oa Addressing two challenges of matrix acidizing in carbonate fields: High permeability contrasts and water mitigation

Context and objectives The dominant majority of the oil and gas reservoirs in the Middle East and in Qatar in particular are composed of carbonate porous media. Therefore, a better description of the heterogeneous carbonate porous media is a key challenge that will ultimately lead to efficiently unlock and develop new reserves. One of the main characteristics of carbonate rocks is their high reactivity in contact with hydrochloric acids. Therefore, matrix acidizing producer wells in carbonate formations is a common operational practice that helps to increase the permeability of the damaged or tight near wellbore region. One of the main objectives of matrix acid stimulation is to achieve a good zonal coverage with the acid, especially to stimulate hydrocarbon production from low permeability zones, especially in the presence of high permeability contrasts. However, field applications show that matrix acid stimulation leads often to an insufficient increase of permeability in the targeted region as well as an increase in water production from watered zones. Solution In this context, Qatar Petroleum and TOTAL are jointly investigating improved acid stimulation methodologies in carbonates. Within our testing facilities at Qatar Science and Technology Park (a member of the Qatar Foundation) and in liaison with TOTAL's research headquarters in France, we performed high pressure and temperature single and dual core flooding experiments over a range of four different carbonate rocks with different permeability and pore structures. Results Live and emulsified acids were used as well as Relative Permeability Modifiers (RPMs) and particle-laden diverters. Changes in permeability were measured in real time during the injection across the length of the cores. In addition, pre and post-injection micro-CT scanning allowed the visualization of different dissolution patterns (mainly dominant worm-holing). Changes in porosity induced by the chemical reactions were also deduced based on image analysis. We compared the response of different acid types and assess the impact of RPMs on brine and oil flow. Conclusions The test results will serve as a basis for elaborating new acid pumping sequences for well stimulation an also to benchmark different commercial and academic acid stimulation software. The results can be used to different applications such as carbon storage in heterogeneous carbonates.