RU2059064C1 - Method for insulating gas stratum - Google Patents

Abstract

FIELD: gas production, insulation of gas streaks in wells. SUBSTANCE: method includes pumping water in nearby bottom zone, pressing it through to the depth of stratum insulation, and bringing well into operation. Gel-forming composition and then solidifying composition are additionally pumped ib after pressing through the water to the depth of stratum insulation. EFFECT: higher productivity. 4 cl, 2 dwg, 4 tbl

Description

 The invention relates to the oil and gas industry, in particular to methods for isolating gas interlayers in wells operating oil and gas and gas deposits.

A known method of isolating a gas-saturated part of a formation from an oil-saturated one, comprising injecting an aqueous solution of alkali and alkaline earth metal chlorides into a gas-saturated zone and reducing the pressure in the gas-saturated zone to the evaporation pressure of the aqueous phase, in which the salt precipitates and reduces rock permeability to gas [1 ]
However, the method is not sufficiently reliable and efficient. Low reliability is due to the high solubility of alkali and alkaline earth metal chlorides, as a result of which the insulating screen breaks down over time, and insufficient efficiency is associated with a slight decrease in rock permeability for gas.

 There is also a method of isolating gas occurrences in oil wells when developing fields with a gas cap by creating conditions for hydrate formation in a gas reservoir by injecting at least two volumes of screen into the reservoir, followed by cooling of the reservoir while creating a depression on the reservoir.

 The method is also not sufficiently reliable and efficient. This is due to the fact that when the thermobaric conditions in the formation change, hydrates are easily destroyed and the rock permeability for gas is quickly restored.

 Closest to the proposed one is a method of isolating a gas reservoir, which includes injecting a portion of water into the bottomhole zone, pushing it to the depth of isolation, and putting the well into operation.

 The disadvantages of this method are the low reliability of blocking the gas-saturated part of the formation from oil-saturated and low efficiency of the isolation process. Since the method is based on the equilibrium reversible hydrate formation process when the gas reservoir is saturated with water, in real well operation conditions, after completion of insulation work, hydrates are easily destroyed due to changes in thermobaric conditions, the formation fluid movement in the reservoir resumes, the reservoir saturation with water decreases, and rock permeability for gas eventually recovers quickly. This is confirmed by the results of field tests of the method in the conditions of oil and gas deposits of the Lyantorskoye and Fedorovskoye fields. As these tests showed, the effect of isolating gas breakthroughs by this method is either not achieved at all, or the duration of the insulation effect is very short and does not exceed 1-2 months.

 The aim of the invention is to increase the reliability of blocking the gas-saturated part of the reservoir from oil-saturated and increase the efficiency of the isolation process.

 The goal is achieved by the fact that in the known method of isolating a gas reservoir, which includes injecting a portion of water into the bottomhole zone, pumping it to the depth of the reservoir insulation and putting the well into operation, after pushing the water to the depth of the reservoir isolation, gelling and then cementing cement formulations are pumped into it.

 The isolation of gas inflows by a known method is carried out by pumping water into a gas reservoir. An insulating screen is thus formed due to the equilibrium hydrate formation process. In contrast, the inventive method includes the sequential injection into the reservoir of water, then gelling and, last but not least, cementing compositions. Such a technological scheme is very simple, not limited by economic factors and provides a significant increase in the reliability and efficiency of the process of isolation of gas inflows. The main volume of the insulating screen is formed from water due to the formation of a water-oil emulsion at the gas-oil contact and hydrate formation in the gas reservoir. A smaller volume of the insulating screen is formed by injection into the reservoir of cheap gel-forming compositions. Due to the high and widely adjustable rheological properties of gelling compositions, a complete and uniform coverage by the thickness even of a layer-by-layer inhomogeneous treated formation is achieved, and the high filterability of such compositions into porous media provides a predetermined strike radius along strike. To fix the insulating screen in the formation, a small volume of the cementing slurry is pumped into it, or the injection of the fixing composition is combined with the application of a metal patch on the insulated interval.

