RU2060371C1 - Method for developing nonuniform oil stratum - Google Patents

Abstract

FIELD: oil production. SUBSTANCE: water solution of culture medium to initiate microflora is pumped in stratum during pressure rise. Pumping in period is finished together with finish of pressure increase period. Then period of pressure decrease begins when microorganisms are adopted to stratum conditions. EFFECT: increased oil production.

Description

 The invention relates to the oil industry, and in particular to microbiological methods for the development of oil reservoirs.

 The aim of the invention is to increase the efficiency of development of a heterogeneous oil reservoir.

 This is achieved by the fact that in the method of developing a heterogeneous oil reservoir by alternating periods of increasing and decreasing water injection pressure during the pressure increase period, an aqueous solution of nutrients is pumped into the formation to activate microflora so that the end of the injection coincides with the end of the pressure increase period.

 A comparative analysis of the proposed solutions with the prototype shows that the proposed method meets the criteria of the invention of "novelty."

 As indicated above, after the injection of a solution of nutrients into the reservoir, the formed system must be kept at rest in order to maximize the development of microorganisms. In normal waterflooding, it’s inefficient to specifically shut down injection wells for this purpose, as this violates the basic mode of reservoir development and leads to losses in oil production.

 The proposed method provides for the injection of a nutrient solution during the creation of high pressure (water injection) during cyclic flooding immediately before the period of pressure reduction. In this case, the shutdown of the injection well, necessary for the development of microorganisms, is combined with that provided for in the known method of cyclic water flooding and immediately after the completion of the injection of nutrients. The duration of the shutdown of the injection well in the known method is at least 7 days, and the maximum development of microorganisms occurs 7-8 days after their activation, i.e. the cycle of development of microorganisms fully fits during the shutdown of the well.

 Therefore, a combination of two known methods (microbiological nutrient and cyclic water flooding) allows you to combine the technological modes of both methods and thereby eliminate the violation of the basic operating mode of the injection well, and using the vital products of the developed microorganisms to increase the efficiency of oil displacement by water. No additional sophisticated equipment is required.

 Despite the fact that both methods are separately known, their combined combination gives a synergistic effect, which is expressed in increasing the efficiency of developing a heterogeneous oil reservoir during flooding, which indicates that the proposed method meets the criteria of the invention "significant differences".

 In field conditions, the method is as follows.

A set of preliminary studies is carried out at the site of the oil reservoir, which is developed by alternating periods of increase (T _{decrease pressure} ) and decrease (T _decrease pressure) of water injection pressure, in order to determine the volumes of the aerobic and anaerobic parts of the bottom-hole zone of the injection well, the presence and type microorganisms present in these zones. Depending on the results of microbiological analysis, two variants of the method are possible. Regardless of this, the following conditions are common for both options: a) the duration of the injection of the nutrient solution (T _Zack ) should not exceed the duration of the period of increase in pressure (T _pressure ); b) injection of nutrient solution is performed during the warm season (when the temperature of the injected water is not lower than 15 ° ^C), which is associated with the impossibility of intensive development of microorganisms in cold water. The rest of the year, carry out the usual cyclic injection of water.

If microorganisms are found in water poured from the injection well in an amount of at least 10 ⁴ cells / ml, depending on the type of these microorganisms and the geological and physical characteristics of the formation, the method is carried out in the following sub-options:
1. Aerobes, for example, hydrocarbon-oxidizing bacteria, predominate in the reservoir microflora. To activate them, alternating injection of an aerated aqueous solution of nutrients and non-aerated water is recommended. The duration of the injection to fill the volume of the aerobic part with a nutrient solution is determined by the formula
T _{Zak. 1} ≅ V _{air .} / Q _zak (1) where T _{zak. 1 the} duration of the injection of a nutrient solution, days;
V _{aer the} volume of the aerobic part of the bottom-hole zone of the injection well, m ³ ;
Q _zack rate of injection of nutrient solution, m ³ / day.

If T _Zak . ₁ <T _pressure the nutrient solution is injected in such a way that the end of this injection coincides with the end of the period of increase in pressure, i.e., immediately before the shutdown of the injection well. For example, the duration of the period of pressure increase T _pov.dav. is 10 days, according to calculations, a nutrient solution can be injected in 6 days. Their injection begins after 4 days (10-6) of the pressure increase period.

