Summary
A discussion about horizontal foam-flow behavior in pipes and annular geometry under elevated pressures and temperatures is presented. The study is empirically based and covers the effects of foam quality, foam texture, pressure, temperature, and geometry of the conduit on the rheological response of foams.
Introduction
The use of lightweight fluids in drilling operations is becoming common practice worldwide. These fluids are normally used to induce underbalanced conditions (i.e., to keep the wellbore pressure below the formation's fluid pressure) while drilling in low-pressure reservoirs. This diminishes formation impairment from drilling fluid, enhancing productivity. It also is used to overcome operational difficulties such as stuck pipe and loss of fluid circulation. Other benefits include the reduction of drilling time owing to increased rate of penetration, less bit wearing, and the ability to handle fluid invasion.
Among the numerous types of lightweight fluids used in drilling operations, foam appears as one of the most widely used. This is mainly because foam generates very low equivalent circulating densities while exhibiting good lubrication and hole-cleaning capacity, especially in vertical wells. It also offers a better control over the flow behavior of the phases involved within the well.
To achieve success in drilling operations under this scenario, the understanding and design of properties affecting borehole hydraulics become major issues. Predictive models, chiefly for pressure profile, become even more imperative by the fact that common tools used for logging while drilling do not work properly when lightweight fluids are used, especially in offshore operations. Based on this, it is clear that the rheological characteristics of this compressible non-Newtonian fluid must be understood fully.
Several researchers1-3 have studied foam-flow behavior in pipes in the past. However, there is no general agreement on the rheological description of the foam. The analysis of foam-flow behavior is rather difficult because of the number of variables involved, such as compressibility, flow geometry, foam generation, quality (ratio of gas-phase volume to foam volume), liquid- and gas-phase properties, slippage at the conduit's wall, and non-Newtonian behavior. It becomes even more challenging when annular flow takes place. Therefore, this study focuses on the experimental investigation of pipe and annular foam flow under elevated pressures and temperatures, with the objective of gaining a better understanding of how different variables affect the flow of this complex fluid.
Capillary Viscometry.
When a rheogram for a non-Newtonian fluid is available, it is possible, at least in principle, to predict the laminar-flow properties of such a fluid in conduits of simple cross section. The flow curve for a fluid can be rigorously and easily derived from pressure-drop and flow-rate data obtained with a capillary-tube or pipe viscometer of diameter D and length L.
