Abstract
The criteria for success of any primary cementing job is achieving permanent zonal isolation. Incomplete mud removal will affect the zonal isolation in several different ways and may lead to the development of a communication channel in the annulus and subsequently jeopardize the well integrity.
Nonaqueous fluids (NAF) are incompatible with cement slurries; the quality of the cement placement and set properties will be strongly affected by the presence of the NAF residue down hole. Although this problem can be mitigated through the addition of various chemicals providing compatibility, mud-thinning, reduction of the interfacial tension, and water-wetting functions, the current surfactants and solvents on the market have limited application in terms of temperature and type of drilling fluids. In addition, the current API/ISO testing protocols are generic and results are not reproducible. Recently, improved laboratory procedures have been proposed and these improved experimental methods were used on more than 200 surfactants and solvents. A screening process helped in selecting the optimum chemistry as a function of the conditions (type of base oil, salinity, temperature). This enabled developing design guidelines to select an optimized tensioactive package comprising a limited number of chemicals, from which field users would select the ones to combine for their applications.
The new tensioactive package was used successfully in two field trial wells in the 7-in. liner sections in a mature development field offshore Thailand. After a thorough comparison between the currently used package and the new one, the laboratory results using the field mud show superior cleaning results and efficiency with the new chemical package.
The zonal isolation was confirmed using an ultrasonic imager logging tool. After the two successful field trials, the tensioactive package was selected as the spacer of choice for a critical new development field campaign offshore Thailand in which zonal isolation between production zones was critical for selective production from each of the zones separately.
This paper will describe the newly improved laboratory methodology and selection criteria of the new tensioactive products and provide a detailed case history of the application in the development campaign, including the design, execution and evaluation of the job.
