Mitigation of Formation Damage Caused by Chemical Overdosing in Water Shut-Off Treatments
Authors: Lakatos Istvan , Szentes Gabriella , Toro Maria , Karaffa Zsuzsa , Vago Arpad 
Published: February 2020

Reservoir Conformance Control (RCC) methods may significantly improve IOR/EOR technologies through reduced water production and profile correction. In the past decades, polymer gel methods were predominantly applied with these goals. However, recently the silicates in oilfields and microemulsions in gas fields are highly appreciated by the operators due to their outstanding features and environmental friendly character. That fact is well demonstrated by more than 140 jobs carried out in Hungary, Serbia, and Oman. Although, the statistical data of these projects are attractive (75% technical and 55% economic success), probably much higher profitability could be attained if not underdosing but optimal amount of chemicals were applied to avoid deterioration of well performance (well killing in extreme case). Unfortunately, overdosing might be often realistic because of limited information on wells to be treated. Consequently, developing any water shutoff methods must comprise techniques, which must be used to rehabilitate the productivity, permeability, injectivity. That question is practically not discussed in the literature.

Concerning the barrier formation kinetics and processes, the different methods can be subdivided into two groups: reversible and irreversible gelation techniques. The in-situ formation of polymer gels, whatever its types are, represent the latter one, viz. detrimental effect of chemical overdosing is hard to control even by strong oxidative agents. In contrast, the silicate methods using both external and internal pH control, the hard gel formed after placement, the formation damage can be mitigated by injection of strong alkaline solutions. Similarly, the microemulsion treatment based on phase inversion under reservoir conditions, the barrier (with 5000-10000 cP viscosity) can be disintegrated with post-injection of special organic solvents. These phenomena and processes are addressed with bulk phase studies and flow tests in sandstone cores. Independent parameters of these tests were the type of chemicals, concentration, temperature, and reaction time.

The experimental findings clearly demonstrate that the silicate lamps can be completely dissolved in bulk phase, and the detrimental effect in porous cores can be mitigated by 60-70% improvement of permeability in case of overdosing chemical treatments. Similarly, even more favorable data characterized the disintegration of microemulsion barriers using bulk and flow tests. Special advantages of these mitigation procedure are that environmentally friendly chemicals are used for alleviation of the unintended formation damage.

The experimental results proved that the different silicate and microemulsion methods are based on reversible barrier formation. Recognizing that fact, the design of treatment offers more engineering freedom to use not minimum, but optimum chemical load in treatments without jeopardizing the undersigned formation damage. Nevertheless, this happens, the operator has appropriate technology to eliminate the detrimental effects.