The Research On And Application Of The Cementing Technique For Wells Of Easy-channeling And With Weak Formations

This thesis systematically researches the cementing technique for wells of easy-channeling and with weak formations.According to the characteristics of wells of easy-channeling and with weak formations, a method of controlling annular fluids channeling is proposed combining expanding and thixotropy with lightweight cement slurry. Of the method, the annular fluids channeling is controlled by increasing the pore pressure through adding gas control additive and introducing thixotropic property into the cement slurry. The materials and additives composing the lightweight cement slurry are selected based on analysis of their characteristics. An new anti-channeling lightweight cement slurry is developed through a large number of experiments, which has the characteristic of expanding and thixotropy. The slurry system has the characteristic of low sedimentation, strong thixotropy, high compressive strength at low temperatures, anti-channeling, zero free water, low fluid loss, and adjustable thickening time. Two cement slurries are developed suitable to Lu 9 Region of Luliang Oilfield in Xinjiang. The densities of the slurries are 1.30g/cm3 and 1.50g/cm respectively. The experiments are carried out to study the influence of formation water on compressive strength of the cements.The main measures to prevent lost circulation are analyzed in wells with weak formations including the wells of easy-channeling. For the wells, a displacing method is proposed to prevent lost circulation, which changes the pump rate gradually during the displacing process. With the method., the pressure balance between formation and annular fluids can be achieved and the operation time can also be shortened. With shortened operation time, the required thickening time of the slurry can be reduced, which is beneficial to prevent annular fluids channeling and to the development of the cement's compressive strength. The design approach of balanced-pressure cementing is given for the wells with weak formations. The balanced-pressure cementing designs are done for different kinds of casing cementing operations in Lu 9 Region.The technical measures to increase displacement efficiency are given and discussed for the wells with weak formations. Based on analysis, the following cementing fluids configuration is definitely suggested for the wells with weak formations: density of drilling fluid>densities of preflush and/or spacer< density of slurryviscosity of drilling fluid> viscosities of preflush and/or spacer