All Issue

2017 Vol.27, Issue 3 Preview Page

Research Article

Investigation of Fracture Propagation in Cement by Hydraulic Fracturing Under the Tri-axial Stress Condition

시멘트 시료에 대한 삼축압축 환경에서의 수압파쇄시험 연구

Hee-Sung Riu1
,
Hyun-Sic Jang1
,
Bo-An Jang1*
류 희성1
,
장 현식1
,
장 보안1*
1Department of geophysics, Kangwon National University, Chuncheon, Korea
1강원대학교 지구물리학과
* 교신저자* Corresponding Author
September 2017. pp. 233-244
PDF XML Citation
Abstract

We conducted hydraulic fracturing experiments on cement samples to investigate the dependency of fracture propagation on the viscosity of injection fluid and the in situ stress state. Ten cubic samples (20 cm side length)were produced using cement that was cured in water for more than one month. Samples were placed in a tri-axial compression apparatus with three independent principal stresses. An injection hole was drilled and the sample was hydraulically fractured under a constant injection rate. We measured injection pressures and acoustic emissions (AE)during the experiments, and investigated the fracture patterns produced by hydraulic fracturing. Breakdown pressures increased exponentially with increasing viscosity of the injection fluid. Fracture pat­terns were dependent on differential stress (i.e., the difference between the major and minor principal stresses). At low differen­tial stress, multiple fractures oriented sub-parallel to the major principal stress axis propagated from the injection hole, and in some samples the fracture orientation changed during propagation. However, at high differential stress, a single fracture propa­gated parallel to the major principal stress axis. AE results show similar patterns. At low differential stress, AE source locations were more widespread than at high differential stress, consistent with the fracture pattern results. Our study suggests that hydrau­lic fracturing during shale gas extraction should be performed parallel to the orientation of minimum differential stress.

Keywords
hydraulic fracturing
initial breakdown pressure
viscosity
differential stress

주입액의 점성도와 응력상태에 따른 균열전파 특성을 분석하기 위해 실험실 규모의 수압파쇄시험을 실시하였다. 시험에 사용된 시료는 시멘트 몰탈을 사용하여 제작되었으며, 각 변의 길이가 20 cm인 정육면체 형태이다. 제작된 시료는 최대강도를 갖기 위해 수중에서 약 1달간 양생과정을 거쳤다. 독립적인 가압시스템을 가지고 있는 진삼축압축장치로 시료에 압력을 가하여, 실제의 지반에서 작용하는 원위치응력 상태를 재현하였다. 시추 환경 재현을 위해 시료에 소형 시추공을 천공한 후, 일정한 주 입속도로 수압파쇄시험을 실시하였다. 수압파쇄시험 과정에서 시추공에 주입된 유체의 압력을 실시간으로 측정하였으며, 동시에 미소파괴음(AE)신호를 측정하였다. 수압파쇄시험의 모든 과정이 끝난 후 생성된 균열의 형태를 육안으로 관찰하였다. 일차 파쇄압력은 주입액의 점성도 증가에 따라 지수형태를 보이며 증가하였다. 수압파쇄시험으로 인해 생성된 균열의 형태는 최대주응력과 최소주응력의 차이인 편차응력의 크기에 따라 서로 다른 양상을 보였다. 낮은 편차응력의 조건에서는 단일의 균열이 아닌 다중 균열이 생성되거나, 균열 성장과정에서 방향이 휘어지는 경향을 보였고, 이에 반해 높은 편차응력의 조건에서 생성된 균열은 단일 면상의 균열이 발생하였다. AE 분석에서도 편차응력이 클수록 미세균열이 단일 면상으로 집중되어 발생되는 경향을 보였다. 이러한 연구결과는 수압파쇄 방법을 이용한 암반파쇄에서 편차응력이 클 때보다 작을 때 더 복잡한 균열이 발생된다는 것을 보여준다. 따라서 셰일가스를 개발할 때 생산량을 높이기 위해서는 복잡한 균열을 발생시킬 수 있는 편차응력이 작은 조건에서 수압파쇄가 적용되는 것이 효과적일 것으로 판단된다.