 With this sequence of radial arrangement of gas-insulating materials in the formation as the depression increases when approaching the borehole wall from the depth of the formation (Fig. 2, which shows the depression funnel), the insulating properties of the plugging materials are simultaneously enhanced. In the depth of the formation, where the depression is minimal and tends to zero at a certain distance from the well, the insulating screen is represented by a water-oil emulsion with a high shear gradient sufficient to prevent gas from breaking into the oil-saturated zone of the formation (section 1 in FIG. 2). The radius of such a screen can be of almost any size, as it is created not only by pumping water. As the depression increases when approaching the well, the requirements for the strength of the insulating screen increase, for which purpose a gel-forming composition is pumped into the formation after water (section 2 in FIG. 2). In the zone of maximum depression located near the wall of the well (section 3 in Fig. 2), an insulating screen is formed with the help of a strong fixing cement composition. In addition to creating a reliable obstacle to gas breakthrough in the zone of maximum depression, the fixing composition also plays a crucial role as a material that prevents the removal of water-oil emulsion and gel-forming composition from the development and operation of the well after repair and insulation work (RIR), which ensures a long duration of the insulating effect and the reliability of the method .

 In this case, as a gel-forming composition, a viscoelastic composition such as VUS, CROSS, GOS or liquid glass, or a polymer-silicate solution, or an aqueous solution of a water-soluble organosilicon composition is pumped into the formation. As a fixing composition, an organosilicon grouting composition of the type ВТС, НВТС, АКОР, product 119-204 or an organosilicon grouting composition in combination with a cement mortar, or cement mortar, or injection of a fixing composition are combined with the application of a metal patch on an isolated interval.

 Thus, the introduction of distinctive features from the prototype features in the inventive method due to the sequential strengthening of the strength of the gas insulating screen, synchronized with the magnitude of the depression in the bottomhole zone (funnel depression), as well as by achieving a predetermined insulation radius and reliability of fastening the screen in the reservoir can improve reliability and efficiency a method of isolating gas inflows and obtain a positive effect, which consists in a significant reduction in the volume of associated gas produced, an increase in oil production and enhanced oil recovery for oil and gas reservoirs.

 Figure 1 gives a flowchart of a process for isolating gas inflows in order to justify the radius of the gas insulating screen as a whole and explaining the sizes of the screens represented by the oil-water emulsion, gel-forming and fixing compositions; figure 2 funnel depression during operation of the well.

 Figure 1 shows the sequence of injection of gas-insulating compositions into the well, the types of gelling and fixing compositions used at individual stages of the technological process (TP) for isolating gas inflows, as well as the limit sizes of the radii of the screens created at each stage of the RIR.

где Р_пл пластовое давление;
Р_заб. забойное давление;
R_к радиус контура питания;
r_с приведенный радиус скважины;
r радиус воронки депрессии.The limiting size of the radius of each component of the gas-insulating screen is determined by the degree of change in depression in the near-wellbore zone during well operation (depression funnel) (Fig. 2). The calculation of the funnel of depression is performed according to the formula
PP _PL - (P _PL -P _Zab ) ×

where R _PL reservoir pressure;
R _zab . bottomhole pressure;
R _{to the} radius of the power circuit;
r _{c is the} reduced radius of the well;
r radius of the funnel of depression.

The calculation was performed for the Lyantorskoye field conditions with the following values included in the parameter formula: R _pl. = 210 atm, P _zab 170 atm. R _k = 200 m and r _c = 0.1 m. As can be seen from the graph shown in figure 2, if a gas insulating screen is created in a radius of 30-40 m around the well, the pressure drop between the remote zone and the boundary of the distribution of the insulating agent will be only 4-4.7% of reservoir pressure. For this reason, a part of the gas-insulating screen, consisting of a water-oil emulsion (section 1 in Fig. 2), has the dimensions indicated above, which makes it possible to reliably block the path of gas entry into the well in the event of a gas cone in an oil well operating an oil and gas reservoir. It can also be seen from the graph in FIG. 2 that the zone of propagation of the deep depression funnel, where the pressure drop is more than half of the total pressure drop in the reservoir, has a radius of 8-10 m. In this regard, a more durable part of the gas-insulating screen, consisting of from a gelling composition that has a radius size of up to 10 m (section 2 in FIG. 2). And, finally, near the walls of the well, where the rate of pressure decrease is the highest, a strong fixing cement composition is located within a radius of 1 m.

