SU1317092A1 - Method of eliminating gas manifestations in well - Google Patents

Abstract

The invention relates to the drilling of deep wells and reduces the pressure on the wellbore 1 and the blowout equipment, reduces the time required for the elimination of gas transmission and increases the safety of work. When gas is detected, the gas is washed away by backwashing well 1 by supplying drilling mud (BR) into the annulus. At a depth of gas concentration, the BR is bypassed into the tube space. Further, the BR flow is divided into two directions. The gas is captured by the BD and dispersed in it in the drill pipe 4, i.e. the gas is washed out in the form of a slightly carbonated BD. The degree of gas dispersion and the rate of efflux of carbonated BR from well 1 are controlled by changing the supply of BR to the tube space. The amount of head loss in the flushing hole of the drilling tool is smoothly changed. The magnitude of the pressure differential can be adjusted by varying the cross section of the flush hole. 1 il. I (L 14- 3 S g with o; o to

Description

The invention relates to the drilling of deep wells, in particular, to the elimination of large gas streams in them (LJ.

The aim of the invention is to reduce the pressure on the wellbore and the anti-blowout equipment, to reduce the time for the elimination of the gas supply and to increase the safety of work.

The drawing shows the scheme of elimination in the well gazop1) about the occurrence.

Well 1 has a glast, working with gas 2 circulating in an annular space 3 formed by a well 1 and drill pipes 4 in which an opening 5 is made.

The essence of the method is as follows.

When gas is detected, gas is washed away by backwashing the well by supplying drilling fluid to the annulus. At the depth of gas concentration (the pressure in the well is close to the maximum allowable), the drilling fluid is bypassed into the tube space with subsequent separation of the flow into two directions. The degree of gas dispersion and the rate of elution of carbonated drilling mud from a well are controlled by changing the flow of drilling fluid into the annulus.

When a gas enters a drilling well, it occupies the lower part of the annulus at the initial time. When gas is detected, the well space of the well is sealed with a preventer, and the drill pipes are sealed with a ball valve. The gas has a low density and therefore an overpressure occurs in the preventer. If the hydrostatic pressure of the mud column in the drill pipe balances the reservoir pressure, there is no overpressure in them. The well is at this time in equilibrium with the reservoir pressure. If at this moment in the drilling tool to open the drain opening above the gas stack, then the pressures at the mouth of the annulus and the drill pipes are equalized. They will be equal in size in the annular space of the well and in the drill pipe at the level of the flushing hole. But the downhole pressures of the drilling mud column in the drill pipe and the gas mixture with the drilling fluid in the wellbore space of the well are different in size (drill down1; the downhole pressure is greater). Circulation in the well below the wash hole is stopped, and the drilling fluid circulates in the well just above the wash hole. When yMeHbHjennn pressure loss in the flushing hole occurs

five

circulating mud and gas below the flushing orifice at a rate determined by the difference in the magnitudes of the pressure drop at the bottom of the borehole and in the flushing hole and hydraulic resistances in the circulation system. The gas, the approach to the flush hole, is captured by the drilling fluid and dispersed therein in the drill pipe, i.e. the gas is flushed to the surface as a slightly carbonated mud. The pressure drop between the annular space and the drill pipes can be adjusted over a wide range by varying the rate of flow of the drilling fluid through the flushing hole, since the pressure loss here is determined by the square of its velocity.

. four

where h is the loss of pressure, m;

0 k-coefficient of local hydraulic resistance;

V is the rate of flow of drilling fluid through the flushing hole, m / s; g-acceleration of free fall, m / s. As the gas is flushed out from the annular space, the pressure differential between the downhole pressure of the mud column in the drill pipe and the mixture of gas and mud in the annulus space decreases. Therefore, in order to maintain a given degree of gas dispersion, the pressure drop in the flushing hole must be gradually reduced by changing its flow rate or by increasing the cross-section of the washing hole.

When opening the flushing hole in

In the borehole, the drilling and drilling fluid is circulating until the pressure for the bottom of the gas / mud mixture in the drill pipes and in the annulus of the well

equal to and not equal to the reservoir pressure. When creating a reverse circulation of drilling mud in the well at the moment of opening the wash hole in the well, a pressure loss will occur in the hole in it.

