Discussion on formation mechanism of casing deformation in horizontal wells in deep shale gas of Luzhou area
The Luzhou area in the southern Sichuan Basin is rich in deep shale gas reserves,which makes it an important replacement field of natural gas resources after the middle and shallow shale gas in Changning and Weiyuan.During the development of the northern deep shale gas zone of Luzhou area,however,casing deformation happens frequently in horizontal wells,which has a significant impact on the fracturing construction of horizontal wells and restricts the efficiency of large-scale productivity construction of deep shale gas in this area.Casing deformation is generally believed to be caused by the slip of faults in the strata and its shear and compression effects on horizontal wells,but the casing deformation model based on this theory seldom matches the measurement data.In order to further clarify the mechanism of casing deformation and improve the casing deformation preventing and controlling effect,this paper mainly analyzes 18 horizontal wells with casing deformation in the Lu 203 well block.Based on multi-arm caliper logging,they are compared one by one from the aspects of casing deformation morphology,casing deformation horizon and plane fault development.Finally,two geological models of fault slip and bedding plane slip are established,and different characteristics of casing deformation in these two geological models are analyzed.And the following research results are obtained.First,the casing deformation induced by fault slip presents the following regularities.The casing deformation on the plane only occurs at the intersection of a horizontal well and a fault zone.The theoretical length of casing deformation should be within 10 m.The degree of casing deformation should be approximately symmetrical,with strong deformation in the middle and gradually weakening towards both sides.Second,most of the casing deformations in this area are beyond the predicted fault zones,and the deformation lengths and morphologies of some casing deformation segments do not conform to the characteristics of fault slip.Third,the bedding plane slip can induce multiple similar casing deformations.Under this mechanism,the length of casing deformation is equal to the distance between the wellbore and the slip plane,and the vertical distribution of bedding plane slip is consistent with the degree of bedding development.Fourth,bedding plane slip and fault slip have similar mechanical mechanisms,and the key parameter changes that induce fault/bedding plane slip during drilling and fracturing processes can be analyzed through three-dimensional Mohr circles.In conclusion,besides fault slip,bedding plane slip is another important mechanism that induces casing deformation in shale gas horizontal wells.The research results can provide theoretical guidance for the prevention and control of casing deformation during the large-scale benefit development of deep shale gas reservoirs.
Casing deformation in horizontal wellBedding plane slipFault slipMulti-arm caliper loggingMulti-level fault predictionDeformation lengthDeformation intensityMohr stress circle
国家科技期刊平台
NSTL
万方数据
维普
