Cross-linked plugging agent stimulated by high density brine and preparing method thereof

Abstract

The present invention disclosed a cross-linked plugging agent stimulated by high density brine which comprises main agent: 10 wt %-90 wt %, gelling agent: 0.5 wt %-9 wt % and pure water; wherein the main agent is selected from the group consisting of a Dipotassium phosphate (K.sub.2HPO.sub.4), a Tripotassium phosphate (K.sub.3PO.sub.4) and a Potassium pyrophosphate (K.sub.4P.sub.2O.sub.7), a Potassium Dihydrogen Phosphate (KH.sub.2PO.sub.4), a Sodium dihydrogen phosphate (NaH.sub.2PO.sub.4); the gelling agent is selected from the group consisting of a Xanthan gum and a kappa carrageenan. The gelling time is controlled within 0.5-12 h under an experiment temperature of 90 C.-160 C. The final gelling strength is controlled within D-H. The density is controlled within 1.0-1.55 g/cm.sup.3. The plugging agent is able to be applied in well completion and workover under high temperature, high pressure, multi-pressure series of strata oil and gas environment when temporary blockage and leak proof is required, protection of reservoir near perforations and water plugging.

Claims

1. A cross-linked plugging agent stimulated by high density brine, comprising: main agent: 10 wt %-90 wt %, gelling agent: 0.5 wt %-9 wt % and pure water; wherein the main agent is selected from the group consisting of a Dipotassium phosphate (K.sub.2HPO.sub.4), a Tripotassium phosphate (K.sub.3PO.sub.4) and a Potassium pyrophosphate (K.sub.4P.sub.2O.sub.7) a Sodium dihydrogen phosphate (NaH.sub.2PO.sub.4); wherein the gelling agent is selected from the group consisting of a Xanthan gum and a kappa carrageenan.

2. The cross-linked plugging agent stimulated by high density brine, as recited in claim 1, further comprising main agent of 30 wt %-70 wt %.

3. The cross-linked plugging agent stimulated by the high-density brine, as recited in claim 1, wherein the main agent further comprises a Potassium Dihydrogen Phosphate (KH.sub.2PO.sub.4) and a Sodium dihydrogen phosphate (NaH.sub.2PO.sub.4).

4. The cross-linked plugging agent stimulated by the high-density brine, as recited in claim 1, wherein a density of the plugging agent is controlled within 1.0-1.55 g/cm.sup.3.

5. A method of preparing a cross-linked plugging agent stimulated by high density brine, comprising following steps of: adding main agent, gelling agent into pure water in sequence with respective percentage by mass; stirring evenly; setting an experiment temperature at 90 C.-160 C.; and determining a gelation time and a gelation strength of the plugging agent by gel strength codes; wherein the main agent is 10 wt %-90 wt % and the gelling agent is 0.5 wt %-9 wt %, wherein the main agent is selected from the group consisting of a Dipotassium phosphate (K.sub.2HPO.sub.4), a Tripotassium phosphate (K.sub.3PO.sub.4) and a Potassium pyrophosphate (K.sub.4P.sub.2O.sub.7); wherein the gelling agent is selected from the group consisting of a Xanthan gum and a kappa carrageenan.

6. The method of preparing a cross-link plugging agent stimulated by high density brine, as recited in claim 4, wherein the main agent is further of 30 wt %-70 wt %.

7. The method of preparing a cross-link plugging agent stimulated by high density brine, as recited in claim 4, wherein the main agent further comprises a Potassium Dihydrogen Phosphate (KH.sub.2PO.sub.4), a Sodium dihydrogen phosphate (NaH.sub.2PO.sub.4).

8. The method of preparing a cross-linked plugging agent stimulated by high density brine, as recited in claim 3, wherein a density of the plugging agent is controlled within 1.0 g/cm.sup.3-1.55 g/cm.sup.3.

