Comparison of Measured and Predicted Pressure Drops in Tubing Predicted Pressure Drops in Tubing for High-Water-Cut Gas Wells Summary. A considerable number of deep >3000 m 10,000 A]) high-volume gas wells in northern Germany show signs of increasing water production (about 800X10-6 M3 /std M3 [135 bbl/MMscf). This paper presents results of tests in gas wells to measure the two-phase (gas/water) pressure drop i the tubing. Experimental data are evaluated and compared with the calculations from over 15 different pressure prediction schemes. Modifications proposed for some of the methods resulted in significantly improved predictions. Introduction In the past, the two-phase pressure drop in gas wells that produce free liquids has received relatively little attention produce free liquids has received relatively little attention in the literature, particularly gas wells that produce free water. For a long time, this was of no concern in the Federal Republic of Germany because there were no gas wells producing at high water cuts, at least not over an extended producing at high water cuts, at least not over an extended period. The start of free-water production in a gas well period. The start of free-water production in a gas well typically signaled the end of the well as a gas producer. This situation changed as more and more wells producing from the Rotliegendes formation went on line. At depths of 3000 m [10,000 ft] and more, this formation represents a major source of gas reserves for Germany. The upper Rotliegendes formation is composed of a sequence of numerous sand layers with intermittent shale breaks. The lower part contains the relatively thick and, in comparison with the overlying sands, rather uniform Haupt sandstone. In the East Hanover gas province, only the upper sands typically are gas-bearing, while the sand at the base is water-bearing even at the structurally highest positions. Fig. 1 shows the typical situation encountered positions. Fig. 1 shows the typical situation encountered in a Rotliegendes gas well. Conclusive evidence indicates that the lower water-bearing sand communicates with the upper gas sands in areas where seismic and geologic interpretations suggest major faulting. The result is a reservoir system consisting of a gas reservoir in excellent communication with an aquifer an order of magnitude larger than the reservoir. The Rotliegendes sands are highly stratified, with streaks of less than 1-md permeability next to streaks of 1,000-md or higher permeability. The initial Rotliegendes (appraisal) wells were all drilled through the gas/water contact and completed with a 13-cm [5-in.] liner for the lowermost string. A 13-cm [5-in.] liner cannot be centralized and is difficult to cement. Therefore, channeling behind the pipe is not uncommon. In the majority of the wells, more pipe is not uncommon. In the majority of the wells, more than one sand is perforated and production commingled. As a result, water problems are often observed very early in the life of a well. This does not mean, however, that the well will die soon thereafter, as illustrated in Fig. 2. This rather typical well experienced water breakthrough 6 years ago but continues to produce at rates above about 10X 103 M3/h [9 MMscf/D]. During this 6-year period, the well has produced in excess of 650X 106 M3 [24 Bscf). In the past, methods based on a single-phase model of the flow process were used for calculating tubing pressure losses. These methods underestimate the actual pressure loss. To forecast well deliverabilities and to optimize depletion from high-watercut gas wells, reliable two-phase pressure-drop correlations are needed to estimate the tubing pressure drop with reasonable accuracy and the advantages of lowering the wellhead pressure and of making operational changes (tubing-string optimization or gas lift). This work highlights investigations to identify correlations that would meet the above-mentioned requirements on Te baas of well test results for Rotliegendes gas wells producing at high water cuts. producing at high water cuts. Data Acquisition The data presented here were obtained from production tests and production control surveys. Such surveys are necessary for the reservoir engineer to plan production and to diagnose well problems; therefore, they are performed routinely. To have more reliable data on hand to performed routinely. To have more reliable data on hand to perform two-phase pressure-drop calculations, the perform two-phase pressure-drop calculations, the measurement effort of these routine operations was increased. Increased effort is necessary because during routine operations, not all parameters required to perform two-phase flow calculations are recorded; if they are recorded, some of the data typically lack the required accuracy. The following sections briefly describe the tested gas wells, the test types used to obtain the data, and the data. Note that volumes refer to German standard conditions, which are 0.1 MPa and 0C (1 atm and 32F) SPEPE p. 165