The interaction between shale bedding planes and fluids significantly weakens their structural integrity,profoundly affecting borehole stability in shale reservoirs.However,traditional analyses often overlook fluid in...The interaction between shale bedding planes and fluids significantly weakens their structural integrity,profoundly affecting borehole stability in shale reservoirs.However,traditional analyses often overlook fluid intrusion from the borehole into the bedding planes,leading to an inaccurate understanding of the mechanisms behind shale deterioration and inadequate guidance for drilling engineering design.This study models the process of drilling fluid permeating bedding shale through fluid intrusion experiments.It evaluates how forces acting on the bedding plane and the drilling cycle affect strength evolution,deriving rules governing changes in the mechanical parameters of both the shale matrix and the bedding planes.We developed a borehole stability calculation model that incorporates bedding plane considerations by integrating the established rules for mechanical parameter changes.The model analyzes the effects of the bedding plane,well inclination angle,wellbore azimuth angle,bedding plane inclination angle,and drilling cycle on the collapse pressure and collapse area with different types of drilling fluids.The results indicate that the presence of bedding planes significantly influences borehole stability.Therefore,both matrix and bedding plane damage should be considered to accurately calculate the collapse pressure and area.The well inclination angle,wellbore azimuth angle,and bedding plane inclination angle also impact borehole stability.It is recommended that the horizontal section of the wellbore be drilled in the direction of the minimum horizontal in situ stress.As the drilling cycle extends,the collapse pressure gradually increases,with the largest increase occurring in the direction of the minimum stress.Additionally,the increase in collapse pressure is greater when using water-based drilling fluid than when using oil-based drilling fluid.These findings provide theoretical insights for drilling engineering design in bedding shale environments,aiming to enhance borehole drilling safety.展开更多
Reservoirs can be developed in the sediment gravity flows.However,high quality reservoirs are found widespread in sediment gravity flows of Gangzhong area,Huanghua depression,Bohai Bay Basin,East China.Characteristics...Reservoirs can be developed in the sediment gravity flows.However,high quality reservoirs are found widespread in sediment gravity flows of Gangzhong area,Huanghua depression,Bohai Bay Basin,East China.Characteristics and formation of these reservoirs are key problems to be solved.Through comprehensive analysis of thin section petrography,scanning electron microscopy and X-ray diffraction,two distinct rules were obtained.1) These high quality reservoirs have apparent characteristics:lithology consists mainly of medium-fine grained sands; moderately-well sorted and rounded; intergranular pores dominating >70% of the entire pores,surface per unit pore volume reaches 15%; average porosity is 21% and average permeability is 55×10-3 μm2.2) Types of sedimentary microfacies and dissolution strongly control on the formation of high quality reservoirs.Main channels and sandy braided bars have the best reservoir properties.Because that sediments are mainly medium-fine grained sands in high-energy environments.The favorable primary porosity and permeability may promote calcite cementation and help to produce more secondary pores.Besides,at the depth of 2500-3200 m,basically matching threshold of oil generation,organic acid expelled when organic matter became mature,and H+ released during clay mineral transformation.These both result in the dissolution of calcite cements and create large volume pores,then physical properties improve correspondingly.Moreover,deep hydrothermal fluid intrusion may also have impacts on the development of secondary pores.展开更多
基金supported by the Heilongjiang Provincial Natural Science Foundation of China(Grant No.LH2022E026).
文摘The interaction between shale bedding planes and fluids significantly weakens their structural integrity,profoundly affecting borehole stability in shale reservoirs.However,traditional analyses often overlook fluid intrusion from the borehole into the bedding planes,leading to an inaccurate understanding of the mechanisms behind shale deterioration and inadequate guidance for drilling engineering design.This study models the process of drilling fluid permeating bedding shale through fluid intrusion experiments.It evaluates how forces acting on the bedding plane and the drilling cycle affect strength evolution,deriving rules governing changes in the mechanical parameters of both the shale matrix and the bedding planes.We developed a borehole stability calculation model that incorporates bedding plane considerations by integrating the established rules for mechanical parameter changes.The model analyzes the effects of the bedding plane,well inclination angle,wellbore azimuth angle,bedding plane inclination angle,and drilling cycle on the collapse pressure and collapse area with different types of drilling fluids.The results indicate that the presence of bedding planes significantly influences borehole stability.Therefore,both matrix and bedding plane damage should be considered to accurately calculate the collapse pressure and area.The well inclination angle,wellbore azimuth angle,and bedding plane inclination angle also impact borehole stability.It is recommended that the horizontal section of the wellbore be drilled in the direction of the minimum horizontal in situ stress.As the drilling cycle extends,the collapse pressure gradually increases,with the largest increase occurring in the direction of the minimum stress.Additionally,the increase in collapse pressure is greater when using water-based drilling fluid than when using oil-based drilling fluid.These findings provide theoretical insights for drilling engineering design in bedding shale environments,aiming to enhance borehole drilling safety.
基金Project(2006CB202300)supported by the National Basic Research Program of China
文摘Reservoirs can be developed in the sediment gravity flows.However,high quality reservoirs are found widespread in sediment gravity flows of Gangzhong area,Huanghua depression,Bohai Bay Basin,East China.Characteristics and formation of these reservoirs are key problems to be solved.Through comprehensive analysis of thin section petrography,scanning electron microscopy and X-ray diffraction,two distinct rules were obtained.1) These high quality reservoirs have apparent characteristics:lithology consists mainly of medium-fine grained sands; moderately-well sorted and rounded; intergranular pores dominating >70% of the entire pores,surface per unit pore volume reaches 15%; average porosity is 21% and average permeability is 55×10-3 μm2.2) Types of sedimentary microfacies and dissolution strongly control on the formation of high quality reservoirs.Main channels and sandy braided bars have the best reservoir properties.Because that sediments are mainly medium-fine grained sands in high-energy environments.The favorable primary porosity and permeability may promote calcite cementation and help to produce more secondary pores.Besides,at the depth of 2500-3200 m,basically matching threshold of oil generation,organic acid expelled when organic matter became mature,and H+ released during clay mineral transformation.These both result in the dissolution of calcite cements and create large volume pores,then physical properties improve correspondingly.Moreover,deep hydrothermal fluid intrusion may also have impacts on the development of secondary pores.
