RU2307923C2 - Method for multipay oil field development - Google Patents

Abstract

FIELD: oil production industry, particularly to develop multipay oil fields, especially ones having reservoirs with oil-filled thickness, low permeability or containing highly-viscous oil.

SUBSTANCE: method involves separating production facilities; determining producing and injection well pattern; drilling wells, producing oil from producing wells and injecting displacing agent through injection wells. Period of oil field reserves recovery is approximated to medium guaranteed well service life period where not more than 20% of producing wells are abandoned for technical reasons by drilling common through well pattern for oil reservoir group of the oil field with well amount increase and development time decrease. At that oil field is developed with the use of all producing wells by serially extracting product from separate reservoir or from group including reservoirs communicated with each other through non-reservoir bridges, with thickness of not more than 30 m in descending order of reservoir productivity beginning from reservoir having the greatest productivity.

EFFECT: increased oil recovery due to usage guaranteed well service life as pattern density optimization and due to control of selected facility exploitation order and regime along with achievement of oil recovery exceeding designed one for current oil field.

2 cl, 2 ex, 1 tbl

Description

The invention relates to the field of the oil industry and can be used to develop multilayer oil fields, especially if their layers have a small oil-saturated thickness, low permeability and contain high viscosity oils.

There is a known method of developing multilayer oil fields, in which each layer is separated into an independent development object with an individual grid of production and injection wells (Ivanova M.M. et al. Oilfield geology and geological foundations of exploration for oil and gas fields. - M., Nedra, 1985 , p. 232). In such a system, the efficiency of oil recovery depends on the parameters of the oil reservoir. With large effective oil saturated thicknesses, significant permeability and oil saturation, as well as low oil viscosity, a high oil recovery coefficient (CIN) is achieved.

The disadvantage of this method is the low efficiency of reserves development at small oil-saturated thicknesses, because in such conditions, for economic reasons, it is impossible to use a dense grid of wells. If a grid of wells with low density is used in deposits with low permeability and oil saturation, as well as with high viscosity of oil, then the oil recovery factor will be low. In addition, an excessive increase in the total number of wells leads to an increase in capital costs.

A known method for the development of multilayer deposits, in which several oil deposits are combined in one development object. With this approach, you can use a grid of wells with a high density and achieve a good oil recovery factor, but only on reservoirs with the best parameters of reservoirs and reservoir fluids (RU No. 2188938, ЕВВ 43/30, 2002).

The disadvantage of this method is the great difficulty in regulating the development process, as a result of which a lot of associated water has to be produced to achieve satisfactory oil recovery. In addition, this method is almost impossible to implement with a significant difference in the depths of the deposits due to the problems of creating the necessary depressions in the producing wells.

A known method for the development of multilayer oil fields, in which independent grid wells are drilled at relatively better development sites with the highest oil-saturated thicknesses. Reserves with low quality reserves (small average oil-saturated thickness, low permeability and oil saturation of the reservoir) are developed as return objects by transferring highly watered wells from the best underlying objects (Bragin Yu.I. et al. Oil and gas field geology and hydrogeology of hydrocarbon deposits. Concepts, definitions, terms. Subsoil - Business Center, p.225).

Due to this sequence, good oil recovery is achieved in reservoirs with worse parameters due to the use of a dense grid of wells of a good development object.

The disadvantage of this method is the long (for decades) conservation of stocks with worse quality. If the development time of the main object and the object of return is long, a significant part of the wells due to accidents, wear and corrosion will be eliminated at the return object, therefore, in real conditions, the density of the grid of wells at the return object is significantly lower than at the main object. In addition, the wells are irrigated at the main facility at different times after commissioning. Due to the difference in commissioning of wells at the return facility, regulation of oil displacement is difficult, and oil recovery factor is reduced. That is why it is impossible to get high oil recovery at the return facility.

There is also a known method of developing multi-layer deposits, by which all oil reservoirs are combined into one common production facility with a common grid of production and injection wells (Ivanova MI and other Oilfield geology and geological foundations of exploration of oil and gas fields. - M., Nedra, 1985, p.236).

However, the combination of oil reservoirs results in an increase in the unevenness of oil displacement by the agent into production wells and, accordingly, a decrease in the average oil share in the total fluid withdrawal.

As a result, when optimizing the density of the grid of wells, the number of wells that will not achieve high oil recovery will be minimally cost-effective. In addition, with large differences in the depths of productive formations, combining a large number of deposits into one object is practically impossible due to the lack of a real possibility of optimizing depressions and repressions on the formation, as well as due to enormous problems with the current and capital repair of wells.

