RU2710050C1 - Method of development of complex deposits with low reservoir pressure and temperature - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to oil industry and can be used in development of wells of oil deposits in conditions of low formation pressures (close to pressure of oil saturation with oil), as well as low reservoir temperatures. Substance of the invention consists in fact that perforation of walls of the well is performed and call of inflow from the formation, differing by the fact that preliminary by properties of deep oil samples there determined is critical temperature of transition of asphaltenes, resins and paraffins dissolved in oil into crystalline state. In case of influx to the well with the help of pressure gage thermometer the value of temperature of oil flowing from productive interlayers and bottom pressure are controlled. For each group of collector permeability maximum permissible depression is calculated, and inflow from productive formation is called for by least depression, at which oil flowing from productive interlayer has critical temperature.

EFFECT: use of the proposed method enables to clean the productive stratum without precipitation and paraffin crystallization, which is ultimately reflected in the increase in the well flow rate.

1 cl, 2 tbl, 2 dwg

Description

The invention relates to the oil and gas industry, in particular, to the challenge of inflow and development of wells drilled into difficult-to-build deposits, characterized by a fractured-pore and cavernous type of reservoir saturated with asphalt-resin-paraffin oils at low reservoir pressures and temperatures.

When developing complex-built reservoirs, under conditions of low reservoir pressures and temperatures, in the presence of cavernous-pore and fractured reservoirs, whose oils contain paraffin, resins and asphaltenes, the creation of high depressions leads to the spread of the depression funnel through highly permeable channels (cracks and cavernous canals) deep into the reservoir. As a result, the gas is ungassed in the bottom-hole formation zone (BHP), which leads to a decrease in oil temperature (adiabatic process), while the dissolved paraffins, resins and asphaltenes contained in it begin to solidify in the reservoir pores, which, as advancements along the capillary channels form crystals and colmatate the collector. As a result, the production rate of wells for reservoirs that combine both high-permeability and low-permeability interlayers can be reduced significantly. first, the deposition of paraffin deposits occurs and leads to a significant decrease in their hydrodynamic conductivity.

Another negative factor when creating high depressions is the formation of gas bubbles, which are also able to block capillary channels and lead to a decrease in the efficiency of cleaning the bottom-hole formation zone.

From the instructions for the development and study of wells in Western Siberian fields RD 39-2-1217-84, it is known that when an inflow from a well is called, it is necessary to create a depression that overcomes the resistance forces of the fluid holding in the pores of the reservoir. In this case, the allowable depression is selected based on the following restrictions:

- water cut prevention;

- ensuring the strength of cement stone in the annular space;

- casing string strength;

- collector stability.

Also, in this instruction, the limitation of depression in wells with a water cut of more than 3%, calculated by the formula ΔР≤Рпл-Рнас, is associated with the prevention of hydrate formation in the wellbore. Moreover, the second condition says that if the water cut is less than 3%, then the depression is calculated by the formula ΔР≤Рпл -0.6 * Рнас, i.e. bottomhole pressure in this case may be lower than the pressure of saturation of oil with gas. Thus, the restriction of depression in the above conditions is prescribed for only one purpose - to prevent the formation of hydrates in the wellbore, because crystallization of dissolved paraffins, resins and asphaltenes would always occur when the maximum temperature of the oil (when degassing) was reached, regardless of its water cut.

Scientific publications do not contain information about the requirements for limiting depression during well development associated with the prevention of precipitation of paraffins, resins, asphaltenes and other sediments that occur when an inflow from a reservoir is called.

A known method of developing a well using a jet pump (patent SU 1797646, IPC E21 B 43/00), which includes a descent into a well of a jet pump, a call for inflow and development of a well, measuring flow rate, and raising the jet pump. An essential feature of this method is the creation of depression below the jet pump, which leads to the influx of fluid from the reservoir.

There is a method of inducing oil flow from a formation by lowering the level of well fluid by compression (patent RU 2095560, IPC ЕВВ 43/27), which includes creating depression on the bottom-hole zone of the formation in a cased hole with a string of tubing by lowering the level of well fluid by displacing its gaseous medium pumped into the annulus of the tubing string.

