RU2850465C1 - Method for extracting liquid minerals prone to temperature phase transition - Google Patents

Abstract

FIELD: mineral extraction.

SUBSTANCE: invention relates to a method for extracting a liquid mineral that is prone to temperature phase transition. The method includes lowering a thermally insulated lift column into a well, pumping into the well and heating the lift column with a heat transfer fluid. Next, the flow from the formation is called up by feeding the fluid into the already heated lift column. The wellhead piping must also have a diameter equal to that of the lift column and must be capable of being connected via at least two parallel, independent fitting batteries and must be kept at a constant temperature of not less than 40 degrees Celsius. When the well is shut down, a heat transfer fluid preheated to 40-50 degrees Celsius is pumped into the pipe space for absorption into the formation. Next, direct circulation is performed through the pipe space with the heat carrier entering the intercolumn space between the lift column and the production casing until the fluid residues are completely washed out of the well.

EFFECT: increased efficiency of well development and the possibility of producing strong brines without the risk of salting the lift column and wellhead equipment.

1 cl, 3 dwg

Description

The invention relates to borehole methods for extracting liquid mineral reserves susceptible to temperature phase transitions, particularly concentrated brines, in the rare metal lithium and bromine mining industry. It prevents salt crystallization from supersaturated natural brines during well extraction.

Concentrated natural brines, containing industrial concentrations of lithium, rubidium, and bromine, saturate deep productive formations and migrate during well production from the wellhead to the wellhead, penetrating permafrost or low-temperature rock intervals in the geological section. These brines become supercooled and undergo a temperature phase transition, resulting in contamination of the well equipment with solids, partial or complete blockage of the wellbore column by precipitating salts, and a reduction or complete cessation of natural brine flow from the wellbore. Salt precipitation in the column and the resulting salt plugs prevent continuous brine production from the wellbore and productive formation.

Fig. 1 shows a diagram of phase relations in the ternary system CaCl ₂ - MgCl ₂ - H ₂ O, in the temperature ranges from -35 to 0 °C (I), from 0 to 20 °C (II), from 20 to 30 °C (III), from 30 to 40 °C (IV), from 40 to 55 °C (V), from 55 to 100 °C (VI); where 1 is the dissolution/melting of calcium chloride hydrates, 2 is the dissolution of tachhydrite, 3 is the dissolution/melting of magnesium chloride hydrates, 4 is the liquid region, 5 is ice in contact with chloride solutions, 6 is the line separating the liquid solution region from the regions of two-phase equilibria, the composition triangle is scaled.

A method is known for extracting a liquid mineral resource prone to a temperature phase transition (RU Patent No. 2229587, E21B 43/00 (2000.01), published on 27.05.2004), according to which, in order to protect the production casing from solid formations settling on it from the extracted liquid mineral resource during its movement from the productive formation to the wellhead, before lowering the production casing into the well, an absorption zone is formed by means of hydraulic fracturing, the productive formation is opened, and during the development process, thermostatting is carried out by pumping a coolant through the inter-column space into the absorption zone.

The method maintains the temperature of industrial lithium-bearing brines transported through elevator pipes from the face to the surface above the onset of salt crystallization. The critical temperature for the onset of salt crystallization from brine is 25°C.

The disadvantage of this method is the possible reduction in the absorption zone intake capacity during operation, and in this case, the inability to provide circulation through the annular space through which the flow of industrial lithium-bearing brines (brine) rises to the surface, as well as the impossibility of simultaneously producing gas, gas condensate and industrial lithium-bearing brines - brine.

A method is known for reducing heat exchange in a well during the development of a multi-layer field (RU Patent No. 2591325, E21B 36/00 (2006.01), E21B 37/00 (2006.01), F04D 13/10 (2006.01), F04F 5/14 (2006.01), published: 20.07.2016), consisting of a thermostatting effect due to the creation of a vacuum behind the production string by including a jet pump in the wellhead piping, which operates due to the formation fluid.

The disadvantages of this method include the necessary periodic replacement of the jet pump due to its erosive wear, as well as a large pressure drop across the pump itself, which can lead to cooling of the formation fluid directly in the wellhead equipment and the precipitation of solid sediment.

The closest in technical essence and the achieved result is the method of borehole extraction of a liquid mineral prone to a temperature phase transition (RU Patent No. 2361067, E21B 43/00 (2006.01), E21B 37/00 (2006.01), published: 10.07.2009), according to which the hot coolant is pumped through a closed circulation system formed by placing an additional suspended process column between the conductor and the production column, connecting, according to the principle of communicating vessels through the wellhead piping, the annular and internal space of the suspended process column and the ground-based tank and pumping equipment.