Of the known methods for developing a multilayer oil field, the closest to the proposed one is the development method, which consists in isolating production facilities, drilling injection and production wells into selected objects, pumping a displacing agent into injection wells and selecting oil from production wells, and the overall increase is a criterion for rational selection of objects initial amplitude oil production rate of design wells (RU No. 2142046, ЕВВ 43/20).

However, when implementing this method, an erroneous design decision on the allocation of production facilities is possible, which is associated with a shortage of initial information obtained from a rare grid of wells, in particular with inaccurate information about the degree of inter-layer heterogeneity.

The basis of the present invention is the creation of a method of developing a multilayer oil field that provides enhanced oil recovery by using the guaranteed density of wells as a criterion for optimizing the grid density and regulating the order and operation mode of the selected facilities with achieving oil recovery exceeding the planned oil recovery factor for this field.

The problem is achieved in that in the method of developing a multilayer oil field, including the selection of production facilities, determining a rational grid for the location of production and injection wells, drilling wells, oil production from production wells and pumping the displacing agent into injection wells, according to the invention, carry out a common through drilling well grid, the density of which is selected from the condition of convergence of the term of development of reserves of the field and the average term of guaranteed well services, and the operation of the facilities is carried out by the entire fund of production wells by sequential selection of products from an individual reservoir or a group of reservoirs connected by jumpers of a non-reservoir with a thickness of not more than 30 m.

It is advisable to operate the facilities sequentially from the bottom up, starting from the bottom deposit, by transferring the production well stock from the underlying to the overlying reservoir as the previous one is developed.

Preferably:

- operation of the facilities should be carried out in the mode of transferring the entire production well stock from one reservoir or group of reservoirs to others as the marginal profitable water cut of the product is reached;

- the operation of facilities is carried out sequentially in decreasing order of productivity of a deposit or group of deposits, starting with the most productive.

The essence of the method is as follows.

The criterion for optimizing the density of the grid of wells is based on the average guaranteed life of the wells (Lysenko VD Innovative development of oil fields. - M., Nedra, 2000, p. 195).

As you know, the guaranteed life of wells depends on many factors, but mainly on the amount and composition of salts of produced and injected water. Over the guaranteed life of the wells, reserves must be depleted at the development site. Otherwise, it is necessary to plan the drilling of a large number of backup wells in place of the retirement wells at the final stage of reservoir exploitation. Drilling of backup wells is always planned and taken into account in the calculations when developing oil fields, taking into account unforeseen accidents, but not more than 20%. With a large number of backup wells, field development becomes unprofitable, since a large number of wells are put into operation at the final stage of development with high water cut and low oil recovery rates.

For the guaranteed service life of production wells in a particular field with the planned technology for stimulating the formation, the approved oil recovery factor for each deposit of the production facility must be achieved. Thus, the guaranteed well life is the period for which, for technical reasons, no more than 20% of the production fund is liquidated. Liquidation of wells for technological reasons is not considered, because after reaching the maximum water cut, production wells and injection wells that have completed the technological task are transferred to overlying objects with the exception of the uppermost last development site.

The guaranteed life of the wells varies on land from 30 to 40 years. In offshore fields, the values of this parameter are significantly less and do not usually exceed 20 years. The guaranteed life of wells is determined based on experience in developing fields with similar geological and field conditions.

With an increase in the number of drilled wells, the distance between the wells decreases, due to which the filtration resistances in the formation decrease when the displacing agent moves from the injection well to the producing one. Due to this, the rate of fluid withdrawal increases by 2–3 times, and drained reserves decrease by a factor of several. As a result, when drilling a development object with a grid with the number of wells n times greater, the pace of development increases by more than n times. Due to this accelerated pace, it is possible to sequentially with high efficiency to develop all the reserves of a group of deposits with fewer wells in a period not exceeding the development time of one formation with an individual rare grid of wells.

Thus, when isolating production facilities, considering each reservoir as an individual one or forming groups of several reservoirs interconnected by non-reservoirs with a thickness of not more than 30 m, the field should be drilled with a common end-to-end grid of wells, the optimal density of which is selected from the convergence condition, t. e. maximum approximation of the planned term for the development of the field’s reserves and the average guaranteed life of the wells, while the operation of the facilities is carried out by the entire stock of production wells by sequentially selecting products from an individual deposit or a group of deposits, connected by jumpers of a non-reservoir, with a thickness of not more than 30 m.

