Improvement of Quantitative Evaluation of Rock Brittleness Based on Stress- Strain Curve

Transcription

1 Advances in Petoleum Exloation and Develoment Vol. 11, No. 1, 2016, DOI: /8237 ISSN X [Pint] ISSN [Online] Imovement of Quantitative Evaluation of Rock Bittleness Based on Stess- Stain Cuve JIANG Dongfeng [a] ; WANG Tingting [a] ; ZHAO Wanchun [a],* ; CHEN Yanqiu [a] ; MA Yuneng [a] [a] Notheast Petoleum Univesity, Daqing, China. *Coesonding autho. Suoted by the National Natual Science Foundation of China ( ), the National Natual Science Foundation of China ( ), China Postdoctoal Foundation (2014M550180), Heilongjiang Postdoctoal Foundation (LBH-TZ-0503), Youth Science Foundation of Notheast Petoleum Univesity (2013NQ105), the Scientific Reseach Fund of Heilongjiang Povincial Deatment of Education ( ), PetoChina Innovation Foundation (2013D ). Received 19 Febuay 2016; acceted 21 Mach 2016 Published online 31 Mach 2016 Abstact Accuate assessment of bittle of ock is the key to the tansfomation of oil and gas esevois. In view of this, Theefoe, though liteatue eseach, summaized moe than 30 kinds of bittleness index, and analysis the limitations of the bittleness evaluation index. A new bittle evaluation index, based on the stess chaacteistics of the stess-stain cuve, and consideing the two kinds of ock beaking behavio, is oosed. And cay out uniaxial comession test to veify the evaluation index of bittleness. The test esults show that the new bittle index can evaluate the two kinds of ock bittleness, which is moe geneal and eliable than othe indexes. The esults have imotant significance to enich and imove the existing evaluation methods of ock bittleness. Key wods: Rock mechanics; Bittleness index; Stess-stain cuve Jiang, D. F., Wang, T. T., Zhao, W. C., Chen, Y. Q., & Ma, Y. P. (2016). Imovement of quantitative evaluation of ock bittleness based on stess-stain cuve. Advances in Petoleum Exloation and Develoment, 11(1), Available fom: URL: htt:// DOI: htt://dx.doi.og/ /8237 INTRODUCTION The bittleness of the ock is closely elated to the ock mass stability and esevoi stimulation in the esevoi engineeing. Bittleness index is an imotant indicato of ock bust ediction. It is diectly elated to the bittle factue of ock mass and stuctue stability of suounding ock in the undegound cavens. At the same time, bittleness index is also an imotant indicato of esevoi mechanical oeties evaluation, wellboe stability evaluation and hydaulic factuing effects evaluation. Thee is no standad, unifom definitions and test methods of bittle ock at esent. Bittleness is defined as the lack of mateial lastic by A. Moley [1] and M. Hetenyi [2]. J. G. Ramsey [3] believed, mateial bittle failue occued when the loss of cohesion within the ock. L. Obet and W. I. Duvall [4] defined bittleness as the oety of mateial such as cast ion and most ock mateial at o slightly exceed the yield stength of the destuction. Cuently, the geology and elated subjects scholas believe that bittleness efes to the chaacteistics of mateial factue o damage befoe it showed minimal o no lastic defomation chaacteistics [5]. Howeve, bittle mateial with oeties have eached the following consensus: (a) Damage occued in the low stain; (b) Bittle failue modes dominated by the intenal contol micocacks; (c) Rock is mostly comosed of fine aticulate matte; (d) High comessive stength, tensile stength atio (Rabbi essue); (e) High esilience enegy; (f) Intenal fiction angle is lage; (g) Cacks develoment comletely when Hadness tests. The oeties of bittle ock ae closely elated to thei mechanical oeties. Many scholas have done a lot of eseach wok in this esect, and they have fomed dozens of bittle evaluation methods (Table 1). Coyight Canadian Reseach & Develoment Cente of Sciences and Cultues 70

