CN103541720A - Technique for rapid evaluation of gas drilling wellbore stability - Google Patents
Technique for rapid evaluation of gas drilling wellbore stability Download PDFInfo
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- CN103541720A CN103541720A CN201310412024.3A CN201310412024A CN103541720A CN 103541720 A CN103541720 A CN 103541720A CN 201310412024 A CN201310412024 A CN 201310412024A CN 103541720 A CN103541720 A CN 103541720A
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Abstract
The invention provides a technique for rapid evaluation of gas drilling wellbore stability. According to the technique for the rapid evaluation of the gas drilling wellbore stability, the gas drilling wellbore stability is analyzed by means of a moderate collapse method. The moderate collapse method comprises the steps that the strength of a stratum is determined according to an indoor rock mechanics experiment, surrounding-well stress of gas drilling is calculated according to the stress state of the stratum, a collapse angle of a well is calculated according to the stress state of the periphery of the well and the strength of the stratum, and the feasibility of gas drilling is analyzed according to the limitation criterion of the collapse angle. The field application proves that safety of gas drilling is guaranteed when the collapse angle is smaller than 30 degrees. The moderate collapse method is put forward based on the combination of the rock mechanics basic theory and actual site drilling, is applied to gas drilling of a plurality of oil and gas fields such as the Puguang gas field and the Niudong gas field and has the advantages of being good in application effect, simple and convenient to operate.
Description
Technical field
The present invention relates to the wellbore stability technical field in oil drilling, be specifically related to gas drilling wellbore stability technology.
Background technology
Air drilling comes from the Utah, USA of the 1950's the earliest, is to using air or other gas a kind of under-balanced drilling technology as circulatory mediator.Gas drilling can increase substantially bit speed, effectively prevent leakage and protect reservoir; especially the exploitation obvious effect of increasing production to low-permeability oil gas reservoir, tight sand petroleum resources; can make fine and close oil-gas reservoir straight well output improve 3 times, horizontal well production improves 10 times.Since the nineties in 20th century, air drilling has obtained development rapidly at home and abroad.According to statistics, U.S.'s underbalance in 2007 and gas drilling number account for the coal bed gas well of the 28%， U.S. 90% of total well number then and adopt gas drilling.China in Chongqing of Sichuan, the oil field such as long celebrating, grand celebration, Tarim Basin or area carried out gas drilling approximately 200 wells; raise speed, administer pernicious leakage, find and protect reservoir effect remarkable; but; during existing gas drilling construction, borehole well instability is serious; cause down-hole accident to take place frequently, become one of bottleneck problem of serious its development of restriction.
Compare with conventional drilling, the particularity of gas drilling wellbore stability has 3 points: first gas drilling is to using gas as circulatory mediator, the pressure that shaft bottom is produced is very little, generally can ignore, and the pressure that conventional drilling produces shaft bottom is very large, for the deep-well that surpasses 3km, more than bottom pressure generally all reaches 30MPa; Secondly, recyclegas in gas drilling can not form and stop fluid at the mud cake of pit shaft and ground interlayer seepage flow on the borehole wall, but can not produce chemical reaction with rock of borehole yet, and drilling fluid produces mud cake at the borehole wall in conventional drilling, can effectively protect stratum, but while drilling fluid and stratum can produce much to the disadvantageous chemical reaction of wellbore stability; The 3rd, after conventional drilling generation borehole well instability, can control by regulating density of drilling liquid and performance, once gas drilling borehole well instability lacks effective wellbore stability measure, very easily cause gas drilling failure, therefore, gas drilling is higher to the requirement of wellbore stability.Due to these particularity of gas drilling, traditional wellbore stability model cannot be suitable for, and invents a kind of simple, practical gas drilling wellbore stability assessment technique most important to applying of gas drilling.
Summary of the invention
The Fast Evaluation that the object of this invention is to provide a kind of gas drilling wellbore stability, utilizes the method to predict simple, convenient, fast the borehole wall stability of gas drilling, and prediction effect is good.