5 of the solution, i.e. the pressure in the annulus of the well will be greater in magnitude than in the drill pipe. The value of the pressure differential can be adjusted by changing the cross section of the drilling mud supply hole into the well (with constant supply of drilling pumps) or the pressure of the mud pumps and set equal in magnitude but inverse to the sign of the pressure difference at the bottom hole of the drilling mud column in the drill pipe

5 and the mixture with the mud in the annular space. The degree of gas dispersion in a drilling fluid can also be set in a wide range (e.g.

from 0.02 to 0.1). When the degree of gas dispersion is 0.05 (five volumes of gas are dispersed in 100 volumes of drilling mud), the bottomhole pressure in drill pipes in a well with a depth of 4000-5000 m will decrease by only 0.08-0.1 MPa, i.e. almost will change. Due to the hydraulic resistances in the drill pipe and the throttling line, the bottomhole pressure in the pipes is large in terms of formation pressure. The value of the bottomhole pressure within certain limits is regulated by the throttle. With the described technology of gas flushing out from the well in it and in the ground blowout equipment, there are no large excess pressures.

Gas washout from the well is as follows.

In a drilling tool, at a predetermined height from the bit, a rotary coupling is installed, which in the normal position closes the flushing holes.

The height of the flushing holes above the bottom of the well is selected taking into account the well design, its depth, the geological features of the particular area and the possible amount of gas entering the well in such a way that when reaching the gas bundle of flushing holes in the well there are no excessive overpressures dangerous for the casing , preventer or capable of producing hydraulic fracturing in formations under the casing shoe.

The cross section of the flushing holes is chosen so that the pressure loss of the drilling fluid when passing through the hole can be adjusted in wide (for example, from 10 MPa to zero).

When gas and oil is detected in the well during drilling, it is immediately stopped, the well is stopped and the annulus is sealed with a preventer, and the drill pipes with a ball valve. The volume of formation fluid entering the well and its type (gas, oil, water) are determined by the change in the volume of drilling mud in the receiving tanks and the overpressure on the pre-fan. If gas entered the well in a volume exceeding the maximum allowable volume, it was eluted from the well according to the proposed method. For this, a throttling line is attached to the driving drill pipe, and mud pumps are connected to the jamming line. The boring tool is unloaded to the bottom and with its reverse rotation open the flushing holes. At this point, open the ball valve and into the annulus

pumping the drilling fluid through the plugging line at a rate such that the pressure drop in the flushing holes is equal to the excess pressure

on preventer in a closed well.

When the steam valve is opened, the wellhead pressures in the drill pipes and the pinhole space of the well are reduced up to atmospheric (with open

Q choke) and due to the energy of compressed gas, the drilling fluid in the drill pipe and behind-the-hole space is set in motion, i.e., its structure is destroyed. Under these conditions, to restore circulation in the well bore mud

5 pressure mud pumps 5.0-10 MPa. The degree of gas dispersion can be set to small. For example, when the circulation rate is below the wash hole 10 cm / s and the circulation rate of the drill

0 solution, in the annular space of the well about 400 cm / s (two pumps of the UNB-1250 feed about 100 l / s into the well at a pressure of 21 MPa or two U8-7.MA2 pumps but into the well about 100 l / s at a pressure of 14.2 MPa) in 100 volumes of drilling mud

About 2.5 equal volumes of gas will be dispersed (dispersion degree 0.025). As gas is washed out of the annulus to maintain a constant degree of gas dispersion in the drilling

In solution, the value of the pressure loss in the flushing hole is gradually reduced. This is done by changing the flow of drilling fluid into the well, thus maintaining the percentage of gas in the solution constant. Injected into the well

5, the drilling fluid is relaxed so that the bottomhole pressure in the borehole, when the circulation of the drilling fluid stops, exceeds the pressure of the gas in the formation.

After nOvTHoro gas flushing out of the well, the circulation of the drilling mud is stopped and the well is sealed. If overpressure occurs at the wellhead, then the required density of the solution is calculated by their value and the solution in the well is replaced with it. In the absence of pressure, the well is depressurized, the flushing holes are closed and drilling continues.

Claims (1)

Invention Formula  A method of eliminating gasification in a well by washing out gas with a drilling fluid, dispersing the gas in the drilling fluid and maintaining a bottomhole pressure above the reservoir, characterized in 5 that, in order to reduce the pressure on the wellbore and the blowout preventer, to reduce the time for the elimination of gas supply and to increase safety 0 1317092 56 works, the gas is washed out of the reverse solution in two directions, with the step-by-step washing the well by supplying the drilling-stump of gas dispersion and the velocity of the solution into the collar space of the wash of the carbonated drilling mud from bypassing it into the tubular space, the holes are regulated by changing the flow the depth of concentration of gas injection, the drilling fluid into the annular space with the subsequent separation of the drilling mud flow.