RU2217576C2 - Process isolating productive and nonproductive formations - Google Patents

Abstract

FIELD: oil and gas production, segregation of formations in well. SUBSTANCE: nonproductive formations are impregnated with gel-forming compound. Casing string is sunk. String clearance is filled with cement mortar. In correspondence with invention nonproductive formations are perforated prior to sinking of casing string. Additional excessive pressure is formed in interval of nonproductive formations in process of impregnation of nonproductive formations in well. EFFECT: enhanced efficiency of process. 1 cl

Description

The invention relates to the oil and gas industry, in particular, to methods for separating formations in a well.

A known method of isolating formations in a well by lowering the casing and filling the annulus with cement mortar [1].

The main disadvantage of this method is that due to the reduction of hydrostatic pressure in the column of cement mortar during its setting, as well as contraction, interstratal flows can occur already at the stage of formation of cement stone. Often there is a suffusion destruction of the cement ring, and the quality of the separation of the layers is reduced.

Closest to the invention in technical essence is a method of separation of productive and non-productive formations, including impregnation of the latter with a gel-forming composition, descent of the casing, filling the annular space with cement [2].

The disadvantage of this method is that the wellbore in the interval of permeable formations is covered with a clay crust, the permeability of which is much lower than that of the formation. The gel-forming composition penetrates the formation through a clay peel by a small amount, and therefore the expected effect of separation of the layers is not achieved.

The task is to increase the efficiency of the method.

The problem is achieved in that in the method of separation of productive and non-productive formations, including impregnation of non-productive formations with a gel-forming composition, casing string descent and filling the annulus with cement mortar, according to the invention, non-productive formations are perforated before the casing descent, and in the process of impregnation in the well in the non-productive interval formations create additional excess pressure. In this case, in the process of impregnation in the well to obtain additional excess pressure create hydrodynamic pulses.

The essence of the invention is to isolate productive formations from non-productive ones with the help of gelling compositions even before the casing string is lowered and cemented. This reduces the likelihood of gas or water flow while waiting for the solidification of cement (OZZ) during the further operation of the wells.

In aggregate, the proposed actions make it possible to saturate the formations with a gel-forming composition by a significant amount, to improve the quality of the separation of the formations.

The proposed method is as follows.

The required volume of the gelling composition and the required height of its column in the well are calculated using the formulas

V = 0.785 D ² hm (1)

H = V / 0.785 d ² = D ² hm / d ² (2),

where V is the volume of the gelling composition, m ³ ;

D is the diameter of the zone to be impregnated, m;

h is the height of the formation to be impregnated, m;

m is the coefficient of porosity, d.e .;

N - column height of the gel-forming composition in the well, m;

d is the diameter of the wellbore, m

After drilling is completed, before the drill pipes are raised, a gel-forming composition, for example, an aqueous solution of water glass (sodium silicate) with a concentration of 5-12% with the addition of 0.6-1% hydrochloric acid, is pumped into the well into the interval of the separable formations. Drill pipes are raised above the column of the gel-forming composition. A perforator, for example cumulative type PKS-80, is lowered into the well. Unproductive formations are perforated, the perforator is removed to the surface.

Then one of the following methods is applied to create additional overpressure in the well to accelerate the filtration of the gelling composition into non-productive formations:

pipes with packers are lowered into the well and the perforated interval is cut off from the rest of the wellbore, additional pressure is created between the packers by pumping fluid from the wellhead;

seal the mouth, for example, using a preventer, and increase the pressure at the mouth to 2-5 MPa for 2-3 hours;

drill pipes are paced for 2-3 hours in order to provide a hydrodynamic increase in pressure at the bottom of the well;

a cord torpedo is lowered into the well in the interval of unproductive formations and blown up.

During the impregnation process, a decrease in the liquid level in the well is monitored in order to assess the volume of the gel-forming composition crushed into non-productive formations.

Drill pipes are pulled to the surface. The casing is lowered into the well and cemented, i.e. fill annular space with cement mortar.

Example. At the Lyantorskoye field, the AS ₁₀ productive formation with a thickness of up to 16 m lies at a depth of 2050 m. Under the productive oil-saturated layer, often without any impervious bridge, a water-saturated layer with a thickness of up to 4 m lies. Under these conditions, the well is flooded in the first 3 months of operation.

In order to ensure reservoir separation in one of the wells of the Lyantorskoye field, it was recommended that the proposed technology be applied. For this, the drill pipes were lowered to a depth of 2070 m.

By the formula (1), the necessary amount of gelling composition was calculated with the following initial data: D = 5 m; h = 4 m; m = 0.2;

V = 0.785 · 5 ^{2 ·} 4 · 0.2 = 15.7 m ³ .

By the formula (2), the necessary height of the column of impregnation fluid in the well was determined: N = 15.7 / 0.785 · 0.21 d ² = 429 m.

We prepared 16 m ^{3 of} gel-forming composition (an aqueous solution of 10% water glass with the addition of 1% hydrochloric acid), pumped it into the interval 2070-1640 m. The drill pipes were raised to the level of 1630 m. The PKS-80 perforator was lowered into the well and the perforated part was perforated formation in the range of 2070-2066 m with a density of 6 shots per 1 linear meter. The punch was removed to the surface. Using a preventer, the mouth was sealed and additional pressure was applied to the column of the gel-forming composition at 2-3 MPa for 2-3 hours.

The mouth was depressurized, the drill pipes were removed to the surface. The casing was lowered into the well and cemented. They mastered the well and received an anhydrous influx of oil.

Thus, the proposed method can improve the quality of separation of the layers, reduce the rate of watering wells.

Sources of information

1. RF patent No. 2095542, M.cl. E 21 B 33/13, 1997

2. Gorodnov V.D. Physico-chemical methods for preventing complications in drilling. - M .: Nedra, p. 194-198 - prototype.

Claims (2)

1. A method of separation of productive and non-productive formations, including the impregnation of unproductive formations with a gel-forming composition, casing string descent, filling the annulus with cement mortar, characterized in that the non-productive formations are perforated before the casing is descent, while creating a well in the interval between unproductive formations additional overpressure. 2. The method according to claim 1, characterized in that the additional excess pressure is created by generating hydrodynamic pulses in the well.