Study on tight plugging oil-based drilling fluid technology for shale in Anchang Block
Aiming at the problem that the shale of Wufeng-Longmaxi Formation in Anchang Block,Guizhou province is prone to collapse,based on the analysis of the mineral coposition and fabric characteristics of the representative shale in this block,the wellbore instability mechanism of the shale in Anchang Block is revealed,the wellbore stability technical countermeasures with multi-scale tight plugging and anti-collapsing as the core are put forward,and a set of tight plugging and anti-collapsing drilling fluid system suitable for this block is constructed.The analysis results of mineral fabric characteristics show that the shale formation in this block has the development of nano-cracks and micron cracks,the size of nano-cracks is less than 100 nm,and the size of micro-cracks and holes are mostly 0.1-2.6 μm,which has nano-micron multi-scale characteristics and weak hydration properties.The composite plugging formula optimized according to the particle size matching principle is composed of rigid superfine calcium carbonate and flexible plugging agent,the plugging effect is the best,which can effectively plug the pores and fractures of the Wufeng-Longmaxi Formation in Anchang Block.The constructed tight plugging anti-collapsing drilling fluid has a filtration loss of only 1.2 mL at 120℃and 3.5 MPa,which can reduce the permeability of shale by more than 90%and effectively prevent pressure transfer.The tight plugging and anti-collapsing drilling fluid is tested in Anye 7-8HF well.No collapse and leakage occurred in the drilling process,and the diameter expansion rate of the test well interval is only 2.64%.Therefore,the tight plugging and anti-collapsing drilling fluid can solve the problem of wellbore instability of the Wufeng-Longmaxi Formation in Anchang Block,and provide technical support for the efficient drilling and development of shale gas in Anchang Block.
万方数据
维普
