A Research Of Cement Slurry For Slim-hole Wells

Slim-hole Wells have a small well diameter and small annular clearance, leading to many difficulties when cementing. The studies found that the difficulties of the cementing of slim-hole Wells are:there is a big annulus friction and circulating pressure loss, leading to high pump pressure and construction risk during cementing process; It is difficult to center small casing, resulting low displacement efficiency; Slim-hole Wells have a thin cement ring, and the compressive strength and impact resistant ability are limited, and the cementing quality is poor.In view of the many difficulties of slim-hole wells’cementing, it puts forward higher requirements on cement slurry. The main performance of requirements are:first of all, it need slurry has better rheological properties; Secondly, the slurry should satisfy low fluid loss, zero free water, good stable performance, adjustable thickening time and other performance requirements; In addition, set cement should be has a high compressive strength and toughness. Among them, good rheological property is the most important guarantee of slim-hole wells’cementing to be successfully completed.In allusion to the special requirements of slurry for slim-hole wells, we focus on rheological properties. On the premise of guaranteeing better rheological properties, we then take comprehensive adjustment of other properties to the appropriate requirements. In order to improve the rheological properties of cement slurry, this paper first presents using class D cement as an additive to constract the cement slurry system; Experiments show that the rheological property is better when using class D cement to build slurry than using class G cement alone. And other various performance can meet the requirements of slim-hole wells’cementing.Through the experiments, we optimized the construction of slurry system of all kinds of additives:fluid loss agent CG88L, retarder H21L-M, dispersant CF44L, defoaming agent CX601L, lightening admixture3M hollow microsphere, enhancer STR, expanding agent EXP-1, toughening agent latex and gelled material class G cement and class D cement, and the reasonable dosage of various additives were determined.By experiments in the optimization, indoor we have constructed two kinds of slurry of different density for slim-hole wells:one is conventional density cement slurry system using class D cement as additive; The other is low density cement slurry system with no class D cement. The two kinds of cement slurry system both have good rheological properties that its readings of300r/min on the viscometer are less than220; And the high temperature and high pressure loss can be controlled within30ml, having a good fluid loss performance; They also have no free liquid and better retrogradation; The compressive strength and impact strength after24hours both reach14MPa and1.6KJ/m2above respectively, having a high compressive strength and impact resistance; The slurry thickening time can be adjustable; Various performances can meet the requirements of slim-hole wells’cementing.