RU2738506C1 - Method for determination of liquid level in well - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: invention relates to practice of operation of oil-producing and water-intake wells with the help of downhole pumping equipment and can be used in oil industry and other industries. Method of fluid level determination in well consists in installation of electrical devices uniformly from wellhead to bottom-hole pump. Devices used are identical heat generating conductors (semiconductors) - thermoresistors connected in parallel to the closed electric circuit together with an ammeter and a voltage source of constant value. Thermoresistors are arranged uniformly along the absolute length of the well from the mouth to the pump. Depth of fluid level in the well is determined from the ammeter reading after a certain time interval after connection of the electric circuit to the voltage source and previously obtained calibration dependence of current strength in circuit from depth of separation of gas and liquid media as a factor of total resistance of electric circuit.

EFFECT: technical result consists in provision of determination of liquid level in constant mode of time without human participation with minimum costs and simultaneous improvement of accuracy of measurements.

1 cl, 1 tbl, 2 dwg

Description

The claimed invention relates to the practice of operating oil production and water wells using downhole pumping equipment and can be used in the oil industry and other industries.

In wells, the annular space (MP) between the tubing string and the casing is filled, as a rule, with two media: gas-air and liquid. The boundary between the media in an active well is called the dynamic fluid level. Its depth from the wellhead is determined with the required frequency to assess the pressure at the inlet of a downhole pump, to determine the volume of oil and water in the well and the characteristics of the productive formation.

Dynamic and static fluid levels in wells are determined using echo sounding of the annular space, that is, the depth of the level is judged by the time of passage of a sound wave in a gas medium (p. 202 in the book: Vasilievsky V.N., Petrov A.I., Well survey operator . Textbook for workers. - M .: Nedra, 1983. - 310 p.). The method is basic in the oil industry, but has several disadvantages. An acoustic signal from the wellhead is usually generated by an oil producer or a researcher using a portable generating device such as Mikon-101 or Sudos. Well work is always associated with a certain hazard due to the increased pressure in the well. The information obtained in this way is, in its essence, a discrete quantity and is often insufficient for making qualified and operational decisions on the operation of the "reservoir - deep pump" system.

There is a known method for assessing the liquid level in a water well according to the RF patent for invention No. 2623756 (publ. 06/29/2017, bulletin 19), according to which the generator and receiver of the acoustic wave are located in the zone of the deep pump, the water level in the well is judged by the waves from the pump to the level and back to the pump. The method is characterized by an error in the presence of gas bubbles in an aqueous medium and a change in the speed of the acoustic signal in a gas-liquid medium in an aqueous multiphase medium.

The closest technical solution to the claimed invention is a method for determining the liquid level in a well according to the RF patent for invention No. 2559979 (publ. 08/20/2015, bull. 23). According to this invention, pressure sensors are stationary and evenly located along the vertical depth of the well from the wellhead to the deep pump, according to the information from which, the boundary of various media is determined by the fracture dependence of pressure on the depth of the sensors. The method has the following disadvantages:

- the vertical depth of phase separation is determined by graphic-analytical method; to determine the liquid level along the absolute length of the well, qualitative data on the elongation of the wellbore relative to the vertical component from the wellhead to the pump are required;

- an electrical circuit of a plurality of pressure sensors is a complex device in which it is necessary for the controller of the control station to receive information from each pressure sensor individually;

- pressure sensors are large enough devices, therefore, their placement, taking into account the armor shells in the limited space of the annular annular space, today presents a structural complexity.

The technical objective of the claimed invention is to create a method for determining the level of liquid in an oil producing and water well in a constant mode of time without human intervention with minimal costs and a simultaneous increase in the accuracy of measurements.

The task is accomplished due to the fact that according to the method for determining the liquid level in the well, which consists in installing electrical devices evenly from the wellhead to the deep pump, the same heat-generating conductors (semiconductors) are used as devices - thermistors connected in parallel in a closed electrical circuit together with an ammeter and a constant voltage source at the wellhead, thermistors are positioned evenly along the absolute length of the well, and the depth of the liquid level in the well is determined by the ammeter reading after a certain time interval after connecting the electrical circuit to the voltage source and the previously obtained calibration dependence of the current in the circuit from the depth of separation of gas and liquid media as a factor in the total resistance of the electrical circuit.

The invention is based on the statement about the linear dependence of the resistance of a heat-generating conductor (semiconductor) of an electric circuit on its temperature. (Sheftel IT Thermistors. Electrical conductivity of 3d-oxides. Parameters, characteristics and applications. Monograph. - Moscow: Publishing house "Nauka": Main edition of physical and mathematical literature, 1973. - 415 p. (P. 303 - second group thermistors).

For example, for a metal conductor, with an increase in its temperature, the electrical resistance increases, and, conversely, with an increase in the semiconductor temperature, its resistance decreases. According to the proposed invention, it is proposed to connect thermistors with the same resistance values in parallel in a circuit with an ammeter and a source of constant voltage of electric current. In downhole conditions, some of the thermistors will be in a gas environment, and some in an oil or water environment. It is known that the thermal conductivity of oil and water is tens of times higher than that of a gaseous medium, for example, air or methane. Therefore, a thermistor in a gaseous environment will heat up by a greater amount than a similar device in oil or water.