Utilize above-mentioned purpose, the present invention adopts following technical scheme:
A Fast Evaluation for gas drilling wellbore stability, the application process of this technology comprises step:
(1) according to indoor Rock Mechanics Test And, determine formation strength;
(2) according to the well circumferential stress of the geostatic stress state computation gas drilling on stratum;
(3) according to the angle of caving in of the stress state of wellbore and formation strength calculating well;
(4) in conjunction with caving in angle limit criterion, the feasibility of analytical gas drilling well.
Wherein, gas drilling borehole wall stress adopts linear elastic theory to analyze, and its stress distribution is:
Wherein, the destruction of the gas drilling borehole wall is chosen more conventional Mohr-Coulomb criterion of strength shaft lining breakage condition and is:
In formula, φ
mangle of internal friction for stratum; C
mcohesion for stratum; σ
1for maximum principal effective stress; σ
3for minimum principal effective stress.
Bringing formula (1) into formula (2) can obtain the angle that the borehole wall occur to destroy and be:
In formula, θ
allowangle for gas drilling cave-in; λ is geostatic stress heterogeneous coefficient,
Gas drilling ground adaptability evaluate Zhong， seminar by tens of implication body the drilling well angle of caving in analyze discovery, work as θ
allowin≤30 ° of situations, it is less that piece is fallen in cave-in, will can not occur to cave on a large scale, thinks to be applicable to carry out gas drilling; Otherwise the borehole wall caves in generation more greatly under gas drilling condition, the risk that bit freezing occurs increases, and is now not suitable for carrying out gas drilling.
Wherein, gas drilling can keep the cave-in angle of drilling safety to meet:
Gas drilling wellbore stability Predicting Technique provided by the invention, be suitable for prediction and the gas drilling feasibility analysis of borehole wall stability in During Air Drilling, the method is the new method proposing on the actual basis combining of the on-the-spot drilling well of rock mechanics basic theory, the method a plurality of oil gas fields such as ,Niu Dong gas field, general phosgene field gas drilling in obtained application, obtained good effect, and method is simple, there is wide promotion prospect.
Accompanying drawing explanation
Fig. 1 is the flow chart of gas drilling wellbore stability Fast Evaluation of the present invention.Fig. 2 appropriateness failure zone angle schematic diagram under condition that caves in.
The specific embodiment
The Fast Evaluation of the gas drilling wellbore stability that the present invention proposes, is described as follows in conjunction with the accompanying drawings and embodiments.
When calculating caving pressure, with mud fluid column pressure balance formation rock in well, the pressure of formation pore fluid is as caving pressure calculated value, and gas column pressure smaller (conventionally negligible) comparatively speaking in well during gas drilling, be not enough to support the borehole wall, lacking under the condition of support, wellbore stability is mainly by certainly surely realizing, this not only requires gas drilling selecting the formation rock creeping into have enough intensity, avoid easily caving in, easy undergauge, the stratum of easy water outlet, also should there is understanding again to borehole well instability mechanism, and then the affect problem of solution cave-in on engineering.Therefore, inventor proposes the appropriateness borehole wall Method of Stability Analysis under condition that caves in and solves the problem of caving in running in engineering.
Similar mud drilling, adopts linear elasticity method to calculate gas drilling borehole wall stress distribution:
Level when θ=90 ° minimally stress orientation is the orientation of circumferential stress maximum, in mud drilling, think that the drilling liquid pressure when borehole wall caves at this place, orientation is called caving pressure, but field operation shows, for gas drilling, due to the impact that does not have drilling fluid on the borehole wall, even if certain caving in occurs the borehole wall, yet can not affect normally and creep into, as long as the gas drilling borehole wall does not occur to cave on a large scale, little fall piece and can carry out well head by gas drilling, can take the borehole wall stability analytical method under appropriate failure condition.So-called appropriateness, allows the borehole wall to have the destruction of less degree, and this destruction can not cause larger engineering accident.
Choose more conventional Mohr-Coulomb criterion of strength the borehole wall stability under appropriate failure condition is analyzed, shaft lining breakage condition is:
In formula, φ
mangle of internal friction for stratum; C
mcohesion for stratum; σ
1for maximum principal effective stress; σ
3for minimum principal effective stress.
