JIP Proposal - Wettability Modifiers for Condensate Banking Reduction
Productivity in wells producing gas-condensate can be impaired by near-wellbore ‘banking’ of the liquid condensate. Injecting a chemical to increase the condensate relative permeability may improve well deliverability. Eugene Balbinski of ECL Technology (eugene.balbinski@ecqc.com) summarises results from a scoping DTI OG-MRP study and outlines an ACHARR approved JIP proposal to investigate wettability modifying chemicals that might mitigate condensate banking effects. The OG-MRP study was undertaken by Nicola Sargent and Andrew Cable (ResLab UK – formerly ECL Technology), and Jeff Masters (ECL Technology). For further information on the JIP proposal contact Alan Wilcockson (alan.wilcockson@ecqc.com, +44 (0)1491 415419) of ECL Technology.
Introduction
Substantial hydrocarbon reserves remain in UKCS gas-condensate fields. Well productivity is often significantly reduced by liquid condensing around producers, impairing further production – this is known as ‘condensate banking’. Increasing condensate relative permeability in the near-wellbore region by wettability alteration may improve the overall deliverability of the well. The application of fluorochemicals to do this is one technique which has been considered.
Figure 1: Schematic Showing Liquid Condensing Around Producing Well
Earlier Work
Tang and Firoozabadi (Reference 1) identified polymers that altered wettability from strongly liquid-wet to intermediately ‘gas-wet’ in dry Berea and Kansas chalk cores at connate brine saturation. Gas and oil relative permeabilities were measured at pressure gradients between 0.1 and 0.3 psi/cm on treated and untreated cores. For the treated core both gas and oil relative permeabilities increased with pressure gradient systematically. As the pressure gradient increased from 0.1 to 0.3 psi/cm in the treated core, the residual oil saturation decreased from 15% to 4%. No decrease was observed in the untreated core.
DTI OG-MRP Work
A short OG-MRP scoping project identified five potentially suitable chemicals for testing in the laboratory. One of these chemicals is currently used in the North Sea, the others are used in applications outside the oil industry, typically as water and oil repellents for porous surfaces such as concrete. Gas-condensate fields often have a high temperature, and therefore suitable chemical agents must have long term thermal stability. Generally available water soluble fluorosurfactants are expensive and in short supply. In contrast, all of the chemicals identified in the scoping project can be supplied in industrial quantities and samples are available for laboratory testing. The cost of the chemicals varies considerably from £1/Kg to £150/Kg. However, the concentration required also varies considerably. All of the chemicals meet basic Health and Safety and environmental requirements.
Joint Industry Proposal
An ACHARR approved Joint Industry Project Proposal focuses on two specific aspects of the chemical treatment required to achieve an appropriate wettability modification. The first of these relates to the economics of the process, and will be addressed through simulation studies using ECL Technology’s in-house compositional simulator, followed by an economic analysis based on the resulting production profiles. A laboratory programme, to be undertaken in parallel with the simulation studies by ResLab UK, would test the suitability of a number of potential wettability modifiers (which might include, but need not be restricted to, chemicals that were screened in the DTI study described above).
Project Benefits
The benefits from the project will be
- Determination of economic applicability of the use of wettability modifiers to reduce condensate banking.
- Development of a method for analysing the benefits of chemical treatment and its economic implications.
- Identification of simple screening criteria for application of chemical treatment to the near well bore region.
- Identification of chemicals to alter wettability to reduce condensate banking.
Project Workscope
Numerical simulations would be used to address the following:
- How large a region around the well bore needs to be treated to give a significant benefit, assuming the treatment modifies the relative permeabilities as reported in Reference 1?
- How sensitive is the treatment to the assumed shape of the relative permeability curves? Is the treatment still economic if the relative permeabilities are more linear, as might be expected at the high flow rates typically encountered near the well bore?
- How long would the alteration in wettability have to last for the treatment to deliver financial benefits?
The following laboratory tests are envisaged:
- Temperature stability
- Brine compatibility
- Concentration of chemical -The concentration of each chemical required to produce a wettability alteration will be measured. A short dry Clachach core will be saturated with a known concentration of each chemical and the wettability measured by an Amott test.
- Effectiveness of treatment on core in the presence of connate brine - A short core will be flooded to connate brine saturation with nitrogen before flooding with one pore volume of each chemical at a concentration identified in the previous section. The wettability will then be measured by an Amott test.
If your company is interested in being a sponsor, of if you would like more information on this JIP proposal please contact Alan Wilcockson at ECL Technology (alan.wilcockson@ecqc.com, +44 (0) 1491 415419).
Reference
- “Relative Permeability Modification in Gas-Liquid Systems Through Wettability Alteration to Intermediate Gas-Wetting.” G.Q. Tang and A. Firoozabadi, SPE 62934, presented at the 2000 SPE Annual Technical Conference and Exhibition held in Dallas, Texas, 1-4 October 2000.