9. A method of applying a cross-linked plugging agent stimulated by the high density brine, comprising a step of applying the plugging agent in well completion and workover under high temperature, high pressure, multi pressure series of strata oil and gas environment when temporary blockage and leak proof is required, protection of reservoir near perforations and water plugging; wherein the cross-linked plugging agent stimulated by the high density brine comprises main agent which is 10 wt %-90 wt %, gelling agent which is 0.5 wt %-9 wt % and pure water, wherein the main agent is high density brine; wherein the main agent is selected from the group consisting of a Dipotassium phosphate (K.sub.2HPO.sub.4) and a Tripotassium phosphate (K.sub.3PO.sub.4) and a Potassium pyrophosphate (K.sub.4P.sub.2O.sub.7); wherein the gelling agent is selected from the group consisting of a Xanthan gum and a kappa carrageenan.

10. The method of preparing a cross-link plugging agent stimulated by high density brine, as recited in claim 7, wherein the main agent further comprises a Potassium Dihydrogen Phosphate (KH.sub.2PO.sub.4), a Sodium dihydrogen phosphate (NaH.sub.2PO.sub.4).

11. The method of applying a cross-linked plugging agent stimulated by the high density brine, as recited in claim 5, comprising a step of applying the plugging agent in well completion and workover under high temperature, high pressure, multi pressure series of strata oil and gas environment when temporary blockage and leak proof is required, protection of reservoir near the perforations and water plugging; wherein a density of the plugging agent is controlled within 1.0-1.55 g/cm.sup.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 illustrates values of elastic modulus and loss modulus in embodiment 1 of various gelling agent content after aging for three days;

[0030] FIG. 2 is a curve chart which displays viscosity and shear force of the plugging agent with 2 wt % of gelling agent content at the initial time, after two days and after five days in embodiment 2;

[0031] FIG. 3 is a shear viscosity curve chart of a cross-linked plugging agent stimulated by high density brine under different temperature in embodiment 6;

[0032] FIG. 4 is an elastic modulus curve chart of the cross-linked plugging agent stimulated by high density brine under different temperature in embodiment 7;

[0033] FIG. 5 is a loss modulus curve chart of the cross-linked plugging agent stimulated by high density brine under different temperature in embodiment 7;

[0034] FIG. 6 is a curve chart which displays flowback time and core permeability recovery rate in embodiment 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0035] The below embodiments further explain the present invention. The embodiments are based on the present invention and give detailed explanation. The protection scope of the present invention does not limited by the below embodiments.

[0036] A cross-linked plugging agent stimulated by high density brine comprises:

[0037] main agent: 10 wt %-90 wt %, gelling agent: 0.5 wt %-9 wt % and pure water.

[0038] The main agent is selected from the group consisting of a Dipotassium phosphate (K.sub.2HPO.sub.4), a Tripotassium phosphate (K.sub.3PO.sub.4) and a Potassium pyrophosphate (K.sub.4P.sub.2O.sub.7),

[0039] wherein the main agent further comprises a Potassium Dihydrogen Phosphate (KH.sub.2PO.sub.4) and a Sodium dihydrogen phosphate (NaH.sub.2PO.sub.4),

[0040] The gelling agent is selected from the group consisting of a Xanthan gum and a kappa carrageenan.

[0041] The cross-linked plugging agent stimulated by the high density brine is able to be applied in well completion and workover under high temperature, high pressure, multi pressure series of strata oil and gas environment when temporary blockage and leak proof is required, protection of reservoir near perforations and water plugging, which is exclusively designed according to geological characteristics of the reservoir, well temperature and plugging agent consumption. The plugging agent is prepared by the following steps of: adding main agent, gelling agent into pure water in sequence with respective percentage by mass; stirring evenly; setting an experiment temperature at 90 C.-160 C.; and determining a gelation time and a gelation strength of the plugging agent by gel strength codes.

Embodiment 1

[0042] A cross-linked plugging agent stimulated by high density brine for temporary blockage comprises the mixture of main agent of 70 wt %, gelling agent of 5 wt %-8 wt % and pure water. The experiment temperature is 120 C. The gelation time and a gelation strength are shown in the below table 2.

TABLE-US-00002 TABLE 2 gelation time and a gelation strength in embodiment 1 Gelling agent Aging time/gel strength code content Wt % Initial 2 h 4 h 12 h 1 D 3 D 5 D 7 D 9 D 12 D 5 A D G G G G G G G G 7 A D G G G G G G G G 8 A D G G G G G G G G

[0043] As shown in Table 2, the gelation time is within 2-4 hours; the final forming strength is G; no syneresis happens within 12 days.

