizontal wells technology is very reasonable; formation hydraulic fracturing technology has been widely used in recent years; in tertiary oil recovery, s eep efficiency and flooding efficiency related technologies have been taken.

Figure 1 .
Figure 1.Location map of Romashkino oil field.

Figure 2 .
Figure 2. Formation top structure of Romashkino oil field.

Figure 3 .
Figure 3. Cross-sectional view of D-I oil layer of Romashkino oil field.

9
The water injection system is further reinforced, the ed area is enlarged, the additional wells are ke ent zones in the later developm inly adju nuous oil layer with low oil production reservoir of n in the A oil layer of Aliye development zo pment zone and carry out side water injection and ho of Qishiming development zone; en-
iant Oil Gas Recovery (A Case of the Heterogeneous Strata of the High Water and the fluid pro w roduction rate and reach the omashkino oilfield carried d out many additional cutting measurements, form 23 Because the cutting width is narrow, the oil layer volume th effective water sweep increases 20%, and the oil production rate increases relatively.Cons erogeneity, point-like injection, selective fillin bile water injection, as well as part of the stratified water injection of injection well with different pressure can be carried out.2) Develop with new wells in new blocksThe development process of Romashkino oilfield begins with middle high production area, and expands the development ar development Zone has been put into operation.In the major development stage, production wells are increased 0 -600 per year, and the injection -100.After 1964, Romashkino oilfield began to drill supplem 3) Take different measures to reduce water production

Table 2 .
Data o