CN107179232B - Method for evaluating stability of shale - Google Patents
Method for evaluating stability of shale Download PDFInfo
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- CN107179232B CN107179232B CN201610131811.4A CN201610131811A CN107179232B CN 107179232 B CN107179232 B CN 107179232B CN 201610131811 A CN201610131811 A CN 201610131811A CN 107179232 B CN107179232 B CN 107179232B
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Abstract
The invention relates to the field of shale stability evaluation, in particular to stability evaluation of inactive shale and/or hard and brittle shale. The method for evaluating the stability of the shale comprises the following steps: step A: coring the shale, and preparing a core sample with uniform size; and B: soaking the core sample in at least two working solutions with different activities, wherein the activities of the working solutions are distributed between 0 and 1, so as to obtain a soaked core sample; and C: and obtaining mechanical strength values of the core sample and the soaked core sample, and obtaining a strength loss ratio according to the mechanical strength values.
Description
Technical Field
The invention relates to the field of shale stability evaluation, in particular to stability evaluation of inactive shale and/or hard and brittle shale.
Background
Shale is affected by sedimentation, its properties vary widely, and it undergoes significant physicochemical interaction with drilling fluids. The evaluation of the stability of the shale is the basis for researching the physicochemical property of the shale, the analysis of the stability of the well wall and the research and development of a drilling fluid system, the evaluation of the stability of the shale can essentially reflect the interaction characteristics between the shale and working fluid, and the evaluation is always a difficult problem which is very concerned at home and abroad and cannot be well solved. The research on the stability evaluation method of the shale is helpful for knowing the mechanism of the borehole instability of the shale and designing a new anti-collapse drilling fluid system and developing the stability research of the non-active shale and/or the hard and brittle shale.
The research related to the scientific and technological papers published in China mostly takes underground rock core cuttings or artificial rock cores as objects to carry out stability evaluation, and the conventional shale stability experiment methods such as a rolling recovery rate experiment, an expansion experiment, a CST experiment method, a soaking experiment and a water absorption diffusion experiment are widely adopted; for example, in the research on the evaluation method for preventing collapse of hard brittle shale in the sand and river street group of the Liaohe oilfield, an improved thermal rolling dispersion method, a mud cake strength measurement method and a dynamic filtration test method are provided for evaluating the stability of the inactive shale and/or the hard brittle shale, and the result can be used for evaluating the performance of the chemical stabilizer. The new method for evaluating the water sensitivity of the shale-the research of the specific hydrophily method-proposes that the specific hydrophily method is applied to the stability evaluation of the deep-well inactive shale and/or the hard brittle shale. The method comprises the steps of measuring the specific surface area and the water absorption capacity of the shale by using the shale debris, and calculating to obtain the water absorption capacity on the unit shale surface area, namely the specific hydrophily of the shale. Although both documents show that the proposed methods are suitable for deep well non-activated shale and/or hard brittle shale stability, one of the biggest drawbacks of these methods is the use of rock debris samples for testing. While the hard and brittle nature of non-activated shale, the long-term tectonic effects result in unique microstructural properties that are destroyed by the methods described herein, making it virtually difficult to effectively assess its stability.
Among the patents related to the presently disclosed method for evaluating the stability of hard and brittle inactive shale, there is also a method for evaluating the stability by means of measuring the change of rock physical properties after fluid soaking, such as "a method for evaluating the hydration properties of laminar hard and brittle shale" (patent number: 201510077077.3), the method comprises the following steps in sequence: coring after describing the rock, and preparing a rock core sample; recovering the core sample to a formation in-situ pore fluid saturation state; measuring the longitudinal wave velocity and the transverse wave velocity of the rock core sample under the in-situ state condition of the stratum, then changing the property of the pore fluid, and measuring the longitudinal wave velocity and the transverse wave velocity of the rock core sample after changing the property of the pore fluid; and evaluating the hydration characteristics of the laminated inactive shale and/or the hard brittle shale according to the change conditions of the longitudinal wave velocity and the transverse wave velocity of the core sample under different pore fluid properties. The hydration stability of the shale can be quantitatively evaluated by using the method. However, the method is only applied to the evaluation of the rock physical properties after the action of certain pore fluid, is more suitable for evaluating the performance of the working fluid, and cannot essentially reflect the stability characteristics of the inactive shale and/or the hard and brittle shale.
Therefore, it is necessary to develop a stability evaluation method capable of reflecting the effect of hydration on the physicochemical properties of shale itself and the influence on the mechanical properties of shale.
