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: 21 wt %-53 wt %, gelling agent: 0.5 wt %-9 wt % and pure water; wherein the saline solution 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); 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 1.2-1.55 g/cm.sup.3.

Claims

1. A cross-linked plugging agent stimulated by high density brine, comprising: main agent: 21 wt %-53 wt %, gelling agent: 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), 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.

2. 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 1.2-1.55 g/cm.sup.3.

3. 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 gel forming time and a gel forming strength of the plugging agent by gel strength codes; wherein the main agent is 47 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.

4. 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 1.2-1.55 g/cm.sup.3.

5. 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 21 wt %-53 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), 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 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 1.2-1.55 g/cm.sup.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 illustrates values of elastic modulus and loss modulus in embodiment 1 of various gelling agent content after aging for three days at 120° C. and then cool to room temperature, G′ is elastic modulus and G″ is viscous modulus;

[0028] FIG. 2 is a curve chart which displays viscosity and shear force of the plugging agent with 3 wt % of gelling agent content at the initial time, after four hours and after 70 hours in embodiment 2;

[0029] FIG. 3 is a shear-viscosity curve chart of a cross-linked plugging agent stimulated by high density brine in 4 hours under different temperature in embodiment 6;

[0030] FIG. 4 is an elastic modulus curve chart of the cross-linked plugging agent stimulated by high density brine in 4 hours under different temperature in embodiment 7;

[0031] FIG. 5 is a viscous modulus curve chart of the cross-linked plugging agent stimulated by high density brine in 4 hours under different temperature in embodiment 7;

[0032] FIG. 6 is a curve chart which displays flowback time and core permeability recovery rate in embodiment 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0033] 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.

[0034] A cross-linked plugging agent stimulated by high density brine comprises:

[0035] main agent: 21 wt %-53 wt %, gelling agent: 0.5 wt % -9 wt % and pure water.

[0036] 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).

[0037] The gelling agent is selected from the group consisting of a Xanthan gum and a kappa carrageenan.

[0038] 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 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 gel forming time and a gel forming strength of the plugging agent by gel strength codes.

Embodiment 1

[0039] A cross-linked plugging agent stimulated by high density brine for temporary blockage comprises the mixture of main agent of 47 wt %, gelling agent of 5 wt %-8 wt % and pure water. The experiment temperature is 120° C. The gel forming time and a gel forming strength are shown in the below table 2.

TABLE-US-00002 TABLE 2 gel forming time and a gel forming strength in embodiment 1 Gelling agent content Aging time/gel strength code Wt % Initial 2 h 4 h 12 h 1D 3D 5D 7D 9D 12D 5 A E F F G G G G G G 6 A E F G G G G G G G 7 A F G H H H H H H H 8 A G H H H H H H H H

[0040] As shown in Table 2, the gel forming time is within 2 hours; the final forming strength is G to H; no syneresis happens within 12 days.

[0041] As shown in FIG. 1, the values of elastic modulus and loss modulus of various gelling agent content after aging for three days and the cool to room temperature prove that the strength of the plugging agent is able to be adjusted by adjusting the gelling agent content.

Embodiment 2

[0042] A cross-linked plugging agent stimulated by high density brine for protection of reservoir near perforations comprises main agent of 47 wt %, gelling agent of 2 wt %-4 wt % and pure water. The experiment temperature is 120° C. The gel forming time and a gel forming strength are shown in the below Table 3.

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

[0043] As shown in table 3, the gel forming time is within 4-8 hours; the final forming strength is 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.

[0044] As shown in FIG. 2, the experiment temperature is 120° C. The viscosity and shear force curve of the plugging agent with 3 wt % of gelling agent content at the initial time, after four hours and after 70 hours 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 4 hours and the plugging agent is high viscosity liquid; The viscosity of the plugging agent is slightly reduced after aging 70 hours. But it is still in high-viscous state, which can maintain plugging performance. Overall, the viscosity of the plugging agent keeps stable within 70 hours at high temperature.

Embodiment 3

[0045] A cross-linked plugging agent stimulated by high density brine for temporary blockage comprises main agent of 47 wt %, gelling agent of 5 wt %-8 wt % and pure water. The experiment temperature is 90° C. The gel forming time and a gel forming strength are shown in the below table 4.

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

[0046] As shown in table 4, the gel forming time is within 2 hours; the final forming strength is 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

[0047] A cross-linked plugging agent stimulated by high density brine for protection of reservoir near perforations comprises main agent of 47 wt %, gelling agent of 2 wt % -4 wt % and pure water. The experiment temperature is 160° C. The gel forming time and a gel forming strength are shown in the below table 5.

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

[0048] As shown in table 5, the gel forming time is within 2-4 hours; the final forming strength is B to E.

Embodiment 5

[0049] A cross-linked plugging agent stimulated by high density brine for temporary blockage comprises main agent of 53 wt %, gelling agent of 5 wt % -8 wt % and pure water. The experiment temperature is 90° C. The gel forming time and a gel forming strength are shown in the below table 6.

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

[0050] As shown in table 6, the gel forming time is within 2 hours; the final forming strength is 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 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

[0051] The formula of the plugging agent stimulated by high density brine in the embodiment is main agent of 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 and wait them cooling to room temperature. The observed viscosities are shown in the FIG. 3. The plugging agent is assumed to be pumped to the objective reservoir in four hours. FIG. 3 shows the status and changing rules of the plugging agent after the plugging agent passes through the casing or oil tube and reaches the objective reservoir. The viscosity of the plugging agent sample decrease with the rising temperature after ageing for four hours, which reaches the 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

[0052] The formula of the plugging agent stimulated by high density brine in the embodiment is the main agent of 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 and wait them cooling to room temperature. The observed elastic and viscous modulus are shown in the FIG. 4 and FIG. 5. The elastic modulus of the plugging agent reaches 10.sup.3 Pa magnitude which is high enough to fulfill the requirement for temporary blockage and leak-off control under positive pressure difference (no fluid loss was observed under 20 MPa positive pressure difference after core temporary plugged as shown in embodiment 8).

Embodiment 8

[0053] The formula of the plugging agent stimulated by high density brine in the embodiment is the main agent of 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 solution was poured into the simulated wellbore to immerse the core front face. The system was sealed and aged for 4 hours at 120° C. And then, fresh water was injected to the top surface of the mature plugging agent to impose positive pressure. 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 bearing capability of the core Pressure Fluid loss No. of K.sub.gi(Dry)/K.sub.gi(Swc) difference 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

[0054] 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.

[0055] 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.

[0056] Chart 8 and FIG. 6 show the core permeability recovery during gas flowback. The experimental result shows that the permeability recovery factor is at least 82% and the flow is induced under 3 MPa negative pressure difference.

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

[0057] 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.