RU2322581C2 - Method for well bottom zone consolidation - Google Patents

Abstract

FIELD: underground well repair, particularly methods to create behind-casing screen in productive reservoir of oil, water and gas wells.

SUBSTANCE: method involves injecting foamed polymeric solution including water-soluble polymer in amount of 1.5-2.5 % by weight, foaming agent in amount of 1-3% by weight, cross-linking foam stabilizing agent in amount of 0.2-0.6% by weight and water in bottomhole formation zone; injecting porous plugging composition including cement grout with 0.3-0.5 water-cement rate taken in amount of 60-80% by weight, above mentioned foamed polymeric solution in amount of 20-40% by weight in bottomhole formation zone. Each of said solutions is characterized by viscosity η and yield point τ change during injection and cross-linkage thereof.

EFFECT: prevention of bottomhole formation zone blocking in slightly cemented reservoirs.

8 cl, 4 tbl, 5 dwg, 1 ex

Description

The present invention relates to techniques and technologies for underground well repair, and in particular to methods for creating an annular filter in a reservoir of oil, water and gas wells.

A known method of fastening the bottom-hole zone of the well, including the descent of the casing string, the injection of cement slurry, its hardening and perforation of the string [1].

The disadvantage of this method is that from the reservoir with poorly cemented rock through the perforation channels, siltstone slurries and sand enter the well, and this leads to clogging of the channels and, as a result, to the shutdown of the well.

The closest in technical essence and the achieved result to the proposed technical solution is the method of fastening the bottom-hole zone of the well, selected for the prototype, which includes pumping a stable and plastic cement grout, the porosity of which is ensured by the presence of acid-soluble inclusions.

In the method of attaching the bottomhole zone of the well, including the preparation of cement slurry with acid-soluble filler, pumping it and curing, drilling, washing the formed stone from salt, shell rock of a fraction of 0.7-1.5 mm in an amount of 10-15 weight is used as an acid-soluble filler. % and additionally, a surfactant is introduced into the grouting mortar in an amount of 0.5-1.0 wt.%.

However, this method does not provide the formation of qualitative permeability of the bottomhole zone after the operation due to changes in the structure of the resulting cement stone, namely as a result of changes in rheological properties in the process of pumping cement into the formation.

According to the prototype, the cement slurry is an aqueous dispersed system based on cement with a filler - shell rock fraction 0.7-1.5. Under static conditions, cement mortar with filler is a sedimentation-resistant system. The static shear stress during the start of structuring, which ensures the ability of the solution to hold suspended particles, is 1000-1800 dPa. After processing, the porosity of the obtained cement stone is 35-40% after treatment with an acid-containing solution.

However, the flow curve of this solution (Fig. 1) is the dependence of shear stress on shear rate, taken in the opposite direction from maximum to minimum during injection and, conversely, from minimum to maximum during structuring, determined using a Reotest-2 re-viscometer "At a temperature of 28.5 ° C (formation temperature PK-1) - shows that a stable and plastic cement grout is a non-Newtonian fluid, that is, the viscosity is not a constant and depends on the shear rate. A cement mortar with a filler - shell rock of fraction 0.7-1.5 is a pseudoplastic fluid, which is characterized by the presence of static shear stress and the absence of ultimate dynamic shear stress, i.e., when a shear stress is applied above the SSS, the structural mesh is destroyed, due to which the shell particles are retained in suspension, the composition no longer has strength characteristics and behaves like a Newtonian fluid. Thus, at shear stresses above 125 dPa, the distribution of the filler in the cement mortar with the filler changes due to sedimentation of suspended particles. Excreted from the solution, the filler settles when the composition moves along the wellbore with a high shear rate, the solution loses uniformity. As a result of this, a porous cement stone is not formed in its entirety and the channels are clogged in the bottom-hole zone of the formation and formation fluids do not enter the wellhead.

In addition, a shell rock released from the cement slurry with the borehole fluid falls onto the pumps, disabling the internal equipment of the borehole.

The aim of the invention is to obtain porous material in its entirety to prevent clogging of the bottomhole zone due to the double fastening of the bottomhole zone of the formation by sequentially pumping the foamed polymer solution, then the porous grouting cement.

