Study On Deliquification Technology Of Horizontal Wells In Daniudi Of Low Permeability Gas Field

Horizontal well development has gradually become the main method to exploit Daniudi of low permeability gas field in the Ordos Basin, owning to its larger drainage area and fully reservoir reconstruction.91 horizontal wells have been completed and put into operation just in 2012 only and 207 horizontal wells in all are planed to be completed during the 12th five-year-plan period, which account for more than 65 percent of total new wells. However, there exists a series of production problems in horizontal well in gas field of Daniudi for now, such as, on the one hand, a lower production, producing water, the larger tubing size, the complex well bore configuration, the serious slippage between gas and liquid, the widespread liquid accumulating and that the flowing law of gas-liquid two-phase in wellbore is complicated which lead to that it is difficult to predict the liquid holdup, the wellbore pressure and other flowing parameters; on the other hand, there exists a unclear understanding about liquid-carrying laws and essences in vertical tubing and inclined tubing of horizontal well and the calculation about the critical gas flow rate of carrying liquid is inaccurate, which have brought difficulties in the productivity proration of horizontal well in the early period and in the production performance analysis. Meanwhile, the widely used types of foam solvent which are applied to vertical wells in gas field of Daniudi present a poor performance of flowing back when utilized in horizontal ones. In other words, the success rate of foam drainage gas recovery is only forty percent. So it is urgent to develop a new foam scrubbing agent. Finally, gas-liquid two phase flowing law in the small tubing string is unclear, which lead to a lack of theory basis to analyze deliquification effect and define principles of choosing well of velocity string. In this paper, a series of studied on theories and engineering technologies were carried out as following.(1)The gas/water production characteristics of horizontal wells in Daniudi gas field were summarized and analyzed and cumulative water-gas ratio curves is classified, which provide basic parameters for choosing deliquification technology.(2)Multiphase pipe flow models widely used in gas and industry were evaluated by tested flowing pressure data of horizontal wells in Daniudi gas field. Correlations of liquid holdup under liquid load-up and unload conditions were proposed base on Gray model and Mukherjee-Brill model. A new combined model was established on the basis of revised liquid holdup correlations.(3)Comprehensively considering the effect of maximum droplet size difference, droplet size, and droplet encountering and coalescing, a new model for predicting the critical gas flow rate of liquid unloading in the vertical tubing was proposed based on gas phase kinetic theory. The reasons for the low critical gas rate of liquid load-up in Daniudi gas field were analyzed and pointed out. The new conception of sub-stable production was proposed.(4)Based on experiment data of droplet entrainment rate and liquid film thickness in inclined pipe tested by Paz et al.(1999), a mathematic model to predict circumferential liquid film thinkness of pipe was established, base on which a model to predict the critical gas flow velocity for continuously carrying liquid film upward is proposed. Considering the liquid unload widespread and has minor negative influence on well productivity in Daniudi gas field, minimum gas flow rate to keep sub-stable production was given from two phase tubing pressure performance.(5)By indoor experiments evaluation of the influence of salinity, condensate content and the methanol content on the performance of foam scrubbing agent, a new low-water-cut effective foam solvent was developed and is successfully used in horizontal wells.(6)Based on study of gas phase, liquid phase and gas-liquid two-phase flowing law in the velocity tubing string using experiment data of gas and water flowing tested by Orville Gaither et al.(1963). The method to design inner diameter and depth of velocity tubing was proposed, and field application was conducted, suitable production conditions for velocity tubing were also summarized.Theory innovations on droplet entrainment and predicting maximum thickness of inclined pipe are important development on complex multiphase flow. Technology innovations on foam drainage gas recovery and velocity string provides technical support for horizontal well exploitation in large scale in Daniudi gas field.