Disclosure of Invention
Based on the defects of the existing stability evaluation method of inactive shale and/or hard and brittle shale, the invention provides a stability evaluation method capable of reflecting the effect of hydration on the physicochemical characteristics of the shale and the influence on the mechanical characteristics of the shale, the method overcomes the defect that the traditional shale stability evaluation method adopts artificial cores pressed by rock debris and cannot reflect the self-structure influence of inactive shale and/or brittle shale, and the evaluation value of the inactive shale and/or the hard brittle shale is generally close to the good value of the stability evaluation, but the defect that the difference cannot reflect the stability difference is not provided, so that the scientific and objective evaluation of the stability of the shale is realized, and the improvement of the effectiveness and the applicability of the stability evaluation of the inactive shale and/or the hard brittle shale is very necessary and meaningful.
The method for evaluating the stability of the shale comprises the following steps: step A: coring the shale, and preparing a core sample with uniform size; the size of the core can be based on the standard core size for rock mechanics measurement, for example
And
one of (1); and B: soaking the core sample in at least two, preferably at least three working solutions with different activities, wherein the activities of the working solutions are distributed between 0 and 1, so as to obtain a soaked core sample; and C: and obtaining mechanical strength values of the core sample and the soaked core sample, and obtaining a strength loss ratio according to the mechanical strength values.
In a particular embodiment, there is further included step I, prior to step a, of determining the activity of at least two, preferably at least three, different working fluids.
In a specific embodiment, the rock mechanical experiment is performed on the rock core sample which is not soaked in the working solution and the soaked rock core sample, so as to obtain the rock mechanical strength value of the rock core sample.
In one embodiment, when the mechanical rock strength value cannot be determined immediately on the soaked core sample, after removal of the soaked core sample, the soaked core sample is preferably sealed, which may simply be wrapped with a plastic wrap or sealed with wax, and the seal removed prior to the mechanical rock strength value determination.
In one embodiment, the strength loss ratio is formulated
Is represented by, wherein mAs the ratio of the loss of strength, σcThe mechanical strength of the core sample may be expressed in units of Mpa, σclIs the mechanical strength of the soaked core sample, which may be in units of Mpa, for example; sigmaclThe subscript l indicates the type of specific working fluid that is applied to the core sample.
According to the strength loss ratio of the shale, the sensitivity of the shale to different working fluids is reflected from the mechanical angle, the larger the value of m is, the more remarkable the hydration effect of the working fluid to the shale is, when the value of m is 1, the complete structural strength loss of the shale is shown, and when the value of m is close to 0, the insensitivity of the shale to the working fluid is shown.
In a specific embodiment, after the step C, the method further comprises a step D of: and defining the water-sensitive stability coefficient of the shale according to the strength loss ratio of the core sample obtained in the working fluid with different activities.
In a specific embodiment, the water sensitivity stability coefficient of the shale is expressed by the formula S ═ (sin (arctan (k)) + mw) And/2, wherein S is the water-sensitive stability coefficient of the shale, k is the slope of the strength loss ratio obtained by the core sample in working fluids with different activities, and m iswThe strength loss ratio obtained for the core sample in pure water. Generally, the higher the water sensitivity stability coefficient is, the stronger the water sensitivity is, and the more significant the strength loss is under the action of the working fluid with high activity.
In a specific embodiment, the following steps are further included between the step a and the step B: and when the shale is stratum rock, restoring the shale to a stratum in-situ pore fluid saturated state. It is also possible to use natural conditions in the chamber regardless of the conditions of the applied formation, which may be selected according to experimental conditions. Restoring the shale to formation in situ pore fluid saturation may be achieved by a saturator.
In a specific embodiment, the immersion time of the core sample in the working fluid is greater than or equal to 12 hours, preferably greater than or equal to 18 hours, and more preferably greater than or equal to 24 hours.
In a specific embodiment, during the soaking of the core sample in the working fluid, formation overburden conditions and temperatures simulating the shale are selected as desired. Generally, underground stratum rock samples are recommended to be operated according to the conditions, so that the underground stratum rock samples are more consistent with stratum environment conditions and truly reflect rock characteristics; if the simulated temperature and pressure test conditions are insufficient or the simulated temperature and pressure test conditions are outcrop rock samples, the simulation temperature and pressure test conditions are discarded properly.
In a particular embodiment, the working fluid is selected from at least two or three of pure water, a water-based drilling fluid, and an oil-based drilling fluid.
