RU2112133C1 - Process isolating absorbing strata - Google Patents

Abstract

FIELD: oil production. SUBSTANCE: in agreement with process grouting mortar is supplied to absorption zone over pouring pipes. Calculated volume of grouting mortar is delivered into absorption zone by portions. These portions alternate with portions of elastoviscous separator. After every portion of grouting mortar with separator it is left in quiescent state in zone close to shaft for time of loss of mobility. During this operation balance of pressures in well and stratum is provided. EFFECT: diminished material expenses, improved quality of isolation of absorption zones.

Description

 The proposal relates to the oil and gas industry, in particular, to methods for eliminating the absorption of flushing fluid during drilling.

 A known method of isolating absorbent layers, including replacing the wash liquid with a working one before injecting the grout, and grouting the grout into the absorbing reservoir is carried out by applying pressure to the latter above the absorption pressure, after which the pipes are raised to a height above the level of the grout and the hydrostatic pressure is increased by replacing working fluid for flushing with a higher density, while monitoring the change in hydrostatic pressure is carried out by changing injected into the wellbore and exiting solutions on the wellhead [1].

The disadvantage of this method is the limited use of it, because it can be used only with an absorption intensity of not more than 15-20 m ³ / h. In practice, drilling operations in such cases are carried out by washing inert fillers on a clay solution. With intense absorption, the use of this method does not give positive results, because the creation of increased pressures leads to the complete disappearance of the cement slurry into the absorbing layer, while the circulation of the solution through the mouth is not observed and it is impossible to determine the level of the cement slurry in the absorption zone.

 The closest technical solution to the technical essence of the proposed is a method of isolation of the absorbing formations, including the injection of cement slurry through drill pipes into the absorption zone with the complete displacement of the mixture from the well into the formation [2].

 The disadvantage of this method is the high consumption of insulation materials and a low success rate of operations. When grouting mixture is injected into the absorption zone of the drilling fluid under the influence of excess pressure (the column height of the mixture and the injection pressure), it spreads around the perimeter of the wells, and when it is pushed into the formation, it is further pushed into the periphery deep into the formation. At the same time, full coverage of the reservoir insulation by power is not achieved.

 The technical result of the invention is to reduce material costs and improve the quality of isolation of absorption zones. The goal is achieved by the described method, including the delivery of cement slurry into the absorption zone through the filling pipes. In this case, the estimated volume of the injected grouting mortar is delivered in batches, alternating each portion with a viscoelastic separator, while ensuring pressure balance in the well and the formation, and after each filing of the grouting mortar with a separator, it is left alone in the near-well zone for the period of loss of mobility. In the method adopted for the prototype, the cement slurry at the bottom of the well is affected by the pressure of the mud column itself and the selling pressure. Under the influence of these pressures, the solution goes into the absorbing layer, the larger the amount of solution pumped, the farther from the bottom it is forced. However, it is not possible to raise the grouting bridge over the entire power of the absorbing layer.

 In the proposed method, the isolation is carried out at equilibrium of pressure in the well and in the reservoir by injecting grouting mortar in separate portions between the viscoelastic separator and leave each portion alone until mobility is lost. All these operations prevent the solution from going deeper into the formation and ensure the creation of an insulating screen over the entire power of the absorbing formation.

 These differences, in our opinion, meet the criterion of "significant differences" of the invention, since the known methods do not possess such properties and do not allow to obtain such a high result as the proposed one, thanks to new distinctive features.

 The method is carried out in the following sequence.