2 JIANG Dongfeng; WANG Tingting; ZHAO Wanchun; CHEN Yanqiu; MA Yuneng (2016). Advances in Petoleum Exloation and Develoment, 11(1), Table 1 Domestic and Foeign Rock Bittleness Index and Test Method Summay Test Method Fomula Fomula descition Liteatue souce Hadness test method H is maco hadness, H m is mico hadness H. Hond and Y. Sanada [5] Pocto imact test Q is less than 0.6 mm debis ecent content, c is uniaxial comessive stength of ock M. M. Potodyakonov [6] Stess-stain cuve τ is eak intensity, τ t is esidual stength A. W. Bisho [7] Stess-stain cuve Ratio of ecoveable stain to total stain Pessue abbi Ratio of uniaxial comessive stength c to tensile stength t Pessue abbi Function of uniaxial comessive stength c and tensile stength 1 Mooe cicle Sine value of intenal fiction angle Stess-stain cuve Hadness test, Factue test B 10 = H/K IC Factue test Hadness test, factue test B 16 = HE/K 2 IC The atio of the ecoveable stain enegy to the total enegy H is coefficient of hadness, K IC is factue toughness K IC is Plane stain factue toughness, y is yield stess, h is the chaacteistics of the samle size H is Hadness coefficient, E isyoung s modulus, K IC is factue toughness Imact test " The ecentage of diamete less than 11.2 mm of fine elastic Penetation test The atio of the maximum imact load and enetation deth Pessue abbi The mean of oduct of uniaxial comessive stength and tensile stength Pessue abbi The function of uniaxial comessive stength and tensile stength atio Penetation test The incemental load and the atio of attenuation of load Stess-stain cuve! # Stess-stain cuve B. R. Lawn and D. B. Mashall [9] Z. P. Bazant and M. T. Kazcmi [10] J. B. Quinn and G. D. Quinn [11] Q. T. Blindheim and A. Buland [11] R. Altindag [12] R. Altindag [12] V. Hajiabdolmajid [13] V. Ajiabdolmajid and P. Kaisc [14] On the function of eak stain and esidual stain t R. Rickman [15] The mean value of the elastic modulus and Poisson s atio afte nomalization R. Rickman et al. [16] Mineal comosition analysis!$ $ Ratio of bittle mineal content to total mineal content A. N. Stavogin and G. Taasov [17] Stess-stain cuve % % " " Ratio of ost factue damage enegy of ock to eak befoe elastic stain enegy Li Qinghui [18] Stess-stain cuve &' The sum of the eak stain index and the ost cuve shae index Zhou Hui [19] 1. BRITTLENESS INDEX OF ROCK BASED ON STRESS STRAIN CURVE Accoding to the analysis of existing bittleness evaluation methods, the ock is the comehensive oety of ock. It is the common esult of the inteaction between the intenal stuctue and the extenal loading conditions of the mateial. Accoding to the definition, it shows that: (a) Bittleness is the comehensive oety of the mateial, is the common function of the intenal stuctue of the mateial and the extenal loading conditions. We need to establish a secific bittleness index in ode to taking bittleness. (b) The bittleness of the mateial will change. Bittleness is a kind of vaiable static state, which is the ability of the mateial to oduce a local factue in the cuent state and fom many dimensions factues. 71 Coyight Canadian Reseach & Develoment Cente of Sciences and Cultues

3 Imovement of Quantitative Evaluation of Rock Bittleness Based on Stess-Stain Cuve Bittleness test is imotant basis of ock esevoi evaluation, select efoation and efom inteval and design of factuing scales. Accoding to the above bittle defines, laboatoy evaluation of ock bittleness need comehensive evaluation, but comlete stess-stain featue can showing the macoscoic and micoscoic chaacteistic of bittle factue, howeve, when the whole stess-stain cuve is obtained, the comession of ock will damage the intenal stuctue, and the evaluation of the bittleness needs to be consideed. So based on the stess stain mechanical chaacteistics in this ae, combined with the ock mineal comosition,we established a bittle evaluation method. In uniaxial comession tests, thee ae two tyes of ocks (I, II) in the bittleness of the aaent monotonic and continuity as shown in Figue 1. Figue 1 Stess and Stain Cuves of Two Kinds of Rock Unde Uniaxial Comession Fom the line of stess and stain, it can be seen the fist is a kind of bittle ock, and the twice is a kind of lasticity and bittle ock. Accoding to the stess-stain cuve at the eak of the mechanical chaacteistics of the definition of the new