Abstract

A new method of obtaining improved zonal isolation using drilling fluid solidification technology has been developed. A water-base drilling fluid is converted into a cementitious slurry by the special method, is called simply MTC(Mud To Cement). The MTC technology used for cementing operation can improve the quality of cementing and reduce the disadvantageous effect resulting from flocculation in the mixture of drilling mud-cement and cracking of solidified cement as the filter cake and drilling fluid in washed out sections thereby contain a hydraulic material. The dispersant's synthesizing and its effect on slurry rheology are the base of MTC technique application. This paper provides two methods of which the dispersant is synthesized by using fractions of C9 which are the by-product of Daqing ethene unit. The dispersant is cheaper, and it can be used for MTC design by experiment's verification. The effects of amounts of dispersant and mud on the rheology of MTC slurry are studied and discussed. The results show that the thickening time of MTC slurry is extended clearly with mixing of dispersant, and the mobility of slurry is improved. We find that there is a low mobility or high consistency region when MTC slurry is making up. The appropriate measures for improving quality of MTC are provided in this paper. Moreover, the rheological model of MTC slurry is studied. Through lots of calculation, the H-B model is the most accurate for describing MTC slurry. Last, the application of MTC technology in Changqing field is introduced.

Introduction

Conversion of drilling fluid(mud) into cement suitable for well cementing operations has been an area of interest within the petroleum industry for over fifty years. Improved zonal isolation in the annular space between casing and borehole has been and continues to be the primary reason for pursuing this technology.

For nearly a century, zonal isolation has been attempted largely by the placement of Portland cement formulations in the annular space. The widely practiced cementing process is plagued by variables which are often difficult to predict or control yet have a critical impact upon the quality of seal achieved. Two of variables include effective removal of the drilling fluid occupying the annulus and the effects of mud or spacer fluid contamination on cement formulation properties in the liquid (slurry) and solid states. With prior art methods and compositions, the displacement of the drilling fluid has been incomplete due to gelation and has often resulted in poor cement bonds or incomplete filling of the casing-to-wellbore annulus with a homogeneous cement.

Mud solidification has been pursued as a means to improve zonal isolation because of (1) better rheological compatibility between the cementing fluid and the mud which contributes to better mud displacement. (2) lower impact of mud contamination on the performance properties of the coverted mud in the fluid and solid state, and (3) improved sealing in the annulus because of the potential solidification of the filter cake and any undisplaced mud.

The conversion of drilling fluid or mud to a cementitious slurry is without some operational problems and undesirable compositional changes. For example, the addition of cementitious materials such as mixtures of lime and silicia and alumina or lime and magnesia, silica and alumina and iron oxide, or cement materials such as calcium sulphate and Portland cements to aqueous drilling fluid can substantially increase the viscosity of the fluid mixture and result in severe flocculation. Efforts to circulate such mixtures through a wellbore can result in a highly unsatisfactory circulation rate, plugging of the wellbore annulus, breakdown of the earth formation in the vicinity of the wellbore and a failure of the cement slurry to properly mix.

On the base of development of Macromolecule synthesizing technology, the MTC technology has been developed really.

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