Detection of water or gas entry into horizontal wells by using permanent downhole monitoring systems

Abstract

With the recent development of temperature measurement systems, continuous wellbore temperature profiles can be obtained with high precision. Small temperature changes can be detected by modern temperature-measuring instruments, such as fiber optic distributed temperature sensors (DTS) in intelligent completions. Analyzing such changes will potentially aid the diagnosis of downhole flow conditions. In vertical wells, temperature logs have been used successfully to diagnose the downhole flow conditions because geothermal temperature differences in depth make the wellbore temperature sensitive to the amount and the type of fluids flowing in the wellbore. Geothermal temperature does not change, however, along a horizontal wellbore, which leads to small temperature variations in horizontal wells, and interpretations of temperature profiles become harder to make than those for vertical wells. For horizontal wells, the primary temperature differences are caused by frictional effects. Therefore, in developing a thermal model for producing horizontal wellbore, subtle temperature changes should be accounted for. This study rigorously derives governing equations for thermal reservoir and wellbore flow and develops a prediction model of temperature and pressure. With the prediction model developed, inversion studies of synthetic and field examples are presented. These results are essential to identify water or gas entry, to guide the flow control devices in intelligent completions, and to decide if reservoir stimulation is needed in particular horizontal sections. This study will complete and validate these inversion studies. The utility and effect of temperature and pressure measurement in horizontal wells for flow condition interpretation have been demonstrated through synthetic and field examples.