Managed Pressure Drilling Technology:A Research on the Formation Adaptability

Existing pressure drilling technologies are based on different principles and display distinct characteristics in terms of control pressure and degree of formation adaptability.In the present study,the constant-bottomhole-pressure(CBHP)and controlled-mud-level(CML)dual gradient drilling methods are considered.Models for the equivalent circulating density(ECD)are introduced for both drilling methods,taking into account the control pressure parameters(wellhead back pressure,displacement,mud level,etc.)and the relationship between the equivalent circulating density curve in the wellbore and two different types of pressure profiles in deep-water areas.The findings suggest that the main pressure control parameter for CBHP drilling is the wellhead back pressure,while for CML dual gradient drilling,it is the mud level.Two examples are considered(wells S1 and B2).For S1,CML dual gradient drilling only needs to adjust the ECD curve once to drill down to the target layer without risk.By comparison,CBHP drilling requires multiple adjustments to reach the target well depth avoiding a kick risk.In well B2,the CBHP method can drill down to the desired zone or even deeper after a single adjustment of the ECD curve.In contrast,CML dual-gradient drilling requires multiple adjustments to reach the target well depth(otherwise there is a risk of lost circulation).Therefore,CML dual-gradient drilling should be considered as a better choice for well S1,while CBHP drilling is more suitable for well B2.

Coupled thermo-hydro analysis of steam flow in a horizontal wellbore in a heavy oil reservoir

A novel model for dynamic temperature distribution in heavy oil reservoirs is derived from the principle of energy conservation.A difference equation of the model is firstly separated into radial and axial difference equations and then integrated.Taking into account the coupling of temperature and pressure in the reservoir and wellbore,models for calculating distributions of the reservoir temperature,reservoir pressure,and water saturation are also developed.The steam injected into the wellbore has a more significant effect on reservoir pressure than on reservoir temperature.Calculation results indicate that the reservoir temperature and pressure decrease exponentially with increasing distance from the horizontal wellbore.The radial variation range of the pressure field induced by steam is twice as wide as that of the temperature field,and both variation ranges decrease from the wellbore heel to the toe.Variation of water saturation induced by steam is similar to the temperature and pressure fields.The radial variation ranges of the reservoir temperature and pressure increase with steam injection time,but rate of increase diminishes gradually.