Clay Shale Hydration Stability Studies

Shale borehole wall stability is one of the great problems that affect the development of drilling technology, and shale hydration is a key factor affecting borehole stability. This is due to Hydration which may cause shale swelling, rock strength descent, pore pressure increase and so on, easy to cause the collapse of the wall. By combining theoretical knowledge of many branchs of learning the thesis has researched the mechanism of shale hydration as well as its dominant factors thoroughly and deeply. the paper presents that controlling hydration stress is the key of inhibiting shale hydration of the shale, is to control the hydration expansion pressure.(1) Through analyzing the mineral composition, structure feature and physical feature of shale, clay shale hydration mechanism, draw hydration seriously affect borehole stability.(2) Through analysis of mechanism of the coupling of chemistry and mechanics of wellbore instability, research that hydration stress is one of the key factors of affecting wellbore stability of shale, and give several methods to determine hydration stress.(3) In the paper, through analyzing the inclined wellbore stress distribution about before and after the hydration, determine the impact of hydration on the mechanical properties of shale, give before and after the hydration mechanical model of the shale, as well as hydration diffusion model, choose the right strength failure criteria, give shale borehole collapse pressure and fracture pressure calculation model, the algorithm, research the impact of hydration on wellbore stability of shale strata.(4) This paper, through the case analyzes the law of shale sidewall moisture content, sidewall surrounding rock stress distribution rule, and analyzes the change law of the collapse pressure curve after clay shale hydration, draw some conclusions, form a theoretical method to predict borehole instability.