RU2467155C1 - Method of isolating unstable and sloughable rocks in construction of inclined and horizontal wells - Google Patents

Abstract

FIELD: oil-and-gas industry.

SUBSTANCE: invention relates to oil industry and may be used in construction of inclined and horizontal wells. Proposed method comprises bottomhole flushing, injecting cementing solution, squeezing said solution and square rod reciprocation. In compliance with this invention, flushing with flushing solution is stopped, mud solution is injected, process is held to equalise pressure in the well and settle mud particles. Thereafter, flushing is resumed. In injecting cementing solution unless its outflow from drill pipes, drill string is revolved. To ensure laminar flow of cementing solution in hole annuity cementing solution is squeezed down at low rate while reciprocation of square rod is performed with amplitude of 1-3 metres.

EFFECT: stable lining.

Description

The invention relates to the oil industry and may find application in the construction of directional and horizontal wells.

During the construction of directional and horizontal wells, in which the trajectory of the wellbore in the interval of passage of unstable and inclined to shedding rocks of the upper horizons has the largest deviation angle, shedding of rocks in the wellbore occurs. This, in turn, provokes emergencies and, as a result, an additional increase in the volume of work and the cost of well construction. As the experience of similar wells previously built at the Romashkinskoye field shows, the isolation of caverns and the prevention of shedding of rocks in areas of unstable rock occurrence can be achieved after repeated isolation work. Additional work leads to a complication of the well, a significant increase in the cost of materials, equipment and construction time of the well, which entails a significant increase in its cost.

A known method of isolation of absorbing formations (RF patent No. 20144433, IPC ЕВВ 13/13, published on June 15, 1994) by pumping cement slurry into the formation from the wellhead through the free end of drill pipes while maintaining constant pressure on the formation, and in order to increase efficiency and the reliability of the insulation before injecting the grouting fluid, the washing fluid is replaced with a working fluid, and the grouting grouting is injected into the absorbing layer by creating a pressure on the latter above the absorption pressure. Then the drill pipes are raised to a height above the level of the cement slurry and the hydrostatic pressure in the wellbore is increased by replacing the working fluid with a flushing fluid with a higher density.

But this method does not solve the problem of isolating unstable and prone to shedding rocks, as it is applicable only to isolate absorbing formations, and creating pressure on the formation with plugging material during crumbling rocks can lead to intensive collapse of the rocks.

A known method of sinking unstable rocks while drilling wells (RF patent No. 2344263, IPC ЕВВ 7/00, published on January 20, 2009), which includes reinforcing the walls of the well in the indicated interval with profile shutoffs, wherein the interval with unstable rocks is deepened and the walls of the well are strengthened in series sections, and the installation of profile overlaps is performed with overlapping overlapping with a consistent decrease in the internal diameter of the installed profile overlaps in the working position when deepening with Irene borehole in the first region of the formation interval or butt sequential extension of the recess portions of the wellbore.

This method is effective, but time-consuming, requires a lot of time for work and has a high cost, in particular, materials (pipes).

Closest to the proposed invention is the method described in RD 153-39.0-590-08 (developed by the TatNIPIneft Institute of OAO Tatneft, 2008, pp. 65-66). The essence of the method consists in the sequential installation of cement bridges from the bottom of the absorbing layer to its roof, as a result of which there is artificial hardening of the rocks that make up the absorption zone and have low strength.

But the known method is not effective in the case when in the zone of unstable rocks the well has a zenith angle of 30 degrees or more, or is horizontal. The disadvantages of this method in relation to the construction of directional and horizontal wells are:

1. Poor flushing of the well, due to the resulting pressure difference in the wellbore and in the annulus, causing clogging of the caverns of the formation with sludge, which prevents the entry of grouting fluid into them and strengthening of unstable rocks of the formation.

2. Incomplete grouting of grouting fluid in caverns of unstable rocks due to turbulent flow of grouting fluid in the annulus as a result of accelerated grouting of the grouting fluid with the process fluid.

3. The deterioration of the strength characteristics of the resulting cement stone due to dilution and facilitation of cement slurry when causing an intensive flow of fluid from the reservoir into the well, due to the pacing of a square rod to its length (amplitude 14-16 m). The proposed invention solves the problem of isolating unstable rocks while drilling directional and horizontal wells in them by the most complete cleaning of cavities from sludge and filling them with grouting mortar.