 The method is as follows.

The underground equipment is removed from the well and tubing pipes (tubing) are put into it for filling, the shoe of which is installed at the lower boundary of the isolation interval or 5-7 m below it. After that, water is pumped into the oil and gas saturated formation at the rate of 80-100 m ³ per 1 m of the gas saturated part of the formation (the first stage of the technological process). Next, one of the types of gel-forming compositions is prepared and pumped through the tubing into the formation in a volume of 60-200 m ³ (second stage of TP). One of the types of fixing compositions in the volume of 4.5-8 m ³ is prepared and pumped through the tubing into the formation (the third stage of TP). The gel-forming and fixing composition is pressed into the formation with water (saline) in a volume equal to the volume of the tubing and, moreover, 0.5 m ³ along the tubing and 0.5 m ³ along the annulus. The well is left closed under the pressure reached at the end of the supply for gelation and solidification of the compositions within 1-3 days. Backwash the well with water (saline) in a volume equal to one and a half times the volume of tubing, and carry out a cycle of work to launch the well into operation.

 Due to the fact that the flowchart of the technological process according to the proposed method at the first stage of the TP provides for the injection of large volumes of water into the formation, it was necessary to quantitatively evaluate the distribution of water injected into the oil and gas saturated formation into gas and oil saturated rocks. Taking into account the losses of water filtered into the oil-saturated zone, and with the known porosity and power of the gas-saturated zone, such a quantitative assessment allows us to calculate the required volume of water necessary to achieve a given radius of the insulating screen.

The distribution of the flow of injected water into the gas and oil-saturated rock was determined in laboratory conditions on the model of oil-and-gas-saturated formation using the filtration unit UIPK-1M. For this, two natural cores of productive sediments of the Lyantorskoye field with known permeabilities, one of which was gas-saturated and the second oil-saturated, were pumped from a total capacity at constant pressure. In experiments, the total flow rate of water pumped through both cores for 60 min was recorded, and the volume of water filtered through gas-saturated (V _g ) and oil-saturated (V _n ) cores was determined at the exits from the core holders. According to the data obtained, the ratio of the volumes of water filtered through gas and oil-saturated cores (V _g / V _n ) was calculated, which quantitatively characterizes the flow distribution.

The results of the experiments are summarized in table 1. From the data of table 1 it is seen that in all experiments, the ratio of V _g / V _{n is} high and varies from 5.3 to 45.2. This indicates a predominant filtration of water into the gas-saturated zone of the formation and a slight filtration into the oil-saturated zone. From table 1 it is also seen that if the permeability of gas and oil-saturated rocks is approximately the same, then the ratio of V _g / V _n is 5.3-6.1 (experiments 1, 4, 5 in table 1). But if the permeability of a gas-saturated rock is higher than that of an oil-saturated rock, then the ratio of V _g / V _n rapidly increases from 6.1 to 45.2 (compare experiments 1, 2, 3 in Table 1). Thus, the above laboratory data confirm the possibility of large-volume water injection mainly into the gas-saturated zone of the formation, which is a fundamentally important point in the implementation of the proposed method.

In the process of pumping water into the oil and gas saturated formation at the first stage of the TP, a water-oil emulsion is formed in the gas-oil contact zone, which, according to the proposed method, acts as an insulating screen. In this regard, in laboratory conditions, the insulating (rheological) properties of oil-water emulsions were studied. For this purpose, oil-water emulsions with different contents in their water were prepared using oil from the Lyantorskoye field and Cenomanian water using a high-speed mixer. In appearance, such emulsions are a porridge-like, almost non-fluid mass of brown color. Special experiments established that the emulsion without the addition of demulsifiers are persistent. Their destruction is not observed with heating for 24 hours at 65 ^{° C} (simulating reservoir conditions). When trying to destroy the emulsion by centrifugation, it was found that it is only partially destroyed. At a rotation speed of 3500-4000 rpm for 10 hours, only 1/3 of the emulsion exfoliates. With a longer centrifugation, further separation of the emulsion does not occur.

