Water producing gas wells may suffer from liquid loading and get killed or their water production may exceed the capacity of the water handling facilities. Just closing off the water producing zone may be unacceptable if they have a large contribution to the gas production. A near well bore chemical treatment using a polymer solution is an option to reduce the water production and maintain the gas production. Once adsorbed to reservoir rock, the polymer may significantly reduce the relative permeability to water in the near well bore area.
Hundreds of gas wells of the Nederlandse Aardolie Maatschappij (The Netherlands) suffer from water production. A simulation study using a radial single well model was carried out to look after the feasibility of a treatment.
The study shows that a treatment based on reduction of the water relative permeability causes a choke effect: both the water and gas flow rates are reduced instead of only the water rate. Moreover, the benefits of a treatment are tempered because of a clean-up effect after injection of the chemicals. A reduction in the water/gas ratio by a factor 2 requires a reduction in the water relative permeability by at least a factor 10.
A well which was killed due to liquid loading at a high water/gas ratio and with a high contribution to the gas production by the water producing interval is a suitable candidate for treatment.
A treatment may also be considered for a well of which the water production exceeds the capacity of the water handling facilities. Provided that the flowing tubing head pressure can be significantly lowered, the loss of gas production from the water producing zone can be compensated by increased gas production from the other intervals.
Hundreds of gas wells of the Nederlandse Aardolie Maatschappij (The Netherlands) suffer from water production, which leads to liquid loading and eventually stop the gas production. One of the possibilities to revive the wells is to carry out a chemical treatment in the near well bore region using relative permeability modifying systems. Relative permeability modifying systems reduce the water relative permeability curve significantly while leaving the gas relative permeability unchanged as much as possible1,2. Hence, such treatments aim to reduce the water to gas production ratio (WGR) so that the well can come back on production. A feasibility study was carried out to screen potential candidate wells for a treatment.
Two candidate wells were selected for which the feasibility study was carried out. These wells were URE-102 of the Ureterp Field and well MAR-101 of the Marum field. In both cases water production results from a rising water table, combined with water coning. For well URE-102 this will cause liquid loading and dying of the well. For well MAR-101 it will lead to restriction of the gas production due to insufficient water handling capacity. As in both cases the water-producing lower interval is a major contributor to the total gas production of the well just closing off the water producing interval is unacceptable.
The feasibility study was based on reservoir engineering simulations, using a radial single well model. Apart from conclusions on benefits for the two candidate wells guidelines were obtained to judge whether a well is a suitable candidate for a treatment. In this paper, the model and the results of the study are discussed.
Well URE-102 started production in 1978. The main data are listed in Table 1. Well URE-102 has seven intervals, of which the bottom one has been mechanically shut-off during the mid nineties because it was watered-out. The next lowest one (interval 6, Table 2) has recently shown an increase in water production, which will lead to liquid loading. During mid nineties, this interval contributed by 40% to the well's gas production (Table 2). Treatment of interval 6 will be the subject of the feasibility study for this well.