CN114414739A - A method for evaluating the plugging effect of combined width fractures - Google Patents

Abstract

The invention discloses a method for evaluating the plugging effect of a fracture with a combined width, comprising the following steps: establishing three visual fracture models with different combined widths; and the formation position of the plugging layer; the results are processed and analyzed through the software. Considering the simultaneous existence of multi-scale combined width fractures in the drilling process and the dynamic change of the fracture width in the process of injecting the plugging slurry, the present invention designs three visual models of combined width fractures that can simulate the development characteristics of different fractures, and obtains accurate and convenient results. Obtain the required data to scientifically evaluate the plugging effect of the combined width fractures.

Description

A method for evaluating the plugging effect of combined width fractures

technical field

The invention relates to the field of working fluid loss control during drilling and completion in the oil and natural gas industry, in particular to a method for evaluating the plugging effect of combined width cracks.

Background technique

Fractured formation is one of the more common formations in the drilling process. Fractured oil and gas reservoirs are widely distributed around the world and have huge resources. The natural fractures in this formation are not only the effective space for oil and gas storage but also the seepage channel for oil and gas migration. However, the existence of natural fractures may lead to the loss of working fluid during drilling and completion, resulting in the loss of a large amount of drilling fluid, prolonging the drilling cycle, affecting the normal progress of geological work, and causing a series of downhole complex situations or accidents. Engineering problems greatly limit the efficient development of oil and gas reservoirs. Due to the difficulty in controlling the leakage of working fluid, the leakage damage is still difficult to effectively control. For a long time, indoor fracture plugging evaluation experiments and on-site fracture plugging operations, the main method of conventional loss control is to add various types and sizes of plugging materials to the drilling fluid at one time to form a leakage prevention that matches the width of the lost fracture. According to the plugging formula, after the drilling fluid is injected into the well, the underground fractures may show multi-scale combined width, the fracture width changes dynamically, or new fractures are generated, etc., resulting in the successful sealing of the narrower fractures and the continuous loss of the wider fractures, or the wider fractures. When the narrow fractures are successfully plugged, it is difficult to meet the simultaneous plugging of multi-scale combined width fractures, which affects the success rate of plugging. At present, there is still a lack of methods to quickly and effectively form plugging layers for fractures of various widths at home and abroad, and it is difficult to scientifically evaluate the plugging layers formed in fractures of various widths.

SUMMARY OF THE INVENTION

In view of the above problems, the present invention provides a method for evaluating the sealing effect of combined width fractures. According to the existing geological layer investigation, the development characteristic types of reservoir fractures are determined, and three combined width fracture models simulating different geological types are designed, so that they can More accurate simulation of crack types encountered in actual working conditions.

The present invention adopts following technical scheme:

A method for evaluating the sealing effect of combined width cracks, comprising the following steps:

S1: Establish three visual fracture models with different combined widths;

S2: Injection of CMC suspensions in the visual fracture models of different combined widths;

S3: Use a micro-flow pump to discharge the liquid, the pressure sensor records the real-time pressure change at the entrance of the crack, and the balance records the real-time leakage change;

S4: inject the suspension containing the loss-stopping material into the visual fracture module of combined width, and obtain the pressure change at each time point, the migration and retention behavior of the loss-stopping material, the sealing time and the formation position of the plugging layer;

S5: Use an industrial microscope to record and take pictures of the entire experimental process, observe the migration and retention state of the plugging material, and use the origin software to correspond to the recorded pressure and leakage changes;

S6: Analyze the changes of pressure and leakage volume corresponding to different states of the leakage plugging material at different times, and obtain the results of the plugging effect of each combination of widths.

Preferably, in the step S1, the three visual fracture models of combined width are respectively a high-angle visual fracture model, a branch visual fracture model, and a parallel visual fracture model.

Preferably, the high-angle visual fracture model simulates the development of reservoir fractures and good connectivity between fractures in an actual situation, and a cylindrical nozzle and a rectangular buffer zone are designed before the fracture entrance.

Preferably, the branch visual fracture model simulates a network fracture with well developed reservoir fractures and good connectivity between fractures in actual conditions, and the front end of the fracture is designed as a cylindrical tip with a rectangular buffer area.

Preferably, the parallel visual fracture model simulates a plurality of fractures with approximately parallel widths when the fracture connectivity of the reservoir is poor in actual conditions.

Preferably, the visual crack model adopts transparent borosilicate glass. The flow and migration behavior of the plugging material can be clearly observed, and it can also withstand a large experimental pressure.

Preferably, in the step S2, the CMC suspension (sodium carboxymethyl cellulose) is a transparent solution used to simulate drilling fluid, the viscosity is 370 mPa·s, and has good suspension and rheology.

