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Maintaining wellbore stability involves significant challenges when drilling in low-permeability reactive shale formations. In the present study, a non-linear thermo-chemo-poroelastic model is provided to investigate the effect of chemical, thermal, and hydraulic gradients on pore pressure and stress distributions near the wellbores. The analysis indicates that when the solute concentration of the drilling mud is higher than that of the formation fluid, the pore pressure and the effective radial and tangential stresses decrease, and v. v. Cooling of the lower salinity formation decreases the pore pressure, radial and tangential stresses. Hole enlargement is the combined effect of shear and tensile failure when drilling in high-temperature shale formations. The shear and tensile damage indexes reveal that hole enlargement occurs in the vicinity of the wellbore at an early stage of drilling. This study also demonstrates that shale wellbore stability exhibits a time-delay effect due to changes in the pore pressure and stress. The delay time computed with consideration of the strength degradation is far less than that without strength degradation. [ABSTRACT FROM AUTHOR]

Liquid invasion is an important transport phenomenon in many geophysical and environmental applications. A new capillary model considering boundary effect is proposed to reveal its mechanism. The boundary fluid layer not only reduces the effective flow radius, but also changes the viscosity of fluid. Thus the capillary force and viscosity resistance increases, however, the increase of capillary force is faster than that of viscosity resistance, therefore the invasion front arrives at the critical distance earlier. [ABSTRACT FROM AUTHOR]

During the development of oil field, well operation fluids will inevitably invade the formation, and insoluble is produced when contaminant ions contained in operation fluids react with formation fluids, which will easily plugs the pores, consequently affecting the flow of formation fluids. It is of remarkable significance for formation damage evaluation to study the laws of contaminant ions transportation and distribution near wellbore. In this study, the characteristics of high-speed percolation and contaminant ions diffusion near wellbore are reasonably considered, and then we established the non-Darcy flow reaction-diffusion equations, from which the contaminant ions distribution and transportation will be illustrated, thereby, the effects of pollutants migration and reaction on porosity and permeability are further studied. Thus, the newly developed model can provide theoretical basis and practical reference for plug removal. [ABSTRACT FROM AUTHOR]

In gas horizontal drilling, the gas with cuttings will go through the annulus at high speed which will lead strong erosion to the drill tools. This paper proposes a cuttings-carried theory and modified the critical cuttings-carried model for the gas-solid flow. Meanwhile, the erosive energy is obtained through simulating the gas-solid mixture in different conditions. The study result has positive significance on the determination of reasonable injection volume by optimizing construction parameters of horizontal well in gas drilling. [ABSTRACT FROM AUTHOR]

A set of surface equipment for monitoring the parameters of fluid and pressure while drilling was developed, and mathematical models for gas reservoir seepage and wellbore two-phase flow were established. Based on drilling operation parameters, well structure and monitored parameters, the wellbore pressure and the gas reservoir permeability could be predicted theoretically for underbalanced horizontal drilling. Based on the monitored gas production along the well depth, the gas reservoir type could be identified. [ABSTRACT FROM AUTHOR]

We developed a new model for fluid movement around the wellbore by introducing a Dirac function, which simplifies a water-injection well as a point source. The effect of porosity on the reaction and diffusion of contaminant ions is also taken into account in the model, making it more reliable in theoretical prediction. [ABSTRACT FROM AUTHOR]