Study On Mechanical Integrity Of Fracturing Cement Ring In Shale Gas Horizontal Well

Owing to its exceptionally abundant quantity of resource and tremendous developing potential, shale gas has become a new highlight of global unconventional gas development. Due to the compactness with ultra-low permeability of its reservoir, drilling exploitation by horizontal well and being exploited by fracturing has been on a worldwide consensus. In the process of fracturing by horizontal well, we have to proceed from mechanical integrity of cement sheath of the horizontal well and conduct research on the well cementation interface at the fracturing section to design a centering guiding device for improving the quality of well cementation in order to ensure the formation of good seamed web to successfully transform the shale reservoir, avoidance of inter-fluid-channeling between fracturing sections to enhance the construction ensemble and to assure the mechanical integrity of cement sheath to prevent shale gas horizontal well from cement channeling during large-scale staged fracturing to eventually achieve the subsection fracturing effects.This paper tries to establish a casing-cement sheath-formation mechanical model close to the actual conditions under the well during fracturing process by the horizontal well through studying the fracturing environment of staged fracturing, solve the theory resolution of concentric cement sheath under high internal pressure through elastic-plastic mechanics and set up eccentric cement sheath mechanical model through conjugate function defined hyperbolic coordinates and have it solved; study and analyze the damage mechanism of cement sheath to obtain cement sheath related mechanical performance parameters meeting execution conditions while the horizontal well is being eccentric; it applies elastic mechanics and fracture mechanics correlated theory to set up a stress extended model for well cementation interface in fracturing section, analyses the critical length of the second cement face under high-internal pressure fracturing and the factors of its impact on the critical length of cementing interface, proposes construction measurement assuring mechanical integrity of cement sheath and perforation distance required to prevent fracturing fluid channeling based on the aforementioned factors, designs a self-adaption drivepipe reduction centering guide to improve centering degree of cement sheath and gives model analysis on finite element mechanism of the key components of the centering guide to ensure its applicability during site operation.This paper systematically studies the mechanical integrity of cement sheath of shale gas horizontal well, presents a whole set of research methods of cement sheath completeness during high-internal pressure fracturing and gives the mechanical performance parameter of cement sheath required for 70MPa fracturing condition. This paper also introduces that the construction parameter and perforation clearance have been optimized in order to prevent channeling during fracturing to ensure the subsection fracturing effects and in the end it designs a self-adaption drivepipe reduction centering guide to improve centering degree of sleeves, which has significant implications on assurance of the mechanical integrity of cement sheath under large-scale fracturing done by shale gas horizontal well.