Application of New Generation Technology to Horizontal Well Production Logging - Examples from the North West Shelf of Australia

Abstract

Abstract The main measurement objectives in production logging are to diagnose well production problems such as the inflow rates and entries of unwanted fluids, supply information for reservoir modeling and provide data to optimize the productivity of future and existing wells. Another important objective is to perform the measurements cost effectively. In a horizontal well fluid density cannot be measured by the gradiomanometer. Other sensors, such as the nuclear fluid densimeter which rely on a decaying radioactive source, are inaccurate (especially in heavy oil/water regimes), environmentally hazardous and only measure within the liner. Undulations in horizontal well trajectories can cause traps of gas and water to be created at the high and low points, and large changes in fluid holdup and velocity with changes in deviation as small as one degree. Such effects can confuse or even completely invalidate the spinner for flow rates. Fluid entries, including those which are unwanted, often occur over much longer sections than those usually found in vertical wells. Consequently, the temperature effects of such entries are often insignificant, thereby decreasing the value of the thermometer. The fluid flow regimes in horizontal wells can be one or a combination of stratified, bubbly and slug flow. This often invalidates the application of models developed for vertical wells. Hence the measurement objectives in horizontal wells frequently prove difficult or impossible to achieve by using traditional tool strings and interpretation techniques. The traditional mode of conveyance of production logging tool strings in a horizontal well is by coiled tubing, which can often be very expensive and make the costs prohibitive. The solution to the measurement problems is to employ technology which has recently been developed specifically to deal with the inadequacies of traditional sensors and interpretation techniques. The cost from rig time of employing such technology have been reduced by ensuring that all sensors are conveyed on just one tool string, thereby minimizing rig up and rig down tasks, and eliminating the necessity to pull out of the hole between logging runs. By employing tractors instead of coiled tubing the costs of conveying these sensors have been reduced further. This paper discusses the problems mentioned above, describes a methodology for solving them, and shows how this has been done successfully in wells in the North West Shelf of Australia. P. 511