A Derivation of Drilling Fluid Modeling for Pr # 2 Well (Kg Basin - India) in Terms of Geo-pressure Gradient and Geo-mechanical Stress for Extra Wellbore Stability of Its over Pressured Highly Reactive - Water Sensitive Shale Column of 1225 Mtrs in 8-½ Inch Borehole from 2883 Mtrs to 4108 Mtrs Tvd: A Critical Analysis of Shear Failure Pressure and

Abstract

Abstract Success of achieving extra well-bore stability in highly reactive shale column of 1225 mtrs, in PR#2, is attributed to adequate pre-well planning, execution of drilling plan and guidelines, and the K+Cl -Polymer Drilling fluid chemistry. Well-bore cleaning and hydraulic modeling in an integrated geo-pressure gradient and critical analysis of shear failure pressure due to chemical osmosis and fluid - shale interaction was the significant attribute on well-bore stability. Pre well modeling of well-bore stability in problematic shale - zones and hole cleaning in its deeper final phase, contributed to stable hole behavior during unexpectedly longer durations on non - drilling downtime for frequent surface equipment failures, etc. Paper critically analyzes shear failure pressure and chemical osmosis during fluid - shale interaction to improve better well construction - design and drilling fluid modeling for productive oil - field economics in entire KG Basin - India. Key conclusions drawn from such a critical analysis of water based K+Cl - K+ Lignite/PHPA Polymer mud system include: Hole cleaning and hydraulic model derived in this analysis, proved to be quite useful in the pre well planning process as well as in post - well analysis on high bore-hole stability.Chemical osmosis and shale - fluid interaction further demonstrated the pore pressure transmission, and geo-pressure variance, and its integration with geo-mechanical stress and shear failure pressure derived the well-bore stability modeling. The case study presented compares original mechanical stability and hydraulic- fracturing estimates with the critical mud weight identified for successfully completing this difficult operation. Descriptions of well-bore stability and fluid losses are presented along with drilling fluid parameters used to combat them. Method used for estimating formation pore pressure, in-situ stresses and formation rock properties are also described. Additionally, possible explanations for differences between planned and actual stability estimates are explored with future recommendations for similar operations.