Experimental method for evaluating adaptability of plugging agent in low permeability crack rock core

A plugging control agent and low-permeability technology, which can be used in earth-moving drilling, wellbore/well components, construction, etc., and can solve the problems of accelerated production decline, high permeability, and unbalanced water flooding degree.

Active Publication Date: 2014-12-10
CHINA UNIV OF PETROLEUM (BEIJING)
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Problems solved by technology

At the same time, the permeability of this type of reservoir generally has obvious anisotropy, and it is easy to cause violent water flooding of oil production wells along the extension direction of fractures during water injection development in oilfields.
Due to the influence of the orientation of fractures, the degree of regional water flooding is extremely unbalanced, the contradictions between layers are gradually intensified, and the water cut is constantly rising. The original adjustment measures and development technologies are gradually not suitable for the needs of oilfield development. The adjustment effect is poor, and the production decline is accelerated; However, there is a large amount of remaining oil in non-fractured directions and positions, because in fractured low-permeability reservoirs, the permeability of fractures is much higher than that of matrix
[0004] At present, the difficulty of plugging adjustment and plugging of major domestic fractured reservoirs is reflected in two aspects: first, the plugging strength is not enough. Since large pores or fractures are usually large, not only higher strength is required for the plugging adjustment agent itself, but also it needs to be combined with the rock The wall bonding strength is high; secondly, the depth of profile control is limited. This technology must solve the contradiction between the injection and migration performance of the plugging agent in the reservoir and the plugging strength. Therefore, the channeling channel of fractured low-permeability reservoir Deep plugging has always been a technical difficulty in the field of water plugging and profile control
In the existing literature reports, there is no systematic evaluation method for the adaptability of plugging modifiers in low-permeability fractured cores, which is exactly the problem to be solved in this research work

Method used

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  • Experimental method for evaluating adaptability of plugging agent in low permeability crack rock core
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  • Experimental method for evaluating adaptability of plugging agent in low permeability crack rock core

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Experimental program
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preparation example Construction

[0041] (1) Preparation of fractured low-permeability core

[0042] ① Fractured columnar core model

[0043] The gas permeability is 30×10 -3 μm 2 The artificial homogeneous columnar core (diameter: 2.5cm, length: 7cm) is used as the matrix, and artificial fractures are made, that is, the core is radially squeezed to create fractures, and the core is pressed into two halves from the middle; The sand grains act as a support to obtain fractures with different fracture widths, and then the two halves of the cores are joined together; considering that the end effect of a single short core is serious, two columnar cores that have been treated above are finally spliced ​​together to obtain Fractured columnar core model with a length of 15-30cm.

[0044] The equivalent permeability of the core after fracturing can be measured by water flooding and calculated according to Darcy's formula. In the state of no confining pressure, since the fractures created are relatively regular, and...

Embodiment 1

[0095] The plugging effect of the modified starch system with different injection volumes on the core was studied, and the appropriate injection volume of the plugging agent was determined at the same time. The specific experimental results are shown in Table 3.

[0096] Table 3 Experimental data of modified starch plugged fracture core

[0097]

[0098]

[0099] The minimum starting pressure gradient in the table is given by figure 2 Calculated using the fitting formula in .

[0100] PV refers to the pore volume of the whole core after fracture creation; V f is the fracture volume.

[0101] When the injection amount of modified starch is 0.05PV, the breakthrough pressure is less than 0.4MPa / m, the plugging rate is lower than 80%, and the sealing effect of the plugging agent on fractures is poor; moreover, the breakthrough pressure gradient of the plugging agent is smaller than the minimum of the matrix Initiate a pressure gradient so that the hypotonic matrix cannot...

Embodiment 2

[0107] Referring to the research results on the injection rate of the modified starch system, the plugging performance of the organic chromium gel on the fractured columnar core was directly studied when the injection rate was 1 times the fracture volume. The experimental results are shown in Table 4.

[0108] Table 4 Experimental data of organic chromium gel plugging fracture cores

[0109]

[0110]

[0111] The minimum starting pressure gradient in the table is given by figure 2 Calculated using the fitting formula in .

[0112] When the gel injection volume is 1 times the fracture volume, the greater the equivalent permeability of the fractured columnar core, the smaller the resistance coefficient, indicating that the gel is easier to inject. Although the core plugging rate of the system after gelling is above 97%, and the breakthrough pressure gradient of the plugging agent is greater than the minimum starting pressure gradient of the low-permeability matrix, the b...

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Abstract

The invention discloses a method for selecting a plugging agent most suitable for a low permeability crack rock core from plugging adjusting agents to be selected. The experimental method comprises the following steps that (1) low permeability crack rock core models are prepared, wherein cracks are manufactured with an artificial low permeability homogeneous columnar rock core and an artificial low permeability homogeneous square rock core as matrixes by referring to actual low permeability crack reservoirs, and a crack columnar rock core model and a crack square rock core model are manufactured; (2) the crack columnar rock core model or the crack square rock core model is taken as a physical model, the plugging performance of different plugging adjusting agents with the injection amount same as the crack size, and the breakthrough pressure gradient, the residual resistance factor and the plugging ratio of each plugging adjusting agent are worked out; firstly, the breakthrough pressure gradient of each plugging adjusting agent is compared with the minimum starting pressure gradient of the model, and the plugging agents with the breakthrough pressure gradients smaller than or equal to the minimum starting pressure gradient are removed; secondly, the plugging rate of the rest of the plugging adjusting agents are compared, and the plugging adjusting agent which larger the plugging rate is, larger the breakthrough pressure gradient is serves as the most adaptive plugging adjusting agent for the low permeability crack rock core.

Description

technical field [0001] The invention belongs to the technical field of oil and gas stimulation, and in particular relates to an experimental method for evaluating the adaptability of a plugging agent in low-permeability fractured rock cores. Background technique [0002] my country's low-permeability oil reservoirs are rich in reserves, mainly distributed in Changqing, Daqing, Jilin and Xinjiang oil regions. With the rapid development of oil exploration and development in my country, the importance of low-permeability reservoirs is becoming more and more apparent, and the proportion of low-permeability reserves in newly proven geological reserves is increasing, and more than 70% of newly proven reserves are low-permeability reserves. It is expected that the reserves discovered in the future will still be dominated by low permeability. Exploring reasonable low-permeability oilfield exploitation technology will contribute to the development of our country's social economy. ...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): E21B33/13E21B47/005
Inventor 赵凤兰侯吉瑞
Owner CHINA UNIV OF PETROLEUM (BEIJING)
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