If T _zak.1 > T _pov.press. , then at a steady rate of injection, it is impossible to manage to pump the entire volume of the nutrient solution during the period of increasing injection pressure. In this case, the injection rate is increased to such a feasible value as to keep within this period of increasing discharge pressure. And then the whole method is implemented as follows: for almost the entire period of pressure increase, an aqueous aerated nutrient solution is pumped into the well. In the next period of pressure increase, unaerated water is pumped into the well, this is repeated throughout the entire heat season (from May to October), and then only unaerated water is pumped in pressure increase cycles.

 2. Anaerobes predominate in the reservoir microflora. In this case, a nutrient solution should be pumped into the volume of anaerobic water and then pushed with water into the anaerobic zone.

The duration of the injection of a nutrient solution T _s and water is determined by the formula
T _{zak. 2} ≅ V _anaer / Q _zak + V _aer / Q _zak, (2) where V _anaer / Q _{zak, the} duration of the injection of the nutrient solution, days;
V _aero / Q _zack, duration of water injection, days.

3. In the reservoir microflora, both aerobes and anaerobes were found. At the same time, a portion of the nutrient solution for anaerobes in the volume of V _{anaer is} first pumped into the well during the period of increasing pressure. and immediately followed by an aerated solution of nutrients for aerobes in the volume of V _aer . The injection time is determined by the formula
T _{Zak. 3} ≅ V _anaer / Q _Zak + V _aer / Q _Zak, (3) where V _anaer / Q _{Zak, the} duration of the injection of a nutrient solution for anaerobes, days;
V _air. / Q _{zack the} time of injection of aerated nutrient solution, days.

If T _zak.2 and T _zak.3 <T _pov.press. , then, similarly to sub-option 1, the duration T _Zak.2 and T _{Zak.3 are} counted from the moment the pressure increase period _ends , and from this moment the nutrient solution is _injected , so that it is completed just before the well stops for a pressure reduction period.

If T _zak.2 and T _zak.3 > T _pov.press. , then reduce T _Zak.2 and T _{Zak.3 by} increasing the rate of injection or reduce the injected volumes.

In the absence of microorganisms in the poured water or at a concentration of less than 10 ⁴ cells / ml, along with nutrients in the same solution, a culture of the corresponding microorganisms is introduced into the formation in such an amount that their concentration in the bottomhole zone is not less than 10 ⁴ cells / ml. The duration of the injection is chosen in accordance with option 1.

PRI me R. A section of the oil reservoir is drilled by one injection and five production wells and is developed by cyclic flooding: fresh water is pumped into the injection well at a rate of 300 m ³ / day for 10 days, and liquid is taken from the production wells during the next 20 days with idle injection. At the time of the implementation of the proposed method, the water content of the extracted products is 60%
Volumes of aerobic and erobic parts of the bottom-hole zone equal to 30 and 25 m ³ , respectively, were determined by means of self-discharge of the injection well. According to the results of microbiological analysis of the poured water, it was found that it contains aerobic hydrocarbon-oxidizing bacteria (BDS) in an amount of 5 · 10 ⁴ cells / ml. The remaining microorganisms are present in trace amounts.

To activate the DRR, 30 m ^{3 of} aerated solution of nitrogen and phosphorus salts should be pumped. This volume at a steady rate of injection can be pumped in 30/300 0.1 days, or 2.4 hours. Given the fact that the duration of the pressure increase cycle is 10 days, this solution is pumped at the end of 10 days and immediately after this stops the injection well for 20 days. In this way, the injections of the nutrient solution are repeated throughout the entire warm season (from May to October), then they are transferred to the water injection.

 Implementation of the proposed method can significantly increase the efficiency of cyclic flooding without additional costs, using technological stops of injection wells, for the development of microorganisms.

Claims (1)

 A method for developing a heterogeneous oil formation by alternating periods of increasing and decreasing water injection pressure, characterized in that during the period of increasing pressure, an aqueous solution of nutrients is pumped into the formation to activate microflora, and the end of the injection of nutrients coincides with the end of the period of increasing pressure.