The rheological properties of water-oil emulsions were studied at ²⁵ ° C using a rotational viscometer "Reotest-2". Table 2 summarizes the results of measurements of the dynamic viscosity of an oil-water emulsion containing 56.6% water at various shear stresses. From the data of Table 2 it can be seen that the investigated emulsion is a non-Newtonian fluid and its viscosity substantially depends on the shear stress. The dynamic viscosity of this emulsion varies from 2617 cps at a shear stress of 99.1 Pa to 446 cps at a shear stress of 2941 Pa. From table 2 it is seen that when the ultimate shear stress (above 1200 Pa) is reached, the structure of the emulsion is destroyed and the apparent (conditional) viscosity of the emulsion no longer depends on the shear stress. Oil-water emulsions have high ultimate shear stresses, which indicates the high insulating properties of such emulsions.

 In the table. Figure 3 shows the results of measurements of the dynamic viscosity of oil-water emulsions prepared from oil from the Lyantorskoye field and Cenomanian water at different water contents. Given that the emulsions are non-Newtonian fluids, to obtain comparable viscosity measurements, they were performed at shear stresses exceeding the limiting values at which the structure of the emulsions is destroyed. From the data of Table 3 it can be seen that as the water content in the oil-water emulsion increases, the viscosity of the emulsion quickly increases from 19.3 cPs for the original oil to 451.6 cPs for the emulsion containing 56.6% water. With a further increase in water content, the viscosity of the emulsion begins to decrease, but remains high. The data table. 3 confirm that water-oil emulsions have high insulating properties in a very wide range of water content in them.

 The proposed method was also tested in field conditions on the oil and gas deposits of the Lyantorskoye and Fedorovskoye fields. The preparation of gas insulating compositions and their injection into the well and into the formation was also carried out using standard technical means used in the overhaul of wells.

Gelling compositions for field testing of the proposed and known methods were prepared as follows. The visco-elastic composition (HCL) was obtained by mixing a 0.6% aqueous solution of polyacrylamide (PAA) with potassium chromium alum. The ratio of the components in the WCS was, wt. PAA 0.6; potassium alum 0.04; water the rest. The organosilicon crosslinked system (CROSS-1) was prepared by mixing a 0.5% aqueous solution of PAA with AKOR-B ₁₀₀ and neonol in the following ratio of components, wt. PAA 0.5; AKOR-B ₁₀₀ 2.5; neonol AF _9-12 grade CHO -3B 2.5; water the rest. Another formulation of the organosilicon crosslinked system (CROSS-2) included the following components, wt. PAA 0.5; ethyl silicate-40 3.3; product 119-204 1.7; neonol AF _9-12 grade SNO-3B 5.0; potassium dichromate 0.04; water the rest. A gel-forming composition (GOS) was prepared by mixing an aqueous solution of PAA and lignosulfonate (KSSB) with potassium dichromate in the following ratio of its constituent components, wt. PAA 0.6; KSSB 0.9; potassium dichromate 0.45; water the rest.

Fixing compositions for the implementation of insulation work on the proposed method was prepared as follows. Organosilicon water-soluble grouting composition (VTS-2) was obtained by mixing ethyl silicate-40, product 119-204 and polyglycol in the following ratio of components, wt. ethyl silicate 33; product 119-204 17; polyglycol 50. Organosilicon neon containing a water-soluble grouting composition (NVTS-1) was obtained by mixing AKOR-B ₁₀₀ and neonol AF _9-12 grade SNO-3B in a ratio of 1: 1 by volume. Another formulation of a neonol-containing water-soluble grouting composition (HBTC2) included the following components, wt. ethyl silicate-40 33; product 119-204 17; neonol AF _9-12 grade CHO-3B 50. The cement mortar used in the proposed method as a fixing composition, or to fix the silicone fixing composition, was prepared according to standard technology with a density of 1.78-1.80 g / cm ³ .