In a particular embodiment, the shale is non-reactive shale and/or hard brittle shale.
Has the advantages that:
the new method for evaluating the stability of the shale, particularly the inactive shale and/or the hard brittle shale (namely the shale without expansive clay minerals such as montmorillonite) comprehensively considers the effects of hydration on the physicochemical characteristics of the shale and the influence on the mechanical characteristics of the shale, and can determine the stability of the shale by reacting a core sample of the standard shale with working fluids with different activities and monitoring the mechanical strength index of the worked working fluid after the action by using a rock mechanics experimental device to obtain the ordered monitoring result of the mechanical indexes of the working fluid and the shale, and meanwhile, a stability prediction formula is established based on the mechanical indexes of the working fluid and the shale, thereby being particularly suitable for evaluating the stability of the inactive shale and/or the hard brittle shale.
Drawings
FIG. 1 is a flow chart of a method of a preferred embodiment of the present invention.
Detailed Description
The invention will be further illustrated by the following preferred examples, without restricting its scope to the following examples.
Example 1
The invention provides a novel method for evaluating the stability of inactive shale and/or hard and brittle shale, which comprises the following steps (shown in figure 1).
Step 1: selecting a Paolaizhen group, a Shaxi Temple group in a certain area,Outcrop rock samples of stratums of the Fujiahe group and the Longmaxi group are taken as experimental objects, core taking is carried out on the outcrop rock samples, and standard core samples with uniform size are prepared
Taking 8 standard core samples from each set of stratum, and counting 32 samples;
step 2: because the outcrop shale sample is adopted in the embodiment, the condition of applying a stratum saturation state is not considered, and an indoor natural condition is adopted;
and step 3: three working fluid fluids are selected to be subjected to activity measurement by an electrowetting meter measurement method, wherein the activity of pure water is 1, the activity of the polysulfonated water-based drilling fluid (3.0% of bentonite, 0.1% of soda, 0.2% of caustic soda, 0.3% of potassium polyacrylate, 3% of sulfonated phenolic resin (dry powder), 3% of sulfonated lignite, 2% of non-fluorescent white asphalt, 1% of polyamine and 1% of hydrolyzed polyacrylonitrile ammonium salt) is 0.85, and the activity of the low-viscosity high-shear oil-based drilling fluid (0# diesel oil, 2% of organic soil, 3% of calcium naphthenate and 20% of CaCl2+ 2% CaO + 3% quaternary ammonium humate + 0.8% calcium alkyl benzene sulfonate + 2% nanosilica) activity was 0.74. Measuring to obtain the water activity of the outcrop shale formation to be 0.5;
and 4, step 4: respectively soaking four sets of stratum core samples in the three types of working fluid for 24 hours under the conditions of normal temperature and normal pressure;
and 5: and (3) carrying out rock mechanics experiment measurement on the rock core sample (namely the original rock) which is not soaked by the working solution and the rock core sample soaked by the working solution to obtain a rock mechanics strength value (completed by adopting a universal rock mechanics triaxial stress meter). When the mechanical strength value of the rock cannot be immediately measured on the soaked core sample, the soaked core sample is preferably sealed after being taken out, the seal can be simply wrapped by preservative film or sealed by wax, and the preservative film or the wax seal is removed before the mechanical strength value of the rock is measured. The strength results are shown in table 1. Wherein the virgin rock is a core sample that is not soaked by any liquid.
Step 6: respectively substituting the obtained data of activity and intensity into a publicFormula (II)
The stability coefficient is obtained through calculation, and the stability evaluation of the hard and brittle shale and/or the inactive shale is realized. Where m is the strength loss ratio, σcThe mechanical strength of the original rock is MPa; sigmaclThe mechanical strength of a rock core sample after being soaked in a specific working fluid is MPa; l represents the type of specific working fluid acting on the core sample. According to the strength loss ratio of the shale, the sensitivity of the shale to different systems is reflected from the mechanical angle, the larger m is, the more remarkable the hydration effect of the working fluid on the shale is, when m is 1, the shale loses the structural strength completely, and when m is close to 0, the shale is insensitive to the systems.
TABLE 1 rock mechanical Strength measurement results (Unit: MPa)
The strength loss ratio of each set of stratum calculated according to the formula is shown in table 2, wherein the calculation result is the average value of the ambient pressure of 15MPa and 30MPa, and the higher the strength loss ratio is, the more serious the strength loss under the working fluid is, and the more prominent the water sensitivity is.
