Oil-absorbing Cementing Slurry Under The Oil-based Drilling Fluid Condition

Under oil-based drilling fluid conditions,cementing operations were limited by the construction conditions such as wellbore conditions,displacement and dosage of pre-displacement fluids,and residual oil-based drilling fluids on the interface could not be displaced and cleaned ideally,thus affecting the strength development and interface cementing quality of the cement sheath.Current research only had a limited solution to improve the wetting and reversal efficiency of the spacer liquid.For this reason,this paper gave the cement slurry an ability of oil absorption to solve the interface residual oil quality problem.An oil absorption type cementing slurry system was developed in the laboratory.The selection of adsorbent and its basic performance,the engineering performance of the oil absorption cement slurry system,conventional mechanical properties under the oil conditions,hydration morphology,hydration reaction rate and the distribution characteristics of the oil and water in the slurry and the pore structure,etc.were experimentally analyzed,and the adsorption mechanism of the adsorbent was explored.The sealing quality of the cement sheath which was under the conditions of the oil-based drilling fluid provides further reliable guarantees.The research results were as follows:Through the experimental screening of adsorbents,a kind of layered crystalline silicate material suitable for Grade G oil-well cement was selected.In order to purify the layered crystal components in the adsorbent raw materials,the siderite impurities in the raw materials were successfully removed by high-temperature baking and acidification.The specific surface area of the adsorbent after purification was increased from 277.34 m2/g to 333.11 m2/g.Surface wettability shows strong lipophilicity.The density of the oil-absorbing cement slurry was adjustable from 1.81-1.98g/cm3.The compressive strength of the cement stone is high,and it is not affected by the adsorbent.The engineering performance was excellent,and it fully meets the cementing construction;there was no new crystalline product found in the hydration product.Only a small amount of crystallites with a low degree of crystallinity were produced,and the cement stone structure was dense.By the difference test between the oil-based drilling fluid and the white oil on the cement slurry,it was found that the white oil component in the oil-based drilling fluid played a major role in the adverse effect of the hydration reaction of the cement slurry.Therefore,the white oil was used to evaluate the oil absorption efficiency.Under the same oil-bearing ratio,the compressive strength and interface cementation strength of oil-absorbing cement slurry maintained at the same age were significantly higher than that of cemented cement,and the hydration performance parameters performed well over the previous year,with higher conductivity values in early hydration.The hydration rate was faster.The difference in hydration rate was closely related to the distribution of two phases of the oil and water phase in the oil-containing cement slurry.Through the identification of the I element in potassium iodide,CT scans and three-dimensional reconstruction analyses had revealed that the oil-absorbing cement slurry was compared with the plain cement,and the structure The distribution of water in the pores was more uniform,there was no accumulation of non-aqueous pores with a pore size of more than 100pm,and the degree of hydration condensation was high.Combined with NMR,the pore size of the pores in the structure was less than 50pm,and the porosity of 25%oil-containing cement slurry was only 34%,the change rate was relatively small.This was due to the electrostatic physisorption of the adsorbent and the oil phase,the oil droplets were gradually adsorbed and dispersed,the hydration reaction environment of the cement ash returned to normal,and the body strength and cementation quality of the cement stone were greatly improved.