PRI me R. In well 2594 of the Lyantorskoye field, repair and insulation works (RIR) were performed in three different ways. Such work was carried out in order to compare the effectiveness of the proposed and known methods in the same geological, physical and technical conditions. Initially, the RIR was carried out by injecting 62 m ^{3 of} VUS into the reservoir (Table 4, where the data from field tests are presented). After that, the well was put into operation. Comparison of the parameters of its work before and after the RIR, are given in table. 4 shows that the insulation effect of this method was not obtained.

Another known method for isolating gas inflows, which was then tested in well 2594, is based on the sequential injection of gelling and fixing compositions into the formation. When implementing this method, 30 m ^{2 of} hydraulic slurry, 2.5 m ^{3 of} silicone-based cementitious compound VTS-2 are injected into the well, and 5 m ^{3 of} cement mortar are fixed. After that, the well was mastered and put into operation. As can be seen from the data of table 4, the parameters of the well after conducting RIR according to the second known method also practically did not improve.

Given the fact that the RIR performed in well 2594 using the two methods described above did not give a positive result, insulation work was performed in this well to eliminate gas inflows using the proposed method. To do this, 1100 m ^{3 of} water, 115 m ^{3 of} gel-forming composition (CROSS-1) and 6.6 m ^{3 of} fixing composition (NVTS-1) were successively pumped into the well and into the formation. As a result of the RIR, a significant positive effect was achieved. Buffer pressure decreased from 110 to 19 atm, annular pressure decreased from 150 to 11 atm, and oil flow rate increased from 0.7 to 16.7 t / day. Thanks to the RIR conducted by the proposed method, the well managed to be transferred to a mechanized method of operation and it is currently working steadily with the help of ESP.

 Insulation work on the proposed method was also performed in well 3546 of the Lyantorskoye field and in wells 4012 and 4021 of the Fedorovskoye field. The RIR technology, the types and volumes of gas-insulating compounds used in each well, as well as the well operation parameters before and after the RIR are summarized in Table 4. From this table. 4 shows that in all cases, the application of the proposed method gives a significant positive result. The effect of isolation at the first two wells has been going on for more than a year and the effect is currently continuing for all wells, which indicates a high reliability of the method.

 To compare the effectiveness of the proposed method with the protothiom method in well 4089 of the Lyantorskoye field, water was pumped into the bottom-hole zone of the formation, selling it to the depth of isolation of the formation, and putting the well into operation. The results of the RIR on the prototype method are given in table. 4, indicate the lack of reliability and effectiveness of this method.

Using the proposed method allows for reliable blocking of the gas-saturated zone of the formation from oil-saturated and increase the efficiency of the process of isolation of gas inflows. At the same time, according to experimental field tests summarized in Table 4, the accident rate during operation of wells that uncovered oil and gas deposits decreases, the buffer and annular pressure decreases to normal values, and the average oil production rate increases by 13.4 t / day and by 14 , 9 thousand m ³ / day, the average daily production of associated gas is reduced. The application of the proposed method for processing sections of oil and gas deposits will increase oil recovery.

Compared with the prototype method, the proposed method will additionally produce 3172 tons of oil and limit the selection of associated gas in the amount of 5751 thousand m ³ in terms of 1 well operation per year.

Claims (4)

 1. METHOD FOR INSULATING A GAS STRING, which includes injecting water into the bottom-hole zone of the formation, pumping it to the depth of the formation isolation and putting the well into operation, characterized in that after the water has been injected into the formation, gelling and then fixing cementing compositions are pumped into it.  2. The method according to claim 1, characterized in that as a gelling composition, a viscoelastic composition, or liquid glass, or a polymer-silicate solution, or an aqueous solution of a water-soluble organosilicon composition is pumped into the formation.  3. The method according to claim 1, characterized in that as a cementing grouting composition, an organosilicon grouting composition, or an organosilicon grouting composition in combination with a cement mortar, or cement mortar are pumped into the formation.  4. The method according to claim 1, characterized in that the injection of the fixing composition is combined with the application of a metal patch on an isolated interval.

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