RU2811501C1 - Method of drilling wells with active brine manifestation - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: technology for eliminating brine manifestations. The method of drilling wells with active brine manifestations includes drilling to the roof of the brine-bearing formation, running and cementing the casing, pressure testing of the casing, opening and drilling of the brine-bearing formation. A pre-prepared cross-linking solution is pumped into the well, the well is kept under pressure for a period of time to prevent the drill string from sticking, an impenetrable screen is formed in the brine=bearing formation as a result of sedimentation after the chemical interaction of the cross-linking solution with formation water in the brine-bearing zone, and monitoring of success of operations to ensure circulation in the well when mud pumps are not working is carried out. In this case, opening and drilling is carried out with back pressure. Backpressure is created and controlled by gradually closing the annular space at the wellhead using the ram preventer's hand wheels. The amount of back pressure is regulated by the degree of overlap of the annular space. In case of excessive intensity of brine manifestation, back pressure is increased. Once an impenetrable screen has formed, back pressure is reduced.

EFFECT: improved reliability of isolation of fractured pressure strata.

1 cl, 3 dwg

Description

The invention relates to the oil and gas industry, namely to the technology for eliminating brine deposits by creating excess backpressure at the wellhead using blowout systems.

There is a known method for ensuring the safety of drilling operations when opening high-pressure formations (Kalinin A.G., Levitsky A.Z. Technology of drilling exploration wells for liquid and gaseous minerals. - M.: Nedra, 1988. - pp. 98-99. Bulatov A .I., Penkov A.I.), which consists of using special weighted drilling fluids to prevent blowouts.

The disadvantages of this method are the need to prepare drilling fluid and maintain technological parameters in conditions of concentrated brine coming from a high-pressure formation, a high risk of emissions and spills of formation fluid on the earth's surface during work, significant time consumption and fluid precipitation.

There is a known method for constructing wells in difficult conditions (RF patent No. 2630519, published on September 11, 2017); this method proposes the option of creating a filtration curtain in the bottomhole zone of the well by injecting brine and magnesia-phosphate cement slurry into the developing formation.

The disadvantage of this method is the need for careful control of the process, since the work is carried out under conditions of controlled mineralization, which, in the event of an error, can get out of control and lead to an accident. Another problem is the possibility of equipment getting stuck due to salt crystallization.

There is a known method for opening high-pressure formations saturated with strong brines (RF patent No. 2735504, published 03.11.2020), which includes drilling and fastening a wellbore to the roof of a high-pressure formation, opening high-pressure formations by drilling, deepening the well, creating an interlayer flow, fastening a high-pressure formation and cementing casing.

The disadvantage of this method is the need for precise and prompt control of pressure during a significant duration of drilling under development conditions, which adversely affects the condition of the equipment and does not allow high-quality monitoring of the filtration characteristics of the developing formation.

There is a known method for opening high-pressure formations saturated with strong brines (RF patent No. 2365735, published on August 27, 2007), in which a absorption zone is formed using hydraulic fracturing, the column is lowered to the roof of the productive horizon, and the brine-producing layer is opened using pumps or the horizon’s own energy carry out the removal of natural brine into a pre-formed zone.

The disadvantage of this method is the need to use equipment for hydraulic fracturing.

There is a known method for isolating formations with manifestations of polymineral waters of a high degree of mineralization (RF patent No. 2691229, published on June 11, 2019), adopted as a prototype. In this method, a blocking screen is created in the formation by sequentially pumping a buffer fluid under pressure into a water-saturated formation with abnormally high formation pressure , which is heated formation water, an insulating composition based on formation water of a high degree of mineralization, into which, when heated, calcium or magnesium chlorides are additionally introduced until they are maximally saturated with formation water at a given temperature, condensed microsilica, chrysotile, after injection of the insulating composition, technological curing is carried out for obtaining a volumetric plugging sediment due to a combination of salt crystal formation factors during natural cooling of the supersaturated composition to reservoir temperature and the presence of highly dispersed and fibrous solid phases that initiate sedimentation and increase the volume of sediment, and subsequent final pressing of the insulating composition into the formation with limited excess pressure for additional compaction of sedimentation products into paste in cracks, completely blocking them and ensuring impermeability to formation water in the zone of penetration of the composition.

The disadvantage of this method is the need to use a large tank fleet to accumulate formation water and prepare process fluids.

The technical result is to increase the reliability of isolation of fractured pressure strata with abnormally high pressure.

The method is illustrated by the following figures:

fig. 1 - preparation for opening the mineral deposits;

fig. 2 - deepening the well under conditions of brine occurrence;

fig. 3 - stitching together the mineral-producing horizon, where:

1 - ram preventer;

2 - cross-linking solution;

3 - drilling fluid;

4 - drill string;

5 - casing;

6 - brine-producing layer;

7 - impenetrable screen.

The method is carried out as follows. Drilling is carried out to the roof of the brine-producing formation 6 (Fig. 1), lowering and cementing of the casing string 5, pressure testing of the casing to a pressure exceeding the pressure of the brine-producing formation by 10%, but less than the hydraulic fracturing pressure of the absorption formation.