Preferably, the rate of liquid discharge in the step S3 is 0.1 to 0.25 ml/min.

Preferably, in the step S4, the plugging material is selected from yellow walnut shell particles with a particle size of 0.75mm-2mm. The bright color of yellow walnut shell particles facilitates the observation of particle behavior during visualization experiments.

The beneficial effects of the invention are: considering the simultaneous existence of multi-scale combined width fractures in the drilling process and the dynamic change of the fracture width in the process of injecting the plugging slurry, three visual models of combined width fractures capable of simulating the development characteristics of different fractures are designed , the state of particle migration and retention in fractures can be clearly seen, and the required data can be obtained accurately and conveniently, so as to scientifically evaluate the plugging effect of combined width fractures.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the accompanying drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present invention, rather than limit the present invention. .

Fig. 1 is the front view schematic diagram of the high-angle crack model of the present invention;

Fig. 2 is the left side view schematic diagram of the middle and high angle crack model of the present invention;

Fig. 3 is the schematic diagram of the right side view of the high-angle crack model of the present invention;

4 is a schematic diagram of a branch fracture model in the present invention;

Figure 5 is a schematic diagram of parallel cracks in the present invention.

Detailed ways

To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are some, but not all, embodiments of the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

Unless otherwise defined, technical or scientific terms used in this disclosure shall have the ordinary meaning as understood by one of ordinary skill in the art to which this disclosure belongs. As used in this disclosure, "comprises" or "comprising" and similar words mean that the elements or things appearing before the word encompass the elements or things recited after the word and their equivalents, but do not exclude other elements or things. "Up", "Down", "Left", "Right", etc. are only used to represent the relative positional relationship, and when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

A method for evaluating the sealing effect of combined width cracks, comprising the following steps:

S1: Establish three visual fracture models with different combined widths. The shape of the model is a cuboid with a size of 100mm × 40mm × 30mm, which consists of an entrance end, a crack channel, and an exit end.

S2: CMC suspension (sodium carboxymethyl cellulose) is injected into the visual fracture model of different combination widths as a transparent solution to simulate drilling fluid, with a viscosity of 370 mPa·s, with good suspension and rheology.

S3: Use a microfluidic pump for drainage, the maximum stroke of the microfluidic pump is 160mm, the stroke resolution is 0.078μm, the stroke accuracy is ±0.5%, and the flow range is 1pl/min-281ml/min. The rate of drainage is 0.1 to 0.25 ml/min.

S4: Use a syringe to inject the suspension containing the plugging material into the combined width visual fracture module. The syringe is a standard 60ml syringe with a diameter of 29.15mm and a flow range of 0.001ul/min-159ml/min. It can be used with a microfluidic pump. Used together to achieve high-precision fluid injection. The syringe is connected to the Visual Crack Module. The pressure change at each time point, the flow and migration behavior of the leakage plugging material, the sealing time and the formation position of the plugging layer are obtained.

S5: Use an industrial microscope to record and take pictures of the entire experimental process, observe the migration and retention state of the plugging material, and use the origin software to correspond to the recorded pressure and leakage changes;

S6: Analyze the changes of pressure and leakage volume corresponding to different states of the leakage plugging material at different times, and obtain the results of the plugging effect of each combination of widths.

In the step S1, the three visual fracture models of combined width are respectively a high-angle visual fracture model, a branch visual fracture model, and a parallel visual fracture model.

The high-angle visual fracture model is shown in Figure 1 to Figure 3, which simulates the development of reservoir fractures and good connectivity between fractures in the actual situation. A cylindrical nozzle and a rectangular buffer zone are designed in front of the fracture entrance. The buffer zone is designed as follows: It is beneficial for the particles in the plugging slurry to enter the fracture. The fracture takes 3mm and 1mm cross-circulation as the entrance and 1mm as the fracture outlet. A wedge-shaped high-angle fracture model is designed.

The branch visualization fracture model is shown in Figure 4, which simulates the network fractures that exist in practice. In actual working conditions, reservoir fractures are developed, and the connectivity between fractures is good. It is characterized by fracture intersection, and the front end of the fracture is designed as a cylindrical tip. It has a rectangular buffer area to ensure that the particles in the branch fractures flow out smoothly when the plugging is not successful. The main channel of the branch fracture is a fracture with an inlet of 3 mm and an outlet of 1 mm, and there is a branch fracture with an inlet of 2 mm and an outlet of 1 mm on the main fracture.