Consider two situations when all thermistors of the same parameters are in two different environments. The first situation - the thermistors are in a gas environment, they heat up, the total resistance of the circuit increases, the current in the circuit decreases, and after a given time, both parameters are fixed at the values of R ₁ and I ₁ . A different picture will form when thermistors are in a liquid medium, since due to the high thermal conductivity of oil or water, more intensive cooling of the thermistors will occur; their temperatures will rise much more slowly; the resistance of the circuit, fixed after a given time, will take a lower value of R ₂ , and the current strength, on the contrary, will be fixed at a higher value of I ₂ .

A diagram of an electrical circuit according to the invention in downhole conditions is shown in FIG. 1, where the following numbers indicate: 1 - well casing, 2 - tubing string, 3 - submersible pump, 4 - thermistors, 5 - voltage source, 6 - ammeter, 7 - electrical cables connecting thermistors, 8 - liquid level in the well, 9 - gaseous medium, 10 - liquid phase.

The operability of the technical solution according to the invention was tested as follows.

A garland of a parallel-assembled electrical circuit, which included 3 PTC-type thermistors of the same size and electrical resistance, equidistant from each other in a circuit at a distance of 50 cm, was investigated as follows:

1. Thermistors (TP) in the electrical circuit were lowered in a suspended state into a dry vertical cylindrical vessel 130 cm high so that the distance between them was 50 cm, and the total circuit length between the upper and lower TP was 100 cm.

1. Voltage of alternating electric current - 220 V.

2. All thermistors are in the air, 6 minutes after the voltage is applied, the ammeter reading is recorded at 108.3 mA.

3. A portion of technical oil was fed into the vessel from its lower side, so that one of the three thermistors was in the technical oil (oil model). 6 minutes after the voltage was applied, a current strength of 129.1 mA was recorded.

4. The oil level was raised so that another thermistor was also in the liquid medium. 6 minutes after the voltage was applied, the ammeter reading was fixed at 150.4 mA.

5. The vessel was filled with oil and all three thermistors were immersed in oil. 6 minutes after the voltage was applied, the ammeter reading was recorded - 172.1 mA.

As a result of the tests of the proposed method, the following calibration table and a graph of the dependence of the current strength (ammeter reading) on the depth of the position of the separation of two media (Fig. 2) were obtained: gas and liquid (oil level in the well).

The calibration dependence of the total resistance of the circuit on the oil level in a vertical vessel (the number of resistances placed in a liquid medium) is shown in Fig. 2.

The total resistance of an electrical circuit with many thermistors N in parallel connection and located in the same environment is expressed by the formula:

Where:

N is the total number of thermistors in the circuit;

R is the resistance of the thermistor.

For a multiphase medium consisting of gas and liquid phases, formula 1 is transformed as follows:

Where:

n _gas is the amount of TP in the gas environment;

n _liquid is the amount of TP in the liquid.

), поэтому в итоге запишем:The liquid level (length of the gas phase in the well) N _{ur is} found as the product of the number of thermistors in the gas medium by the distance between them -

), so we end up with:

In formula (3), the parameters R _water , R _gas are constant values for those thermobaric conditions that formed in the well at certain depths, taking into account the geothermal gradient. The total resistance of an electrical circuit from a set of thermistors R is _generally represented as the ratio of the voltage in the circuit U to the current I, then formula 3 is transformed:

In formula 4, all parameters, except for the current in the circuit I, are constant values, which are converted into constants a and b. Therefore, the dependence of the liquid level on the ammeter reading is a linear dependence, which is confirmed by the data in Table 1. In downhole conditions, taking into account the existence of a geothermal gradient, this dependence will not exactly correspond to Formula 4, therefore, the application provides for a preliminary construction of the calibration dependence of the current in the circuit on the depth separation of gas and liquid media as a factor in the total resistance of the electrical circuit.

Changing the liquid level in the well to obtain a calibration dependence can be performed in several ways, for example, by changing the performance of a downhole pump. After each change in the level of the liquid, it is necessary to measure the depth of this level in an acceptable way, for example, by a traditional acoustic method, and at the same time measure the current in the electrical circuit of a plurality of thermistors. The amount of TP in the parallel circuit will determine the accuracy of measuring the fluid level in the well. For example, when 100 such elements are installed on a total length of 1 km from the wellhead to the pump, the measurement accuracy will be 10 m.Today acoustic methods do not have such accuracy for many reasons, therefore, upon request, the required positive result is achieved. And in comparison with the prototype - RF patent for invention No. 2559979 - the considered application is economically profitable for oil-producing enterprises, since the cost of a standard thermistor is about a hundred times less than the cost of a pressure sensor made of a piezoelectric element.

According to the authors, the novelty and significant difference according to the invention are the following provisions, reflected in the application:

- the liquid level is determined remotely with the required frequency according to the ammeter (current in the circuit);

- the ammeter reading is taken after a certain time necessary to stabilize the temperature and resistance of the thermistor, which can be in different environments depending on the liquid level in the well.

Claims (1)

A method for determining the liquid level in a well, which consists in installing electrical devices evenly from the wellhead to a deep pump, characterized in that the same heat-generating conductors (semiconductors) are used as devices - thermistors connected in parallel into a closed electric circuit together with an ammeter and a constant voltage source values, thermistors are arranged evenly along the absolute length of the well from the wellhead to the pump, and the depth of the liquid level in the well is determined by the ammeter reading after a certain time interval after connecting the electric circuit to the voltage source and the previously obtained calibration dependence of the current in the circuit on the depth of the gas and liquid separation environments as a factor in the total resistance of the electrical circuit.

Images