Study On Improving Cementing Strength Of Cementing Interface By Mud Cake Modification

The presence of weak cementing interfaces reduces the cementing quality of the second cementing interface,weakens the interlayer isolation ability,induces oil and gas water channeling,seriously threatens the production safety of oil and gas wells,and also affects the subsequent oil and gas production efficiency.In view of the above problems,in order to weaken the weak cementing interface and enhance the cementing strength of the second cementing interface,this paper firstly analyzes the causes of the weak cementing interface in complex formations and evaluates the performance of the mud cake,and defines the way to modify the mud cake.In this paper,we investigate a mud cake modifier that can effectively enhance the cementing strength of weak cemented interfaces,determine the composition and mechanism of the mud cake modifier,and evaluate the compatibility and temperature adaptation of the modifier with the drilling fluid.Interior interface cementation experiments were conducted to evaluate the interface enhancement effect of the mud cake modifier,the mud cake formation process,and the mud cake structure study.Finally,the feasibility and effectiveness of the mud cake modification method to improve cement quality is demonstrated through field experiments.The study shows that the low strength of mud cake is the main reason for the weak interface of cementing in low permeability and dense formation,and improving the solidification ability of mud cake,enhancing its toughness and enhancing the affinity between mud cake and cement are effective ways to improve the weak interface of cementing.The mud cake modifier consists of the organic compound carboxylate JBDJ-1,sodium metasilicate JBDJ-3,silicate mineral ZQDJ-1,and organic resin ZR-JBX.Modifiers mainly thicken the hygroscopic film by introducing polar groups,and alter the interaction forces between clay particles to reduce the thickness of the mud cake;The introduction of calcium silicate promotes the formation of silicate-hardening material in the mud cakes and increases the strength of the mud cakes;Flexible micron-sized particles are introduced to improve the toughness of the mud cake by gap filling.A suitable formulation of the mud cake modifier was investigated based on polymer drilling fluid and brine drilling fluid prepared in the laboratory,and the mud cake enhancement and interface enhancement were evaluated.It has been shown that for polymer drilling fluids,the formula for the mud cake modifier is: JBDJ-1:JBDJ-3: ZQDJ-1: Zr-JBX = 5:1:8:1 with an appropriate dosage of 0.8%.Under these conditions,the strength of the mud cake is increased by a factor of 2.3,the toughness of the mud cake is increased by a factor of 20.9,and the bonding strength of the cemented interface is increased by a factor of 6.7.For brine-based drilling fluids,the mud cake modifier is formulated as: JBDJ-1: JBDJ-3: ZQDJ-1: Zr-JBX = 7:3:7:1 with an appropriate dosage of1.2 %.Under these conditions,the strength of the mud cake increased by 69.1%,the thickness of the mud cake decreased by 62.6%,and the bonding strength at the second interface of the cement was increased by a factor of 5.8.Field slurry was used to test the interface enhancement effect,and it was shown that when 0.9% of the mud cake modifier was added to the field slurry,the cemented interface bonding strength increased to 7.2 times that without the additive.The mud cake modifier was applied to the field test of well R70.The results show that the cementing strength and quality of the second interface is above average,accounting for 92.4 %.Compared to the average second interface cementing rate of 89.67%for the entire interval of oil production wells in the block in the first half of 2021,the cementing quality has significantly improved.It can be seen that the mud cake modification method not only improves the performance of the mud cake,but also realizes the integral solidification of the mud cake and the cement ring,increases the bonding force at the interface between the cement ring,the mud cake and the borehole wall,and achieves the purpose of improving the bonding strength on both sides of cementing.