Investigation of waterflood improvement for heavy oil carbonate reservoirs - crude oil/brine/rock interactions

Water injection has been used in the oil industry for a long time. This oil recovery method is considered relatively inexpensive and water is easy to inject, even in hostile environments such as high pressure/temperature or deep reservoirs. Compared to other oil recovery methods, water injection received less attention because it was assumed that there were neither reactions nor interactions with the reservoir fluids or reservoir rocks. This meant that the water, being immiscible with crude oil, was simply regarded as a way to displace the trapped oil. However, the use of water injection as a natural wettability modifier has recently gained significant attention, due to the discovery of the importance of physico-chemical interactions between the crude oil compounds and the water composition. In this regard, the term smart water has been adopted for the idea of designing the injection brine composition in order to enhance oil recovery. Even though the alteration or modification of the composition of the injection water has been mentioned by various researchers, the findings and conclusions are not consistent. Whilst some laboratory and field applications have had successful outcomes, there are cases in which smart water was not found to make any significant difference. The goal of this research was to investigate if some of the suggested mechanisms behind the smart fluids injection would apply to carbonate reservoirs, with a special focus on heavy oils. Occurrence of rock dissolution, as a mechanism for oil production, has previously been documented. However, the reasons for its presence have not entirely been found or described. This research shows that dissolution occurs as a direct and strong effect of the flow of injected water in contact with the crude oil. This work describes the results of a comprehensive set of experiments to investigate the importance and the extent of rock dissolution during water injection in carbonate heavy oil reservoirs. In addition, the results of the experimental work performed in this research with smart waters demonstrate that a substantial additional amount of heavy crude oil can be obtained under secondary as well as tertiary injection of appropriately designed water composition. The findings from these experiments firstly revealed the generation of acidic water, which is derived from the interaction between injected fluids and crude oils. Further examinations showed that this acidic water is not detected by complex laboratory tests. Finally, it was also found that not all crude oils could generate the acidic water which is the cause of rock dissolution. In this work, practical analysis helped to elucidate the real importance of the crude oil/injection water interactions. The laboratory tests that are presented essentially provide an insight into the impact of the chemical interaction between crude oil and injection water with the rock. The results suggest that the chemical interaction between crude oil and injected water may be one of the main reasons for the increased efficiency in response to the use of the smart waters for the improvement of oil production. The mechanisms that trigger the oil production for the studied crude oils in carbonate reservoirs may be linked to both changes of wettability and effect of the rock dissolution

Dissolution of Rock During Smart Water Injection in Heavy Oil Carbonate Reservoirs by Natural Generation of Acidic Water

Smart waters have been studied for enhanced oil recovery in carbonate reservoirs, gaining significant attention from research groups and oil industry companies. However, there is a general consensus that the complexity of the fluids/rock system governs their effects, much fundamental knowledge is lacking, and many questions and uncertainties remain. For instance, the existence of rock dissolution in carbonate rocks, as a mechanism for oil production, has previously been documented. This work specifically focused on the interaction oil–brine–rock and its effect on rock dissolution. Carbonate rocks (limestones and dolomites), brines, and heavy crude oils were individually analyzed and then systematically mixed with each other to gain a comprehensive understanding of their interactions. Five heavy crude oils with different properties were tested under similar reservoir conditions (≈92 °C). Results revealed the generation of acidic water derived from the interaction between injected fluids and crude oils. Not all crude oils could produce acidic water, which is the cause of rock dissolution. This research suggests that the chemical interaction between crude oil and injected water may be one of the main reasons for the increased efficiency in response to the use of the smart waters for the improvement of oil production. Basic analyses that are presented here essentially provide an insight into the impact of the chemical interaction between crude oil and injection water with the rock. Finally, coreflood experiments were performed using a dolomitic core in order to monitor and verify the presence of dissolution during the flow of fluids. A basic crude oil was selected for this purpose. Effluent analysis, pH measurements, and permeability evaluations corroborated the influence caused by smart water injection as acidic water in contact with the rock. The findings of these experiments prove that is possible to predict and control the occurrence of the dissolution, observing interactions of crude oil and injection water.The authors would like to acknowledge financial support for this work provided by the National Council of Science and Technology and the Ministry of Energy of Mexico (Conacyt-Sener-Hicrocarburos)

Analogous Reservoirs to Chicontepec, Alternatives of Exploitation for this Mexican Oil Field

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