There is a method of inducing inflow from the formation (patent RU 2209948, IPC ЕВВ 43/18), which consists in creating depression on the bottomhole zone of the formation by lowering the level in the well achieved by displacing fluid from the pipes with the air phase injected simultaneously with the aqueous phase through the head into annular space of the tubing string, which leads to a decrease in bottomhole pressure (creating depression) and the influx of formation fluid into the well, which subsequently exits through the tubing cavity.

The disadvantage of these methods is the lack of restrictions on creating maximum depressions, which under conditions of low pressures and temperatures will lead to the loss of tar, paraffins and asphaltenes from the oil as a result of a sharp decrease in the temperature of the oil (due to gas evolution) and the latter become blocked by capillary channels, as well as closing of natural cracks.

The invention is known (patent SU 1772346, IPC E21 B 43/18), designed to develop wells and call the inflow from the fractured and fissure-cavernous reservoirs. The essence of this method is to periodically increase the pressure on the bottomhole formation zone with its subsequent discharge. The pressure is varied from the crack opening pressure to the pressure corresponding to the minimum inflow from the formation.

The disadvantage of this method is the forced and deep penetration of the borehole fluid into the bottomhole zone, which will lead to a deterioration of reservoir properties, and the creation of minor depressions (at which there will be minimal inflow from the formation) will not allow for a qualitative cleaning of the reservoir.

There is a method of preventing the loss of paraffin (copyright certificate 315756, claimed 04/18/1969, IPC E21 43/24). The essence of this method is to maintain pressure at the bottom of injection and production wells, at which paraffin does not crystallize in the reservoir, which leads to an increase in oil recovery coefficient.

The disadvantage of this method is that the pressure at the bottom of the well is maintained during its operation, carried out after the well development process, and does not prevent the precipitation of paraffins, resins and asphaltenes when the inflow is caused and the bottom-hole zone of the formation is cleaned due to excessively created depressions. Thus, providing a bottomhole pressure greater than the crystallization pressure of paraffin in oil in the known method does not lead to an increase in well production due to the late implementation of measures to prevent the loss of paraffins from oil.

As the closest analogue (prototype), the method of well development was selected (patent RU 2179239, ЕВВ 43/25). The essence of this method is to perforate the well, create a depression determined by studying the mechanical properties of soil samples from the formation, which increase the permeability of the rock (creating cracks due to the destruction of the rock), maintain the depression until the fluid production rate increases, and then reduce the depression to operational values.

The disadvantage of the method taken as a prototype is the creation of maximum depressions, in which, at low reservoir pressures and temperatures, tar, paraffins and asphaltenes (paraffin paraffin) will fall out of oil, which will lead to mudding of the bottomhole zone, which will ultimately reduce the potential production rate of the well .

The objective of the claimed method is to increase the flow rate of wells by creating optimal conditions for development, under which the bottom-hole zone of the formation is cleaned, which ensures the prevention of clogging of the capillary channels with asphaltenes, resins and paraffins dissolved in oil and becoming solid when the critical temperature of the oil is reached.

The essence of the invention lies in the fact that the perforation of the walls of the well and the inflow from the formation are performed, characterized in that the critical temperature of the transition of the asphaltenes, resins and paraffins to the crystalline state, dissolved in the oil, is determined previously by the properties of the deep oil samples. When the inflow into the well is called with the help of a manometer-thermometer, the temperature of oil flowing from productive layers and bottomhole pressure are controlled. For each group of the permeability of the reservoir, the maximum allowable depression is calculated, and the inflow from the reservoir is called at the least depression, at which the oil flowing from the reservoir is at a critical temperature.

The technical result of the proposed method is achieved by preventing colmatation of the bottomhole zone of the reservoir with substances contained in oil in dissolved form and passing into a crystalline (solid) state due to changes in thermobaric conditions (oil degassing), which change due to the creation of unreasonably high depressions. In addition, subject to the well development regimes, the well is brought to the regime more quickly, and there are no costs for additional measures (processing of the bottomhole formation zone, shooting).

