Study On The Mud Cake Enhancement Method And The Mechanism

After oil well drilling,a certain thickness and poor strength mud cake would be made on well-bore and casing wall.The existence of the mud cake would harm the cementation between cement and well-bore or base.At finally,the performance of cementing strength would become poor.In this paper,in order to improve the performance of mud cake and well cementing quality,improve the mud cake strength and the compatibility between mud cake and the cement as the starting point,the hardening mechanism for mud cake in cement filtrate as the theoretical basis,an effective modification methods to increase mud cake strength（GX）was studied,the effect on the modification of mud cake and the enhancement of cementing strength by GX method was tested,the modification mechanism of mud cake by GX method was analyzed.The main conclusions were obtained as follow:1 Based on the analysis of the interaction between the ions and mud cake in the cement filtrate,the mechanism mode of the mud cake in cement filtrate was established combining the clay hydration mechanism.It was found that after curing in the cement filtrate,the mud cake strength would increased,and it would have a significant influence on the mud cake strength with the change of curing temperature and the curing time.In cement filtrate,Ca²⁺,CO32-and OH– would have different degree of enhancement effect on mud cake strength.In the alkaline condition,Ca²⁺ could make the mud cake strength increase to 707 times as high as the blank mud cake.The main reasons of enhacing mud cake strength were that the gels which cement filtrate promoted to produce would get the dispersed clay particles together,at the same time,some calcium carbonate,calcium hydroxide,calcium silicate which generated in cement filtrate would fill among the clay particles to improve the renitency of clay,the others covering on the surface of clay particle to reduce the amount of clay hydration expansion and incrence the strength of mud cake.2 As the mud cake hardening model in cement filtrate as the foundation,a effective way to improve properties of mud cake（GX）which was adding 1.05% hardener LXAB in drilling fluid firstly,stirring well to prepare mud cake,and then the preparation mud cake,in turn,at 1.3% QX-1,0.4% QX-2,0.3% QX-3 activator in aqueous solution getting for 30 min.The bentonite mud cake strength and the field mud cake strength increnced to 32 and 38 times respectively,and the mud cake performance had been greatly improved by the method.The first and second cementing strength is respectively increased to 11 and 18 times by the GX method with the field drilling fluid.The hardened and activation mechanism of the mud cake in GX method was that the hardener LXAB was as a skeleton support among the clay particles to resist the pressure of the formation and then,QX-1 damaging the key of Si-O-Si,Al-O-Al and Si-O-Al to open the channel of mud cake and generate the free silicon,the QX-2 to make the free silica got,and the free silica combined with Ca²⁺ to form gel material to get clay particles together,finally QX-3 induced the ions of cement filtrater into the mud cake,further to generate a large number of C-S-H gel,calcium hydroxide which would improve the density of the mud cake structure,the mud cake strength and the compatibility between mud cake and cementing cement.