The parallel visual fracture model is shown in Figure 5. In actual working conditions, there are few single fractures, and most of them are combined width fractures. However, when the fracture connectivity of reservoir fractures is poor, multiple fractures are almost parallel fractures, and they appear as multiple fractures. kind of width. There are two cracks in the module, one crack is 3mm at the inlet end and 2mm at the outlet end, and the other is a crack with a combined width of 2mm at the inlet end and 1mm at the outlet end.

The visual crack model adopts transparent borosilicate glass. The flow and migration behavior of the plugging material can be clearly observed, and it can also withstand a large experimental pressure.

In the step S4, the plugging material is selected from yellow walnut shell particles with a particle size of 0.75mm-2mm. Red nylon particles can also be selected for plugging experiments. The bright color of yellow walnut shell particles facilitates the observation of particle behavior during visualization experiments.

In the combined width fracture, the two fractures have the same inlet end and inlet pressure, the force of the suspension in the narrower fracture is greater than that in the wide fracture, and the wider fracture will become the main channel of the combined width fracture. After the particles enter the fractures, multi-stage single-particle bridging occurs in the narrower fractures, which can be quickly blocked in a short time. The flow velocity of the suspension in the narrower fractures becomes slower, and the flow velocity in the wider fractures becomes faster and becomes the mainstream channel, which improves the The plugging probability, the particle size is similar to the outlet end of the wider fracture, and it is easy to form a stable double-particle bridging in the fracture, thereby forming an effective plugging layer. After an effective plugging layer is formed in the larger fracture, the flow velocity in the two fractures is gradually similar, so that the sealing layer in the narrower fracture becomes denser. The plugging effect of the combined width fractures can be easily evaluated by the pressure change at each time point, the flow and migration behavior of the plugging material, the sealing time and the formation position of the plugging layer.

The above are only preferred embodiments of the present invention, and do not limit the present invention in any form. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Technical personnel, within the scope of the technical solution of the present invention, can make some changes or modifications to equivalent embodiments of equivalent changes by using the technical content disclosed above, but any content that does not depart from the technical solution of the present invention, according to the present invention Any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solutions of the present invention.

Claims (9)

1. A method for evaluating the plugging effect of a combined width crack is characterized by comprising the following steps:

s1: establishing three different combined width visual crack models;

s2: injecting CMC suspension liquid into the visual crack models with different combined widths;

s3: discharging liquid by using a micro-flow pump, recording real-time pressure change at a crack inlet by using a pressure sensor, and recording real-time leakage change by using a balance;

s4: injecting suspension containing a plugging material into the combined width visualization fracture module to obtain pressure change of each time point, migration and retention behaviors of the plugging material, sealing time and a forming position of a plugging layer;

s5: recording and photographing the whole experimental process through an industrial microscope, observing the migration retention state of the plugging material, and corresponding the recorded pressure and leakage change through origin software;

s6: and analyzing the pressure and leakage amount changes corresponding to different states of the plugging material at different time to obtain the result of the plugging effect of the cracks with each combined width.

2. The method for evaluating the plugging effect of the combined-width fracture according to claim 1, wherein the three combined-width visual fracture models in the step S1 are a high-angle visual fracture model, a branch visual fracture model and a parallel visual fracture model.

3. The method for evaluating the plugging effect of the combined-width fracture as claimed in claim 2, wherein the high-angle visual fracture model simulates the conditions of reservoir fracture development and better connectivity among fractures in actual conditions, and a cylindrical pipe orifice and a rectangular buffer zone are designed before the fracture entrance.

4. The evaluation method of the combined width fracture plugging effect according to claim 2, wherein the branch visualization fracture model simulates reticular fractures with good reservoir fracture development and connectivity among fractures in actual conditions, and the rear end of the fracture is designed to be a cylindrical tip and is designed to be a rectangular buffer area.

5. The method for evaluating the plugging effect of the fractures with the combined width according to claim 2, wherein the parallel visualization fracture model simulates a plurality of fractures with the widths approximately parallel when the connectivity of the reservoir fractures is poor in practical conditions.

6. The evaluation method of the combined width crack sealing effect according to any one of claims 1 to 5, characterized in that the visual crack model adopts transparent borosilicate glass.

7. The method for evaluating the effect of blocking the combined-width crack according to claim 1, wherein the viscosity of the CMC suspension in the step S2 is 370 mPa-S.

8. The method for evaluating the effect of plugging cracks with combined width according to claim 1, wherein the liquid discharge speed in step S3 is 0.1 to 0.25 ml/min.

9. The method for evaluating the plugging effect of the cracks with the combined width as claimed in claim 1, wherein in the step S4, yellow walnut shell particles with the particle size of 0.75mm-2mm are selected as the plugging material.

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