The disadvantages of this method include the complication of the wellbore design and wellhead casing due to the need for an additional large-diameter casing (which significantly impacts well construction costs), and the low efficiency of heating the wellbore casing. This is due to the presence of a significant number of "heat shields," and the heat transfer fluid first heats the production casing, which in turn heats a fairly large volume of fluid between the production casing and the wellbore casing. Only then does the wellbore casing itself and the fluid within it heat up. Experience has shown that insufficient fluid heating can lead to the crystallization of salts from natural brines, leading to fouling of the wellbore casing and wellhead casing.

The objective of the proposed invention is to develop a method (sequence of operations) in the well development cycle by maximizing the preservation of natural heating of the lift column in order to increase the efficiency of production of formation fluids from high-pressure formations saturated with strong brines, without the formation of salt crystals in the lift column and wellhead piping by reducing heat loss.

The technical result is increased efficiency of well development and the ability to extract strong brines without the risk of "salting" the elevator column and wellhead casing.

The technical result is achieved by the proposed method for extracting a liquid mineral prone to temperature phase transition. This method includes protecting the wellbore tubing from solids deposited on the tubing walls during the mineral's movement from the productive formation to the wellhead by thermostatting the tubing within a geological section with low temperatures (below 35°C), within the range of probable phase transition. This method is distinguished by studying the brine's mineral composition before well completion, plotting the dependence of brine salt crystallization temperature on density and mineralization. This method is also distinguished by using thermally insulated tubing as the tubing during well completion. Before putting the well into production, a heat transfer fluid heated to 50-60 degrees Celsius is injected through thermally insulated tubing into the tubing string, exiting into the annular space between the tubing string and the production casing, and subsequently circulating in the heat transfer injection system. This effectively warms up the tubing string before putting it into production. Once the tubing string has warmed up, circulation of the heat transfer fluid is stopped. Inflow from the formation is then stimulated by injecting fluid into the already heated tubing string. The wellhead assembly must also have a diameter equal to the tubing string diameter and be capable of being choke-tested through at least two parallel, independent choke banks. It must also be maintained at a constant temperature of at least 40 degrees Celsius.

The temperature of the brine exiting the well is measured on a continuous basis, and when the brine temperature approaches the crystallization temperature according to previously constructed graphs, as well as when the well operation is stopped, a light liquid is pumped - brine from the brine accumulator, preheated to 40-50 degrees Celsius, into the tubular space for absorption into the formation.

The brine from the brine accumulator is stable because it loses some of its natural salts due to salting out due to changes in the thermobaric conditions at the wellhead relative to the reservoir conditions.

The main advantage of the proposed method is the minimization of energy consumption for heating the elevator only at the most critical moments when starting the well for production and when it is stopped.

All operations in the bottomhole formation zone and well operations (replacing brine heated to 40-50 degrees Celsius with heavy drilling mud, killing a well with abnormally high formation pressure (AHFP), switching the well to a drilling mud with a lower density) are carried out with the mandatory placement of a hot (not lower than 40°C) light liquid - natural brine (after its stabilization, i.e., the discharge of a certain amount of salts into the pit during cooling) in the bottomhole formation zone (BZZ) and the lower (100 m) part of the wellbore.

The anomalously high formation pressure (AHFP) formations selected for development, saturated with strong brines, are superreservoirs with formation pressure gradients of 2.42 MPa over 10 m or more and permeabilities in Darcy units (1000 mD or more). These formations are also characterized by high injectivity values under overbalance of 1 kgf/ ^cm2 above formation pressure. This effect allows for well shut-in and reinjection of preheated clear fluid (e.g., brine from a brine reservoir). After fluid is released into the near-wellbore zone, direct circulation through the tubing space is possible, with the coolant exiting into the annular space between the tubing string and the production casing until the remaining fluid is completely flushed from the well.

In case of a decrease in the flow rate of concentrated brine, heated fresh process water with a temperature above 50 degrees Celsius is periodically (once every 12, 24 or 36 hours) injected into the elevator column with a pressure drop into the bottomhole formation zone (it is also permissible to use steam and heated process water together).

Hydrochloric acid baths and large-volume acid treatments with flushing of reaction products with fresh process water are possible. An example of the invention.

As an example, typical conditions are shown when drilling into local layers saturated with strong brines, with abnormally high formation pressure and high filtration-capacity properties at one of the oil and gas condensate fields of the Lena-Tunguska hydromineral-oil and gas province.

The depth of lowering the production casing string is 178 mm - 1890 m.

Next is an open shaft 1890-1920 m with a diameter of 152.4 mm

The depth of the high-pressure brine-saturated formation is 1900-1920 m.

The pressure in the high-pressure gas-saturated formation is 47.7 MPa (formation pressure gradient is 2.511 MPa per 10 m).

The flow rate of a highly permeable brine-saturated formation with abnormally high pressure is up to 7000 ^m3 /day with a depression of up to 12 MPa.

