Study of optimum tubing size in Iraqi oil field.

This study represents Badra Oil Field which is located in the East of Iraq has been producing oil for seven years causing production to drop in many oil wells. In 2017 several low production wells switched to unstable performance in the field. It was clearly recognized that wells having almost similar completion design, PVT properties, perforation intervals and depths of production layers could perform in different modes. Most wells are completed with (5 ½ x 4 ½) inch and (5 ½ x 3 ½) inch tubing strings. Flow interruptions were accompanied by rapid reduction of wellhead temperature, the impossibility of taking samples and zero production rate on the flow meter. It was clearly defined that well switches over to gas. During some time after troubles have started, it was still possible to bring wells back to normal production by reducing the choke size. However, later on, as reservoir pressure was depleted, it was necessary to shut the wells for several days to pressure build-up in three production wells (X-1, X-2, and X-3). In search of a solution to that problem, it was decided to perform the wells performance analysis using Pipesim/2017 Ver.2 software. The main purpose of Nodal analysis conducted in Pipesim was problems identifying and finding the optimal solutions. Latest Well test data and test Separator measurements were used as reference points. One of the tasks was the identification of regularities in high production and low production wells. Analysis of modeling results conducted taking into account collocation of receiving modeling results with real wells behavior and exclusion of results that are not in line with common sense. Obtained results clearly show two categories of wells: low production with a rate of around (500) m3/d, and high production with a rate of (1000) m3/d. The main issue related to low production wells is gas slippage and liquid hold-up effect due to the low production rate for relatively large tubing. The low production rate in turn comes to poor well inflow due to reservoir pressure depletion. For high production wells, the main issue is the choking effect created by the lower part of the tubing string (3 ½) inch and (4 ½) inch depending on the well's completion. This is reflected by the impossibility of reaching the target Flowing-Bottom Hole Pressure (FBHP) (200) bar. FBHP on most high production wells is higher than the target (200) bar, but this effect disappears after a while due to a reduction in reservoir pressure and production rate. The final recommendation for new wells with low production and wells after work over is to install (3 ½) inch tubing from top to bottom with Cut to release production packer where packer installation is necessary. [ABSTRACT FROM AUTHOR]