The solution to the problem is achieved by the fact that in the method of isolating unstable rocks during the construction of deviated and horizontal wells, including flushing the well, injecting grouting cement, pushing grouting mortar, pacing a square rod, according to the invention, flushing the well with washing fluid is stopped, the clay solution is being pumped, exposure is made for equalization of pressure in the well and sedimentation of the remaining particles of sludge, and then resume flushing. When injecting cement slurry until it leaves the drill pipe in the annulus, the drill pipe string is rotated. In order to ensure the laminar flow regime of the cement mortar in the annulus, the cement slurry is pressed at low speeds, and the square rod is paced with an amplitude of 1-3 meters.

The features of the invention are:

1. Flushing the well with flushing fluid, alternating with the injection of mud and holding for 3-5 minutes to equalize the pressure in the wellbore.

2. Injection of cement slurry into the well.

3. Rotation of the drill pipe string.

4. Punching cement slurry at low speeds to avoid the emergence of turbulent and the creation of a laminar flow regime of cement slurry in the annulus.

5. Walking a square rod with an amplitude of 1-3 meters.

Sign 2 is common with the prototype, signs 1, 4 and 5 are significantly different from the prototype, and sign 3 is new.

The method is as follows. The open end of the drill pipe (OKBT) is installed 25-30 m below the bottom of the zone of shedding rocks. The cementing unit is tied with a hard line to the pressure pipe and the well is flushed with washing liquid. During washing from the caverns of unstable crumbling rocks, the largest particles of drill cuttings are washed out. Due to the fact that in this interval of the formation, the wellbore deviates from the vertical by 30 degrees or more, or is horizontal, complete washing out of the fine sludge from the caverns by the flushing fluid. To eliminate this drawback, the method injected a clay solution in a volume of 6-10 m ³ and when it reaches the mouth, the washing is stopped, holding for 3-5 minutes. This time is enough to equalize the pressure in the well. In this case, the particles of the clay solution, falling into the caverns, bind the remnants of the cuttings cuttings and, due to the lack of pressure difference in the wellbore and in the annulus, are in suspension. Then, resuming the flushing of the well, the residual sludge adhering to the particles of the clay solution is washed to the surface, which subsequently ensures a more complete filling of the caverns with cement mortar.

Next, carry out the process of pumping cement slurry and forcing it into the well. To create a laminar flow of grouting mortar in the annulus, it is forced through the process fluid at a low speed of the cementing unit, for example, to the second.

During the injection of grouting mortar until the calculated moment of its exit from the drill pipe into the annulus, the drill pipe string is rotated. The additional pressure created on the grouting column in the well, in turn, creates pressure in the annulus, contributing to a more complete displacement of the flushing fluid from the caverns, and the laminar flow regime of the grouting grout ensures complete replacement of the flushing fluid in the caverns with cement.

In order to avoid sticking of drill pipes in the wellbore, they are paced by lowering and raising a square rod. Reducing the amplitude of the pacing of a square rod, for example, to 1-3 m, avoids sticking of drill pipes, while minimizing the mixing zone of the cement slurry with well fluid and produced water. This prevents the dilution and relief of cement slurry, which helps to maintain the strength properties of the resulting cement stone.

At the end of the grouting process, the drill string is lifted, and then the wellbore is flushed with technical water.

Thus, the application of the described method will allow for high-quality washing of the wellbore, the most complete filling of caverns of unstable formation rocks with grouting mortar, which ensures the formation of a durable cement stone that insulates the zone of unstable and prone to shed formation rocks.

This method has been successfully applied in the construction of directional wells of bush No. 8 under the city of Aznakayevo, as well as in other wells in the areas of the activity of NGDU Aznakaevskneft. All wells had an anti-aircraft angle of more than 30 degrees and a large design displacement of up to 1400 m, while the design program for the construction of wells and the geological and technical outfit laid the probability of isolation of crumbling rocks by installing a profile crossover OLKS. The application of the proposed technology significantly reduced the cost of constructing new wells and contributed to an increase in the commercial drilling speed of these wells.

Claims (1)

A method of isolating unstable and prone to shedding rocks during the construction of directional and horizontal wells, including flushing the well, injecting grout, grouting grout, pacing a square rod to its length, characterized in that the flushing of the well is alternated with the injection of clay mud, making exposure for 3-5 minutes, the cement slurry is pressed at low speeds and until the drill pipe exits the drill string, the drill string is rotated, while hazhivanie square bar is carried out with an amplitude of 3.1 m.