The density of strong brine is up to 1470 kg/ ^m3 .

Before well development, the mineral composition of the brine was studied and two graphs were plotted: a graph of the dependence of the crystallization temperature of salts from brine on density and a graph of the dependence of the crystallization temperature of salts from brine on mineralization (Figs. 2, 3). Fig. 2 shows the dependence of the temperature of the onset of salt precipitation from brine (crystallization temperature) on density, where the abscissa axis is density, g/l, and the ordinate axis is crystallization temperature, °C. Fig. 3 shows the dependence of the temperature of the onset of salt precipitation from brine (crystallization temperature) on mineralization, where the abscissa axis is mineralization, g/l, and the ordinate axis is crystallization temperature, °C.

During development, a thermally insulated tubing string (TIS) of 73 mm diameter with a wall thickness of 5.5 mm (with an 89 mm outer diameter coupling) was lowered into the well to a depth of 1,870 m. Insulated tubing can be used in accordance with Russian Patent No. 2719863. The interior of the 73 mm TIS was tied to a wellhead assembly for the extraction of strong brines. Next, a coolant heated to 50-60 degrees Celsius was injected into the tubing space of the TIS, exiting into the annular space between the TIS and the 178 mm production casing (PC), where it was then cycled through the coolant injection system. After the TIS had warmed up, circulation of the coolant was stopped. Next, an influx from the formation was stimulated (by replacing the well with _{a CaCl2} brine with a density of 1.25 g/ ^cm3 heated to 50-60 degrees Celsius, followed by a release of excess pressure and opening the tubular space to create a natural depression on the formation) with the fluid exiting the formation into the already heated elevator column, while the wellhead casing was also selected with an equal diameter equal to the diameter of the elevator column, and was kept under conditions of constant heating of at least 40 degrees Celsius.

Next, the temperature of the brine exiting the well was measured on a continuous basis. In turn, when the brine temperature approached the crystallization temperature according to the previously constructed dependence (for example, at a brine density of 1.42 g/ ^cm3, when the temperature of the brine exiting the well at the wellhead approached 25 degrees Celsius, according to Fig. 2), as well as during well shutdowns, a light liquid (brine from the brine accumulator, preheated to 50-60 degrees Celsius) was pumped into the tubing space for absorption into the formation to displace the potentially hazardous fluid (in terms of scale deposits) from the lift and wellbore. After the fluid was forced into the bottomhole zone of the formation, direct circulation was carried out through the tubing space with the coolant exiting into the annular space between the lift string and the production casing until the remaining fluid was completely washed out of the well.

In cases where the concentrated brine flow rate decreased, heated fresh process water at a temperature above 50 degrees Celsius was injected periodically (initially every 12 hours, then every 24 hours, and then every 36 hours). A combined use of steam and heated process water was also tested, injecting a mixture of steam and water into the wellbore casing and forcing it into the near-wellbore zone. All these experiments successfully achieved the desired results.

Claims (1)

A method for extracting a liquid mineral prone to a temperature phase transition, including protecting the wellbore tubing from solid formations deposited on the walls of the tubing from the mineral being extracted during its movement from the productive formation to the wellhead by thermostatting the tubing in an interval of a geological section with temperatures below 35 degrees Celsius, in the interval of a probable phase transition, characterized in that before well development, the mineral composition of the brine is studied and graphs are constructed of the dependence of the crystallization temperature of salts from the brine on the density and on mineralization, subsequently in the well development cycle, thermally insulated tubing is used as the tubing, and before the well is put into production, a coolant heated to 50-60 degrees Celsius is supplied through the thermally insulated tubing into the tubing with its outlet into the annular space between the tubing and the production casing column with subsequent cycling in the coolant injection system, then after heating the lifting column, the circulation of the coolant is stopped, then an influx from the formation is called up by feeding fluid into the already heated lifting column, while using a wellhead piping of an equal diameter equal to the diameter of the lifting column, and having the ability to choke through at least two parallel choke batteries independent of each other, maintain the wellhead piping under conditions of constant heating of at least 40 degrees Celsius, then continuously measure the temperature of the brine coming out of the well, and when the brine temperature approaches the crystallization temperature according to previously constructed graphs, and also when stopping the well operation, pump a light liquid - brine from the brine accumulator, preheated to a temperature of 50-60 degrees Celsius, into the tube space for absorption into the formation, then perform direct circulation through the tube space with the outlet of the coolant in the annular space between the lifting column and the production casing until the remaining fluid is completely washed out of the well, while when the flow rate of the concentrated brine stream decreases, heated fresh process water with a temperature of 50-60 degrees Celsius or a combination of steam and heated fresh process water is injected into the lifting column with squeezing into the bottomhole formation zone once every 12 hours, or once every 24 hours, or once every 36 hours.