عنوان مقاله [English]
Shale formation instability is the main source of many problems in drilling operation causing significant costs and wasting time. Prior to drilling, mechanical stresses are less than fracture resistance of rock and chemical conditions are in balance within the formation. Because of that, in this balanced situation, the formation is stable. However, shear, tensile and compressive forces vary around the wellbore after drilling operations. Under these conditions, the rocks around the well become unstable. On the other hand, while the formation contacts with drilling fluid, chemical interactions occur, one of possible reasons for the wellbore instability. Hydraulic pressure transmission and osmotic pressure are the main mechanisms of shale formation instability. Thus it is very vital to delay the pore pressure increase surrounding the well. This can be achieved by adding various salts and applying different types of nano-particles or polymers to block the shale pores to improve the shale membrane properties. In order to prevent consequential problems associated with shale formations, it is necessary to study the formation characteristics and evaluate changes occurred due to rock-fluid interaction. Hence, in this paper, the field equations governing the problem have been derived based on the linear chemo-poroelastic theory. Since Diffusion equations are mainly fully coupled, therefore by using analytical/ numerical methods, these equations have been decoupled and solved finally. The simulation results show that the proposed model can appropriately simulate the pore pressure transmission test (PPTT) and shale formation behavior contact with drilling fluid.
. Sherwood J. D., “Biot poroelasticity of a chemically active shale,” Proc. R. Soc. London, 440, p. 365, 1993 . Biot M. A. “General theory of three-dimensional consolidation,” J. Appl. Phys., 12, p. 155, 1941.##
. رحیم زاده کیوی، ا.، "شبیهسازی پایداری دیواره چاه دارای شیل و مقایسه با نتایج آزمایشگاهی،" پایاننامه کارشناسی ارشد دانشگاه صنعتی امیرکبیر، 1392.##