Abstract
Throughout the last years, considerable efforts have been made to increase the quality of reservoir monitoring, as to improve managing and predictability. The quality improvement in reservoir management achieved with the acquisition of bottomhole data through the use of permanent downhole gauges, PDGs, is so remarkable[1,],[2,] that today the requisite of PDG installation, mainly in wet x-mas tree completions, is nearly out of question[3,] either for oil or gas producers or for water or gas injectors. Unfortunately, corresponding progress has not been attained with respect to the individualized flow measurement per well[4,], or better yet, per completion interval in a single well, despite the recent advances in technology available to this effect[5,],[6 ].
This paper presents results obtained through measurement of downhole flow rate and its correction to surface conditions from a well under commingled production zone. Earlier, Puntel [7,] presented a first case in Portuguese considering one completion zone with a well that has, between the completion equipments, two PDG Mandrels, one of them measuring pressure between string and casing; the other measuring the pressure within the production string. These PDGs are located almost at the same vertical depth, but are related to different flow areas, so that the pressure difference recorded between them can also be used to calculate the total flow rate. Furthermore, another typical installation provides access to two or more completed zones, allowing individual annular pressure measurements. This completion scheme also provides ICV[8,],[9 ] control, turning it possible to calculate individual zone contributions through almost the same methodology adopted to the one zone base case.
The flow rate is obtained by means of the Bernoulli equation[10,], assuming measurement of differential pressure between two flow sections with different cross sectional areas or otherwise, the Darcy-Weisbach equation[11,], referring to the pressure loss through long pipes with same cross sectional area. Thermodinamic functions as well as a simple calibration procedure provide volumetric flow rate correction from bottomhole to surface pressure and temperature conditions. Deviation from ideal behavior can indicate change in flow regime or, for instance, scale buildup[12 ] inside production tubing. Those techniques are feasible with high precision for single-phase liquid flow, a condition observed more frequently at bottomhole conditions. Field examples are provided to illustrate all presented cases.