The packer is lowered on the filling pipes and set it 50-100 m above the complication zone. Then 0.2-0.4 m ^{3 of} viscoelastic separator (VURA) is delivered (pumped) through the filling (drill) pipes, then 0.5-1.5 m ^{3 of} cement slurry and again 0.2-0.4 m ^{3 of} VURA , i.e. the estimated volume of the injected cement slurry is delivered in portions. Each serving is alternated with WUR. As a VUR, you can use any known viscoelastic fluids, for example, hypane, viscous solutions of polyacrylamides, carboxymethyl cellulose, etc., and as a cement slurry, any solution based on cement or other materials. All this is forced into the interval of the absorption zone with buffer liquid - industrial water. Selling is carried out using a cementing unit at low speeds. In the process of delivering the cement slurry to the absorption zone, pressure is balanced in the well and formation. When selling cement slurry with a viscoelastic separator goes deep into the reservoir and clogs pores and cracks. The presence of a lower portion of the viscoelastic separator prevents erosion of the cement slurry by the wellbore fluid, and the upper portion of the VUR prevents the erosion of the grout by the buffer fluid. Due to the presence of viscoelastic separators, the cement slurry does not erode, it does not go deeper into the reservoir when subsequent portions of the cement slurry are injected. Then prepare a new portion of the cement slurry and in the same way pumped into the zone of complication. Each subsequent portion is pumped after a certain time - equal to the time of the loss of mobility of the cement slurry, which is individual for each formulation.

 Batch injection of grouting mortar allows you to get an insulating screen over the entire capacity of the absorbing layer, because, being between the separation plugs from the VUR, the solution can not spread over a distant distance into the reservoir, and subsequent portions injected after loss of mobility of the solution and at low speeds, layered on the previous ones, while increasing the height of the insulating screen.

The number of portions is determined specifically for each well, and the amount of cement slurry in the portion, equal to 0.5-1.5 m ³ , is due to the fact that when the volume of the solution is increased, the condition of pressure equilibrium in the well and reservoir is not observed.

So the hydrostatic pressure at the bottom of the well is:
P = H γ g,
Where
γ is the density of the washing liquid, kg / m ³ ,
g is the acceleration of gravity, m / s ² ,
H - vertical bottom hole depth, m

 Based on the formula, the pressure on the bottom of the wells at H = 1000 m during the injection of cement slurry is 18 MPa, and with the proposed method - 10.3 MPa.

P = 1000 • 960 • 10 - 40 • 1800 • 10 = 10.3 MPa,
Where
1000 kg / m ³ - the density of water, 960 m - the height of the column of squeezing liquid, 40 m - the height occupied by the grouting mortar volume of 0.5 m ³ , 1800 kg / m ³ - the density of the solution. Therefore, the pressure on the bottom of the well by the proposed method will decrease by 7.7 MPa (77 atm).

 Example.

 The method was carried out in the field at the well. 103 "D" of the Romashkinskoye field of Tatarstan with isolation of the zones of complication.

Well data:
Slaughter at the beginning of the work - 963 m
Tool failure - 935-937 m
Tool failure - 941-941.5 m
Drilling at a complete loss of drilling fluid circulation - 935-963
Pickup absorbance at zero gauge pressure - 60 m / h
To isolate the complication zone, a hydraulic-mechanical packer was installed at a depth of 802 m, then cement grout was pumped in the following sequence.

0.2 m ³ viscoelastic separator based on polyacrylamide, 1 m ³ cement slurry with a / p = 0.5 m and again 0.2 m ³ viscoelastic separator. The solutions were forced into the absorption zone without leaving a cement bridge in the well. They did not receive excess pressure during the sale.

 Each subsequent portion was pumped 30 minutes after the previous one - after the loss of mobility of the first portion. In total, five servings of the solution were pumped. The last portion of the solution was partially left in the wellbore.

 After 6 hours of cement hardening, the well was examined for injectivity. At an overpressure of 30 atm, the well did not accept.

 Then a cement bridge was drilled in the range of 887–963 m and, with a circulation of 90% solution, drilling continued to a depth of 1033 m. When isolating the complication zone, 7 tons of cement, 0.36 tons of calcium chloride and 1.5 tons of polyacrylamide were consumed.

 The technical and economic advantage of the proposed method is as follows. Due to the alternate injection of portions of the grouting mortar between the WURs, the height of the grouting jumpers increases. As a result, the absorption channels are blocked over the entire thickness of the formation. This leads to a 5-10-fold reduction in material costs and a 40% reduction in the time of isolation of complication zones.

Claims (1)

 A method of isolating an absorbent formation, including the delivery of cement slurry to the absorption zone through filling pipes, characterized in that the estimated volume of injected grouting mortar is delivered in batches, alternating each portion with a viscoelastic separator, while balancing the pressure in the well and formation, and after each portion of the grout with a separator, it is left alone in the near-well zone for the time of loss of mobility.