Environmentally Acceptable Cement Fluid Loss Additive

Abstract

The need for environmentally acceptable cement additives has encouraged the development of new additives based on biopolymers, especially in the North Sea area where environmental regulations are very strict. The main challenge is to develop environmentally acceptable chemicals that meet the relevant environmental legislation and operational criteria, and thus could replace synthetic materials that are currently being used. This paper will describe the development of a cement fluid loss additive that meets the challenges described above. Cellulose-type materials have been used for decades as additives to control cement fluid loss. These are PLONOR (pose little or no risk) listed materials, which means they do not have to be subjected to testing protocols. They were agreed upon by all OSPARCOM (Oslo-Paris Commission) countries, and thus, required no further extensive ecotoxicity testing before introduction. However, cellulose-type materials that have been used so far have several limitations: their fluid loss control properties decrease at temperatures above 200°F, their salt tolerance is limited and over-retardation problems can occur at low temperature. Furthermore, the slurry viscosity to fluid loss ratio is unfavorable compared to that of currently available synthetic fluid loss additives. When these cellulose type materials are combined with other additives to help improve their performance, the environmental advantages are compromised, and the resulting substance can no longer be listed as PLONOR. This paper describes the development of a modified cellulose (HEC) type of cement fluid loss product. It is salt tolerant, it can perform well up to temperatures as high as 280°F and is environmentally acceptable. After extensive laboratory testing, the production has been scaled up for introduction and a successful field trial has been performed in the North Sea area. Background Information Ensuring that cement slurry performs according to design parameters can be essential for the success of any job involving cement. Obtaining an appropriate cement slurry can require intensive laboratory testing until the slurry design meets design specifications. The selection of a fluid loss additive is important for cement placement and zonal isolation. Fluid loss additives help prevent water loss from the slurry, and thus, help prevent cement bridging in the annulus. Restricting fluid loss also protects water-sensitive formations. Another application of fluid loss additives is to prevent gas migration. The transition of the cement slurry from a liquid to a solid phase causes the hydrostatic pressure to drop and can allow gas to percolate through the unset cement. By preventing leak-off of interstitial water to permeable formations the influx of gas can be reduced. To help protect the environment in the North Sea, the OSPARCOM has implemented a system called the harmonized mandatory control system (HMCS) regulating the use and discharge of offshore exploration & production chemicals1,2. According to previous OSPARCOM regulations, each country has the right to implement their own stringent requirements other than those provided in the OSPARCOM guidelines. More recently implemented guidelines introduce a pre-screening scheme3, which new products must pass, while products with certain unfavorable environmental properties are prohibited in the North Sea, or are given temporary permission for use. OSPARCOM countries like The United Kingdom, Norway, Denmark and The Netherlands all accepted the harmonized pre-screening system. According to OSPARCOM, the materials that are allowed for use in the North Sea need either to be PLONOR-listed or to pass the relevant ecotoxicity tests. The PLONOR list contains generally accepted non-harmful materials. If a material is not on the PLONOR list it needs to be ecotoxicologically tested with respect to biodegradability, bioaccumulation and toxicity. The ecotoxicological tests to be used are specified in the OSPARCOM guidelines.

Improvement of Cement Properties Using a Single Multi-functional Polymer

“…The FFC of the slurry is measured based on the method, explained in the [16]. Large values of slurry water loss is harmful and can decrease the quality of cementing job significantly [17].…”

Shale Cuttings Addition to Wellbore Cement and Their Effect on Unconfined Compressive Strength

“…Cellulose materials are often used in cement slurries to prevent fluid loss but have proved to be unreliable in both high-and low-temperatures as well as in areas with a high salt concentration [8]. Examples of cellulose materials commonly used in wellbore cement include hydroxyethyl cellulose (HEC), methyl hydroxyethyl cellulose (MHEC), and carboxymethyl hydroxyethyl cellulose (CMHEC), which when hydrated, immediately increase the slurry viscosity [9].…”