[0044] As shown in FIG. 1, the values of elastic modulus and loss modulus of various gelling agent content after aging for three days prove that the strength of the plugging agent is able to be adjusted by adjusting the gelling agent content.

Embodiment 2

[0045] A cross-linked plugging agent stimulated by high density brine for protection of reservoir near perforations comprises main agent of 70 wt %, gelling agent of 1.5 wt %-3 wt % and pure water. The experiment temperature is 160 C. The gelation time and a gelation strength are shown in the below Table 3.

TABLE-US-00003 TABLE 3 gelation time and a gelation strength in embodiment 2 Gelling agent Aging time/gel strength code content Wt % Initial 4 h 8 h 1 D 2 D 3 D 4 D 1.5 A B D D D D A syneresis 2 A B D D D D D syneresis 2.5 A B E E E E E syneresis 3 A B E E E E E

[0046] As shown in table 3, the gelation time is within 4-8 hours; the final forming strength is D or E; syneresis and degradation occur on the third day; the plugging agent degrades to solid-free and low viscosity fluid 48 hours after syneresis begins.

[0047] As shown in FIG. 2, the viscosity and shear force curve of the plugging agent with 2 wt % of gelling agent content at the initial time, after two days and after five days illustrates the viscosity of the plugging agent at the initial time is below 100 mPa.Math.s and is able to be pumped easily; the viscosity of the plugging agent increases significantly after two days and the plugging agent is high viscosity liquid; the plugging agent degrades to solid-free fluid after five days and the viscosity is below 50 mPa.Math.s, which is able to be discharged in well flushing cycle without gel breaking.

Embodiment 3

[0048] A cross-linked plugging agent stimulated by high density brine for temporary blockage comprises main agent of 70 wt %, gelling agent of 6 wt %-8 wt % and pure water. The experiment temperature is 90 C. The gelation time and a gelation strength are shown in the below table 4.

TABLE-US-00004 TABLE 4 gelation time and a gelation strength in embodiment 3 Gelling agent Aging time/gel strength code content Wt % Initial 2 h 4 h 12 h 1 D 3 D 5 D 7 D 9 D 12 D 6 A D F F F F F F F F 7 A D F G G G G G G G 8 A D G H H H H H H H

[0049] As shown in table 4, the gelation time is within 2-4 hours; the final forming strength is F, G or H; no syneresis happens within 7 days. The plugging agent is able to be applied in temporary blockage and water plugging when different gel strength is required.

Embodiment 4

[0050] A cross-linked plugging agent stimulated by high density brine for protection of reservoir near perforations comprises main agent of 70 wt %, gelling agent of 2.5 wt %-4 wt % and pure water. The experiment temperature is 90 C. The gelation time and a gelation strength are shown in the below table 5.

TABLE-US-00005 TABLE 5 gelation time and a gelation strength in embodiment 4 Gelling agent Aging time/gel strength code content Wt % Initial 2 h 4 h 12 h 1 D 3 D 5 D 7 D 9 D 12 D 2.5 A A B B B C C C C C 3 A A C D D D D D D D 3.5 A B D E E E E E E E 4 A C D E E E E E E E

[0051] As shown in table 5, the gelation time is within 2-4 hours; the final forming strength is C, D or E; no syneresis happens within 7 days. The plugging agent is able to be applied in protection of reservoir near perforations when different gel strength is required.

Embodiment 5

[0052] A cross-linked plugging agent stimulated by high density brine for temporary blockage comprises main agent of 70 wt %, gelling agent of 5 wt %-8 wt % and pure water. The experiment temperature is 90 C. The gelation time and a gelation strength are shown in the below table 6.

TABLE-US-00006 TABLE 6 gelation time and a gelation strength in embodiment 5 Gelling agent Aging time/gel strength code content Wt % Initial 2 h 4 h 12 h 1 D 3 D 5 D 7 D 9 D 12 D 5 A D F F G G G G G G 6 A D F G G G G G H H 7 A E G H H H H H H H 8 A F H H H H H H H H

[0053] As shown in table 6, the gelation time is within 2-4 hours; the final forming strength is C, D or E; no syneresis happens within 7 days. The plugging agent is able to be applied in temporary blockage and water plugging when different gel strength is required.

