Experimental Study On Long-term Sealing Performance Of Cement Stone Under In-situ Combustion

Heavy oil thermal recovery process usually undergoes steam stimulation and steam flooding.In order to increase the recovery rate of heavy oil,heavy oil fire flooding is performed.In this period,the cementing cement ring needs long-term high temperature above 500? and Under high CO2 corrosion environment,can heavy cement cement be able to meet the requirements of the harsh working conditions?Is it possible to maintain the integrity of the cement stone and the interlayer insulation of the cement ring?Is it necessary to increase the cost of upgrading the cement slurry system in the current situation where the development efficiency of heavy oil has dropped sharply or even resulted in losses?It has become one of the key issues that urgently needs to be answered in oil fields with large quantities of heavy oil resources,such as Xinjiang Oilfield and Liaohe Oilfield.For this reason,in light of the deficiencies in previous studies,the paper has re-examined the changes in working conditions of cement stone in the thermal recovery process,improved and improved the measurement equipment and methods for the cement concrete maintenance,and studied the continuous conditions of thermal recovery wells.Conventional sand-impregnated cement stone and modified Portland cement stone and their high-temperature corrosion-resistance performance provide reliable theoretical and technical support for scientific decision-making of the above-mentioned oil fields and improvement of heavy oil development benefits.In this paper,first from the point of view of indoor experiment simulation actual conditions,comprehensive consideration of the temperature of the fire line,water environment,bottom hole pressure,etc.,to develop a simulated laboratory device that meets the actual service conditions of the thermal cement cement stone,and according to the actual thermal wells Working conditions design corresponding parameters to achieve more realistic simulation results.Next,from the perspective of materials science,through the testing of mechanical properties,permeability and porosity,phase composition analysis,and microscopic morphology observation,the high-temperature resistance and failure evolution rules of conventional sand-impregnated cement stone were studied;Chemical properties such as chemical composition and mineral composition,combined with the strength development of cement stone under high and low temperature conditions,investigated the properties of aged high-grade soil and graphite-modified portland cement stone;tested the different corrosion environments of modified Portland cement stone.Under the following compressive strength,porosity,permeability,macroscopic and microscopic morphology,etc.,the corrosion resistance of the modified Portland cement stone was evaluated;through the interface cementation strength mold development,experimental method improvement,mechanical properties testing,etc.The regularity of the interface cementation strength of conventional sand-impregnated cement and modified Portland cement was explored.The results show that:(1)The temperature drop rate,water-moisture environment,and external constraints during the simulation experiment have a significant effect on the strength of the cement stone in the thermal recovery process and should be fully considered.Otherwise,it will lead to The simulation results deviate from the actual downhole conditions;(2)Lowering the heating and cooling rate,the water-moisture environment,and the external restraint conditions are conducive to maintaining the stability of the cement stone during the thermal recovery process;(3)Conventional sand-impregnated cement stone indoors In the study of actual working conditions,the high temperature performance meets the requirements of steam stimulation and steam flooding of thermal recovery wells,and the strength and temperature decline during fireflooding,and the failure is severe.(4)Modified silicic acid added to aged soil and graphite The high temperature resistance of the salt cement stone meets the requirement of a series of working conditions of the thermal recovery well.It can help the long-term normal production of the thermal recovery well during the oil-burning period;(5)The modified Portland cement stone has excellent corrosion resistance and is acidic or oxygen-rich.Corrosion environment can help cement stone to reduce the strength of the recession,to achieve the role of long-term sealing;(6)Conventional sand cement and modified cement stone in the fire when the interface is cemented poor ability The main research direction is the end of the experiment.The high-temperature failure mechanism of conventional sand-impregnated cement stone:The change of phase and micro-morphology caused by the high-temperature environment in the condition of the burned oil reservoir is the essential reason for the deterioration and failure of the conventional sand-filled cement stone.When the temperature is 300?,the hydration product C-S-H gel and Ca(OH)2 are dehydrated and decomposed slightly.The strength of the sand-impregnated cement stone decreases,the permeability increases,and the cement stone is at the critical point of deterioration and failure.When the high temperature is 400?,the sand-filled cement stone slightly cracks and swells,and the hydration product dehydrates and decomposes in a large amount,and the cement stone deteriorates and deteriorates,which can no longer meet the requirements for the integrity of the cement cement stone.At 500 ?.the compressive strength of Gaza cement stone is<14 MPa,and it is impossible to test it.Excellent mechanism of high-temperature resistance of modified Portland cement stone:At 500?,the new hydration products of modified Portland cement stone contain xonotlite(C6S6H),granomerite(C5S2H)and different silicic acid radicals.The degree of polymerization of calcium silicate hydrates C4.5S6H3.5,C6S3H,etc.are generated in large quantities,which contributes to the stability of the compressive strength of the cement stone,and the cement stone exhibits a very strong elastic deformation capability.In addition,the modified Portland cement shows strong resistance to CO2 corrosion.In the low temperature water-soluble CO2 corrosive environment,the compressive strength does not decrease,and a large amount of corrosion product CaCO3 is found in the corrosion layer,and its morphology belongs to a stable calcite form.The compressive strength of the modified Portland cement stone in the oxygen-enriched corrosive environment fluctuates but the overall trend is upward.The modified cement stone and the formation water produce ion exchange in a closed environment,and new hydration products adhere to the cracks.To fill up the pores and make up for the impact of cement stone strength due to high temperature recession.