Study On Anti - Collapse Technology Of Horizontal Well Drilling Fluid In Longmaxi Formation Of Changning,

Horizontal well technology is one of shale gas exploration and development of key technologies, and drilling horizontal wells in technology, especially in borehole stability of shale gas drilling technology is shale gas technology research focus in recent years, long-term horizontal wells cost constraints and develop the core benefits and difficulties. The existence of shale gas horizontal drilling long horizontal section collapsed during the problem, the use of oil-based drilling fluid is used as a drilling fluid, but the higher cost of oil-based drilling fluid, affecting the development of shale gas drilling efficiency.This paper selects Changning district Longmaxi shale outcrop as the research object, the first use of physical and chemical analysis and X-ray diffraction analysis of the basic physical characteristics of shale, and then analyzed the mechanism of induced collapse combination shale rock mechanics, clarified shale block and suppress anti-collapse mechanism limits proposed to block water gravity and capillary pore water to prevent transfer of hydrostatic pressure point of view. The experimental study of the effects of the mineral composition of the clay shale hydration and anti-swelling regular categories shale hydration inhibitor law expanded clay crystal layer, then collapse pressure drilling shale formations have been studied, and the pressure to collapse, collapse cycle optimization method for drilling, including the optimization of drilling fluid components, optimized drilling fluid density optimize the drilling position, optimizing drilling long horizontal section of the cycle and so on.Through the mechanism and cause the collapse of shale sloughing mechanism, achieved the following understanding:(1) Longmaxi total shale clay minerals are relatively low, mainly in the non-expanded mineral illite, mixed with a small amount Eamonn layer, shale hydration expansion weak, weak structural surface shale exist and lead to micro-pore pressure transmission crack propagation, fracture shale dispersion, resulting in lower overall strength of shale is the main cause of damage.(2) State of presence of water in the shale has bound water and free water in two forms, is a combination of water suppression solve part, blocking only solve part of the free water, free water and part of the water and capillary water including gravity to0. lμm pore size limit less than0.1μm capillary water is not passed, but by combining water, bound water can not pass the hydrostatic pressure, so long as the transfer from block to block hydrostatic pore water can all shale into capillary pore water and the boundaries of the following combination of porosity water that can theoretically prevent hydrostatic transfer.(3) Ability to inhibit shale and shale inhibitor related to the content of montmorillonite, smectite content increases with the majority of inhibitors inhibit diminished capacity, the ability to inhibit potassium silicate not affect the content of montmorillonite.(4) Shale bedding structure and micro-fracture it petrography and rock mechanics presents the macroscopic and microscopic features of elastic anisotropy and strength anisotropy, and therefore there is an optimal deviation across the unstable layer. (5) Microfracture channel shale is the main transmission channel pressure, well-week stress transfer and mass transfer process can reduce the rock strength make certain stabilization period, research Longmaxi easily collapse shale formation collapse collapse cycle combined cycle chart, oil-based drilling fluids sloughing cycle inhibition strong long strong blocking of water-based drilling fluid sloughing cycle, only within the sloughing cycle through the formation, and completed the task completion within the optimal time.