The method of well development is implemented as follows.

In the process of testing (testing) or researching a well under thermobaric conditions as close as possible to the reservoir (the pressure in the wellbore is greater than the pressure of oil saturation with gas), an oil sample is taken by a depth sampler, in laboratory conditions, using the rotational viscometer, the temperature at which crystallization of paraffins begins oil (Figures 1-2). which is taken as the minimum allowable for oil when leaving the bottomhole formation zone (critical temperature). The temperature of the oil flowing out of the reservoir is controlled using a depth gauge-thermometer lowered into the well on a geophysical cable when determining the profile of the inflow from the reservoir. In the process of determining the temperature, the bottomhole pressure is recorded simultaneously with a manometer-thermometer. At the same time, temperature and pressure are recorded for productive layers with different permeabilities in several wells.

In FIG. Figures 1 and 2 show measurement plots for two deep oil samples. In FIG. 1 shows the temperature dependence of shear stress. In FIG. 2 shows the temperature dependence of shear stress.

The crystallization temperature of paraffins in oil was determined using a rotational viscometer when the sample was thermostated at 30 ° С and the temperature gradually decreased at a constant speed and the temperature of crystallization of oil paraffins began to reach 1, at which resistance to rotation of the rotational viscometer cylinder appeared, which was displayed by the recording device as a sharp increase shear stress 2.

With further operation of the viscometer and rotation of the rotor, the structures of crystallized paraffins were destroyed to small ones and no longer resisted rotation, therefore, the readings of the recording device were again stabilized 3.

The subsequent spasmodic increase in the shear stress 4 indicates the mass crystallization of oil paraffins 5.

Thus, the first sharp jump in the values of the device 2 corresponds to the formation of the first crystals, that is, the temperature at which crystallization of paraffins begins, and the second jump in the values of 4 corresponds to the precipitation of most of the paraffin crystals in the sample, that is, the temperature of mass crystallization.

After determining the critical temperature and the corresponding bottomhole pressure for each permeability group, the maximum possible depression is calculated at which the deposition of paraffin will not occur from the oil. A table is formed with various groups of permeabilities and the corresponding maximum possible depressions (table 1), which are subsequently guided for high-quality development of wells. In this case, depression during well development is selected based on the conditions of reservoir permeability, including the presence or absence of highly permeable layers, and should not be more than the maximum depression (ΔР) for the layer with the highest permeability indicated in the table.

R _z.aspo - fixed bottomhole pressure when the temperature of the onset of crystallization of paraffins dissolved in the oil leaving the bed, MPa

R _pl - reservoir pressure, MPa

The causal relationship between the set of essential features of the proposed method and the achieved technical result is confirmed by the results of the pilot works and is reflected in the statistical data shown in table 2. The table shows that the average production rate for wells mastered using the proposed method in 2015 40% higher than in the wells developed in 2012-2014 (according to the technology, where the depression was not limited, when inflow was caused and the bottom hole was cleaned).

Literary sources:

1) Mordvinov. A.A. Development of production wells: Textbook.-Ukhta: USTU, 2004. - 107 s, ill.

2) Lysenko V.D. Vital problems of field development on the pages of the journal "Oil Economy", M.ZAO "Publishing House" Oil Economy "issue-10.2010. from. 43.

3) Instructions for the development and exploration of wells in Western Siberian fields RD 39-2-1217-84, Krasnodar, 1985. MINISTRY OF OIL INDUSTRY.

Claims (1)

The method of developing complex reservoirs with low reservoir pressures and temperatures, including perforating the walls of the well and causing inflow from the reservoir, characterized in that the critical temperature of the transition of asphaltenes, resins and paraffins to a crystalline state, determined by the properties of deep oil samples, is determined during development the oil temperature and bottomhole pressure, and the calculation of the maximum allowable depressions is based on the fixed bottomhole pressures, at which At the same time, oil reached a critical temperature, flowing out from productive layers with different permeabilities.

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