Table 2 strength loss ratio results
Secondly, according to the formula S ═ sin (arctan (k)) + mw) Calculating to obtain the water sensitivity stability coefficient of each set of stratum, wherein S is the water sensitivity stability coefficient of the shale, k is the slope of the strength loss ratio of the core sample obtained in the working fluid with different activities, and m iswThe strength loss ratio obtained for the core sample in pure water. The water sensitive stability factor results of the present invention are shown in Table 3.
Generally, the higher the stable water sensitivity qualitative coefficient is, namely the stronger the water sensitivity is, under the action of high activity, the more significant the strength loss is, the highest the water sensitivity stability coefficient of the rock sample of the beard river group stratum in each set of stratum is, the worst the stability of the set of stratum is, the most complex situations are in the actual drilling process, and the evaluation result is reliable; meanwhile, by utilizing the water sensitivity stability coefficient, the strength of stratum rocks soaked by working solutions with different activities can be estimated, and further the strength change of the stratum can be predicted, so that the stability analysis of the well wall is carried out.
TABLE 3 Water sensitive stability coefficient results
Claims (10)
1. A method for evaluating shale stability, comprising the steps of:
step A: coring the shale, and preparing a core sample with uniform size;
and B: soaking the core sample in at least two working solutions with different activities, wherein the activities of the working solutions are distributed between 0 and 1, so as to obtain a soaked core sample;
and C: obtaining mechanical strength values of the rock core sample and the soaked rock core sample, and obtaining a strength loss ratio according to the mechanical strength values;
step D: defining a water-sensitive stability coefficient of the shale according to the strength loss ratio obtained by the core sample in the working fluid with different activities, wherein the water-sensitive stability coefficient of the shale is expressed by the formula S ═ (sin (arctan (k)) + mw) And/2, wherein S is the water-sensitive stability coefficient of the shale, k is the slope of the strength loss ratio obtained by the core sample in working fluids with different activities, and m iswThe strength loss ratio obtained for the core sample in pure water.
2. The method according to claim 1, wherein in step B, the core sample is soaked in at least three working fluids with different activities having an activity distribution between 0 and 1 to obtain a soaked core sample.
3. The method of claim 1, wherein the strength loss ratio is formulated
where m is the strength loss ratio, σcIs the mechanical strength, σ, of the core sampleclThe mechanical strength of the soaked core sample.
4. The method according to any one of claims 1-3, further comprising, between the step A and the step B, the steps of: and when the shale is stratum rock, restoring the shale to a stratum in-situ pore fluid saturated state.
5. The method of any one of claims 1 to 3, wherein the core sample has a size of
And
one kind of (1).
6. The method according to any one of claims 1 to 3, wherein the core sample is immersed in the working fluid for a period of time equal to or greater than 12 hours.
7. The method of claim 6, wherein the core sample is soaked in the working fluid for a time period of 18 hours or more.
8. The method of claim 6, wherein the core sample is soaked in the working fluid for a time period of 24 hours or more.
9. The method of any one of claims 1-3, wherein the working fluid is selected from the group consisting of pure water, water-based drilling fluids, and oil-based drilling fluids.
10. A method according to any one of claims 1-3, characterized in that the shale is non-reactive shale and/or hard brittle shale.
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| CN109900568A (en) * | 2017-12-08 | 2019-06-18 | 中国石油化工股份有限公司 | The evaluation method of shale strength reduction degree in a kind of shale borehole well instability research |
| CN108106938B (en) * | 2017-12-21 | 2018-09-21 | 西南石油大学 | A method of experiment determines that acid solution influences dense carbonate Young's modulus |
| CN109115628A (en) * | 2018-07-27 | 2019-01-01 | 中国石油集团川庆钻探工程有限公司长庆钻井总公司 | A kind of method for estimating stability of drilling fluid to rock stratum |
| CN109236285B (en) * | 2018-09-30 | 2022-02-18 | 西南石油大学 | Single-well undisturbed stratum mechanical profile calculation method and system |
| CN109115625A (en) * | 2018-10-08 | 2019-01-01 | 西南石油大学 | A kind of shale hydration dynamic changes of strength variation test new equipment |
| CN110146534A (en) * | 2019-06-03 | 2019-08-20 | 中国石油大学(华东) | Sandstone acid rock reaction effect visualizes quantitative evaluation method |
| CN112255159B (en) * | 2020-10-10 | 2021-08-10 | 西南石油大学 | Comprehensive evaluation method for hydration capacity of heterogeneous shale reservoir |
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