RU2381359C1 - Method for measurement of disposal amount in production well tubing string - Google Patents

Abstract

FIELD: oil-and-gas industry.

SUBSTANCE: invention can be used for development of oil fields with a big content of asphaltene, resin and paraffin. To define disposals volume in well tubing, equipped with sucker-rod well pump, fill in sequentially a clearance between tubing pipes and a rod string with liquids of different densities. Define a load on device polished stock after every filling, estimate disposal amount using mathematical correlation.

EFFECT: tubing pipes diagnosing related to disposal grade and timely decision making on ARPD removal from pipes, washing them away with corresponding solvent.

Description

The present invention relates to the downhole extraction of asphalt-resin-paraffin oils using a sucker rod pumping unit (SHGNU).

The exploitation of oil fields with a significant content of asphaltenes, resins and paraffins is complicated by the fact that over time the annular space between the elevator pipes and rods is filled with deposits, usually consisting of paraffins, resins, asphaltenes with a small proportion of mechanical impurities, salts and water. Deposits increase friction between the surfaces of the pipes and rods, narrow the annular space between them, thereby increasing mechanical stresses on the pump plunger and rod string. Ultimately, these two factors lead to lower well productivity and breakage of the rod string.

To extend trouble-free and efficient operation of such wells, it is necessary to periodically diagnose elevator pipes for sediment content. According to the results of such studies, elevator pipes with a significant amount of paraffin need to be washed with solvent through the annulus.

The volume of deposits in the elevator pipes can be determined by patterning the inner surface of the elevator pipes without lifting them to the surface (B.A. Mazepa. Partitioning of oil gathering systems and oilfield equipment. - M .: Nedra, 1966. - p.30-31). The method requires depressurization of the well, carrying out numerous tripping operations with templates and samplers of various shapes.

A known method for diagnosing the state of the annular space of the producing well (RF patent No. 2199005, published on 02.20.2003), by which using the acoustic signal, its reflection and further interpretation, it is possible to judge the distribution of oil fractions and paraffin plugs along the wellbore. The implementation of the method requires special equipment and technology. In addition, using this method it is impossible to estimate the amount of paraffin in the elevator pipes of the well.

In surface pipelines of oil, gas and water collection, treatment and transportation systems, the volume of deposits is defined as the difference between the internal volume of a clean pipeline and a pipeline with deposits. The last parameter is found by filling the pipeline cavity with a fixed volume of liquid of increased density using a liquid separator for the pipeline according to RF patent No. 2324552 (publ. 05.20.08, bull. No. 14).

This approach cannot be applied to the well due to the fact that the end of the column of elevator pipes is at a depth of several hundred meters and is hydraulically connected to the reservoir, therefore it is not able to be controlled by the researcher by the volume of injected fluid in the elevator pipes.

The aim of the invention is the development of technology for determining the volume of deposits in adhesive form on the inner surfaces of the elevator pipes of wells with SSHU, without lifting the elevator pipes.

This goal is achieved in that the annular space between the lift pipes and the rod string is successively filled with liquids with significantly different densities ρ ₁ and ρ ₂ , after each filling, the load value P ₁ and P ₂ on the polished rod is determined at the moment of closing the discharge valve of the plunger during its course up a working well by dynamography of a downhole pump. As liquids with different densities, those that are inert to deposits by dissolving ability are selected. Therefore, their volumes in the elevator pipes will be the same (V ₁ = V ₁ = V), and the masses will be different due to differences in densities. The friction force between the rods, pipes and deposits when filling the pipes with such fluids will also be close to each other:

Loads P ₁ and P ₂ consist of the weight of the rod string M _pcs , the friction forces between the rod string, lift pipes and paraffin deposits F _Tr and the mass of fluid in the lift pipes:

The free volume of space between the elevator pipes and rods, not occupied by deposits, is determined from the difference (1) and (2):

The volume of deposits in the elevator pipes V _ex determined by the formula (4)

where: π is the geometric constant;

l is the length of the lift pipes from the wellhead to the pump;

D is the inner diameter of the elevator pipes;

d is the averaged diameter of the rods;

P ₁ , P ₂ - the load on the polished rod during the stroke of the plunger up, respectively, when filling the elevator pipes with liquids with different densities ρ ₁ and ρ ₂ .

The proposed method is implemented as follows:

1. The existing well with SHGU stops, in the annulus (the area between the casing and the elevator pipes), the pressure and fluid level are measured. A pump unit of the CA-320 type is connected to an angular valve (gate valve) of the annular space and high-density mineralized water (ρ ₁ = 1180 kg / m ³ ) with anticorrosive additives is pumped. The injection is carried out until the water fills the elevator pipes through the valves of the submersible pump. The moment of filling the elevator pipes with a fluid with a density ρ ₁ is determined by the appearance of this fluid in the flow line (VL) of the well connected to the elevator. For fidelity, periodic sampling of liquid with overhead lines is organized with a measurement of their density.

2. The deep rod pump is put into operation for a short period of time (10-12 swings) to determine the load P ₁ on the polished rod string of the rod.

3. Lift pipes are filled with a relatively light fluid, for example, oil with ρ ₂ = 800 kg / m ³ according to the same technology described in paragraph 1 of the application description.

4. The well is put back into operation and after 10-12 strokes of the rocking machine, the load on the polished rod P _{2 is} determined by a dynamograph. With these data, the volume of deposits in the elevator pipes is determined by the formula (4), a decision is made to continue the operation of the SHGNU or the need for preventive flushing of the elevator pipe string with the solvent of the deposits.

Consider the implementation of the method on practical data. Oil with a high content of asphaltenes, paraffins and resins is extracted from the well with a sucker rod pump at a depth of 1000 m. The internal diameter of the elevator pipes is D = 62 mm, and the average diameter of the rod string is d = 21 mm.

The elevator pipes were successively filled with liquids with densities:

ρ ₁ = 1800 kg / m ³ and ρ ₂ = 800 kg / m ³ .

The following loads on the polished rod are obtained:

P ₁ = 3800 kg and P ₂ = 3040 kg

By the formula (4) we find the volume of deposits in the elevator pipes:

Calculations show that on the inner surface of the elevator pipes 0.671 m ^{3 of} AFS was deposited. To remove it, it is recommended to wash the elevator pipes with an effective organic solvent in a volume of 4-5 m ³ .

In our opinion, the proposed method allows to extend the time of efficient and trouble-free operation of a complicated well, to exclude such time-consuming and expensive operations, such as lifting elevator pipes to the surface and their heat treatment with hot steam to remove deposits.

Claims (1)

A method for determining the volume of deposits in a column of elevator pipes of a producing well, which consists in filling the cavity of the column of pipes with liquid of increased density, characterized in that for a well equipped with a sucker rod pump unit, the annular space between the elevator pipes and the rod string is successively filled with liquids with significantly different densities and not having the ability to dissolve deposits, after each filling determine the load on the polished rod at the time of closing tiya of the discharge valve of the plunger during its upward movement by dynamography of a deep pump, and the volume of deposits V _exl is determined by the formula:
V _ex = π · (D ² -d ² ) · 1 / 4- (P ₁ -P ₂ ) / (ρ ₁ -ρ ₂ ),
where π is the geometric constant;
l is the length of the lift pipes from the wellhead to the pump;
D is the inner diameter of the elevator pipes;
d is the averaged diameter of the rods;
P ₁ , P ₂ - the load on the polished rod, respectively, when filling the elevator pipes with liquids with different densities ρ ₁ and ρ ₂ .