키워드
수압파쇄
일차파쇄압력
점성도
편차응력
References
1
Ali, N. D., Kamran, G., Kaveh, A., and Yan, J., 2015, The effect of natural fracture dip and strike on hydraulic fracture prop­agation, International Journal of Rock Mechanics and Min­ing Sciences, 75, 210-215.
10.1016/j.ijrmms.2015.02.001
2
Bohloli, B. and Pater, C. J., 2006, Experimental study on hydraulic fracturing of soft rocks: Influence of fluid rhe­ology and confining stress, Journal of Petroleum Science and Engineering, 53, 1-12.
10.1016/j.petrol.2006.01.009
3
Brown, E. T. and Hoek, E., 1978, Trends in relationships between measured in situ stresses and depth, International Journal of Rock Mechanics and Minning Science ' Geo­mechanics Abstracts, 15, 211-215.
10.1016/0148-9062(78)91227-5
4
Chen, Y., Nagaya, Y., and Ishida, T., 2015, Observation of frac­tures induced by hydraulic fracturing in anisotropic granite, Rock Mechanics and Rock Engineering, 48, 1455-1461.
10.1007/s00603-015-0727-9
5
Chitrala, Y., Sondergeld, C. H., and Rai, C. S., 2012, Microseis­mic studies of hydraulic fracture evolution at different pumping rates, SPE Americas Unconventional Resources Conference, Society of Petroleum Engineers, Pittsburgh, SPE-155768-MS.
10.2118/155768-MS
6
Chitrala, Y., Moreno, C., Sondergeld, C., and Rai, C., 2013, An experimental investigation into hydraulic fracture propa­gation under different applied stresses in tight sands using acoustic emissions, Journal of petroleum Science and Engi­neering, 108, 151-161.
10.1016/j.petrol.2013.01.002
7
Cipolla, C. L., Warpinski, N. R., Mayerhofer, M. J., Lolon, E., and Vincent, M. C., 2010, The Relationship between frac­ture complexity, reservoir properties, and fracture treatment design, SPE Annual Technical Conference and Exhibition, Society of Petroleum Engineers, Colorado, SPE-115969­MS.
10.2118/115769-PA
8
Goodman, R. E., 1989, Introduction to Rock Mechanics, Sec­ond Edition, Jone Wiley ' Sons, 576p.
9
Goncalves da silva, B., Li, B. Q., Moradian, Z., Germaine, J. T., and Einstein, H. H., 2015, Development of a test setup capa­ble of producing hydraulic fracturing in the laboratory with image and acoustic emission monitoring, 49th US Rock mechanics/Geomechanics Symposium, American Rock Mechanics Association, San Francisco, ARMA-2015-141.
10
Guo, T., Zhang, S., Qu, Z., Zhou, T., Xiao, Y., and Gao, J., 2014, Experimental study of hydraulic fracturing for shale by stimulated reservoir volume, Fuel, 128, 373-380.
10.1016/j.fuel.2014.03.029
11
Heo, C., 2014, Experimental study on hydraulic fracturing using different injection fluids and rates, MSc Thesis, Seoul national university, 98-100(in Korean with English abstract).
12
Hou, B., Chen, M., Li, Z., Wang, Y., and Diao, C., 2014, Prop­agation area evaluation of hydraulic fracture networks in shale gas reservoirs, Petroleum Exploration and Develop­ment, 41, 833-838.
10.1016/S1876-3804(14)60101-4
13
Hubbert, M. K. and Willis, D. G., 1957, Mechanics of hydraulic fracturing, Petroleum Transaction American Society of Min­ing Engineers, 210, 153-168.
14
Ishida, T., Chen, Q., and Mizuta, Y., 1997, Effect of injected water on hydraulic fracturing deduced from acoustic emis­sion monitoring, Pure and Applied Geophysics, 150, 627­646.
10.1007/s000240050096
18
Ishida, T., Chen, Q., Mizuta, Y., and Roegiers, J. C., 2004, Influence of fluid viscosity on the hydraulic fracturing mech­anism, Journal of Energy Resources Technology, 126, 190­200.
10.1115/1.1791651
19
Ito, T. and Nagano, Y., 2015, Development of Experimental Apparatus for Real-time Observation of hydraulic fracture in Unconsolidated Sands by X-ray CT Method, 49th Rock Mechanics/Geomechanics Symposium, American Rock Mechanics Association, San Francisco, ARMA-2015-612.
20
Molenda, M., Stockhert, F. B. S., and Alber, M., 2015, Acoustic emission monitoring of laboratory scale hydraulic fracturing experiments, 49th US Rock mechanics/Geomechanics Sym­posium, American Rock Mechanics Association, San Fran­cisco, ARMA-2015-069.
21
Perry, K. and Lee, J., 2007, Unconventional gas reservoirs-tight gas, coal seams, and shales, facing the hard truths about energy, The National Petroleum Council, 54p.
22
Simpson, N. D. J., Stroisz, A., Bauer, A., Vercoort, A., and Holt, R. M., 2014, Failure mechanics of anisotropic shale during brazilian tests, 48th US Rock mechanics/Geome­chanics Symposium, Minneapolis, ARMA-2014-7399.
23
Stanchits, S., Surdi, A., Edelman, E., and Suarez-Rivera, R., 2012, Acoustic emission and ultrasonic transmission mon­itoring of hydraulic fracture initiation and growth in rock samples, 30th European Conference on Acoustic Emission Testing ' 7th International Conference on Acoustic Emis­sion, Granada.
24
Stroisz, A. M., Fj ccr, E., Pradhan, S., Stenebraten, J., Lund, H. K., and Sønstebø, E. F., 2013, Fracture initiation and prop­agation in reservoir rocks under high injection pressure, 47th US Rock Mechanics/Geomechanics Symposium, American Rock Mechanics Association, San Francisco, ARMA-2013­513.
25
Xu, D., Hu, R., Gao, W., and Xia, J., 2015, Effects of laminated structure on hydraulic fracture propagation of shale, Petro­leum Exploration and Development, 42, 573-579.
10.1016/S1876-3804(15)30052-5
26
Zhang, G. Q. and Fan, T., 2014, A high-stress tri-axial cell with pore pressure for measuring rock properties and simulating hydraulic fracturing, Measurement, 49, 236-245.
10.1016/j.measurement.2013.11.001
27
Zoback, M. D. and Pollard, D. D., 1978, Hydraulic fracture propagation and the interpretation of pressure time records for in-situ stress determination, 19th U.S. Symposium on Rock Mechanics(USRMS), American Rock Mechanics Association, Reno, ARMA-1978-0014.
Information
  • Publisher :Korean Society of Engineering Geology
  • Publisher(Ko) :대한지질공학회
  • Journal Title :The Journal of Engineering Geology
  • Journal Title(Ko) :지질공학
  • Volume : 27
  • No :3
  • Pages :233-244
  • Received Date : 2017-07-31
  • Revised Date : 2017-08-24
  • Accepted Date : 2017-08-26
  • DOI :https://doi.org/10.9720/kseg.2017.3.233
Journal Informaiton The Journal of Engineering Geology The Journal of Engineering Geology
Online Submission
  • NRF
  • KOFST
  • KISTI Current Status
  • KISTI Cited-by
  • crosscheck
  • orcid
  • open access
  • ccl
Journal Informaiton Journal Informaiton - close