During cave-in, meeting circumferential stress is major principal stress, makes formation anisotropy coefficient
can obtain σ
θ=σ
h[(1+ λ)+2 (1-λ) cos2 θ].By σ
θsubstitution formula (2):
Separating this equation obtains:
In gas drilling ground adaptability is evaluated, inventor by tens of implication body the drilling well angle of caving in analyze discovery, work as θ
allowin≤30 ° of situations, it is less that piece is fallen in cave-in, will can not occur to cave on a large scale, thinks to be applicable to carry out gas drilling; Otherwise the borehole wall caves in generation more greatly under gas drilling condition, the risk that bit freezing occurs increases, and carries out in this case gas drilling and has down hole problem.
Wherein, gas drilling can keep the cave-in angle of drilling safety to meet:
This formula can characterize and be subject to three-dimensional stress Sidewall Surrounding Rock failure zone along the appropriate damage envelope of θ direction.θ wherein
allowfor the angle that allows to cave in, as shown in Figure 2.
Above embodiment is only for illustrating the present invention; and be not limitation of the present invention; the those of ordinary skill in relevant technologies field; without departing from the spirit and scope of the present invention; can also make a variety of changes and modification; therefore all technical schemes that are equal to also belong to category of the present invention, and scope of patent protection of the present invention should be defined by the claims.
Claims (4)
1. a Fast Evaluation for gas drilling wellbore stability, is characterized in that, the method comprises the following steps:
According to indoor Rock Mechanics Test And, determine formation strength;
According to the well circumferential stress of the geostatic stress state computation gas drilling on stratum;
According to the angle of caving in of the stress state of wellbore and formation strength calculating well;
In conjunction with the angle limit criterion of caving in, the feasibility of analytical gas drilling well.
2. the Fast Evaluation of gas drilling wellbore stability as claimed in claim 1, is characterized in that, the methods analyst Well-bore Stability During Gas Drilling that has adopted appropriateness to cave in the method.
3. the Fast Evaluation of gas drilling wellbore stability as claimed in claim 1 or 2, is characterized in that, has set up the design formulas of cave-in angle in During Air Drilling in the method:
4. the Fast Evaluation of gas drilling wellbore stability as claimed in claim 1, is characterized in that, has determined and has guaranteed the critical angle of caving in that gas drilling creeps into safely, thereby determined the condition of Fast Evaluation gas drilling feasibility in the method
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105003247A (en) * | 2014-04-23 | 2015-10-28 | 中国海洋石油总公司 | Low-density drilling feasibility fast evaluation method |
| CN106599360A (en) * | 2016-11-08 | 2017-04-26 | 清华大学 | Surrounding-well stress calculation method and calculation device |
| CN109187228A (en) * | 2018-09-30 | 2019-01-11 | 西南石油大学 | A kind of indoor evaluation method of shale formation drilling fluid stabilizing borehole ability |
| CN110018056A (en) * | 2019-04-15 | 2019-07-16 | 中国石油大学(北京) | A kind of sandstone reservoir wellbore stability evaluation experimental device and method |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105003247A (en) * | 2014-04-23 | 2015-10-28 | 中国海洋石油总公司 | Low-density drilling feasibility fast evaluation method |
| CN106599360A (en) * | 2016-11-08 | 2017-04-26 | 清华大学 | Surrounding-well stress calculation method and calculation device |
| CN106599360B (en) * | 2016-11-08 | 2019-08-16 | 清华大学 | Well circumferential stress calculation method and computing device |
| CN109187228A (en) * | 2018-09-30 | 2019-01-11 | 西南石油大学 | A kind of indoor evaluation method of shale formation drilling fluid stabilizing borehole ability |
| CN110018056A (en) * | 2019-04-15 | 2019-07-16 | 中国石油大学(北京) | A kind of sandstone reservoir wellbore stability evaluation experimental device and method |
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Application publication date: 20140129 |