AADE-18-FTCE-065 Micro-composite as a Fluid Loss Additive for Oil Well Cementing

To ensure long term well integrity, it is crucial to maintain the properties of an oil well cementing slurry until it sets. High fluid loss can change the properties of cement slurry greatly causing improper cement displacement and setting. It is essential to reduce the fluid loss particularly for cementing of long horizontal wells, high-pressure, high-temperature (HPHT) wells, and wells with potential for gas migration. Synthetic polymers such as vinyl sulphonates, polyethylenimine (PEI), or styrene-butadiene (SBR) latexes are the only fluid loss additives suitable for HPHT oil well cementing. The commercially available HPHT fluid loss additives are expensive and have one or more of the following drawbacks; increases the viscosity of the cement slurry at low temperature, retardation of the cement hardening process or poor functionality in salt-containing cement, etc. Moreover, in strict HSE regulated areas like the Norwegian Continental Shelf, chemicals such as SBR latex and PEI are banned. While a wide range of HPHT fluid loss chemistries are available, there is a need for cost efficient additives for HPHT cementing. Multifunctional additives providing filtration control, mitigating the risk of gas migration and improving the cement bonding are highly desirable. This paper presents a newly developed micro-composite material and its application as fluid loss additive for oil well cementing. Successful tests were conducted in cement slurries in a wide range of densities from 1.30 2.40 SG. Saturated saltcontaining cement was also used. The filtration control was tested at elevated temperature up to 200°C with positive results. As such this composite material can be considered as a universal fluid loss additive for oil well cementing covering a wide range of temperatures and cement systems. Supplementary, micro-composite material provides gas migration control. Introduction The main function of an oil well cement is to maintain its integrity throughout its life time. Oil well cement is introduced into the well in form of a slurry. It is crucial to maintain the properties of cement slurry until it sets. Any significant change in the slurry properties such as the rheological properties, or the volume of fluid loss during the displacement until it hardens, can cause cement failure, which should be avoided at all costs. Generally, oil well cement is formulated with water content of 40-45wt% by the weight of cement. The loss of a large amount of water will lead to significant change in water/cement ratio causing improper cement displacement and unpredictable cement placement and setting. Hence, reducing the fluid loss particularly for cementing of long horizontal wells, HPHT wells with narrow pressure windows, and wells with potential for gas migration is essential. Fluid loss control mechanisms rely on impairing the permeability of the formation through creating filter cakes both inside the formation (internal filter cake) and on the surface of the formation (external filter cake). The permeability of the filter cake is reduced through plugging pore throats by swollen particles such as hydrocolloidal particles or by inorganic particles such as Microsilica. The permeability of the formation is further reduced by increasing the viscosity of the aqueous continuous phase using highly water-soluble polymers. An increase in fluid viscosity reduces the flow rates through filter cake. Below are the commonly used fluid loss additives for oil well cementing.