The collapse pressure of an open-hole wellbore and the initiation pressure of lost-circulation fractures directly determine the safe mud weight window during drilling.In light of the limitations of traditional lost-circulation pressure calculation methods under collapsed non-circular borehole conditions,as well as the neglect of borehole size effects,the displacement discontinuity method and a dual criterion(tensile strength and fracture toughness)were used to establish a numerical model,clarifying the characteristics of lost-circulation pressure variation for both circular and non-circular“cat ear”collapsed boreholes.The multiple initiation positions and deviation characteristics of lost-circulation fractures in elongated collapsed boreholes and their effects on lost-circulation pressure were also investigated.Numerical simulation results indicate that the lost-circulation pressure for both circular and non-circular“cat ear”collapsed boreholes exhibits a size effect.However,the lost-circulation pressure of a purely“cat ear”-shaped borehole does not differ significantly from that of a purely circular borehole.For small-sized boreholes,the lost-circulation pressure is governed by fracture toughness and is markedly influenced by size,whereas for large boreholes,fracture initiation is governed by tensile strength and the size effect is weaker.As the “cat ear” borehole elongates and the local radius at the initiation point increases,the mud weight window gradually widens.Axial elongation of the “cat ear” borehole causes lost-circulation fractures to deviate from the maximum principal stress direction,leading to four fracture initiation points around the borehole and the formation of an X-shaped lost-circulation fracture pattern.This study provides reference for addressing lost-circulation issues in collapsed open-hole wellbores during drilling.
LI Shuai
,
XU Jiangwen
,
WANG Mingxing
,
GONG Jie
,
CHEN Xi
,
FU Haifeng
,
YAN Xingming
,
QIAN Fengxue
. Numerical simulation of lost-circulation fracture initiation in collapsed wellbores[J]. Special Oil & Gas Reservoirs, 2026
, 33(2)
: 159
-165
.
DOI: 10.3969/j.issn.1006-6535.2026.02.018
[1] 李文哲,于兴川,赖燕,等.深层脆性页岩井钻井液漏失机理及主控因素[J].特种油气藏,2022,29(3):162-169.
LI Wenzhe,YU Xingchuan,LAI Yan,et al.Mechanism and main controlling factors of drilling fluid loss in deep brittle shale wells[J].Special Oil & Gas Reservoirs,2022,29(3):162-169.
[2] FURUI K,FUH G F F,MORITA N.Casing-and screen-failure analysis in highly compacting sandstone fields[J].SPE Drilling & Completion,2012,27(2):241-252.
[3] 朱亮,张春阳,楼一珊,等.两种漏失压力计算模型的比较分析[J].天然气工业,2008,28(12):60-61.
ZHU Liang,ZHANG Chunyang,LOU Yishan,et al.Comparative analysis of two calculation models for leakage pressure[J].Natural Gas Industry,2008,28(12):60-61.
[4] CARTER B J.Size and stress gradient effects on fracture around cavities[J].Rock Mechanics and Rock Engineering,1992,25(3):167-186.
[5] 罗天雨.水力压裂多裂缝基础理论研究[D].成都:西南石油大学,2006.
LUO Tianyu.Research on the basic theory of multi-fracture hydraulic fracturing[D].Chengdu:Southwest Petroleum University,2006.
[6] ITO T,HYASHI K.Physical background to the breakdown pressure in hydraulic fracturing tectonic stress measurements[J].International journal of rock mechanics and mining sciences & geomechanics abstracts.Pergamon,1991,28(4):285-293.
[7] ZHANG X,JEFFREY R G,BUNGER A P.Hydraulic fracture growth from a non-circular wellbore[C].ARMA-11-333,2011:1-12.
[8] ZHOU S.A program to model the initial shape and extent of borehole breakout[J].Computers & Geosciences,1994,20(7/8):1143-1160.
[9] JOLFAEI S,LAKIROUHANI A.Initiation pressure and location of fracture initiation in elliptical wellbores[J].Geotechnical and Geological Engineering,2023,41(8):4487-4506.
[10] ZOBACK M D,KOHLI A H.Unconventional reservoir geomechanics:shale gas,tight oil,and induced seismicity[M].Ambridge:Cambridge University Press,2019:233-262.
[11] CROUCH S L,STARFIELD A M,RIZZO F J.Boundary element methods in solid mechanics[J].Journal of Applied Mechanics,1983,50(3):704.
[12] DUNDURS J,MURA T.Interaction between an edge dislocation and a circular inclusion[J].Journal of the Mechanics and Physics of Solids,1964,12(3):177-189.
[13] OLSON J E.Fracture aperture,length and pattern geometry development under biaxial loading:a numerical study with applications to natural,cross-jointed systems[J].Geological Society London Special Publications,2007,289(1):123-142.
[14] TADA H,PARIS P C,IRWIN G R.The stress analysis of cracks handbook[M].New York:ASME Press,2000:52-54.
[15] 赖欢,沈仲辉,周雷,等.层理和临界长度对页岩水力压裂的影响研究[J].地下空间与工程学报,2023,19(增刊1):192-200,218.
LAI Huan,SHEN Zhonghui,ZHOU Lei,et al.Study on the influence of bedding and critical length on shale hydraulic fracturing[J].Chinese Journal of Underground Space and Engineering,2023,19(S1):192-200,218.
[16] LECAMPION B.Modeling size effects associated with tensile fracture initiation from a wellbore[J].International Journal of Rock Mechanics and Mining Sciences,2012,56:67-76.
[17] CHEN D,HE B L,WANG Y S,et al.Prediction of leakage pressure during a drilling process based on SSA-LSTM[J].Energies,2023,16(9):2608.