Embodiment 6: The Relation of Shear Force and Viscosity of the Cross-Linked Plugging Agent Stimulated by High Density Brine Under Different Temperature is as Below

[0054] The formula of the plugging agent stimulated by high density brine in the embodiment is the main agent which density is 1.5 g/cm.sup.3 and gelling agent of 3 wt %. The prepared plugging agent is put into a laboratory oven ageing for four hours under 90 C., 120 C., 140 C., and 160 C. respectively. The plugging agent is assumed to be pumped to reservoir in four hours. FIG. 3 shows the viscosities of the plugging agent when the plugging agent passes through the casing or oil tube and reaches the target place. The viscosity of the plugging agent sample decrease with the rising temperature after ageing for four hours, which reaches a magnitude of 10.sup.4 mPa.Math.s. The plugging agent is in a semi-solid status, which does not easily loss in the reservoir and is able to bear pressure.

Embodiment 7: The Elastic and Loss Features of the Cross-Linked Plugging Agent Stimulated by High Density Brine Under Different Temperature

[0055] The formula of the plugging agent stimulated by high density brine in the embodiment is the main agent which density is 1.5 g/cm.sup.3 and gelling agent of 6 wt %. The prepared plugging agent is put into a laboratory oven ageing for four hours under 90 C., 120 C., 140 C., and 160 C. respectively. The observed elastic and loss modulus are shown in the FIG. 4 and FIG. 5. The elastic modulus reaches the magnitude of 10.sup.3 Pa and the gel strength is high enough to fulfill the requirement for temporary blockage and leak-proof task under pressure difference (no fluid loss in the reservoir under 20 MPa pressure difference after temporary blockage shown in embodiment 8).

Embodiment 8

[0056] The formula of the plugging agent stimulated by high density brine in the embodiment is the main agent which density is 1.5 g/cm.sup.3 and gelling agent of 6 wt %. The core (with saturated formation water) is put in an integrated displacement equipment. Sufficient plugging agent stimulated by high density brine covers a front end of the simulated well casing. Pure water is injected on the plugging agent stimulated by high density brine to simulate the working fluid. Pressure is applied on the front end of the core to simulate the pressure difference on the well casing. The chart 7 shows the observed the fluid loss from a back end of the core.

TABLE-US-00007 CHART 7 data sheet of the pressure bearing capability of the core Pressure No. of K.sub.gi(Dry)/K.sub.gi(Swc) difference Fluid loss rate core (mD) (MPa) (ml/min) 1 54.25/5.49 20 0 5 528/219 20 0.012 7 2056/961 20 0.05

[0057] wherein K.sub.gi(dry) stands for the gas permeability of the dry core; K.sub.gi(Swc) stands for the gas permeability at irreducible water saturation S.sub.wc.

[0058] After being blocked for two hours under a pressure difference of 20 MPa, filter cake forms on the contact surface of the core and the gelling agent. The filter cake prevents the gelling agent from leak deep into the core (no more than 3 mm-5 mm) and fluid loss. The permeability is able to be rapidly recovered after the filter cake is being removed.

[0059] Chart 8 and FIG. 6 show the permeability recovery of the flowback after the blockage. After the being blocked for two hours under a pressure difference of 20 MPa, the filter cake on the front end of the core is being removed, the core is put in the displacement equipment and the displacement is reversed by gas to simulate the well cleaning process during the flowback and the induced flow of the reservoir. The experiment result shows: the permeability is able to recover to 80% of permeability before the blockage after the reservoir being blocked under 20 MPa and the flow is induced under 3 MPa negative pressure difference.

TABLE-US-00008 CHART 8 the recovery of permeability of the core Flowback breakthrough Permeability recover No. of K.sub.gi(Swc) K.sub.gf pressure rate after two hours core (mD) (mD) (MPa) (%) 1 5.49 5.00 2.74 91 5 219 186 2 85 7 961 788 1.8 82

[0060] wherein K.sub.gi(Swc) stands for the gas permeability at irreducible water saturation S.sub.wc. K.sub.gf stands for the gas permeability after flowback breakthrough by air.

[0061] The embodiments above are just an exemplary and based on the contrivance of the present invention. The embodiments are not a limitation of the present invention. All modifications and alterations are within the protection scope of the present invention.