Summary The effect of pipe diameter on liquid-loading initiation has been investigated experimentally with pipes having internal diameters of 5.1- (2-) and 10.2-cm (4-in.). Two-phase-flow parameters, such as pressure gradient and liquid holdup, were measured. Flow characteristics were determined by visual observation with a high-speed video camera. Critical gas-flow rate for liquid-loading initiation was identified, and comparisons between the two pipe diameters were presented. The critical superficial-gas velocity corresponding to the minimum pressure gradient was found to be faster for the smaller diameter. When the comparison was carried out in terms of mass-flow rates, critical flow rate for liquid loading in a 5.1-cm (2-in.) pipe was less than that in a 10.2-cm (4-in.) pipe. This verifies the use of velocity strings to extend the production life of the gas wells. Additionally, comparison of the data with available mechanistic-model prediction showed significant discrepancies. Possible reasons for these discrepancies are discussed.

The effect of pipe diameter on liquid loading initiation has been experimentally investigated using 2-in and 4-in pipe diameters. Two-phase flow parameters such as pressure gradient and liquid holdup were measured. Flow characteristics were determined by visual observation using a high speed video camera. Critical gas flow rate for liquid loading initiation has been identified and comparison between the two pipe diameters is presented. The critical superficial gas velocity corresponding to the minimum pressure gradient is larger for the smallest diameter. When the comparison is carried out in terms of mass flow rates, critical flow rate for liquid loading in 2-in pipe is smaller than that in 4-in. pipe. This supports the use of velocity strings to extend the production life of the gas well. Additionally, comparison of the data with available mechanistic models prediction shows significant discrepancies. Possible reasons for these discrepancies are presented.

The deposition of scale in the near-well formation and production string can result in a significant decrease in well productivity. Properly designed scale inhibitor squeezes can successfully prevent scale deposition and extend well performance. Even though most wells in the Tengiz field produce virtually water free oil (less than 1% watercut (WC)), inorganic scales have been observed in many of these wells. Frequent acid stimulations are required to maintain the optimum well performance. An extensive research project was initiated to reduce the need for frequent acid treatments and still maintain well deliverability at sustained rates. To identify an effective scale inhibitor product, inhibitor-brine compatibility testing and dynamic tube-blocking performance testing were conducted. Field application of the selected inhibitor in both low and high rate wells has verified the effectiveness of the squeezes. Treatment with the scale inhibitor attained sustainable well productivity and delayed the need for subsequent acid stimulation treatments. This paper will share the best practices in scale inhibitor design, inhibitor selection, identification of well candidates, the execution and post treatment surveillance stages. Case studies shown to illustrate the performance of scale inhibitor squeezes in Tengiz.

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