bittle evaluation index. The new bittleness evaluation index fistly defines the ost eak stess eduction degee: Pk =. (1) Among them: fo the eak stess, fo the esidual stess, the value ange of 0~1. Post eak stess eduction ate K: actan( ). (2) K = 90 actan ( ) is the angle between the eak afte eak stess to educe the esidual stess and the sloe and eak vetical. K is the nomalized angle. The value ange of K is -1~1; the hysical meaning of the eesentative: The geate the angle, educe the stess of the same should be changed, the less bittle. The angle is smalle, the moe bittle. When the angle is less than <=0, the ocks belong to ue bittle, angle is negative, they belong to the sue bittle ock. Define bittleness evaluation index is: B=Pk K, (3) actan( ). (4) B = 90 When K is zeo, howeve, the case is shown in Figue 2: Figue 2 Residual Stess of Pue Bittle (K = 0) Rock bittleness can t be distinguished. Howeve, when the ock is ue bittle, the main influence factos which cause the diffeence of the esidual stess o the eak stess ae changed into the mineal comosition of the ock. Theefoe, the definition of bittle mineal coefficient of ock G: W k G =. (5) W W k fo the ock mineal content; W fo the total weight of the ock. Based on the above factos, the evaluation index of bittleness is established on the basis of the two kinds of ock beaking behavio: PK B = e G, (6) actan( ) 90 Wk B e a. (7) = + W Rock bittleness evaluation index is used to chaacteize bittleness, the weake the ock is, the moe close to zeo, the stonge the bittleness, the geate the bittleness index. Coyight Canadian Reseach & Develoment Cente of Sciences and Cultues 72

4 JIANG Dongfeng; WANG Tingting; ZHAO Wanchun; CHEN Yanqiu; MA Yuneng (2016). Advances in Petoleum Exloation and Develoment, 11(1), APPLICABILITY TEST OF B 2.1 Diffeent Rock Uniaxial Stess State Unde Uniaxial Stess State In ode to veify the bittleness index in descibing the moe diffeent kinds of ock bittle chaacteistics of adatability, the selection of mable, ganite, cement mota, shale and sandstone 5 ock mateials wee uniaxial comession test, 5 in comession test stess-stain cuve as shown in Figue 3, and the bittleness evaluation method fo the evaluation of the five kinds of ock bittle. Figue 4 Stess and Stain Cuves Unde Diffeent Confining Pessues Table 3 Rock Bittleness Index Unde Diffeent Confining Pessues Confining Pessue (MPa) The bittleness index Figue 3 Stess and Stain Cuves of 5 Kinds of Rock Unde Uniaxial Comession Unde Uniaxial Comession Table 2 Bittleness Evaluation Index of 2 Kinds of Diffeent Rocks Unde the Same Confining Pessue Rock Tye The bittleness index Ganite Shale Sandstone Mable Rock Coal Rock Fom Table 2 can be seen, mable, ganite, sandstone and the degee of bittleness deceases gadually. Theefoe, the bittleness evaluation method can bette evaluation of bittle ock degee. 2.2 Diffeent Secies of Rock Should be Veified Unde Stess To descibe the ock unde diffeent confining essue, bittle vaiation, with a deth of shale and ocessed into a diamete is 25 mm cylinde secimen and loading design confining essue is 0 MPa, 15 MPa and 35 MPa thee confining essue, due to the chaacteistics of the bittle factue of at of the samles, the exeiment of axial stess and defomation contol of load, the loading ate is M/S. By loading the stess stain cuve as shown in Figue 4. As can be seen fom Table 3, in the laboatoy test, shale with the confining essue inceases, the shale bittleness deceases, but because of the confining essue, the ock beaking delay, the geate the damage, the stain becomes smalle. CONCLUSION (a) The method of evaluating ock bittleness at home and aboad is summaized, and the advantages and disadvantages of the method ae analyzed. Fom two kinds of behavio of bittle factue of ock, it is a comehensive chaacteization of intenal and extenal factos. The bittle index of science should not only be able to chaacteize the damage of the ock, but also can be chaacteized by the degee of ock bittleness when the damage is simila. (b) A new method fo evaluating ock bittleness is oosed. The bittleness evaluation index is comosed of the ost eak damage degee and the atio of the ock mineals, which can comehensively evaluate the stength and difficulty of the bittle failue of the ock. The method can accuately evaluate the ock bittleness, and edict the degee of the same ock bittleness. (c) By comaing with othe evaluation indices, the esults ae simila to those of othe indexes, but moe accuate. At the same time, in this ae, 3 kinds 73 Coyight Canadian Reseach & Develoment Cente of Sciences and Cultues

