Horizontal wells -Overbalanced

•Most horizontal wells are completed without cementing or perforation –May have slotted liners –Open Hole completion –Gravel Pack completion Horizontal wells – Overbalanced Mud Systems •A horizontal mud system should have the following characteristics: –Formation damage control: •The horizontal mud system should not contain clays or acid-insoluble weight materials which can migrate into the formation and plug pores. •It should be formulated with breakable or acid-soluble viscosifiers, fluid-loss materials and properly sized plugging agents, all of which limit fluid loss to the formation and assure good clean-up. •The filtrate should be formulated to prevent clays in the producing zone from swelling, migrating or plugging the formation. –Formation damage control cont. •The filtrate should be formulated to prevent clays in the producing zone from swelling, migrating or plugging the formation •The filtrate should be compatible with formation fluids so that it will not precipitate mineral scales. •The fluid and filtrate should not change the wetting characteristics of the formation from either water-wet to oil-wet or from oil-wet to water-wet. •The filtrate should not form emulsions with formation fluids and block the formation. –Drillability: •The horizontal mud system should provide good hole-cleaning, lubricity and inhibition. •It should minimize hole enlargement and provide wellbore stability. –Compatibility with completion equipment and procedures: •Particles should be sized for formation pore throat bridging yet be small enough to pass through completion equipment. •The fluid should be formulated with acid-soluble, water-soluble, oxidizer-degradable or solvent soluble materials, which will not cause precipitates or emulsions. •Breakers should be compatible with formation fluids and horizontal mud system filtrate. •Susceptibility to different types of formation damage varies greatly and is dependent on the formation type and well conditions. •Some formations tolerate a wider range of horizontal mud system composition more than others. •When production is from carbonate fractures, significant amounts of insoluble materials can be tolerated without a significant reduction in productivity. –Usually, fluids which invade these types of formations can be produced back from the well •Lower permeability sandstones and depleted or unconsolidated sandstone reservoirs do not tolerate fluid and particle invasion without causing extensive damage. –Detailed knowledge of the formation, permeability, pore pressure, mineralogy and formation fluid composition must be called upon to assist in selecting the proper horizontal mud system