In the method of fixing the bottom-hole zone of the well, including the injection of a porous cement slurry into the near-well zone of the formation, a foamed polymer solution is pre-pumped containing, wt%: water-soluble polymer 1.5-2.5, blowing agent 1-3, foam crosslinker-stabilizer 0, 2-0.6, the aqueous phase - the rest, and the porous cement slurry contains, wt.%: Cement mortar with a water-cement ratio of 0.3-0.5 - 60-80, the specified foamed polymer solution is 20-40, each of which solutions, pre-injected specified polymer and poros the same cement, characterized by a change in viscosity η and the ultimate dynamic shear stress - τ during injection and structuring within η _max / η _min - 2.4-3.9 and τ _p / τ _zak - 1.3-2.7, where η _max is the maximum viscosity during structuring, MPa · s, η _min is the minimum viscosity during injection, MPa · s, τ _p is the ultimate dynamic shear stress during structuring, dPa, τ _Zak is the maximum dynamic shear stress during injection , dpa.

As a blowing agent can be used nitrogen, air, natural gas to obtain a foam with a multiplicity of 0.2-0.6. As the water-soluble polymer, polyacrylamide and / or carboxymethyl cellulose and / or sodium styrene maleate and / or polysaccharides can be used. Sodium alkylbenzenesulfonate and / or sulfanol and / or VVP neftenol and / or neonol can be used as a blowing agent.

As the crosslinker-stabilizer of the foam, potassium dichromate and / or sodium dichromate and / or potassium chrome alum and / or potassium alum and / or sodium acetate can be used. Fresh water and / or produced water and / or CaCl ₂ solution and / or KCl solution and / or NaCl solution can be used as the aqueous phase.

Porous cement slurry is prepared sequentially: first, cement mortar, then foamed polymer solution, then they are mixed, and to ensure uniform distribution of the foamed polymer solution during structuring in the caverns of the formation, the solutions are injected into the well with a time interval of 30-40 minutes.

In the proposed method, before the formation of a porous cement filter, a foamed polymer solution is pumped. The foamed polymer solution is an elastic foam-like system of a partially crosslinked polymer solution with gas bubbles enclosed within it. When it moves in the wellbore at high shear rates, the resulting polymer skeleton does not collapse, but the macromolecules are stretched by a crosslinked elastic polymer, gas bubbles are deformed, but the strength of the structural network is sufficient to hold gas bubbles in solution. After removing the injection voltage in a static state at the temperature of the reservoir, gas bubbles expand, the foamed polymer solution increases in volume, filling voids and cavities, hardening, maintaining porosity. The flow curves of the injection of the foamed cross-linked polymer solution and the restoration of its structure during structuring are shown in Fig.2.

As can be seen from figure 2, the flow curves of a crosslinked foamed polymer solution are characterized by the presence of SNA and the ultimate dynamic shear stress. The restoration of the structure after unloading is characterized by a measure of thixotropy, which is determined by the ratio of the maximum viscosity of the onset of structuring to the minimum viscosity of the destroyed structure during the injection η _max / η _min . The degree of destruction of the structural grid during pumping of the solution and its restoration during structuring is determined by the ratio of the ultimate dynamic shear stress during structuring to the ultimate shear stress during injection τ _pp / τ _zak .

Table 1 shows the rheological characteristics during the injection and structuring of compositions with different component ratios, as well as the porosity of the samples after the study.

As a result of research, the composition of the dispersed medium of the foamed polymer solution, wt.%:

Water soluble polymer 1.5-2.5

Frother 1-3

Stapler 0.2-0.6

The aqueous phase - the rest

As shown by the results of a study of rheological properties and porosity, the proposed technology allows the delivery of a foamed polymer solution that is practically not destroyed during pumping.

In addition, the foamed polymer solution in contact with formation water expands further, absorbing water, creating a waterproof barrier. At the same time, oil is easily filtered through a porous foamed polymer. The foamed polymer composition has good adhesion to the rock and sand holding ability, while maintaining mechanical inclusions (sand, silt rock inclusions, etc.) in suspension, without creating dense sand plugs (figure 3).

Then a porous cement slurry is pumped, which, after hardening, forms a porous cement stone. Porous cement slurry is a composition based on a cement mortar with a water-cement ratio of 0.3-0.8 and a foamed polymer solution in a ratio that provides the necessary rheological indicators of injection and the beginning of structuring and hardening of the filter with a porosity of at least 30-40 vol.% For 48-36 hours. The flow curves of pumping the filter and the start of structuring are shown in Fig.4. The rheological parameters of the porous cement slurry, hardening time and porosity of the obtained filter are shown in table 4. Figure 5 shows a photograph of the obtained filter with an increase of 90 times.

As a result of laboratory studies, the composition of the porous filter, vol.%:

Cement mortar with a water-cement ratio of 0.35-0.40 - 60-80.

Foamed polymer solution 20-40.

Concrete example

The method is as follows.

