| At present,most of the world’s medium and high permeability oilfields have entered the middle and late stages,and people’s attention has gradually shifted to the development of low permeability and ultra-low permeability reservoirs.The water-blocking effect,as an important damage method in the development process of ultra-low permeability reservoirs,deserves our attention.The Tugerming section of the northern Kuqa structural belt is a typical ultra-low permeability sandstone reservoir.Among them,Mingnan 1 well has relatively shallow burial depth and relatively good physical properties,and belongs to medium-high permeability reservoirs,which can provide a comparative effect for water-blocking damage research,and more comprehensively recognize the damage forms of water-blocking damage in ultra-low permeability reservoirs.In this paper,laboratory experiments,X-whole rock clay diffraction,constant velocity mercury intrusion,scanning electron microscopy,and cast thin sections were used to conduct in-depth analysis and research on the mechanism of water-blocking damage.Taking the Tugerming section of the northern Kuqa structural belt as an example,the method of understanding the water-blocking experiment was explored,and the on-site drilling fluid system was improved for water-blocking damage,and the following knowledge was obtained:The five wells studied(Tudong 2,Tuxi 1,Tuge 4,Tuzi 2,Tuzi 4)belong to ultra-low permeability sandstone reservoirs,and the reservoir of Well Mingnan 1 is a medium-high permeability reservoir.The degree of water-blocking damage of the five low-permeability wells tested were all serious.The water-blocking damage prediction of the Tugerming section of the study area was performed according to the APT_i method,and the results were basically in line with the laboratory test.Other wells except Mingnan 1 The APT_i values are all less than 0.8,and the water-blocking damage is very serious.The fractal dimension is used to describe the ultra-low permeability sandstone reservoir.The main reservoir pore structure in the study area is more complicated.Based on the percolation characteristics experiment,the fractal dimension is compared with the final water content per unit volume of pores.It is concluded that the main reservoirs in the study area have strong self-absorption capacity.Through the test of wetting contact angle,it is clear that the cores in the study area are all hydrophilic.According to the further subdivision of the contact angle,it can be seen that Tudong 2,Tuzi 2,and Tuzi 4 are strongly hydrophilic.The study on driving pressure found that the relationship between water-blocking effect and water saturation was described.The effect of clay minerals on water-blocking damage was studied.The hydration expansion of clay minerals had a serious impact on the reservoir pores.Except for the Tuge 4 well,the water sensitivity damage rates of other research wells were relatively high.The damage was evaluated as moderate to strong.The method of unlocking water-blocking is discussed,and a series of methods such as increasing pressure drop,extending shut-in time,reducing surface tension,injecting dry gas,heating the formation,hydraulic fracturing,and eliminating blockage of drilling fluid filter cake are considered.An experimental test was performed on the water flooding method to solve the water-blocking,and the characteristics of two different stages of understanding the water-blocking were described.The mutual solvent hydrolytic lock was tested,and methanol was selected as the unlocking reagent.It was found that the addition of methanol had a certain effect on the release of water-blocking damage in ultra-low permeability sandstone reservoirs.The damage degree of the drilling fluid formula to the reservoir was tested,the performance of the drilling fluid was tested,and the original drilling fluid formula was improved.It was found that the improved formula had good damage to the reservoir,especially in reducing water-blocking damage.effect. |
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