In multilayer deposits, such geological conditions are often encountered when it is practically impossible and impractical to develop each deposit individually from bottom to top. So, for example, it is often difficult to separate deposits with small depth differences that are difficult to separate during operation due to overflows between the layers along the annular space of the wells. In such cases, it is advisable to develop in turn from the bottom up not individual deposits, but groups of deposits. The combination of deposits into one development object can be forced due to small oil-saturated thicknesses, low initial oil saturation of the reservoir, low permeability of the reservoirs, as well as with small thicknesses of the impermeable reservoir between the deposits. With small oil-saturated thicknesses and low initial oil saturation, separate development of each object involves the use of a grid of low-density wells, which will result in low oil recovery. A dense grid cannot be used in such conditions, since the amount of oil produced does not economically justify the cost of drilling wells. With low permeability of productive formations, the separate development of oil deposits will lead to low well production rates, which will turn out to be unprofitable.

If the bulkheads of the impermeable rocks between the deposits are small, then in real conditions it is not possible to operate the deposits separately. When perforating production cores, cumulative perforators are most often used, which contribute to the partial destruction of cement stone not only in the perforation interval, but several meters above and below this interval. Due to the destruction of cement stone, in fact, deposits are developed jointly even with formally separate exploitation.

If the thickness of the non-reservoir between the deposits is significant (more than 20 m), then, using modern technologies, it is possible to develop each deposit separately, regardless of the depth of its occurrence. In this case, they begin operation from the most productive development facility, and end the drainage of reserves with the worst facility. With this option, profitability of the development is easily achieved and, therefore, it is possible to use a higher density of the grid of wells, at which a higher oil recovery is achieved.

With small thicknesses of the non-collector bridges between the individual development sites, it is very difficult to isolate the perforated reservoirs located above the reservoir being introduced into the development. It is especially difficult to do this if a deposit with significantly worse productivity is introduced into the development, and it is necessary to isolate the overlying development object with high productivity. In this case, it is necessary to start operation from the lowest development object, and then, after extracting the reserves of the lower object, switch to the overlying one. Thus, bottom-up reserves are sequentially developed. Field operation ends with drainage of reserves of the uppermost development object.

If the field has many deposits and most of them are characterized by low productivity, small oil-saturated thicknesses or small thicknesses of the non-reservoir between the deposits, then it is advisable to combine neighboring deposits into one development object. With this characteristic of the field’s structure, the reserves of not each individual deposit are sequentially developed, but the reserves of each development object in turn, and some development objects may consist of one highly productive deposit, in which the impermeable bridges of the collector above and below (roof and sole) have a large thickness. In this option, a higher oil recovery will be achieved over the entire guaranteed life of the wells in the field.

Thus, according to the proposed method for the development of a multilayer field, the selected development objects can be put into operation, starting from the lowest and ending with the development of the highest object, by sequentially transferring the entire well stock from one object to another overlying one. In this case, the selected density of the grid will ensure the consistent development of reserves from all the layers of this group.

In the presence of insulating materials that allow reliably overlapping the intervals of perforation in the wells, it is possible to switch from one development object to another not only from the bottom up, but also in an arbitrary order. For example, if development objects are introduced in decreasing order of magnitude of their productivity, then operation begins with the most productive ones, which ensures the improvement of economic indicators.

The exploitation of deposits or groups of deposits can be carried out in the mode of transferring the entire well stock from one reservoir or group of deposits to others as the marginal cost-effective water cut of wells is reached, i.e. production wells are shut off after reaching the maximum water cut. The values of the maximum water cut, at which the wells can still be operated cost-effectively, range from 95% to 99%. The better the economic indicators of the project, the greater the marginal water cut, the greater the oil recovery achieved. In addition, when connecting to the development of facilities on a “from best to worst” basis, the development of a multi-layer field with the most unproductive facility ends, the oil recovery rate at which is very slow. The timing of the development of the last worst facility can not be limited to the guaranteed life of the wells. A significant part of the well stock (approximately 40-60%) remains operational not 30-40 years, but 50-60 years or more. Due to the significant life of the last unproductive facility, it is also possible to increase oil recovery.

The following are examples of the proposed method.

Example No. 1.

A multilayer field has 47 productive formations, the bridges between which vary in thickness from 0.5 m to 95 m. With such a large number of objects, it is impossible to develop each of them separately for the guaranteed life of the well. Therefore, some layers are combined into one development object, in accordance with the data shown in table 1.