After this, the brine-producing formation is opened using drilling fluid 3 with a density that provides hydrostatic pressure of the drilling fluid corresponding to the formation pressure and the depth of the brine-producing formation. After opening the brine-producing formation, brine manifestation begins - the influx of concentrated brine - brine - into the well from the formation. To control the intensity of mineral deposits, by gradually closing the annular space at the wellhead using the steering wheels of the ram preventer 1, back pressure is created on the mineral deposits formation. The amount of backpressure is regulated by the degree of overlap of the annular space. In case of excessive intensity of rapomanifestation, the back pressure is increased.

Under conditions of mineralization, drilling of the mineralization formation is continued and a pre-prepared cross-linking solution 2 is pumped into the well (Fig. 2). When the crosslinker reaches the bottom, the drilling pumps are stopped and the ram preventer is used to completely block the annular space, as a result of which the circulation in the well stops. The well is maintained under pressure for a period of time to prevent sticking of the drill string 4 (Fig. 3). After holding under pressure, the ram preventer is fully opened and the drill string is retracted.

As a result of the chemical interaction of the cross-linking solution with formation water, a sediment forms in the mineralization zone, forming an impenetrable screen 7 (Fig. 3) around the well. The formed screen excludes the inflow from the mineral deposits. After the formation of an impermeable screen, by gradually opening the annular space at the wellhead using the steering wheels of the ram preventer 1, the back pressure on the formation being opened is reduced. The success of the operation is monitored by the presence of circulation in the well when the mud pumps are not working. If there is no circulation, they conclude that there is no mineralization and continue drilling. In the event of reoccurrence of cancer manifestations, the method is re-implemented.

Example. Justification of the method for use in a gas condensate field well in Eastern Siberia. The depth of brine occurrence is 1608 m, the density of brine is 1300 kg/m ³ . The diameter of the open trunk is 295.3 mm.

The pressure of the brine-producing formation is calculated as follows:

where q _зс - brine flow rate with free outflow, m ³ / day; C _prod - coefficient of specific productivity of brine collector, Р _зс - pressure at the bottom with free outflow, MPa.

Mathematical modeling of circulation is carried out using a computer. For the case under consideration, ΔР _tr is 2.07 MPa. Based on this, the amount of back pressure required during the opening process is:

Р _nagn =1.05Р _pl -Р _gs +ΔР _tr =1.05⋅29.82-17.98+2.07=15.04 (MPa)

where R _gs - hydrostatic pressure, MPa; ΔР _tr - pressure loss due to friction in drill pipes, MPa.

Calculation of bottomhole pressure in a well when eliminating mineral deposits is carried out according to the following relationship:

P _zab =P _gs +P _boost -ΔP _tr =17.98+15.04-2.07=30.95 (MPa)

To eliminate the manifestation, the creation of an impenetrable screen is required. The screen must withstand the pressure drop:

ΔР=1.05Р _pl -Р _gs =29.82⋅1.5-17.98=13.5 (MPa)

To guarantee the effectiveness of insulation work, the required length of the radius of the screen is determined from the condition that the partial derivative of the depression along the radius of the depression funnel in the absence of movement of the brine on the outer contour of the screen should not exceed the value determined by the formula (Zozulya G.P., Kleshchenko I.I., Geykhman M.G., Chabaev L.U. Theory and practice of choosing technologies and materials for repair and insulation work in oil and gas wells: Textbook. - Tyumen: Tyumen State Oil and Gas University, 2002. - 138 pp.):

where P is the pressure drop that the insulating screen can withstand, MPa; ρ _r - density of brine, kg/m ³ .

Calculation using this method is carried out using a computer. To create an impermeable screen with a strength of 13.5 MPa, the radius of the screen should be 3.5 m. Thus, the volume of the required crosslinker solution is:

V=πmh((r+0.1) ² -r _c ² )=2.2 (m ³ )

where m is the open porosity of the formation; h - screen thickness, which, according to the work conditions, is assumed to be 2 m; r _c - well radius, m.

Let's calculate the time to pump the solution:

where Q is the pump flow rate, m ³ /h.

The holding time, based on laboratory experiments and the need to prevent sticking, is 60 minutes.

Total duration of the operation:

t _total =t _close +60=22.3+60=82.3 (min)

The use of the claimed method makes it possible to eliminate mineral deposits without stopping the drilling process and replacing the drilling fluid due to the use of a cross-linking solution and regulation of wellhead pressure.

Claims (1)

A method of drilling wells in the presence of active mineral deposits, including drilling to the top of the mineral deposits formation, running and cementing the casing, pressure testing of the casing, opening and drilling of the mineral deposits formation, pumping a pre-prepared cross-linking solution into the well, holding the well under pressure for a period of time to prevent sticking drill string, the formation of an impenetrable screen in the brine formation as a result of sedimentation after the chemical interaction of the cross-linking solution with formation water in the brine zone and control of the successful operation of the presence of circulation in the well when the drilling pumps are not working, characterized in that opening and drilling is carried out with back pressure , backpressure is created and controlled by gradual blocking of the annular space at the wellhead using the steering wheels of the ram preventer, the amount of backpressure is regulated by the degree of blocking of the annular space, in case of excessive intensity of mineralization, the backpressure is increased, after the formation of an impenetrable screen, the backpressure is reduced.

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