SU1652508A1 - Borehole cementing method - Google Patents

Abstract

The invention relates to the drilling of oil and gas wells. The goal is to prevent fluid from penetrating into the annular space due to blocking the fluid-forming formation by the dispersed phase of the non-hardening suspension. The cement slurry and the non-hardening suspension are sequentially pumped into the well and brought to the annular space above the roof of the fluid-forming formation. a suspension of reduced sedimentation stability with a settling time of the dispersed phase is shorter than the setting time of the cement slurry. The density of the suspension is 1800 3000 kg / m. As a non-hardening suspension, m. used buffer liquid Barite, hematite, lead compounds can be used as ut gel

Description

The invention relates to the drilling of oil and gas wells, and to the cementing of casing strings in the presence of gas-conducting formations.

The purpose of the invention is to prevent the penetration of fluid into the annulus due to blockage of the fluid-forming formation by the dispersed phase of the non-hardening suspension.

The method of cementing wells is carried out as follows.

A hardening cement slurry and a non-hardening suspension are pumped into the well in a manner such that the suspension is located above the top of the fluid-bearing formation. At the same time, the non-hardening suspension should have reduced sedimentation stability and has a settling time of the dispersed phase less than the setting time of the cement slurry at a density of 1800-3000 kg / m3. Particles of the dispersed phase precipitate under the influence of gravitational forces and the caulk of the fluid-forming reservoir until the beginning of the hydrostatic pressure of the column of the tampon mortar during the waiting time for cement hardening (RPZ) to begin to decrease. Thus, fluid formation caused by cannula formation is prevented - the stone in the process of cementing.

A buffer liquid can be used as a non-hardening suspension. As ut utitel can be

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barite, hematite, lead compounds are used.

The table shows the properties of suspensions with a different content in comparison with the properties of the cement slurry.

The high density of the buffer fluid (1800–3000 kg / m3) and its increased mixing instability provide a turbulent mode of its flow in the well, which improves the displacement of the drilling fluid from the annulus during cementing.

The sequence of the method.

Calculate the volume q of one running meter of the well annular space above the fluid-bearing formation. Determine the required volume of buffer fluid, increased sedimentation instability, which, depending on the dispersion medium used (barite, hematite, insoluble lead oxide salts, etc.) will be at least (60-100) q, m. Calculate the volume Vi of the annular space of the well in the range from the design height of the cement slurry to the calculated depth of the upper level of the buffer fluid column. Calculate the volume of the W-hole space from the casing shoe to the calculated depth of the lower level of the buffer fluid column. Calculate the internal volume of the ultrasonic casing from the shoe to the stop ring. A cement solution with a volume of VL is pumped into the well in succession with a buffer fluid of increased instability in volume / BZ, cement solution in volume ().

The entire pumped volume is delivered to the annulus, and the buffer fluid with a density of 1800-3000 kg / m is placed above the reservoir, which is potentially fluid-prone.

The well is left to rest for the time required to harden the cement. At this time, the dispersed medium (e.g. particles of barite, hamatite, insoluble lead salts, etc.) drops out of the buffer fluid under the action of gravitational forces and clogs the fluid-forming layer, making the annulus impermeable to formation fluid.

PRI me R 1. A well with a depth of 600 m and a diameter of 245 mm is cased to a depth of 200 m with a conductor with a diameter of 324 mm. Fluid-containing formation is located at a depth of 220-250 m, i.e. 20-50 m below the conductor shoe. Volume 1 running meter annular space, 0236 m3 / m.

To obtain a buffer liquid of 1 m density of 2500 kg / m, 200 kg of barite and 200-300 liters of dispersion medium will be needed.

In this case, a reduction of 2.4 m3 is required.

buffer fluid to place it in

annular space at a height of 100 m:

4800 kg is required for its preparation

barite and 480-720 l of dispersion medium.

Calculate the volume of the annulus Vi space 0 from the wellhead to the upper level of the buffer fluid column in the annular space

 0.0236 m3 / m 3.54 m3

Depending on the design of the well 5, this volume can be represented by either a plug-in solution or a drilling mud.

Calculate the volume of the annulus / 2 from the lower level of the buffer fluid column in the annulus to the casing shoe

 m "0.0236 m3 / m - 8.26 m3.

Volume / 2 - represented by cement slurry.

5 Calculate the internal volume of the casing of the ultrasound from the shoe to the stop ring, taking into account that the latter is located 20 m above the shoe

Uz-20 m-0.0484 .97 m3. 0The volume of ultrasound is represented by cementing.

solution.

Thus, after sequential injection into the well surface of the above volumes (Vi, Ub, V2 and Ultrasound.), A buffer-5 fluid is placed in the top of the fluid-containing formation, which is located at a depth of 250 m.

In the RPF process, solid particles of the dispersion medium fall out of the buffer 0 fluid, forming a sediment layer that blocks and clogs the fluid-containing formation at a depth of 250 m.

EXAMPLE 2 To obtain a buffer liquid of 1 m with a density of 1,800 kg / m of pon-5, 1,100 kg of barite and 600 liters of dispersion medium are obtained.

EXAMPLE 3. To obtain a buffer liquid of 1 m with a density of 3000 kg / m, more than 2000 kg of hematite and 300-350 liters of a dispersion medium will be needed.

The buffer fluid can be positioned both in the open hole and in the cased part of the annulus.

The method of cementing wells is advisable to apply in reservoirs that are potentially prone to gas production, but do not have commercial reserves, which will ensure the reduction of just wells due to poor separation of the reservoirs and the protection of the subsoil and the environment.

Claims (1)

The invention method of cementing wells, including the sequential injection of hardening cement slurry and non-hardening slurry and delivering them into the hole above the roof of the fluidizing reservoir, characterized in that, in order to prevent fluid from penetrating into the annular cavity Because of the blockage of the fluid-forming layer by the dispersed phase of a non-hardening suspension, a suspension of reduced sedimentation stability with a settling time of the dispersed phase less than the setting time of the cement slurry is used as a non-hardening suspension, and the suspension density is 1800 - 3000 kg / m3. The settling time of the gel from the buffer fluid and its rheological properties in comparison with the OZT time of the cement slurry  May vary depending on the fineness of grinding. A density of 1500-2000 is provided by barite; density is provided by hematite; 2500-3500 insoluble lead salts, etc.