Performance evaluation on water-producing gas wells based on gas & water relative permeability curves: A case study of tight sandstone gas reservoirs in the Sulige gas field, Ordos Basin

An outstanding issue in the oil and gas industry is how to evaluate quantitatively the influences of water production on production performance of gas wells. Based on gas–water flow theories, therefore, a new method was proposed in this paper to evaluate quantitatively the production performance of water-producing gas wells by using gas & water relative permeability curves after a comparative study was conducted thoroughly. In this way, quantitative evaluation was performed on production capacity, gas production, ultimate cumulative gas production and recovery factor of water-producing gas wells. Then, a case study was carried out of the tight sandstone gas reservoirs with strong heterogeneity in the Sulige gas field, Ordos Basin. This method was verified in terms of practicability and reliability through a large amount of calculation based on the actual production performance data of various gas wells with different volumes of water produced. Finally, empirical formula and charts were established for water-producing gas wells in this field to quantitatively evaluate their production capacity, gas production, ultimate cumulative gas production and recovery factor in the conditions of different water–gas ratios. These formula and charts provide technical support for the field application and dissemination of the method. Study results show that water production is serious in the west of this field with water–gas ratio varying in a large range. If the average water–gas ratio is 1.0 (or 2.0) m3/104 m3, production capacity, cumulative gas production and recovery factor of gas wells will be respectively 24.4% (or 40.2%), 24.4% (or 40.2%) and 17.4% (or 33.2%).