At this field, the development time of the facilities is different and varies from 1.5 to 6 years, if you use a grid of wells with a density of 4 ha / well, i.e. when the distance between the wells is 200 m. The reserves development time in the first deposit is 3 years, the second deposit is 1.5 years, the third is 2 years, the 4th is 2 years, the 5th is 2 years, the 6th is 6 years 7th - 3 years, 8th - 3 years, 9th - 2 years, 10th - 5 years and 11th - 4 years. In general, taking into account the drilling period of 6.5 years, the development period of the entire field will reach 40 years, i.e. will not exceed the guaranteed life of the wells. First, deposit No. 2, which is characterized as the most productive, is introduced, then, as productivity decreases, deposit No. 9 is introduced, then less productive No. 5, then No. 4, then No. 3, then No. 8, followed by No. 7, then No. 1 , then No. 11, then No. 10 and the last, deposit No. 6, which is characterized by the lowest productivity, is commissioned. The last deposit has been developed for 6 years by the entire stock of drilled wells, and then its operation can be continued with a smaller stock of wells as the emergency wells are liquidated. Due to this strategy, in highly productive deposits, due to a very dense grid of wells, oil recovery will be achieved in a short period of time, which will be 5-10 points higher than the oil recovery factor approved when calculating reserves, since the approved oil recovery factor was based on traditional development methods. The greatest increase in oil recovery will be achieved in deposits with low reservoir properties, since such deposits are characterized by significant discontinuity and fragmentation, as well as low sandiness. On the worst deposits, the increase in oil recovery will be 10-20 points. As a result, due to the proposed strategy for the development of multi-layer deposits, the oil recovery factor will average 15 points.

Table 1 Distribution of deposits by development objects №№ of the development object No. of oil deposits included in the corresponding development object one 1, 2, 3 and 4 2 5 3 6, 7 and 8 four 9, 10 and 11 5 12, 13 and 14 6 15, 16, 17, 18, 19, 20, 21 and 22 7 23, 24, 25, 26 and 27 8 28, 29, 30, 31 and 32 9 33 and 34 10 35, 36, 37, 38, 39, 40, 41 and 42 eleven 43, 44, 45, 46 and 47

Example No. 2.

In a multilayer field at different depths, there are 10 oil deposits that differ in parameters such as oil-saturated thickness, permeability, porosity, initial reservoir oil saturation, viscosity and density of oil under reservoir conditions, but coinciding in plan. Based on the provision of a rapprochement between the term for developing the field’s reserves and the average guaranteed life of the wells, a total of 500 wells need to be drilled in the field. In this case, the total development period of all the deposits will not exceed 30 years and will be equal to the guaranteed well life. First, the lowest reservoir is put into operation, and then the wells are subsequently transferred to the overlying facility. Wells are transferred to an overlying facility after reaching the planned oil recovery factor for the given object, taking into account maximization of oil recovery in the field as a whole.

It has been confirmed by feasibility studies that a satisfactory profitability of sequential reserves development is achieved if reserves are sequentially developed by drilling 500 wells and reserves are first developed at the lowest level and then, after reaching the maximum water cut in the lower object, all wells are transferred to the overlying object. Thus, reserves of all deposits are sequentially developed, ending with the uppermost one. Due to drilling a dense grid of wells, the average production rates and injectivity of injection wells increase, and the drainage area per 1 well is reduced so that the maximum water cut (98%) of production wells at the element of the well placement system is achieved 2 years after putting them into operation . However, taking into account the drilling time for a large number of wells, the development period of the lowest reservoir increases to 7 years. The development period for one element of the well placement system for each subsequent facility is 2-3 years. The last well, the last well, is transferred to the last well after 27 years, and the drainage of this development object ends after 30 years. Thus, in general, all ten oil deposits will be developed in 30 years.

Due to the proposed development method, the coverage of formations by an impact due to a denser grid of wells, larger pressure gradients and greater efficiency of control methods will increase by about 1.5 times from 60% to 90%, and the average displacement coefficient due to greater heating of formations saturated with highly viscous oil, will increase by about 1.2 times. Thus, oil recovery will increase 1.8 times from 35% to 63%.

Claims (2)

1. The method of developing a multilayer oil field, including the allocation of production facilities, determining the grid location of production and injection wells, drilling wells, oil production from production wells and pumping a displacing agent into injection wells, characterized in that the field’s production life is close to the average guaranteed well service, in which, for technical reasons, no more than 20% of the production well stock is eliminated, for which a total well is drilled heat of wells for a group of deposits of the field with an increase in the number of wells and accelerated development time, while exploitation of the field is carried out by the entire fund of production wells by sequential selection of products from an individual deposit or group of deposits of the field, connected by jumpers of a non-reservoir, with a thickness of not more than 30 m, in decreasing order their productivity, starting with the most productive. 2. The method according to claim 1, characterized in that the operation of the objects is carried out sequentially from the bottom up, starting from the bottom reservoir, by transferring the production fund of wells from the underlying to the overlying reservoir as the previous one is developed.