5 Imovement of Quantitative Evaluation of Rock Bittleness Based on Stess-Stain Cuve of exeiments ae caied out unde the condition of exeiment, and the bittleness of ock is inceased with the incease of mineal content. The exeimental esults meet the bittle factue chaacteistics of ock. Needs to be ointed out is that the evaluation index of bittleness is in Hui Zhou bittleness evaluation method based on imoved. Consideing the sue bittle factue chaacteistics of ock and solve the ue bittle ock evaluation index in the constant 0, e analyzes and deduces the calculation fomula. REFERENCES [1] Moley, A. (1944). Stength of mateials (.71-72). London: Longman Geen. [2] Heteny, M. (1966). Handbook of exeimental stess analysis (.23-25). New Yok: John Wiley. [3] Ramsay, J. G. (1967). Folding and factuing of ocks (.44-47). London: McGaw-Hill. [4] Obet, L., & Duvall, W. I. (1967). Rock mechanics and the design of stuctues in ock (.78-82). New Yok: John Wiley. [5] Honda, H., & Sanada, Y. (1956). Hadness of coal. Fuel, 35, 451. [6] Potodyakonov, M. M. (1963). Mechanical oeties and dill ability of ocks. Pae esented at Poceedings of the 5 th Symosium on Rock Mechanics, Twin Cities, USA. [7] Bisho, A. W. (1967). Pogessive failue with secial efeence to the mechanism causing it. Pae esented at Poceedings of the Geotechnical Confeence, Oslo, Noway. [8] Hucka, V., & DAS, B. (1974). Bittleness detemination of ocks by diffeent methods. Intenational Jounal of Rock Mechanics and Mining Sciences and Geomechanics Abstacts, 11(10), [9] Lawn, B. R., & Mashall, D. B. (1979). Hadness, toughness and bittleness: An indentation analysis. Jounal of Ameican Ceamic Society, 62(7/8), [10] Bazant, Z. P., & Kazemi, M. T. (1990). Detemination of factue enegy, ocess zone length and bittleness numbe fom size effect, with alication to ock and concete. Intenational Jounal of Factue, 44, [11] Quinn, J. B., & Quinn, G. D. (1997). Indentation bittleness of ceamics: A fesh aoach. Jounal of Mateials Science, 32(16), [12] Altindag, R. (2003). The coelation of secific enegy with ock bittleness concet on ock cutting. Jounal of the South Afican Institute of Mining and Metallugy, 103(3), [13] Hajiabdolmajida, V., Kaise, P. K., & Matin, C. D. (2002). Modeling bittle failue of ock. Intenational Jounal of Rock Mechanics and Mining Sciences, 39(6), [14] Cou, H., Bilgin, N., & Tuncdemi, H. (2003). A set of indices based on indentation test fo assessment of ock cutting efomance and ock oeties. Jounal of the South Afican Institute of Mining and Metallugy, 103(9), [15] Ajiabdolmajid, V., & Kaise, P. (2003). Bittleness of ock and stability assessment in had ock tunneling. Tunnelling and Undegound Sace Technology, 18(1), [16] Rickman, R., Mullen, M., & Pete, E. (2008, Setembe). A actical use of shale etohysics fo stimulation design otimization: All shale lays ae not clones of the Banett shale. Pae esented at SPE Annual Technical Confeence and Exhibition, Denve, Coloado, USA. [17] Stavogin, A. N., & Taasov, B. G. (2001). Exeimental hysics and ock mechanics ( ). New Yok: Taylo and Fancis Gou. [18] Li, Q. H., Chen, M., Jin, Y., Wang, F. P., Hou, B., & Zhang, B. W. (2012). Indoo evaluation method fo shale bittleness and imovement. Chinese Jounal of Rock Mechanics and Engineeing, 31(8), [19] Zhou, H., Meng, F. L., Zhang, C. Q., Xu, R. C., & Lu, J. J. (2014). Quantitative evaluation of ock bittleness based on stess-stain cuve. Chinese Jounal of Rock Mechanics and Engineeing, 6, Coyight Canadian Reseach & Develoment Cente of Sciences and Cultues 74