The drilling mud used in Mumbai offshore is Starch / XC polymer mud, KCL- PHPA and oil based mud etc. The main objective of NDDF is to drill the pay zone with minimum skin damage to the productive formation, especially when such skin depends on several physical and chemical factors related to the formation and the mud: mineralogical composition, fluid properties in situ, cake quality, solids content and porous throat size distribution as well as chemical products that compose the drilling fluid. A critical factor cited in many of the references is the need to uniformly remove the filter cake from the entire completion interval.
Detailed Lab studies were carried out with different combination of acids with additives, oxidizer and mutual solvent at 900C for evaluating the most effective formulation with available chemicals.
The solubility of NDDF (PHPA based) is maximum (95.4%) in the formulation of 15% HCl + 1% ACI + 1% surfactant. + 1% EDTA +1% APS + 5% EGMBE.
This formulation seems to be the optimum formulation for removing the filter cake of NDDF after the GP job.
There is more than 85% retained permeability after the treatment with customized formulation observed in pack flow study.
The NDDF sample passed through an 80 mesh screen under 100 psi differential pressure maintained in a filter press apparatus.
Key words: NDDF (non- damaging drilling fluid)
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