Abstract
Industry testing procedures such as ANSI/API 13B-1 describe a method for measuring fluid loss and studying filter-cake formation against a medium of either a filter paper or a porous disc, without giving information about potential formation damage. Considering the thickness of the discs, it may also be possible to extend the method to gain an insight into aspects of formation damage. A new experimental set-up and methodology was created to evaluate changes to the porous discs after HTHP testing to generate insight into signs of formation damage, such as changes in disc mass and permeability. Such measurements were enabled by placing the disc in a cell, which allowed for reverse flow of fluid to lift off the filter-cake. Experiments were conducted with different drilling fluid compositions to evaluate the use of the new methodology. The first test series showed consistent changes in disc mass as a function of the additives applied into the fluid. The data yield insights into how the discs are sealed and to which degree solids, fibers or polymers are entering the discs. A second series of tests were set up to extend the procedure to also measure changes in the disc’s permeability to air and water. The results showed that there was a positive correlation between changes in disc mass and changes in permeability. The conclusions are that the methodology may enable identifying signs of formation damage and that further studies should be conducted to optimize the method.
Highlights
Different types of lost circulation materials (LCMs) are available for preventative or reactive treatment of fluid loss using procedures such as ANSI/API 13B-1 [1]
The inclusion of additional procedures to those described in ANSI/API 13B-1 yielded information relevant to obtaining a better understanding of fluid loss and giving an insight into how various drilling fluid compositions seal permeable formations and how they may impact future reservoir permeability
By extending the testing procedure with (i) a moisture analyzer and (ii) reverse flow equipment and a procedure for reverse flow and breaker fluid application it was possible to measure the increases in disc mass accurately
Summary
Different types of lost circulation materials (LCMs) are available for preventative or reactive treatment of fluid loss using procedures such as ANSI/API 13B-1 [1]. In 2015, Alsaba et al [12] studied lost circulation materials of different shapes and their ability to seal fractures up to 2000 μm They concluded that PSD had a significant effect on the seal integrities, and in particular the D90 value. 2019 [17] conducted experiments with long-term (14 days) static aging of drilling fluids and testing of fluid properties including filtration behavior and formation damage tests on sandstone samples and reservoir rock They concluded that lower solids content in the drilling fluid would result in a slower build-up of the filter-cake, allowing for a higher amount of fluid filtrate invasion to occur. The introduction of a moisture analyzer to precisely measure the mass change of the discs may be such a cost-effective method for identifying formation damage
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