In a sand-producing oil well, cased with a column, opened by perforation in the interval of the reservoir, and equipped with a tubing tubing deflated to the perforation interval using the CA-320 aggregate and compressor, with the mixing of the components, a foamed polymer solution is prepared in a 2/3 volume the fixed zone is about 2 m ³ and it is pumped into highly permeable, weakly cemented sections of the formation. The composition is aged in the reservoir for 10-30 minutes to structure and ensure adhesion of the foamed polymer solution to the rock due to the thermal expansion of gas bubbles.

During this time, a composition of porous grouting mortar is prepared.

In the compartment of the unit ЦА-320, a calculated amount of 0.3 m ^{3 of} foamed polymer solution is prepared. In the intermediate tank, a cement mortar is prepared with a water-cement ratio of 0.35-0.40 in an amount of 0.7 m ³ . While stirring at a low unit speed, a foamed polymer solution is added to the finished solution.

The resulting mixture is pumped into the perforation zone, partially crushed into the reservoir, blocking the perforation zone, left on the OZC for 48 hours. Then a cement beaker is drilled and fluid flow is induced in the usual manner.

The technology was used at the Severo-Pokurskoye field, block 30, well 43 for selective waterproofing of the formation with a high content of solids (0.2 wt.%). The water cut of the product was 95%. In the well, the absorption of the solution was observed, injectivity 570/80.

In the measuring unit of the CA-320 unit, 2 m ^{3 of} foamed polymer solution was prepared. 1.5 m ^{3 of the} composition was pumped into the formation at a low speed of the cementing unit AC-320.

Prepared 80 wt.% Cement mortar with a water-cement ratio of 0.36. In the measuring unit, the unit was thoroughly mixed with 20 wt.% The composition of the foamed polymer solution. The resulting porous cement slurry was crushed into the reservoir, blocking the perforation zone. Pressure 180 atm. After 48 hours, we drilled a “glass”, mastered the well in the usual way.

The water content of the products decreased and amounted to 82%, the content of solids is 0.01 wt.%.

Information sources

1. A.B.Suleymanov and others. Technique and technology of overhaul of wells. M .: Nedra, 1987, p. 28-33.

2. RF patent No. 2005165 by class. ЕВВ 33/138, 1993, BI No. 47.

3. RF patent No. 2172814 according to class. ЕВВ 33/138, Е21В 43/32, 2001.

Claims (8)

1. The method of fastening the bottom-hole zone of the well, including the injection into the borehole zone of the formation of a porous cement slurry, characterized in that pre-injected foamed polymer solution containing, wt.%: Water-soluble polymer 1.5-2.5, blowing agent 1-3, crosslinker the foam stabilizer is 0.2-0.6, the aqueous phase is the rest, and the porous cement slurry contains, wt.%: cement mortar with a water-cement ratio of 0.3-0.5: 60-80, the specified foamed polymer solution 20-40, in addition, each of the solutions - pre-pumped - specified polymer and porous grouting are characterized by a change in viscosity η and ultimate dynamic shear stress τ during injection and structuring within η _max / η _min 2.4-3.9 and τ _p / τ _zak 1.3-2.7, where η _max — maximum viscosity during structuring, MPa · s; η _min - the minimum viscosity during the injection process, MPa · s; τ _p - the ultimate dynamic shear stress in the process of structuring, dPa; τ _Zack - the ultimate dynamic shear stress during the injection, dPa. 2. The method according to claim 1, characterized in that nitrogen, air, and natural gas are used as a blowing agent to produce foam with a multiplicity of 0.2-0.6. 3. The method according to claim 1, characterized in that polyacrylamide and / or carboxymethyl cellulose and / or sodium styrene maleate and / or polysaccharides are used as a water-soluble polymer. 4. The method according to claim 1, characterized in that sodium alkylbenzenesulfonate is used as a blowing agent; and / or sulfonol, and / or neftenol VVD, and / or neonol. 5. The method according to claim 1, characterized in that as the crosslinker-stabilizer of the foam, potassium dichromate and / or sodium dichromate and / or potassium chrome alum and / or potassium alum and / or sodium acetate are used. 6. The method according to claim 1, characterized in that fresh water and / or produced water and / or CaCl ₂ solution and / or KCl solution and / or NaCl solution are used as the aqueous phase. 7. The method according to claim 1, characterized in that the porous cement slurry is prepared sequentially: first a cement mortar, then a foamed polymer solution, then they are mixed. 8. The method according to claim 1, characterized in that to ensure uniform distribution of the foamed polymer solution during structuring in the caverns of the formation, the injection of solutions into the well is carried out with a time interval of 30-40 minutes

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